Issue #1803 - Convert std::*<T>::value/::type to _v and _t suffixes.

This excludes uses in third-party libs in our tree.

accessible/atk/Platform.cpp

@@ -18,10 +18,6 @@
 #endif
 #include <gtk/gtk.h>
 
-#if (MOZ_WIDGET_GTK == 3)
-extern "C" __attribute__((weak,visibility("default"))) int atk_bridge_adaptor_init(int*, char **[]);
-#endif
-
 using namespace mozilla;
 using namespace mozilla::a11y;
 
@@ -33,12 +29,20 @@ extern "C" {
 typedef GType (* AtkGetTypeType) (void);
 typedef void (*GnomeAccessibilityInit) (void);
 typedef void (*GnomeAccessibilityShutdown) (void);
+#if (MOZ_WIDGET_GTK == 3)
+typedef int (*AtkBridgeAdaptorInit) (int*, char***);
+#endif
 }
 
 static PRLibrary* sATKLib = nullptr;
 static const char sATKLibName[] = "libatk-1.0.so.0";
 static const char sATKHyperlinkImplGetTypeSymbol[] =
   "atk_hyperlink_impl_get_type";
+#if (MOZ_WIDGET_GTK == 3)
+static PRLibrary* sAtkBridgeAdaptorLib = nullptr;
+static const char sAtkBridgeAdaptorLibName[] = "libatk-bridge-2.0.so.0";
+static const char sAtkBridgeAdaptorInitSymbol[] = "atk_bridge_adaptor_init";
+#endif
 
 gboolean toplevel_event_watcher(GSignalInvocationHint*, guint, const GValue*,
                                 gpointer);
@@ -127,6 +131,38 @@ LoadGtkModule(GnomeAccessibilityModule& aModule)
     return NS_OK;
 }
 
+#if (MOZ_WIDGET_GTK == 3)
+static bool
+InitAtkBridgeAdaptor()
+{
+  AtkBridgeAdaptorInit initBridge =
+    reinterpret_cast<AtkBridgeAdaptorInit>(
+      PR_FindFunctionSymbolAndLibrary(sAtkBridgeAdaptorInitSymbol,
+                                      &sAtkBridgeAdaptorLib));
+
+  if (!initBridge) {
+    sAtkBridgeAdaptorLib = PR_LoadLibrary(sAtkBridgeAdaptorLibName);
+    if (sAtkBridgeAdaptorLib) {
+      initBridge =
+        reinterpret_cast<AtkBridgeAdaptorInit>(
+          PR_FindFunctionSymbol(sAtkBridgeAdaptorLib,
+                                sAtkBridgeAdaptorInitSymbol));
+      if (!initBridge) {
+        PR_UnloadLibrary(sAtkBridgeAdaptorLib);
+        sAtkBridgeAdaptorLib = nullptr;
+      }
+    }
+  }
+
+  if (!initBridge) {
+    return false;
+  }
+
+  initBridge(nullptr, nullptr);
+  return true;
+}
+#endif
+
 void
 a11y::PlatformInit()
 {
@@ -181,9 +217,7 @@ a11y::PlatformInit()
   // Init atk-bridge now
   PR_SetEnv("NO_AT_BRIDGE=0");
 #if (MOZ_WIDGET_GTK == 3)
-  if (atk_bridge_adaptor_init) {
-    atk_bridge_adaptor_init(nullptr, nullptr);
-  } else
+  if (!InitAtkBridgeAdaptor())
 #endif
   {
     nsresult rv = LoadGtkModule(sAtkBridge);
@@ -228,6 +262,13 @@ a11y::PlatformShutdown()
         sAtkBridge.init = nullptr;
         sAtkBridge.shutdown = nullptr;
     }
+#if (MOZ_WIDGET_GTK == 3)
+    if (sAtkBridgeAdaptorLib) {
+        // Do not shutdown/unload atk-bridge; an exit function registered by
+        // the bridge will take care of it.
+        sAtkBridgeAdaptorLib = nullptr;
+    }
+#endif
 #if (MOZ_WIDGET_GTK == 2)
     if (sGail.lib) {
         // Do not shutdown gail because

build/moz.configure/old.configure

@@ -164,6 +164,7 @@ def old_configure_options(*options):
     '--enable-negotiateauth',
     '--enable-nfc',
     '--enable-npapi',
+    '--enable-npapi-gtk2',
     '--enable-nspr-build',
     '--enable-official-branding',
     '--enable-official-vendor',

devtools/client/inspector/shared/tooltips-overlay.js

@@ -143,7 +143,8 @@ TooltipsOverlay.prototype = {
     // Font preview tooltip
     if (type === VIEW_NODE_VALUE_TYPE && prop.property === "font-family") {
       let value = prop.value.toLowerCase();
-      if (value !== "inherit" && value !== "unset" && value !== "initial" && value !== "revert") {
+      if (value !== "inherit" && value !== "unset" && value !== "initial" &&
+          value !== "revert" && value !== "revert-layer") {
         tooltipType = TOOLTIP_FONTFAMILY_TYPE;
       }
     }

devtools/client/shared/css-angle.js

@@ -10,7 +10,8 @@ const SPECIALVALUES = new Set([
   "initial",
   "inherit",
   "unset",
-  "revert"
+  "revert",
+  "revert-layer"
 ]);
 
 const {getCSSLexer} = require("devtools/shared/css/lexer");

devtools/client/shared/widgets/FilterWidget.js

@@ -99,7 +99,14 @@ const filterList = [
 ];
 
 // Valid values that shouldn't be parsed for filters.
-const SPECIAL_VALUES = new Set(["none", "unset", "initial", "inherit", "revert"]);
+const SPECIAL_VALUES = new Set([
+  "none",
+  "unset",
+  "initial",
+  "inherit",
+  "revert",
+  "revert-layer"
+]);
 
 /**
  * A CSS Filter editor widget used to add/remove/modify

devtools/shared/css/color.js

@@ -20,7 +20,8 @@ const SPECIALVALUES = new Set([
   "inherit",
   "transparent",
   "unset",
-  "revert"
+  "revert",
+  "revert-layer"
 ]);
 
 /**

devtools/shared/css/generated/mach_commands.py

@@ -43,7 +43,7 @@ class MachCommands(MachCommandBase):
         if not os.path.exists(generated_dir):
             generated_dir = mozpath.join(self.topsrcdir, 'platform',
                 'devtools/shared/css/generated')
-        else:
+        if not os.path.exists(generated_dir):
             raise Exception('Directory expected at %s does not exist.' % generated_dir)
         self.generated_dir = generated_dir
 
@@ -75,6 +75,9 @@ class MachCommands(MachCommandBase):
         contents = subprocess.check_output([xpcshell_path, '-g', gre_path,
                                             '-a', browser_path, script_path],
                                            env = sub_env)
+        if not isinstance(contents, str):
+            contents = contents.decode('utf-8')
+
         # Extract just the output between the delimiters as the xpcshell output can
         # have extra output that we don't want.
         contents = contents.split('DEVTOOLS_CSS_DB_DELIMITER')[1]
@@ -88,13 +91,13 @@ class MachCommands(MachCommandBase):
         destination_path = mozpath.join(self.generated_dir,
             'properties-db.js')
 
-        with open(js_template_path, 'rb') as handle:
+        with open(js_template_path, 'r') as handle:
             js_template = handle.read()
 
         preamble = '/* THIS IS AN AUTOGENERATED FILE.  DO NOT EDIT */\n\n'
         contents = string.Template(js_template).substitute(substitutions)
 
-        with open(destination_path, 'wb') as destination:
+        with open(destination_path, 'w') as destination:
             destination.write(preamble + contents)
 
         print(('The database was successfully generated at ' + destination_path))

dom/base/nsAttrValue.h

@@ -274,7 +274,7 @@ public:
     }
 
     template<typename T,
-             typename = typename std::enable_if<std::is_enum<T>::value>::type>
+             typename = typename std::enable_if_t<std::is_enum_v<T>>>
     EnumTable(const char* aTag, T aValue)
       : tag(aTag)
       , value(static_cast<int16_t>(aValue))

dom/plugins/ipc/PluginInstanceChild.cpp

@@ -55,7 +55,12 @@ using namespace std;
 #include <gtk/gtk.h>
 #include <gdk/gdkx.h>
 #include <gdk/gdk.h>
+#if (GTK_MAJOR_VERSION == 3)
+#include <gtk/gtkx.h>
+#endif
+#ifdef MOZ_ENABLE_NPAPI_GTK2
 #include "gtk2xtbin.h"
+#endif
 
 #elif defined(OS_WIN)
 
@@ -208,7 +213,9 @@ PluginInstanceChild::PluginInstanceChild(const NPPluginFuncs* aPluginIface,
     memset(&mWsInfo, 0, sizeof(mWsInfo));
 #ifdef MOZ_WIDGET_GTK
     mWsInfo.display = nullptr;
+#ifdef MOZ_ENABLE_NPAPI_GTK2
     mXtClient.top_widget = nullptr;
+#endif
 #else
     mWsInfo.display = DefaultXDisplay();
 #endif
@@ -620,15 +627,17 @@ PluginInstanceChild::NPN_SetValue(NPPVariable aVar, void* aValue)
         NPWindowType newWindowType = windowed ? NPWindowTypeWindow : NPWindowTypeDrawable;
 #ifdef MOZ_WIDGET_GTK
         if (mWindow.type != newWindowType && mWsInfo.display) {
-           // plugin type has been changed but we already have a valid display
-           // so update it for the recent plugin mode
-           if (mXEmbed || !windowed) {
-               // Use default GTK display for XEmbed and windowless plugins
-               mWsInfo.display = DefaultXDisplay();
-           }
-           else {
-               mWsInfo.display = xt_client_get_display();
-           }
+            // plugin type has been changed but we already have a valid display
+            // so update it for the recent plugin mode
+#ifdef MOZ_ENABLE_NPAPI_GTK2
+            if (!mXEmbed && windowed) {
+                mWsInfo.display = xt_client_get_display();
+            } else
+#endif
+            {
+                // Use default GTK display for XEmbed and windowless plugins.
+                mWsInfo.display = DefaultXDisplay();
+            }
         }
 #endif
         mWindow.type = newWindowType;
@@ -1214,12 +1223,18 @@ bool PluginInstanceChild::CreateWindow(const NPRemoteWindow& aWindow)
     if (mXEmbed) {
         mWindow.window = reinterpret_cast<void*>(aWindow.window);
     }
+#ifdef MOZ_ENABLE_NPAPI_GTK2
     else {
         Window browserSocket = (Window)(aWindow.window);
         xt_client_init(&mXtClient, mWsInfo.visual, mWsInfo.colormap, mWsInfo.depth);
         xt_client_create(&mXtClient, browserSocket, mWindow.width, mWindow.height); 
         mWindow.window = (void *)XtWindow(mXtClient.child_widget);
-    }  
+    }
+#else
+    else {
+        mWindow.window = reinterpret_cast<void*>(aWindow.window);
+    }
+#endif
 #else
     mWindow.window = reinterpret_cast<void*>(aWindow.window);
 #endif
@@ -1239,7 +1254,7 @@ void PluginInstanceChild::DeleteWindow()
   if (!mWindow.window)
       return;
 
-#ifdef MOZ_WIDGET_GTK
+#ifdef MOZ_ENABLE_NPAPI_GTK2
   if (mXtClient.top_widget) {     
       xt_client_unrealize(&mXtClient);
       xt_client_destroy(&mXtClient); 
@@ -1321,7 +1336,7 @@ PluginInstanceChild::AnswerNPP_SetWindow(const NPRemoteWindow& aWindow)
         CreateWindow(aWindow);
     }
 
-#ifdef MOZ_WIDGET_GTK
+#ifdef MOZ_ENABLE_NPAPI_GTK2
     if (mXEmbed && gtk_check_version(2,18,7) != nullptr) { // older
         if (aWindow.type == NPWindowTypeWindow) {
             GdkWindow* socket_window = gdk_window_lookup(static_cast<GdkNativeWindow>(aWindow.window));
@@ -1456,19 +1471,27 @@ PluginInstanceChild::Initialize()
     if (mWindow.type == NPWindowTypeWindow) {
         AnswerNPP_GetValue_NPPVpluginNeedsXEmbed(&mXEmbed, &rv);
 
+#ifdef MOZ_ENABLE_NPAPI_GTK2
         // Set up Xt loop for windowed plugins without XEmbed support
         if (!mXEmbed) {
            xt_client_xloop_create();
         }
+#endif
     }
 
-    // Use default GTK display for XEmbed and windowless plugins
+    // Use default GTK display for XEmbed and windowless plugins.
     if (mXEmbed || mWindow.type != NPWindowTypeWindow) {
         mWsInfo.display = DefaultXDisplay();
     }
+#ifdef MOZ_ENABLE_NPAPI_GTK2
     else {
         mWsInfo.display = xt_client_get_display();
     }
+#else
+    else {
+        mWsInfo.display = DefaultXDisplay();
+    }
+#endif
 #endif 
 
     return true;
@@ -4656,7 +4679,7 @@ PluginInstanceChild::Destroy()
 
     mPendingAsyncCalls.Clear();
     
-#ifdef MOZ_WIDGET_GTK
+#if defined(MOZ_WIDGET_GTK) && defined(MOZ_ENABLE_NPAPI_GTK2)
     if (mWindow.type == NPWindowTypeWindow && !mXEmbed) {
       xt_client_xloop_destroy();
     }

dom/plugins/ipc/PluginInstanceChild.h

@@ -36,7 +36,7 @@
 
 #include <map>
 
-#ifdef MOZ_WIDGET_GTK
+#if defined(MOZ_WIDGET_GTK) && defined(MOZ_ENABLE_NPAPI_GTK2)
 #include "gtk2xtbin.h"
 #endif
 
@@ -462,6 +462,8 @@ private:
     NPSetWindowCallbackStruct mWsInfo;
 #ifdef MOZ_WIDGET_GTK
     bool mXEmbed;
+#endif
+#ifdef MOZ_ENABLE_NPAPI_GTK2
     XtClient mXtClient;
 #endif
 #elif defined(OS_WIN)

dom/plugins/ipc/PluginModuleChild.cpp

@@ -12,6 +12,9 @@
 
 #ifdef MOZ_WIDGET_GTK
 #include <gtk/gtk.h>
+#if (GTK_MAJOR_VERSION == 3)
+#include <gtk/gtkx.h>
+#endif
 #endif
 
 #include "nsIFile.h"
@@ -1101,7 +1104,11 @@ _getvalue(NPP aNPP,
                 return InstCast(aNPP)->NPN_GetValue(aVariable, aValue);
             } 
             else {
+#ifdef MOZ_ENABLE_NPAPI_GTK2
                 *(void **)aValue = xt_client_get_display();
+#else
+                *(void **)aValue = DefaultXDisplay();
+#endif
             }          
             return NPERR_NO_ERROR;
         }

dom/plugins/ipc/moz.build

@@ -143,11 +143,13 @@ LOCAL_INCLUDES += [
 
 DEFINES['FORCE_PR_LOG'] = True
 
-if CONFIG['MOZ_WIDGET_TOOLKIT'] != 'gtk3':
-    CXXFLAGS += CONFIG['TK_CFLAGS']
-else:
+if (CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk3' and
+        CONFIG['MOZ_ENABLE_NPAPI'] and
+        CONFIG['MOZ_ENABLE_NPAPI_GTK2']):
     # Force build against gtk+2 for struct offsets and such.
     CXXFLAGS += CONFIG['MOZ_GTK2_CFLAGS']
+else:
+    CXXFLAGS += CONFIG['TK_CFLAGS']
 
 CXXFLAGS += CONFIG['MOZ_CAIRO_CFLAGS']
 

dom/url/URL.cpp

@@ -1789,17 +1789,26 @@ URL::IsValidURL(const GlobalObject& aGlobal, const nsAString& aURL,
   return URLWorker::IsValidURL(aGlobal, aURL, aRv);
 }
 
-bool
-URL::CanParse(const GlobalObject& aGlobal, const nsAString& aURL,
-              const Optional<nsAString>& aBase) {
+already_AddRefed<URL>
+URL::Parse(const GlobalObject& aGlobal, const nsAString& aURL,
+           const Optional<nsAString>& aBase)
+{
   ErrorResult rv;
   RefPtr<URL> parsed = URL::Constructor(aGlobal, aURL, aBase, rv);
   if (rv.Failed() || !parsed) {
     rv.SuppressException();
-    return false;
+    return nullptr;
   }
 
-  return true;
+  return parsed.forget();
+}
+
+bool
+URL::CanParse(const GlobalObject& aGlobal, const nsAString& aURL,
+              const Optional<nsAString>& aBase)
+{
+  RefPtr<URL> parsed = URL::Parse(aGlobal, aURL, aBase);
+  return !!parsed;
 }
 
 already_AddRefed<URLSearchParams>

dom/url/URL.h

@@ -88,6 +88,10 @@ public:
   IsValidURL(const GlobalObject& aGlobal, const nsAString& aURL,
              ErrorResult& aRv);
 
+  static already_AddRefed<URL>
+  Parse(const GlobalObject& aGlobal, const nsAString& aURL,
+        const Optional<nsAString>& aBase);
+
   static bool
   CanParse(const GlobalObject& aGlobal, const nsAString& aURL,
            const Optional<nsAString>& aBase);

dom/url/tests/test_url.html

@@ -448,6 +448,34 @@
                 !URL.canParse("/static/client/runtime.js", "mailto:test@example.com"),
                 "URL.canParse rejects root-relative input against opaque mailto: base",
             );
+            ok("parse" in URL, "URL.parse exists");
+            is(URL.parse.length, 1, "URL.parse has one required argument");
+            var parsed = URL.parse("/static/client/runtime.js", "x:/");
+            ok(parsed instanceof URL, "URL.parse returns a URL object on success");
+            is(parsed.href, "x:/static/client/runtime.js", "URL.parse resolves against a base");
+            is(URL.parse("/static/client/runtime.js"), null, "URL.parse returns null for invalid input");
+            is(
+                URL.parse("/static/client/runtime.js", "mailto:test@example.com"),
+                null,
+                "URL.parse returns null for an invalid base/input combination",
+            );
+
+            var conversionOrder = [];
+            parsed = URL.parse(
+                { toString: function() { conversionOrder.push("url"); return "child"; } },
+                { toString: function() { conversionOrder.push("base"); return "https://example.com/root/"; } },
+            );
+            is(conversionOrder.join(","), "url,base", "URL.parse converts its arguments in order");
+            is(parsed.href, "https://example.com/root/child", "URL.parse uses converted arguments");
+
+            var sentinel = {};
+            var thrown;
+            try {
+                URL.parse({ toString: function() { throw sentinel; } });
+            } catch (e) {
+                thrown = e;
+            }
+            is(thrown, sentinel, "URL.parse propagates argument conversion exceptions");
             SimpleTest.doesThrow(() => {
                 new URL("/static/client/runtime.js", "mailto:test@example.com");
             }, "constructor rejects root-relative input against opaque mailto: base");

dom/url/tests/urlApi_worker.js

@@ -301,6 +301,64 @@ onmessage = function () {
     !URL.canParse("/static/client/runtime.js", "mailto:test@example.com"),
     "URL.canParse rejects root-relative input against opaque mailto: base",
   );
+  ok("parse" in URL, "URL.parse exists");
+  is(URL.parse.length, 1, "URL.parse has one required argument");
+  let parsed = URL.parse("/static/client/runtime.js", "x:/");
+  ok(parsed instanceof URL, "URL.parse returns a URL object on success");
+  is(
+    parsed.href,
+    "x:/static/client/runtime.js",
+    "URL.parse resolves against a base",
+  );
+  is(
+    URL.parse("/static/client/runtime.js"),
+    null,
+    "URL.parse returns null for invalid input",
+  );
+  is(
+    URL.parse("/static/client/runtime.js", "mailto:test@example.com"),
+    null,
+    "URL.parse returns null for an invalid base/input combination",
+  );
+
+  const conversionOrder = [];
+  parsed = URL.parse(
+    {
+      toString() {
+        conversionOrder.push("url");
+        return "child";
+      },
+    },
+    {
+      toString() {
+        conversionOrder.push("base");
+        return "https://example.com/root/";
+      },
+    },
+  );
+  is(
+    conversionOrder.join(","),
+    "url,base",
+    "URL.parse converts its arguments in order",
+  );
+  is(
+    parsed.href,
+    "https://example.com/root/child",
+    "URL.parse uses converted arguments",
+  );
+
+  const sentinel = {};
+  let thrown;
+  try {
+    URL.parse({
+      toString() {
+        throw sentinel;
+      },
+    });
+  } catch (e) {
+    thrown = e;
+  }
+  is(thrown, sentinel, "URL.parse propagates argument conversion exceptions");
   let mailtoRelativeFailed = false;
   try {
     new URL("/static/client/runtime.js", "mailto:test@example.com");

dom/webidl/URL.webidl

@@ -23,6 +23,7 @@ interface URL {
   [Throws]
   stringifier;
   
+  static URL? parse(USVString url, optional USVString base);
   static boolean canParse(USVString url, optional USVString base);
 
   [Throws]

gfx/2d/DrawTargetSkia.cpp

@@ -1117,6 +1117,7 @@ DrawTargetSkia::BorrowCGContext(const DrawOptions &aOptions)
                         kCGImageAlphaOnly :
                         kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Host;
 
+#if defined(MAC_OS_X_VERSION_10_6) && (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_6)
   mCG = CGBitmapContextCreateWithData(mCanvasData,
                                       mCGSize.width,
                                       mCGSize.height,
@@ -1126,6 +1127,15 @@ DrawTargetSkia::BorrowCGContext(const DrawOptions &aOptions)
                                       bitmapInfo,
                                       NULL, /* Callback when released */
                                       NULL);
+#else
+  mCG = CGBitmapContextCreate(mCanvasData,
+                              mCGSize.width,
+                              mCGSize.height,
+                              8, /* bits per component */
+                              stride,
+                              mColorSpace,
+                              bitmapInfo);
+#endif
   if (!mCG) {
     ReleaseBits(mCanvasData);
     NS_WARNING("Could not create bitmap around skia data\n");

gfx/2d/ScaledFontMac.cpp

@@ -115,7 +115,7 @@ ScaledFontMac::GetPathForGlyphs(const GlyphBuffer &aBuffer, const DrawTarget *aT
   return ScaledFontBase::GetPathForGlyphs(aBuffer, aTarget);
 }
 
-#if !defined(MAC_OS_X_VERSION_10_7) || (MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_7)
+#ifndef USE_SKIA
 void
 ScaledFontMac::CopyGlyphsToBuilder(const GlyphBuffer &aBuffer, PathBuilder *aBuilder, const Matrix *aTransformHint)
 {

gfx/2d/ScaledFontMac.h

@@ -32,7 +32,7 @@ public:
   virtual SkTypeface* GetSkTypeface();
 #endif
   virtual already_AddRefed<Path> GetPathForGlyphs(const GlyphBuffer &aBuffer, const DrawTarget *aTarget);
-#if !defined(MAC_OS_X_VERSION_10_7) || (MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_7)
+#ifndef USE_SKIA
   virtual void CopyGlyphsToBuilder(const GlyphBuffer &aBuffer, PathBuilder *aBuilder, const Matrix *aTransformHint);
 #endif
   virtual bool GetFontFileData(FontFileDataOutput aDataCallback, void *aBaton);

gfx/skia/skia/include/core/SkColorPriv.h

@@ -24,15 +24,21 @@
  *  Skia's 32bit backend only supports 1 sizzle order at a time (compile-time).
  *  This is specified by 4 defines SK_A32_SHIFT, SK_R32_SHIFT, ... for G and B.
  *
- *  For easier compatibility with Skia's GPU backend, we further restrict these
- *  to either (in memory-byte-order) RGBA or BGRA. Note that this "order" does
- *  not directly correspond to the same shift-order, since we have to take endianess
- *  into account.
+ *  For easier compatibility with Skia's GPU backend, Skia normally restricts
+ *  these to either (in memory-byte-order) RGBA or BGRA. Mozilla's big-endian
+ *  PowerPC port uses CoreGraphics' native ARGB pixels, so we also accept ARGB.
+ *  Note that this "order" does not directly correspond to the same shift-order,
+ *  since we have to take endianess into account.
  *
  *  Here we enforce this constraint.
  */
 
 #ifdef SK_CPU_BENDIAN
+    #define SK_ARGB_A32_SHIFT   24
+    #define SK_ARGB_R32_SHIFT   16
+    #define SK_ARGB_G32_SHIFT   8
+    #define SK_ARGB_B32_SHIFT   0
+
     #define SK_RGBA_R32_SHIFT   24
     #define SK_RGBA_G32_SHIFT   16
     #define SK_RGBA_B32_SHIFT   8
@@ -43,6 +49,11 @@
     #define SK_BGRA_R32_SHIFT   8
     #define SK_BGRA_A32_SHIFT   0
 #else
+    #define SK_ARGB_A32_SHIFT   0
+    #define SK_ARGB_R32_SHIFT   8
+    #define SK_ARGB_G32_SHIFT   16
+    #define SK_ARGB_B32_SHIFT   24
+
     #define SK_RGBA_R32_SHIFT   0
     #define SK_RGBA_G32_SHIFT   8
     #define SK_RGBA_B32_SHIFT   16
@@ -54,10 +65,18 @@
     #define SK_BGRA_A32_SHIFT   24
 #endif
 
-#if defined(SK_PMCOLOR_IS_RGBA) && defined(SK_PMCOLOR_IS_BGRA)
-    #error "can't define PMCOLOR to be RGBA and BGRA"
+#if (defined(SK_PMCOLOR_IS_RGBA) && defined(SK_PMCOLOR_IS_BGRA)) || \
+    (defined(SK_PMCOLOR_IS_RGBA) && defined(SK_PMCOLOR_IS_ARGB)) || \
+    (defined(SK_PMCOLOR_IS_BGRA) && defined(SK_PMCOLOR_IS_ARGB))
+    #error "can't define PMCOLOR to more than one byte order"
 #endif
 
+#define LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_ARGB  \
+    (SK_A32_SHIFT == SK_ARGB_A32_SHIFT &&    \
+     SK_R32_SHIFT == SK_ARGB_R32_SHIFT &&    \
+     SK_G32_SHIFT == SK_ARGB_G32_SHIFT &&    \
+     SK_B32_SHIFT == SK_ARGB_B32_SHIFT)
+
 #define LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_RGBA  \
     (SK_A32_SHIFT == SK_RGBA_A32_SHIFT &&    \
      SK_R32_SHIFT == SK_RGBA_R32_SHIFT &&    \
@@ -76,6 +95,10 @@
 #define SK_G_INDEX  (SK_G32_SHIFT/8)
 #define SK_B_INDEX  (SK_B32_SHIFT/8)
 
+#if defined(SK_PMCOLOR_IS_ARGB) && !LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_ARGB
+    #error "SK_PMCOLOR_IS_ARGB does not match SK_*32_SHIFT values"
+#endif
+
 #if defined(SK_PMCOLOR_IS_RGBA) && !LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_RGBA
     #error "SK_PMCOLOR_IS_RGBA does not match SK_*32_SHIFT values"
 #endif
@@ -84,19 +107,22 @@
     #error "SK_PMCOLOR_IS_BGRA does not match SK_*32_SHIFT values"
 #endif
 
-#if !defined(SK_PMCOLOR_IS_RGBA) && !defined(SK_PMCOLOR_IS_BGRA)
+#if !defined(SK_PMCOLOR_IS_ARGB) && !defined(SK_PMCOLOR_IS_RGBA) && !defined(SK_PMCOLOR_IS_BGRA)
     // deduce which to define from the _SHIFT defines
 
-    #if LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_RGBA
+    #if LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_ARGB
+        #define SK_PMCOLOR_IS_ARGB
+    #elif LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_RGBA
         #define SK_PMCOLOR_IS_RGBA
     #elif LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_BGRA
         #define SK_PMCOLOR_IS_BGRA
     #else
-        #error "need 32bit packing to be either RGBA or BGRA"
+        #error "need 32bit packing to be either ARGB, RGBA, or BGRA"
     #endif
 #endif
 
 // hide these now that we're done
+#undef LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_ARGB
 #undef LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_RGBA
 #undef LOCAL_PMCOLOR_SHIFTS_EQUIVALENT_TO_BGRA
 
@@ -131,19 +157,38 @@ static inline uint32_t SkPackARGB_as_BGRA(U8CPU a, U8CPU r, U8CPU g, U8CPU b) {
            (g << SK_BGRA_G32_SHIFT) | (b << SK_BGRA_B32_SHIFT);
 }
 
+static inline SkPMColor SkPackARGB_as_PMColor(U8CPU a, U8CPU r, U8CPU g, U8CPU b) {
+    SkASSERT_IS_BYTE(a);
+    SkASSERT_IS_BYTE(r);
+    SkASSERT_IS_BYTE(g);
+    SkASSERT_IS_BYTE(b);
+    return (a << SK_A32_SHIFT) | (r << SK_R32_SHIFT) |
+           (g << SK_G32_SHIFT) | (b << SK_B32_SHIFT);
+}
+
 static inline SkPMColor SkSwizzle_RGBA_to_PMColor(uint32_t c) {
 #ifdef SK_PMCOLOR_IS_RGBA
     return c;
-#else
+#elif defined(SK_PMCOLOR_IS_BGRA)
     return SkSwizzle_RB(c);
+#else
+    return SkPackARGB_as_PMColor((c >> SK_RGBA_A32_SHIFT) & 0xFF,
+                                 (c >> SK_RGBA_R32_SHIFT) & 0xFF,
+                                 (c >> SK_RGBA_G32_SHIFT) & 0xFF,
+                                 (c >> SK_RGBA_B32_SHIFT) & 0xFF);
 #endif
 }
 
 static inline SkPMColor SkSwizzle_BGRA_to_PMColor(uint32_t c) {
 #ifdef SK_PMCOLOR_IS_BGRA
     return c;
-#else
+#elif defined(SK_PMCOLOR_IS_RGBA)
     return SkSwizzle_RB(c);
+#else
+    return SkPackARGB_as_PMColor((c >> SK_BGRA_A32_SHIFT) & 0xFF,
+                                 (c >> SK_BGRA_R32_SHIFT) & 0xFF,
+                                 (c >> SK_BGRA_G32_SHIFT) & 0xFF,
+                                 (c >> SK_BGRA_B32_SHIFT) & 0xFF);
 #endif
 }
 
@@ -412,8 +457,7 @@ static inline SkPMColor SkPackARGB32(U8CPU a, U8CPU r, U8CPU g, U8CPU b) {
     SkASSERT(g <= a);
     SkASSERT(b <= a);
 
-    return (a << SK_A32_SHIFT) | (r << SK_R32_SHIFT) |
-           (g << SK_G32_SHIFT) | (b << SK_B32_SHIFT);
+    return SkPackARGB_as_PMColor(a, r, g, b);
 }
 
 static inline uint32_t SkPackPMColor_as_RGBA(SkPMColor c) {
@@ -547,8 +591,7 @@ static inline SkPMColor SkFastFourByteInterp(SkPMColor src,
  *  values are premultiplied in the debug version.
  */
 static inline SkPMColor SkPackARGB32NoCheck(U8CPU a, U8CPU r, U8CPU g, U8CPU b) {
-    return (a << SK_A32_SHIFT) | (r << SK_R32_SHIFT) |
-           (g << SK_G32_SHIFT) | (b << SK_B32_SHIFT);
+    return SkPackARGB_as_PMColor(a, r, g, b);
 }
 
 static inline

gfx/skia/skia/include/core/SkImageInfo.h

@@ -82,8 +82,13 @@ enum SkColorType {
     kN32_SkColorType = kBGRA_8888_SkColorType,
 #elif SK_PMCOLOR_BYTE_ORDER(R,G,B,A)
     kN32_SkColorType = kRGBA_8888_SkColorType,
+#elif defined(MOZ_SKIA) && SK_PMCOLOR_BYTE_ORDER(A,R,G,B)
+    // Big-endian PowerPC Mozilla surfaces use native uint32 ARGB memory.
+    // Moz2D's legacy A8R8G8B8_UINT32 format aliases to B8G8R8A8, so keep
+    // kN32 on Skia's BGRA path while the channel shifts above describe ARGB.
+    kN32_SkColorType = kBGRA_8888_SkColorType,
 #else
-    #error "SK_*32_SHFIT values must correspond to BGRA or RGBA byte order"
+    #error "SK_*32_SHIFT values must correspond to BGRA, RGBA, or Mozilla ARGB byte order"
 #endif
 };
 

gfx/skia/skia/include/gpu/GrTypes.h

@@ -275,17 +275,19 @@ enum GrPixelConfig {
 static const int kGrPixelConfigCnt = kLast_GrPixelConfig + 1;
 
 // Aliases for pixel configs that match skia's byte order.
-#ifndef SK_CPU_LENDIAN
-    #error "Skia gpu currently assumes little endian"
-#endif
 #if SK_PMCOLOR_BYTE_ORDER(B,G,R,A)
     static const GrPixelConfig kSkia8888_GrPixelConfig = kBGRA_8888_GrPixelConfig;
     static const GrPixelConfig kSkiaGamma8888_GrPixelConfig = kSBGRA_8888_GrPixelConfig;
 #elif SK_PMCOLOR_BYTE_ORDER(R,G,B,A)
     static const GrPixelConfig kSkia8888_GrPixelConfig = kRGBA_8888_GrPixelConfig;
     static const GrPixelConfig kSkiaGamma8888_GrPixelConfig = kSRGBA_8888_GrPixelConfig;
+#elif defined(MOZ_SKIA) && SK_PMCOLOR_BYTE_ORDER(A,R,G,B)
+    // Mozilla's big-endian PowerPC path stores native 32-bit pixels as ARGB,
+    // while Moz2D routes those surfaces through Skia's BGRA color type.
+    static const GrPixelConfig kSkia8888_GrPixelConfig = kBGRA_8888_GrPixelConfig;
+    static const GrPixelConfig kSkiaGamma8888_GrPixelConfig = kSBGRA_8888_GrPixelConfig;
 #else
-    #error "SK_*32_SHIFT values must correspond to GL_BGRA or GL_RGBA format."
+    #error "SK_*32_SHIFT values must correspond to GL_BGRA, GL_RGBA, or Mozilla ARGB format."
 #endif
 
 // Returns true if the pixel config is a GPU-specific compressed format

gfx/skia/skia/src/codec/SkCodecPriv.h

@@ -306,7 +306,11 @@ static inline SkPMColor premultiply_argb_as_bgra(U8CPU a, U8CPU r, U8CPU g, U8CP
         b = SkMulDiv255Round(b, a);
     }
 
+#ifdef SK_PMCOLOR_IS_ARGB
+    return SkPackARGB_as_PMColor(a, r, g, b);
+#else
     return SkPackARGB_as_BGRA(a, r, g, b);
+#endif
 }
 
 static inline bool is_rgba(SkColorType colorType) {

gfx/skia/skia/src/core/SkPM4f.h

@@ -51,10 +51,16 @@ struct SkPM4f {
     Sk4f to4f_pmorder() const { return swizzle_rb_if_bgra(this->to4f()); }
 
     SkPMColor toPMColor() const {
+#ifdef SK_PMCOLOR_IS_ARGB
+        Sk4f value = this->to4f();
+        Sk4b bytes = SkNx_cast<uint8_t>(value * Sk4f(255) + Sk4f(0.5f));
+        return SkPackARGB_as_PMColor(bytes[3], bytes[0], bytes[1], bytes[2]);
+#else
         Sk4f value = swizzle_rb_if_bgra(this->to4f());
         SkPMColor result;
         SkNx_cast<uint8_t>(value * Sk4f(255) + Sk4f(0.5f)).store(&result);
         return result;
+#endif
     }
 
     void toF16(uint16_t[4]) const;

gfx/skia/skia/src/core/SkPM4fPriv.h

@@ -22,29 +22,50 @@ static inline float get_alpha(const Sk4f& px) {
 
 
 static inline Sk4f Sk4f_fromL32(uint32_t px) {
+#ifdef SK_PMCOLOR_IS_ARGB
+    return Sk4f(SkGetPackedR32(px), SkGetPackedG32(px),
+                SkGetPackedB32(px), SkGetPackedA32(px)) * (1/255.0f);
+#else
     return SkNx_cast<float>(Sk4b::Load(&px)) * (1/255.0f);
+#endif
 }
 
 static inline Sk4f Sk4f_fromS32(uint32_t px) {
+#ifdef SK_PMCOLOR_IS_ARGB
+    return { sk_linear_from_srgb[SkGetPackedR32(px)],
+             sk_linear_from_srgb[SkGetPackedG32(px)],
+             sk_linear_from_srgb[SkGetPackedB32(px)],
+                    (1/255.0f) * SkGetPackedA32(px) };
+#else
     return { sk_linear_from_srgb[(px >>  0) & 0xff],
              sk_linear_from_srgb[(px >>  8) & 0xff],
              sk_linear_from_srgb[(px >> 16) & 0xff],
                     (1/255.0f) * (px >> 24)          };
+#endif
 }
 
 static inline uint32_t Sk4f_toL32(const Sk4f& px) {
+#ifdef SK_PMCOLOR_IS_ARGB
+    Sk4b bytes = SkNx_cast<uint8_t>(Sk4f_round(px * 255.0f));
+    return SkPackARGB_as_PMColor(bytes[3], bytes[0], bytes[1], bytes[2]);
+#else
     uint32_t l32;
     SkNx_cast<uint8_t>(Sk4f_round(px * 255.0f)).store(&l32);
     return l32;
+#endif
 }
 
 static inline uint32_t Sk4f_toS32(const Sk4f& px) {
     Sk4i  rgb = sk_linear_to_srgb(px),
          srgb = { rgb[0], rgb[1], rgb[2], (int)(255.0f * px[3] + 0.5f) };
 
+#ifdef SK_PMCOLOR_IS_ARGB
+    return SkPackARGB_as_PMColor(srgb[3], srgb[0], srgb[1], srgb[2]);
+#else
     uint32_t s32;
     SkNx_cast<uint8_t>(srgb).store(&s32);
     return s32;
+#endif
 }
 
 

gfx/skia/skia/src/core/SkTextBlob.cpp

@@ -121,9 +121,10 @@ SkDEBUGCODE(static const unsigned kRunRecordMagic = 0xb10bcafe;)
 namespace {
 struct RunRecordStorageEquivalent {
     RunFont  fFont;
-    SkPoint  fOffset;
     uint32_t fCount;
-    uint32_t fFlags;
+    SkPoint  fOffset;
+    SkTextBlob::GlyphPositioning fPositioning;
+    bool     fExtended;
     SkDEBUGCODE(unsigned fMagic;)
 };
 }

gfx/skia/skia/src/core/SkXfermode4f.cpp

@@ -44,6 +44,25 @@ static Sk4x4f load_4_srgb(const void* vptr) {
 
     Sk4x4f rgba;
 
+#ifdef SK_PMCOLOR_IS_ARGB
+    rgba.r = { sk_linear_from_srgb[SkGetPackedR32(ptr[0])],
+               sk_linear_from_srgb[SkGetPackedR32(ptr[1])],
+               sk_linear_from_srgb[SkGetPackedR32(ptr[2])],
+               sk_linear_from_srgb[SkGetPackedR32(ptr[3])] };
+
+    rgba.g = { sk_linear_from_srgb[SkGetPackedG32(ptr[0])],
+               sk_linear_from_srgb[SkGetPackedG32(ptr[1])],
+               sk_linear_from_srgb[SkGetPackedG32(ptr[2])],
+               sk_linear_from_srgb[SkGetPackedG32(ptr[3])] };
+
+    rgba.b = { sk_linear_from_srgb[SkGetPackedB32(ptr[0])],
+               sk_linear_from_srgb[SkGetPackedB32(ptr[1])],
+               sk_linear_from_srgb[SkGetPackedB32(ptr[2])],
+               sk_linear_from_srgb[SkGetPackedB32(ptr[3])] };
+
+    rgba.a = SkNx_cast<float>(Sk4i(SkGetPackedA32(ptr[0]), SkGetPackedA32(ptr[1]),
+                                   SkGetPackedA32(ptr[2]), SkGetPackedA32(ptr[3]))) * (1/255.0f);
+#else
     rgba.r = { sk_linear_from_srgb[(ptr[0] >>  0) & 0xff],
                sk_linear_from_srgb[(ptr[1] >>  0) & 0xff],
                sk_linear_from_srgb[(ptr[2] >>  0) & 0xff],
@@ -60,15 +79,28 @@ static Sk4x4f load_4_srgb(const void* vptr) {
                sk_linear_from_srgb[(ptr[3] >> 16) & 0xff] };
 
     rgba.a = SkNx_cast<float>((Sk4i::Load(ptr) >> 24) & 0xff) * (1/255.0f);
+#endif
 
     return rgba;
 }
 
 static void store_4_srgb(void* ptr, const Sk4x4f& p) {
+#ifdef SK_PMCOLOR_IS_ARGB
+    uint32_t* dst = (uint32_t*)ptr;
+    Sk4i r = sk_linear_to_srgb(p.r);
+    Sk4i g = sk_linear_to_srgb(p.g);
+    Sk4i b = sk_linear_to_srgb(p.b);
+    Sk4i a = Sk4f_round(255.0f*p.a);
+    dst[0] = SkPackARGB_as_PMColor(a[0], r[0], g[0], b[0]);
+    dst[1] = SkPackARGB_as_PMColor(a[1], r[1], g[1], b[1]);
+    dst[2] = SkPackARGB_as_PMColor(a[2], r[2], g[2], b[2]);
+    dst[3] = SkPackARGB_as_PMColor(a[3], r[3], g[3], b[3]);
+#else
     ( sk_linear_to_srgb(p.r) <<  0
     | sk_linear_to_srgb(p.g) <<  8
     | sk_linear_to_srgb(p.b) << 16
     | Sk4f_round(255.0f*p.a) << 24).store(ptr);
+#endif
 }
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
@@ -391,7 +423,7 @@ SkXfermode::D32Proc SkXfermode::GetD32Proc(SkXfermode* xfer, uint32_t flags) {
 #include "SkColorPriv.h"
 
 static Sk4f lcd16_to_unit_4f(uint16_t rgb) {
-#ifdef SK_PMCOLOR_IS_RGBA
+#if defined(SK_PMCOLOR_IS_RGBA) || defined(SK_PMCOLOR_IS_ARGB)
     Sk4i rgbi = Sk4i(SkGetPackedR16(rgb), SkGetPackedG16(rgb), SkGetPackedB16(rgb), 0);
 #else
     Sk4i rgbi = Sk4i(SkGetPackedB16(rgb), SkGetPackedG16(rgb), SkGetPackedR16(rgb), 0);

gfx/skia/skia/src/gpu/GrDrawTarget.cpp

@@ -251,7 +251,7 @@ bool GrDrawTarget::drawBatches(GrBatchFlushState* flushState) {
             if (currentRT) {
                 static const GrGpuCommandBuffer::LoadAndStoreInfo kBasicLoadStoreInfo
                     { GrGpuCommandBuffer::LoadOp::kLoad,GrGpuCommandBuffer::StoreOp::kStore,
-                      GrColor_ILLEGAL };
+                      static_cast<GrColor>(GrColor_ILLEGAL) };
                 commandBuffer.reset(fGpu->createCommandBuffer(currentRT,
                                                               kBasicLoadStoreInfo,   // Color
                                                               kBasicLoadStoreInfo)); // Stencil

gfx/skia/skia/src/opts/Sk4px_none.h

@@ -69,11 +69,18 @@ inline Sk4px Sk4px::Wide::div255() const {
 }
 
 inline Sk4px Sk4px::alphas() const {
+#ifdef SK_PMCOLOR_IS_ARGB
+    return Sk16b((*this)[ 0], (*this)[ 0], (*this)[ 0], (*this)[ 0],
+                 (*this)[ 4], (*this)[ 4], (*this)[ 4], (*this)[ 4],
+                 (*this)[ 8], (*this)[ 8], (*this)[ 8], (*this)[ 8],
+                 (*this)[12], (*this)[12], (*this)[12], (*this)[12]);
+#else
     static_assert(SK_A32_SHIFT == 24, "This method assumes little-endian.");
     return Sk16b((*this)[ 3], (*this)[ 3], (*this)[ 3], (*this)[ 3],
                  (*this)[ 7], (*this)[ 7], (*this)[ 7], (*this)[ 7],
                  (*this)[11], (*this)[11], (*this)[11], (*this)[11],
                  (*this)[15], (*this)[15], (*this)[15], (*this)[15]);
+#endif
 }
 
 inline Sk4px Sk4px::Load4Alphas(const SkAlpha a[4]) {
@@ -91,19 +98,33 @@ inline Sk4px Sk4px::Load2Alphas(const SkAlpha a[2]) {
 }
 
 inline Sk4px Sk4px::zeroAlphas() const {
+#ifdef SK_PMCOLOR_IS_ARGB
+    return Sk16b(0, (*this)[ 1], (*this)[ 2], (*this)[ 3],
+                 0, (*this)[ 5], (*this)[ 6], (*this)[ 7],
+                 0, (*this)[ 9], (*this)[10], (*this)[11],
+                 0, (*this)[13], (*this)[14], (*this)[15]);
+#else
     static_assert(SK_A32_SHIFT == 24, "This method assumes little-endian.");
     return Sk16b((*this)[ 0], (*this)[ 1], (*this)[ 2], 0,
                  (*this)[ 4], (*this)[ 5], (*this)[ 6], 0,
                  (*this)[ 8], (*this)[ 9], (*this)[10], 0,
                  (*this)[12], (*this)[13], (*this)[14], 0);
+#endif
 }
 
 inline Sk4px Sk4px::zeroColors() const {
+#ifdef SK_PMCOLOR_IS_ARGB
+    return Sk16b((*this)[ 0], 0,0,0,
+                 (*this)[ 4], 0,0,0,
+                 (*this)[ 8], 0,0,0,
+                 (*this)[12], 0,0,0);
+#else
     static_assert(SK_A32_SHIFT == 24, "This method assumes little-endian.");
     return Sk16b(0,0,0, (*this)[ 3],
                  0,0,0, (*this)[ 7],
                  0,0,0, (*this)[11],
                  0,0,0, (*this)[15]);
+#endif
 }
 
 }  // namespace

gfx/skia/skia/src/opts/SkColorCubeFilter_opts.h

@@ -72,6 +72,10 @@ static void color_cube_filter_span(const SkPMColor src[],
         // color is BGRA (SkColor order), dst is SkPMColor order, so may need to swap R+B.
     #if defined(SK_PMCOLOR_IS_RGBA)
         color = SkNx_shuffle<2,1,0,3>(color);
+    #elif defined(SK_PMCOLOR_IS_ARGB)
+        Sk4b bytes = SkNx_cast<uint8_t>(color);
+        dst[i] = SkPackARGB32NoCheck(a, bytes[2], bytes[1], bytes[0]);
+        continue;
     #endif
         uint8_t* dstBytes = (uint8_t*)(dst+i);
         SkNx_cast<uint8_t>(color).store(dstBytes);

gfx/skia/skia/src/ports/SkFontHost_mac.cpp

@@ -73,7 +73,39 @@ static CFArrayRef SkCTFontManagerCopyAvailableFontFamilyNames() {
 #ifdef SK_BUILD_FOR_IOS
     return CFArrayCreate(nullptr, nullptr, 0, nullptr);
 #else
+#if defined(MAC_OS_X_VERSION_10_6) && (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_6)
     return CTFontManagerCopyAvailableFontFamilyNames();
+#else
+    CFMutableArrayRef familyNames =
+            CFArrayCreateMutable(kCFAllocatorDefault, 0, &kCFTypeArrayCallBacks);
+    if (!familyNames) {
+        return nullptr;
+    }
+
+    ATSFontFamilyIterator iterator;
+    OSStatus status = ATSFontFamilyIteratorCreate(kATSFontContextGlobal,
+                                                  nullptr,
+                                                  nullptr,
+                                                  kATSOptionFlagsDefaultScope,
+                                                  &iterator);
+    if (status != noErr) {
+        CFRelease(familyNames);
+        return nullptr;
+    }
+
+    ATSFontFamilyRef family;
+    while (ATSFontFamilyIteratorNext(iterator, &family) == noErr) {
+        CFStringRef familyName = nullptr;
+        if (ATSFontFamilyGetName(family, kATSOptionFlagsDefault, &familyName) == noErr &&
+            familyName) {
+            CFArrayAppendValue(familyNames, familyName);
+            CFRelease(familyName);
+        }
+    }
+
+    ATSFontFamilyIteratorRelease(&iterator);
+    return familyNames;
+#endif
 #endif
 }
 
@@ -908,6 +940,7 @@ CGRGBPixel* Offscreen::getCG(const SkScalerContext_Mac& context, const SkGlyph&
 
         // Skia handles quantization and subpixel positioning,
         // so disable quantization and enabe subpixel positioning in CG.
+#if defined(MAC_OS_X_VERSION_10_6) && (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_6)
         CGContextSetAllowsFontSubpixelQuantization(fCG, false);
         CGContextSetShouldSubpixelQuantizeFonts(fCG, false);
 
@@ -916,6 +949,7 @@ CGRGBPixel* Offscreen::getCG(const SkScalerContext_Mac& context, const SkGlyph&
         // then CG cannot draw the glyph in the correct location without subpixel positioning.
         CGContextSetAllowsFontSubpixelPositioning(fCG, true);
         CGContextSetShouldSubpixelPositionFonts(fCG, true);
+#endif
 
         CGContextSetTextDrawingMode(fCG, kCGTextFill);
 
@@ -971,7 +1005,13 @@ CGRGBPixel* Offscreen::getCG(const SkScalerContext_Mac& context, const SkGlyph&
     // So always make the font transform identity and place the transform on the context.
     point = CGPointApplyAffineTransform(point, context.fInvTransform);
 
+#if defined(MAC_OS_X_VERSION_10_7) && (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_7)
     CTFontDrawGlyphs(context.fCTFont, &glyphID, &point, 1, fCG);
+#else
+    CGContextSetFont(fCG, CTFontCopyGraphicsFont(context.fCTFont, NULL));
+    CGContextSetFontSize(fCG, CTFontGetSize(context.fCTFont));
+    CGContextShowGlyphsAtPositions(fCG, &glyphID, &point, 1);
+#endif
 
     SkASSERT(rowBytesPtr);
     *rowBytesPtr = rowBytes;
@@ -1682,6 +1722,7 @@ SkAdvancedTypefaceMetrics* SkTypeface_Mac::onGetAdvancedTypefaceMetrics(
 
 static SK_SFNT_ULONG get_font_type_tag(const SkTypeface_Mac* typeface) {
     CTFontRef ctFont = typeface->fFontRef.get();
+#if defined(MAC_OS_X_VERSION_10_6) && (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_6)
     AutoCFRelease<CFNumberRef> fontFormatRef(
             static_cast<CFNumberRef>(CTFontCopyAttribute(ctFont, kCTFontFormatAttribute)));
     if (!fontFormatRef) {
@@ -1711,6 +1752,35 @@ static SK_SFNT_ULONG get_font_type_tag(const SkTypeface_Mac* typeface) {
             //Just the presence of the FontForge 'FFTM' table seems to throw it off.
             return SkSFNTHeader::fontType_WindowsTrueType::TAG;
     }
+#else
+    AutoCFRelease<CFStringRef> postScriptName(CTFontCopyPostScriptName(ctFont));
+    if (!postScriptName) {
+        return 0;
+    }
+
+    ATSFontRef atsFont =
+            ATSFontFindFromPostScriptName(postScriptName, kATSOptionFlagsDefault);
+    if (atsFont == kInvalidFont) {
+        return 0;
+    }
+
+    SkSFNTHeader header;
+    ByteCount headerSize = sizeof(header);
+    if (ATSFontGetTableDirectory(atsFont, headerSize, &header, &headerSize) != noErr ||
+        headerSize < sizeof(header.fontType)) {
+        return 0;
+    }
+
+    switch (header.fontType) {
+        case SkSFNTHeader::fontType_OpenTypeCFF::TAG:
+        case SkSFNTHeader::fontType_WindowsTrueType::TAG:
+        case SkSFNTHeader::fontType_MacTrueType::TAG:
+        case SkSFNTHeader::fontType_PostScript::TAG:
+            return header.fontType;
+        default:
+            return SkSFNTHeader::fontType_WindowsTrueType::TAG;
+    }
+#endif
 }
 
 SkStreamAsset* SkTypeface_Mac::onOpenStream(int* ttcIndex) const {

js/src/jit/CodeGenerator.cpp

@@ -8185,7 +8185,7 @@ CodeGenerator::visitStoreElementV(LStoreElementV* lir)
 template <typename T> void
 CodeGenerator::emitStoreElementHoleT(T* lir)
 {
-    static_assert(std::is_same<T, LStoreElementHoleT>::value || std::is_same<T, LFallibleStoreElementT>::value,
+    static_assert(std::is_same_v<T, LStoreElementHoleT> || std::is_same_v<T, LFallibleStoreElementT>,
                   "emitStoreElementHoleT called with unexpected argument type");
 
     OutOfLineStoreElementHole* ool = new(alloc()) OutOfLineStoreElementHole(lir);
@@ -8244,7 +8244,7 @@ CodeGenerator::visitStoreElementHoleT(LStoreElementHoleT* lir)
 template <typename T> void
 CodeGenerator::emitStoreElementHoleV(T* lir)
 {
-    static_assert(std::is_same<T, LStoreElementHoleV>::value || std::is_same<T, LFallibleStoreElementV>::value,
+    static_assert(std::is_same_v<T, LStoreElementHoleV> || std::is_same_v<T, LFallibleStoreElementV>,
                   "emitStoreElementHoleV called with unexpected parameter type");
 
     OutOfLineStoreElementHole* ool = new(alloc()) OutOfLineStoreElementHole(lir);

js/src/jsstr.cpp

@@ -2871,8 +2871,8 @@ static JSString* ReplaceAll(JSContext* cx, JSLinearString* str,
 
     // Step 13.
     StringBuffer result(cx);
-    if (std::is_same<StrChar, char16_t>::value ||
-      std::is_same<RepChar, char16_t>::value) {
+    if (std::is_same_v<StrChar, char16_t> ||
+      std::is_same_v<RepChar, char16_t>) {
         if (!result.ensureTwoByteChars()) {
           return nullptr;
         }
@@ -2954,8 +2954,8 @@ static JSString* ReplaceAllInterleave(JSContext* cx, JSLinearString* str,
 
     // Step 13.
     StringBuffer result(cx);
-    if (std::is_same<StrChar, char16_t>::value ||
-        std::is_same<RepChar, char16_t>::value) {
+    if (std::is_same_v<StrChar, char16_t> ||
+        std::is_same_v<RepChar, char16_t>) {
         if (!result.ensureTwoByteChars()) {
             return nullptr;
         }

js/src/vm/CharacterEncoding.cpp

@@ -309,26 +309,26 @@ InflateUTF8StringToBuffer(ContextT* cx, const UTF8Chars src, CharT* dst, size_t*
             while (v & (0x80 >> n))
                 n++;
 
-        #define INVALID(report, arg, n2)                                \
-            do {                                                        \
-                if (Action == CountAndReportInvalids) {                 \
-                    report(cx, arg);                                    \
-                    return false;                                       \
-                } else if (Action == AssertNoInvalids) {                \
-                    MOZ_CRASH("invalid UTF-8 string: " # report);       \
-                } else {                                                \
-                    if (Action == Copy) {                               \
-                        if (std::is_same<decltype(dst[0]), Latin1Char>::value) \
-                            dst[j] = CharT(REPLACE_UTF8_LATIN1);        \
-                        else                                            \
-                            dst[j] = CharT(REPLACE_UTF8);               \
-                    } else {                                            \
-                        MOZ_ASSERT(Action == CountAndIgnoreInvalids ||  \
-                                   Action == FindEncoding);             \
-                    }                                                   \
-                    n = n2;                                             \
-                    goto invalidMultiByteCodeUnit;                      \
-                }                                                       \
+        #define INVALID(report, arg, n2)                                  \
+            do {                                                          \
+                if (Action == CountAndReportInvalids) {                   \
+                    report(cx, arg);                                      \
+                    return false;                                         \
+                } else if (Action == AssertNoInvalids) {                  \
+                    MOZ_CRASH("invalid UTF-8 string: " # report);         \
+                } else {                                                  \
+                    if (Action == Copy) {                                 \
+                        if (std::is_same_v<decltype(dst[0]), Latin1Char>) \
+                            dst[j] = CharT(REPLACE_UTF8_LATIN1);          \
+                        else                                              \
+                            dst[j] = CharT(REPLACE_UTF8);                 \
+                    } else {                                              \
+                        MOZ_ASSERT(Action == CountAndIgnoreInvalids ||    \
+                                   Action == FindEncoding);               \
+                    }                                                     \
+                    n = n2;                                               \
+                    goto invalidMultiByteCodeUnit;                        \
+                }                                                         \
             } while (0)
 
             // Check the leading byte.

js/src/vm/String.h

@@ -1138,7 +1138,7 @@ class StaticStrings
     }
 
     template <typename CharT,
-              typename = typename std::enable_if<!std::is_const<CharT>::value>::type>
+              typename = typename std::enable_if_t<!std::is_const_v<CharT>>>
     MOZ_ALWAYS_INLINE JSAtom* lookup(CharT* chars, size_t length) {
         // Collapse the remaining |CharT*| to |const CharT*| to avoid excess
         // instantiations.

js/src/vm/TypedArrayCommon.h

@@ -677,12 +677,12 @@ class ElementSpecific
             return true;
         }
 
-        if (std::is_same<T, int64_t>::value) {
+        if (std::is_same_v<T, int64_t>) {
             JS_TRY_VAR_OR_RETURN_FALSE(cx, *result, ToBigInt64(cx, v));
             return true;
         }
 
-        if (std::is_same<T, uint64_t>::value) {
+        if (std::is_same_v<T, uint64_t>) {
             JS_TRY_VAR_OR_RETURN_FALSE(cx, *result, ToBigUint64(cx, v));
             return true;
         }

layout/inspector/inDOMUtils.cpp

@@ -953,11 +953,12 @@ inDOMUtils::GetCSSValuesForProperty(const nsAString& aProperty,
       GetOtherValuesForProperty(propertyParserVariant, array);
     }
   }
-  // All CSS properties take initial, inherit, unset, and revert.
+  // All CSS properties take initial, inherit, unset, revert, and revert-layer.
   InsertNoDuplicates(array, NS_LITERAL_STRING("initial"));
   InsertNoDuplicates(array, NS_LITERAL_STRING("inherit"));
   InsertNoDuplicates(array, NS_LITERAL_STRING("unset"));
   InsertNoDuplicates(array, NS_LITERAL_STRING("revert"));
+  InsertNoDuplicates(array, NS_LITERAL_STRING("revert-layer"));
 
   *aLength = array.Length();
   char16_t** ret =

layout/style/CSSVariableDeclarations.cpp

@@ -8,19 +8,227 @@
 #include "CSSVariableDeclarations.h"
 
 #include "CSSVariableResolver.h"
+#include "CSSVariableValues.h"
 #include "nsCSSScanner.h"
 #include "nsRuleData.h"
 
-// These four special string values are used to represent specified values of
-// 'initial', 'inherit', 'unset', and 'revert'.  (Note that none of these are
-// valid variable values.)
+// These special string values are used to represent specified values of
+// CSS-wide keywords.  (Note that none of these are valid variable values.)
 #define INITIAL_VALUE "!"
 #define INHERIT_VALUE ";"
 #define UNSET_VALUE   ")"
 #define REVERT_VALUE  ">"
+#define REVERT_LAYER_VALUE  "]"
+
+static const int32_t kRevertLayerMask = 0x000fffff;
+static const int32_t kRevertLayerImportant = 0x00100000;
+static const int32_t kRevertLayerOriginShift = 21;
+static const int32_t kLayerIndexMax = 0x000fffff;
+static const int32_t kCascadeRankStride = kLayerIndexMax + 1;
 
 namespace mozilla {
 
+static bool
+IsRevertLayerValue(const nsString& aValue)
+{
+  return StringBeginsWith(aValue, NS_LITERAL_STRING(REVERT_LAYER_VALUE));
+}
+
+static bool
+ValueMightResolveToRevertLayer(const nsString& aValue)
+{
+  return IsRevertLayerValue(aValue) ||
+         aValue.Find(NS_LITERAL_STRING("revert-layer")) != kNotFound;
+}
+
+static int32_t
+PackRevertLayerData(SheetType aLevel, bool aIsImportant,
+                    int32_t aLayerIndex)
+{
+  MOZ_ASSERT(aLayerIndex >= 0 && aLayerIndex <= kRevertLayerMask);
+  return (uint32_t(aLevel) << kRevertLayerOriginShift) |
+         (aIsImportant ? kRevertLayerImportant : 0) |
+         (aLayerIndex & kRevertLayerMask);
+}
+
+static void
+SetRevertLayerData(nsString& aValue, const nsRuleData* aRuleData)
+{
+  aValue.AssignLiteral(REVERT_LAYER_VALUE);
+  aValue.AppendInt(PackRevertLayerData(aRuleData->mLevel,
+                                       aRuleData->mIsImportantRule,
+                                       aRuleData->mLayerIndex));
+}
+
+static bool
+UnpackRevertLayerData(const nsString& aValue, SheetType& aLevel,
+                      bool& aIsImportant, int32_t& aLayerIndex)
+{
+  if (!IsRevertLayerValue(aValue) ||
+      aValue.Length() == NS_LITERAL_STRING(REVERT_LAYER_VALUE).Length()) {
+    return false;
+  }
+
+  nsresult rv;
+  nsAutoString metadata;
+  metadata.Assign(Substring(aValue,
+                            NS_LITERAL_STRING(REVERT_LAYER_VALUE).Length()));
+  int32_t packed = metadata.ToInteger(&rv);
+  if (NS_FAILED(rv)) {
+    return false;
+  }
+
+  aLevel = SheetType(uint32_t(packed) >> kRevertLayerOriginShift);
+  aIsImportant = (packed & kRevertLayerImportant) != 0;
+  aLayerIndex = packed & kRevertLayerMask;
+  return true;
+}
+
+static int32_t
+LayerIndexRank(bool aIsImportant, int32_t aLayerIndex)
+{
+  MOZ_ASSERT(aLayerIndex >= 0);
+  MOZ_ASSERT(aLayerIndex <= kLayerIndexMax);
+  return aIsImportant ? kLayerIndexMax - aLayerIndex : aLayerIndex;
+}
+
+static int32_t
+CascadePrecedenceRank(SheetType aLevel, bool aIsImportant,
+                      int32_t aLayerIndex)
+{
+  int32_t bucket = 0;
+  bool isLayeredOrigin = false;
+
+  switch (aLevel) {
+    case SheetType::Agent:
+      bucket = aIsImportant ? 14 : 0;
+      isLayeredOrigin = true;
+      break;
+    case SheetType::User:
+      bucket = aIsImportant ? 13 : 1;
+      isLayeredOrigin = true;
+      break;
+    case SheetType::PresHint:
+      bucket = 2;
+      break;
+    case SheetType::SVGAttrAnimation:
+      bucket = 3;
+      break;
+    case SheetType::Doc:
+      bucket = aIsImportant ? 10 : 4;
+      isLayeredOrigin = true;
+      break;
+    case SheetType::ScopedDoc:
+      bucket = aIsImportant ? 9 : 5;
+      isLayeredOrigin = true;
+      break;
+    case SheetType::StyleAttr:
+      bucket = aIsImportant ? 11 : 6;
+      break;
+    case SheetType::Override:
+      bucket = aIsImportant ? 12 : 7;
+      break;
+    case SheetType::Animation:
+      bucket = 8;
+      break;
+    case SheetType::Transition:
+      bucket = 15;
+      break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("unexpected cascade level");
+      break;
+  }
+
+  return bucket * kCascadeRankStride +
+         (isLayeredOrigin ? LayerIndexRank(aIsImportant, aLayerIndex) : 0);
+}
+
+static bool
+ShouldIgnoreForRevertLayerData(SheetType aSourceLevel,
+                               bool aSourceImportant,
+                               int32_t aSourceLayerIndex,
+                               SheetType aCandidateLevel,
+                               bool aCandidateImportant,
+                               int32_t aCandidateLayerIndex)
+{
+  int32_t candidateRank =
+    CascadePrecedenceRank(aCandidateLevel, aCandidateImportant,
+                          aCandidateLayerIndex);
+  int32_t sourceRank =
+    CascadePrecedenceRank(aSourceLevel, aSourceImportant, aSourceLayerIndex);
+
+  if (candidateRank >= sourceRank) {
+    return true;
+  }
+
+  if (!aSourceImportant) {
+    return false;
+  }
+
+  if (aSourceLevel == SheetType::StyleAttr) {
+    return aCandidateLevel == SheetType::StyleAttr ||
+           aCandidateLevel == SheetType::Animation;
+  }
+
+  int32_t normalBoundary =
+    CascadePrecedenceRank(aSourceLevel, false, aSourceLayerIndex);
+  return candidateRank >= normalBoundary;
+}
+
+static bool
+ShouldIgnoreForRevertLayerValue(const nsString& aTargetValue,
+                                SheetType aCandidateLevel,
+                                bool aCandidateImportant,
+                                int32_t aCandidateLayerIndex)
+{
+  SheetType sourceLevel;
+  bool sourceImportant;
+  int32_t sourceLayerIndex;
+  if (!UnpackRevertLayerData(aTargetValue, sourceLevel, sourceImportant,
+                             sourceLayerIndex)) {
+    return false;
+  }
+
+  return ShouldIgnoreForRevertLayerData(sourceLevel, sourceImportant,
+                                        sourceLayerIndex, aCandidateLevel,
+                                        aCandidateImportant,
+                                        aCandidateLayerIndex);
+}
+
+static bool
+ShouldIgnoreForRevertLayerValue(const nsString& aTargetValue,
+                                const nsRuleData* aRuleData)
+{
+  return ShouldIgnoreForRevertLayerValue(aTargetValue, aRuleData->mLevel,
+                                         aRuleData->mIsImportantRule,
+                                         aRuleData->mLayerIndex);
+}
+
+static bool
+ShouldIgnoreForRevertLayerSourceValue(const nsString& aTargetValue,
+                                      const nsString& aCandidateValue)
+{
+  SheetType candidateLevel;
+  bool candidateImportant;
+  int32_t candidateLayerIndex;
+  if (!UnpackRevertLayerData(aCandidateValue, candidateLevel,
+                             candidateImportant, candidateLayerIndex)) {
+    return false;
+  }
+
+  return ShouldIgnoreForRevertLayerValue(aTargetValue, candidateLevel,
+                                         candidateImportant,
+                                         candidateLayerIndex);
+}
+
+static bool
+IsComputedRevertLayerValue(const nsString& aValue)
+{
+  nsAutoString trimmed(aValue);
+  trimmed.CompressWhitespace(true, true);
+  return trimmed.EqualsLiteral("revert-layer");
+}
+
 CSSVariableDeclarations::CSSVariableDeclarations()
 {
   MOZ_COUNT_CTOR(CSSVariableDeclarations);
@@ -47,6 +255,8 @@ CSSVariableDeclarations::operator=(const CSSVariableDeclarations& aOther)
   }
 
   mVariables.Clear();
+  mRevertLayerSources.Clear();
+  mRevertLayerFallbacks.Clear();
   CopyVariablesFrom(aOther);
   return *this;
 }
@@ -57,6 +267,15 @@ CSSVariableDeclarations::CopyVariablesFrom(const CSSVariableDeclarations& aOther
   for (auto iter = aOther.mVariables.ConstIter(); !iter.Done(); iter.Next()) {
     mVariables.Put(iter.Key(), iter.UserData());
   }
+  for (auto iter = aOther.mRevertLayerSources.ConstIter();
+       !iter.Done(); iter.Next()) {
+    mRevertLayerSources.Put(iter.Key(), iter.UserData());
+  }
+  for (auto iter = aOther.mRevertLayerFallbacks.ConstIter();
+       !iter.Done(); iter.Next()) {
+    RevertLayerFallbackList* list = mRevertLayerFallbacks.LookupOrAdd(iter.Key());
+    list->mItems = iter.UserData()->mItems;
+  }
 }
 
 bool
@@ -87,6 +306,9 @@ CSSVariableDeclarations::Get(const nsAString& aName,
   } else if (value.EqualsLiteral(REVERT_VALUE)) {
     aType = eRevert;
     aTokenStream.Truncate();
+  } else if (IsRevertLayerValue(value)) {
+    aType = eRevertLayer;
+    aTokenStream.Truncate();
   } else {
     aType = eTokenStream;
     aTokenStream = value;
@@ -101,7 +323,8 @@ CSSVariableDeclarations::PutTokenStream(const nsAString& aName,
   MOZ_ASSERT(!aTokenStream.EqualsLiteral(INITIAL_VALUE) &&
              !aTokenStream.EqualsLiteral(INHERIT_VALUE) &&
              !aTokenStream.EqualsLiteral(UNSET_VALUE) &&
-             !aTokenStream.EqualsLiteral(REVERT_VALUE));
+             !aTokenStream.EqualsLiteral(REVERT_VALUE) &&
+             !aTokenStream.EqualsLiteral(REVERT_LAYER_VALUE));
   mVariables.Put(aName, aTokenStream);
 }
 
@@ -129,6 +352,12 @@ CSSVariableDeclarations::PutRevert(const nsAString& aName)
   mVariables.Put(aName, NS_LITERAL_STRING(REVERT_VALUE));
 }
 
+void
+CSSVariableDeclarations::PutRevertLayer(const nsAString& aName)
+{
+  mVariables.Put(aName, NS_LITERAL_STRING(REVERT_LAYER_VALUE));
+}
+
 void
 CSSVariableDeclarations::Remove(const nsAString& aName)
 {
@@ -143,16 +372,49 @@ CSSVariableDeclarations::MapRuleInfoInto(nsRuleData* aRuleData)
   }
 
   if (!aRuleData->mVariables) {
-    aRuleData->mVariables = new CSSVariableDeclarations(*this);
-  } else {
-    for (auto iter = mVariables.Iter(); !iter.Done(); iter.Next()) {
-      nsDataHashtable<nsStringHashKey, nsString>& variables =
-        aRuleData->mVariables->mVariables;
-      const nsAString& aName = iter.Key();
-      if (!variables.Contains(aName)) {
-        variables.Put(aName, iter.UserData());
+    aRuleData->mVariables = new CSSVariableDeclarations;
+  }
+
+  for (auto iter = mVariables.Iter(); !iter.Done(); iter.Next()) {
+    nsDataHashtable<nsStringHashKey, nsString>& variables =
+      aRuleData->mVariables->mVariables;
+    const nsAString& name = iter.Key();
+    nsString value = iter.UserData();
+    nsString valueSource;
+    SetRevertLayerData(valueSource, aRuleData);
+    if (value.EqualsLiteral(REVERT_LAYER_VALUE)) {
+      value = valueSource;
+      aRuleData->mConditions.SetUncacheable();
+    }
+
+    nsString existingValue;
+    if (variables.Get(name, &existingValue)) {
+      if (IsRevertLayerValue(existingValue)) {
+        if (ShouldIgnoreForRevertLayerValue(existingValue, aRuleData)) {
+          continue;
+        }
+      } else {
+        nsString sourceValue;
+        if (aRuleData->mVariables->mRevertLayerSources.Get(name,
+                                                           &sourceValue) &&
+            !ShouldIgnoreForRevertLayerValue(sourceValue, aRuleData)) {
+          RevertLayerFallbackList* fallbacks =
+            aRuleData->mVariables->mRevertLayerFallbacks.LookupOrAdd(name);
+          RevertLayerFallback* fallback = fallbacks->mItems.AppendElement();
+          fallback->mValue = value;
+          fallback->mSource = valueSource;
+        }
+        continue;
       }
     }
+
+    variables.Put(name, value);
+    if (ValueMightResolveToRevertLayer(value)) {
+      aRuleData->mVariables->mRevertLayerSources.Put(name, valueSource);
+    } else {
+      aRuleData->mVariables->mRevertLayerSources.Remove(name);
+      aRuleData->mVariables->mRevertLayerFallbacks.Remove(name);
+    }
   }
 }
 
@@ -172,8 +434,9 @@ CSSVariableDeclarations::AddVariablesToResolver(
                      false);
     } else if (value.EqualsLiteral(INHERIT_VALUE) ||
                value.EqualsLiteral(UNSET_VALUE) ||
-               value.EqualsLiteral(REVERT_VALUE)) {
-      // Values of 'inherit', 'unset', and 'revert' don't need any handling,
+               value.EqualsLiteral(REVERT_VALUE) ||
+               IsRevertLayerValue(value)) {
+      // Values of 'inherit', 'unset', 'revert', and 'revert-layer' don't need any handling,
       // since it means we just need to keep whatever value is currently in
       // the resolver.  This is because the specified variable declarations
       // already have only the winning declaration for the variable and no
@@ -190,6 +453,83 @@ CSSVariableDeclarations::AddVariablesToResolver(
   }
 }
 
+void
+CSSVariableDeclarations::ResolveRevertLayerFallbacks(
+                                             const CSSVariableValues* aInherited,
+                                             CSSVariableValues* aOutput) const
+{
+  for (auto iter = mRevertLayerSources.ConstIter();
+       !iter.Done(); iter.Next()) {
+    const nsAString& name = iter.Key();
+    nsString value;
+    nsCSSTokenSerializationType firstToken, lastToken;
+    if (!aOutput->Get(name, value, firstToken, lastToken)) {
+      continue;
+    }
+
+    if (!IsComputedRevertLayerValue(value)) {
+      continue;
+    }
+
+    const RevertLayerFallbackList* fallbacks = mRevertLayerFallbacks.Get(name);
+    if (fallbacks) {
+      nsString sourceValue = iter.UserData();
+      bool foundFallback = false;
+      for (uint32_t i = 0, n = fallbacks->mItems.Length(); i < n; i++) {
+        const RevertLayerFallback& fallback = fallbacks->mItems[i];
+        if (ShouldIgnoreForRevertLayerSourceValue(sourceValue,
+                                                 fallback.mSource)) {
+          continue;
+        }
+
+        if (IsRevertLayerValue(fallback.mValue)) {
+          sourceValue = fallback.mSource;
+          continue;
+        }
+
+        CSSVariableValues inheritedValues(*aOutput);
+        if (aInherited->Get(name, value, firstToken, lastToken)) {
+          inheritedValues.Put(name, value, firstToken, lastToken);
+        } else {
+          inheritedValues.Remove(name);
+        }
+
+        CSSVariableDeclarations fallbackDeclarations;
+        fallbackDeclarations.mVariables.Put(name, fallback.mValue);
+
+        CSSVariableValues fallbackValues;
+        CSSVariableResolver resolver(&fallbackValues);
+        resolver.Resolve(&inheritedValues, &fallbackDeclarations);
+
+        if (!fallbackValues.Get(name, value, firstToken, lastToken)) {
+          aOutput->Remove(name);
+          foundFallback = true;
+          break;
+        }
+
+        if (IsComputedRevertLayerValue(value)) {
+          sourceValue = fallback.mSource;
+          continue;
+        }
+
+        aOutput->Put(name, value, firstToken, lastToken);
+        foundFallback = true;
+        break;
+      }
+
+      if (foundFallback) {
+        continue;
+      }
+    }
+
+    if (aInherited->Get(name, value, firstToken, lastToken)) {
+      aOutput->Put(name, value, firstToken, lastToken);
+    } else {
+      aOutput->Remove(name);
+    }
+  }
+}
+
 size_t
 CSSVariableDeclarations::SizeOfIncludingThis(
                                       mozilla::MallocSizeOf aMallocSizeOf) const
@@ -200,6 +540,22 @@ CSSVariableDeclarations::SizeOfIncludingThis(
     n += iter.Key().SizeOfExcludingThisIfUnshared(aMallocSizeOf);
     n += iter.Data().SizeOfExcludingThisIfUnshared(aMallocSizeOf);
   }
+  n += mRevertLayerSources.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  for (auto iter = mRevertLayerSources.ConstIter(); !iter.Done(); iter.Next()) {
+    n += iter.Key().SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+    n += iter.Data().SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+  }
+  n += mRevertLayerFallbacks.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  for (auto iter = mRevertLayerFallbacks.ConstIter(); !iter.Done(); iter.Next()) {
+    n += iter.Key().SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+    const RevertLayerFallbackList* list = iter.UserData();
+    n += aMallocSizeOf(list);
+    n += list->mItems.ShallowSizeOfExcludingThis(aMallocSizeOf);
+    for (uint32_t i = 0, len = list->mItems.Length(); i < len; i++) {
+      n += list->mItems[i].mValue.SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+      n += list->mItems[i].mSource.SizeOfExcludingThisIfUnshared(aMallocSizeOf);
+    }
+  }
   return n;
 }
 

layout/style/CSSVariableDeclarations.h

@@ -7,10 +7,13 @@
 #ifndef mozilla_CSSVariableDeclarations_h
 #define mozilla_CSSVariableDeclarations_h
 
+#include "nsClassHashtable.h"
 #include "nsDataHashtable.h"
+#include "nsTArray.h"
 
 namespace mozilla {
 class CSSVariableResolver;
+class CSSVariableValues;
 } // namespace mozilla
 struct nsRuleData;
 
@@ -43,7 +46,8 @@ public:
     eInitial,      // 'initial'
     eInherit,      // 'inherit'
     eUnset,        // 'unset'
-    eRevert        // 'revert'
+    eRevert,       // 'revert'
+    eRevertLayer   // 'revert-layer'
   };
 
   /**
@@ -97,6 +101,15 @@ public:
    */
   void PutRevert(const nsAString& aName);
 
+  /**
+   * Adds or modifies an existing entry in this set of variable declarations
+   * to have the value 'revert-layer'.
+   *
+   * @param aName The variable name (not including any "--" prefix that would
+   *   be part of the custom property name) whose value is to be set.
+   */
+  void PutRevertLayer(const nsAString& aName);
+
   /**
    * Adds or modifies an existing entry in this set of variable declarations
    * to have a token stream value.
@@ -132,15 +145,36 @@ public:
    */
   void AddVariablesToResolver(CSSVariableResolver* aResolver) const;
 
+  /**
+   * Applies stored lower-priority declarations for custom property values that
+   * resolved to 'revert-layer'.
+   */
+  void ResolveRevertLayerFallbacks(const CSSVariableValues* aInherited,
+                                   CSSVariableValues* aOutput) const;
+
   size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
 
 private:
+  struct RevertLayerFallback
+  {
+    nsString mValue;
+    nsString mSource;
+  };
+
+  struct RevertLayerFallbackList
+  {
+    nsTArray<RevertLayerFallback> mItems;
+  };
+
   /**
    * Adds all the variable declarations from aOther into this object.
    */
   void CopyVariablesFrom(const CSSVariableDeclarations& aOther);
 
   nsDataHashtable<nsStringHashKey, nsString> mVariables;
+  nsDataHashtable<nsStringHashKey, nsString> mRevertLayerSources;
+  nsClassHashtable<nsStringHashKey, RevertLayerFallbackList>
+    mRevertLayerFallbacks;
 };
 
 } // namespace mozilla

layout/style/CSSVariableValues.cpp

@@ -121,6 +121,21 @@ CSSVariableValues::Put(const nsAString& aName,
   }
 }
 
+void
+CSSVariableValues::Remove(const nsAString& aName)
+{
+  size_t id;
+  if (!mVariableIDs.Get(aName, &id)) {
+    return;
+  }
+
+  mVariables.RemoveElementAt(id);
+  mVariableIDs.Clear();
+  for (size_t i = 0, n = mVariables.Length(); i < n; i++) {
+    mVariableIDs.Put(mVariables[i].mVariableName, i);
+  }
+}
+
 void
 CSSVariableValues::CopyVariablesFrom(const CSSVariableValues& aOther)
 {

layout/style/CSSVariableValues.h

@@ -94,6 +94,11 @@ public:
            nsCSSTokenSerializationType aFirstToken,
            nsCSSTokenSerializationType aLastToken);
 
+  /**
+   * Removes an entry in this set of variable values.
+   */
+  void Remove(const nsAString& aName);
+
   /**
    * Copies the variables from this object into aResolver, marking them as
    * computed, inherited values.

layout/style/Declaration.cpp

@@ -576,6 +576,7 @@ Declaration::GetPropertyValueInternal(
   const nsCSSValue* tokenStream = nullptr;
   uint32_t totalCount = 0, importantCount = 0,
            initialCount = 0, inheritCount = 0, unsetCount = 0, revertCount = 0,
+           revertLayerCount = 0,
            matchingTokenStreamCount = 0, nonMatchingTokenStreamCount = 0;
   CSSPROPS_FOR_SHORTHAND_SUBPROPERTIES(p, aProperty,
                                        CSSEnabledState::eForAllContent) {
@@ -603,6 +604,8 @@ Declaration::GetPropertyValueInternal(
       ++unsetCount;
     } else if (val->GetUnit() == eCSSUnit_Revert) {
       ++revertCount;
+    } else if (val->GetUnit() == eCSSUnit_RevertLayer) {
+      ++revertLayerCount;
     } else if (val->GetUnit() == eCSSUnit_TokenStream) {
       if (val->GetTokenStreamValue()->mShorthandPropertyID == aProperty) {
         tokenStream = val;
@@ -640,9 +643,19 @@ Declaration::GetPropertyValueInternal(
                                               nsCSSValue::eNormalized);
     return;
   }
+  if (revertLayerCount == totalCount) {
+    // Simplify serialization below by serializing revert-layer up-front.
+    nsCSSValue revertLayer;
+    revertLayer.SetRevertLayerValue();
+    revertLayer.AppendToString(eCSSProperty_UNKNOWN, aValue,
+                               nsCSSValue::eNormalized);
+    return;
+  }
   if (initialCount != 0 || inheritCount != 0 || unsetCount != 0 ||
-      revertCount != 0 || nonMatchingTokenStreamCount != 0) {
-    // Case (2): partially initial, inherit, unset, revert, or token stream.
+      revertCount != 0 || revertLayerCount != 0 ||
+      nonMatchingTokenStreamCount != 0) {
+    // Case (2): partially initial, inherit, unset, revert, revert-layer,
+    // or token stream.
     return;
   }
   if (tokenStream) {
@@ -1535,6 +1548,7 @@ Declaration::GetPropertyValueInternal(
           case eCSSUnit_Initial:
           case eCSSUnit_Unset:
           case eCSSUnit_Revert:
+          case eCSSUnit_RevertLayer:
             return true;
           case eCSSUnit_Enumerated:
             // return false if there is a fallback value or <overflow-position>
@@ -1749,6 +1763,10 @@ Declaration::AppendVariableAndValueToString(const nsAString& aName,
       aResult.AppendLiteral("revert");
       break;
 
+    case CSSVariableDeclarations::eRevertLayer:
+      aResult.AppendLiteral("revert-layer");
+      break;
+
     default:
       MOZ_ASSERT(false, "unexpected variable value type");
   }
@@ -1989,6 +2007,10 @@ Declaration::GetVariableValue(const nsAString& aName, nsAString& aValue) const
         aValue.AppendLiteral("revert");
         break;
 
+      case CSSVariableDeclarations::eRevertLayer:
+        aValue.AppendLiteral("revert-layer");
+        break;
+
       default:
         MOZ_ASSERT(false, "unexpected variable value type");
     }
@@ -2059,6 +2081,11 @@ Declaration::AddVariable(const nsAString& aName,
       variables->PutRevert(aName);
       break;
 
+    case CSSVariableDeclarations::eRevertLayer:
+      MOZ_ASSERT(aValue.IsEmpty());
+      variables->PutRevertLayer(aName);
+      break;
+
     default:
       MOZ_ASSERT(false, "unexpected aType value");
   }

layout/style/StyleAnimationValue.h

@@ -489,7 +489,7 @@ public:
   void SetNoneValue();
   void SetIntValue(int32_t aInt, Unit aUnit);
   template<typename T,
-           typename = typename std::enable_if<std::is_enum<T>::value>::type>
+           typename = typename std::enable_if_t<std::is_enum_v<T>>>
   void SetIntValue(T aInt, Unit aUnit)
   {
     static_assert(mozilla::EnumTypeFitsWithin<T, int32_t>::value,

layout/style/nsCSSDataBlock.cpp

@@ -48,6 +48,102 @@ ShouldIgnoreColors(nsRuleData *aRuleData)
          !aRuleData->mPresContext->UseDocumentColors();
 }
 
+static const int32_t kLayerIndexMax = 0x000fffff;
+static const int32_t kCascadeRankStride = kLayerIndexMax + 1;
+
+static int32_t
+LayerIndexRank(bool aIsImportant, int32_t aLayerIndex)
+{
+  MOZ_ASSERT(aLayerIndex >= 0);
+  MOZ_ASSERT(aLayerIndex <= kLayerIndexMax);
+  return aIsImportant ? kLayerIndexMax - aLayerIndex : aLayerIndex;
+}
+
+static int32_t
+CascadePrecedenceRank(SheetType aLevel, bool aIsImportant,
+                      int32_t aLayerIndex)
+{
+  int32_t bucket = 0;
+  bool isLayeredOrigin = false;
+
+  switch (aLevel) {
+    case SheetType::Agent:
+      bucket = aIsImportant ? 14 : 0;
+      isLayeredOrigin = true;
+      break;
+    case SheetType::User:
+      bucket = aIsImportant ? 13 : 1;
+      isLayeredOrigin = true;
+      break;
+    case SheetType::PresHint:
+      bucket = 2;
+      break;
+    case SheetType::SVGAttrAnimation:
+      bucket = 3;
+      break;
+    case SheetType::Doc:
+      bucket = aIsImportant ? 10 : 4;
+      isLayeredOrigin = true;
+      break;
+    case SheetType::ScopedDoc:
+      bucket = aIsImportant ? 9 : 5;
+      isLayeredOrigin = true;
+      break;
+    case SheetType::StyleAttr:
+      bucket = aIsImportant ? 11 : 6;
+      break;
+    case SheetType::Override:
+      bucket = aIsImportant ? 12 : 7;
+      break;
+    case SheetType::Animation:
+      bucket = 8;
+      break;
+    case SheetType::Transition:
+      bucket = 15;
+      break;
+    default:
+      MOZ_ASSERT_UNREACHABLE("unexpected cascade level");
+      break;
+  }
+
+  return bucket * kCascadeRankStride +
+         (isLayeredOrigin ? LayerIndexRank(aIsImportant, aLayerIndex) : 0);
+}
+
+static bool
+ShouldIgnoreForRevertLayer(const nsCSSValue& aTargetValue,
+                           const nsRuleData* aRuleData)
+{
+  SheetType sourceLevel = aTargetValue.GetRevertLayerOriginValue();
+  bool sourceImportant = aTargetValue.GetRevertLayerImportanceValue();
+  int32_t sourceLayerIndex = aTargetValue.GetRevertLayerLayerIndexValue();
+  MOZ_ASSERT(sourceLevel != SheetType::Unknown,
+             "revert-layer should have cascade metadata before mapping");
+
+  int32_t candidateRank =
+    CascadePrecedenceRank(aRuleData->mLevel, aRuleData->mIsImportantRule,
+                          aRuleData->mLayerIndex);
+  int32_t sourceRank =
+    CascadePrecedenceRank(sourceLevel, sourceImportant, sourceLayerIndex);
+
+  if (candidateRank >= sourceRank) {
+    return true;
+  }
+
+  if (!sourceImportant) {
+    return false;
+  }
+
+  if (sourceLevel == SheetType::StyleAttr) {
+    return aRuleData->mLevel == SheetType::StyleAttr ||
+           aRuleData->mLevel == SheetType::Animation;
+  }
+
+  int32_t normalBoundary =
+    CascadePrecedenceRank(sourceLevel, false, sourceLayerIndex);
+  return candidateRank >= normalBoundary;
+}
+
 /**
  * Tries to call |nsCSSValue::StartImageLoad()| on an image source.
  * Image sources are specified by |url()| or |-moz-image-rect()| function.
@@ -175,7 +271,8 @@ MapSinglePropertyInto(nsCSSPropertyID aTargetProp,
   // CSSVariableImageTable, to give them the appropriate lifetime.
   MOZ_ASSERT(aTargetValue->GetUnit() == eCSSUnit_TokenStream ||
              aTargetValue->GetUnit() == eCSSUnit_Null ||
-             aTargetValue->GetUnit() == eCSSUnit_Revert,
+             aTargetValue->GetUnit() == eCSSUnit_Revert ||
+             aTargetValue->GetUnit() == eCSSUnit_RevertLayer,
              "aTargetValue must only be a token stream (when re-parsing "
              "properties with variable references) or null");
 
@@ -365,6 +462,10 @@ nsCSSCompressedDataBlock::MapRuleInfoInto(nsRuleData *aRuleData) const
         if (aRuleData->mLevel >= target->GetCascadeOriginValue()) {
           continue;
         }
+      } else if (target->GetUnit() == eCSSUnit_RevertLayer) {
+        if (ShouldIgnoreForRevertLayer(*target, aRuleData)) {
+          continue;
+        }
       } else if (target->GetUnit() != eCSSUnit_Null) {
         continue;
       }
@@ -377,8 +478,18 @@ nsCSSCompressedDataBlock::MapRuleInfoInto(nsRuleData *aRuleData) const
       // the rule walking will have just updated aRuleData.
       if (val->GetUnit() == eCSSUnit_TokenStream) {
         val->GetTokenStreamValue()->mLevel = aRuleData->mLevel;
+        val->GetTokenStreamValue()->mIsImportant = aRuleData->mIsImportantRule;
+        val->GetTokenStreamValue()->mLayerIndex = aRuleData->mLayerIndex;
       } else if (val->GetUnit() == eCSSUnit_Revert) {
         aRuleData->mConditions.SetUncacheable();
+      } else if (val->GetUnit() == eCSSUnit_RevertLayer) {
+        nsCSSValue revertLayer;
+        revertLayer.SetRevertLayerValue(aRuleData->mLevel,
+                                        aRuleData->mIsImportantRule,
+                                        aRuleData->mLayerIndex);
+        aRuleData->mConditions.SetUncacheable();
+        MapSinglePropertyInto(iProp, &revertLayer, target, aRuleData);
+        continue;
       }
       MapSinglePropertyInto(iProp, val, target, aRuleData);
     }
@@ -819,6 +930,17 @@ nsCSSExpandedDataBlock::MapRuleInfoInto(nsCSSPropertyID aPropID,
   MOZ_ASSERT(dest->GetUnit() == eCSSUnit_TokenStream &&
              dest->GetTokenStreamValue()->mPropertyID == aPropID);
 
+  if (src->GetUnit() == eCSSUnit_RevertLayer) {
+    nsCSSValueTokenStream* tokenStream = dest->GetTokenStreamValue();
+    nsCSSValue revertLayer;
+    revertLayer.SetRevertLayerValue(tokenStream->mLevel,
+                                    tokenStream->mIsImportant,
+                                    tokenStream->mLayerIndex);
+    aRuleData->mConditions.SetUncacheable();
+    MapSinglePropertyInto(physicalProp, &revertLayer, dest, aRuleData);
+    return;
+  }
+
   CSSVariableImageTable::ReplaceAll(aRuleData->mStyleContext, aPropID, [=] {
     MapSinglePropertyInto(physicalProp, src, dest, aRuleData);
   });

layout/style/nsCSSKeywordList.h

@@ -481,6 +481,7 @@ CSS_KEY(repeat-x, repeat_x)
 CSS_KEY(repeat-y, repeat_y)
 CSS_KEY(reverse, reverse)
 CSS_KEY(revert, revert)
+CSS_KEY(revert-layer, revert_layer)
 CSS_KEY(ridge, ridge)
 CSS_KEY(right, right)
 CSS_KEY(rl, rl)
@@ -814,4 +815,3 @@ CSS_KEY(text-before-edge, text_before_edge)
 CSS_KEY(use-script, use_script)
 CSS_KEY(-moz-crisp-edges, _moz_crisp_edges)
 CSS_KEY(space, space)
-

layout/style/nsCSSParser.cpp

@@ -9126,6 +9126,10 @@ CSSParserImpl::ParseVariant(nsCSSValue& aValue,
           aValue.SetRevertValue(mLevel);
           return CSSParseResult::Ok;
         }
+        else if (eCSSKeyword_revert_layer == keyword) {
+          aValue.SetRevertLayerValue();
+          return CSSParseResult::Ok;
+        }
       }
       if ((aVariantMask & VARIANT_NONE) != 0) {
         if (eCSSKeyword_none == keyword) {
@@ -9330,7 +9334,8 @@ CSSParserImpl::ParseVariant(nsCSSValue& aValue,
          tk->mIdent.LowerCaseEqualsLiteral("initial") ||
          (tk->mIdent.LowerCaseEqualsLiteral("unset") &&
           nsLayoutUtils::UnsetValueEnabled()) ||
-         tk->mIdent.LowerCaseEqualsLiteral("revert")))) {
+         tk->mIdent.LowerCaseEqualsLiteral("revert") ||
+         tk->mIdent.LowerCaseEqualsLiteral("revert-layer")))) {
     aValue.SetStringValue(tk->mIdent, eCSSUnit_Ident);
     return CSSParseResult::Ok;
   }
@@ -9406,6 +9411,7 @@ CSSParserImpl::ParseCustomIdent(nsCSSValue& aValue,
       keyword == eCSSKeyword_initial ||
       keyword == eCSSKeyword_unset ||
       keyword == eCSSKeyword_revert ||
+      keyword == eCSSKeyword_revert_layer ||
       keyword == eCSSKeyword_default ||
       (aPropertyKTable &&
         nsCSSProps::FindIndexOfKeyword(keyword, aPropertyKTable) >= 0)) {
@@ -12595,6 +12601,12 @@ CSSParserImpl::ParseChoice(nsCSSValue aValues[],
         }
         found = ((1 << aNumIDs) - 1);
       }
+      else if (eCSSUnit_RevertLayer == aValues[0].GetUnit()) { // one revert-layer, all revert-layer
+        for (loop = 1; loop < aNumIDs; loop++) {
+          aValues[loop].SetRevertLayerValue();
+        }
+        found = ((1 << aNumIDs) - 1);
+      }
     }
     else {  // more than one value, verify no inherits, initials, unsets, or reverts
       for (loop = 0; loop < aNumIDs; loop++) {
@@ -12610,7 +12622,8 @@ CSSParserImpl::ParseChoice(nsCSSValue aValues[],
           found = -1;
           break;
         }
-        else if (eCSSUnit_Revert == aValues[loop].GetUnit()) {
+        else if (eCSSUnit_Revert == aValues[loop].GetUnit() ||
+                 eCSSUnit_RevertLayer == aValues[loop].GetUnit()) {
           found = -1;
           break;
         }
@@ -12658,7 +12671,8 @@ CSSParserImpl::ParseBoxProperties(const nsCSSPropertyID aPropIDs[])
       if (eCSSUnit_Inherit == unit ||
           eCSSUnit_Initial == unit ||
           eCSSUnit_Unset == unit ||
-          eCSSUnit_Revert == unit) {
+          eCSSUnit_Revert == unit ||
+          eCSSUnit_RevertLayer == unit) {
         return false;
       }
     }
@@ -12766,7 +12780,8 @@ CSSParserImpl::ParseBoxCornerRadius(nsCSSPropertyID aPropID)
   if (dimenX.GetUnit() != eCSSUnit_Inherit &&
       dimenX.GetUnit() != eCSSUnit_Initial &&
       dimenX.GetUnit() != eCSSUnit_Unset &&
-      dimenX.GetUnit() != eCSSUnit_Revert) {
+      dimenX.GetUnit() != eCSSUnit_Revert &&
+      dimenX.GetUnit() != eCSSUnit_RevertLayer) {
     if (ParseNonNegativeVariant(dimenY, VARIANT_LP | VARIANT_CALC, nullptr) ==
         CSSParseResult::Error) {
       return false;
@@ -12831,7 +12846,8 @@ CSSParserImpl::ParseBoxCornerRadiiInternals(nsCSSValue array[])
     if (eCSSUnit_Inherit == unit ||
         eCSSUnit_Initial == unit ||
         eCSSUnit_Unset == unit ||
-        eCSSUnit_Revert == unit)
+        eCSSUnit_Revert == unit ||
+        eCSSUnit_RevertLayer == unit)
       return false;
   }
 
@@ -13642,6 +13658,7 @@ CSSParserImpl::ParseFontDescriptorValue(nsCSSFontDesc aDescID,
             aValue.GetUnit() != eCSSUnit_Initial &&
             aValue.GetUnit() != eCSSUnit_Unset &&
             aValue.GetUnit() != eCSSUnit_Revert &&
+            aValue.GetUnit() != eCSSUnit_RevertLayer &&
             (aValue.GetUnit() != eCSSUnit_Enumerated ||
              (aValue.GetIntValue() != NS_STYLE_FONT_WEIGHT_BOLDER &&
               aValue.GetIntValue() != NS_STYLE_FONT_WEIGHT_LIGHTER)));
@@ -13905,7 +13922,8 @@ CSSParserImpl::ParseImageLayersItem(
       if (keyword == eCSSKeyword_inherit ||
           keyword == eCSSKeyword_initial ||
           keyword == eCSSKeyword_unset ||
-          keyword == eCSSKeyword_revert) {
+          keyword == eCSSKeyword_revert ||
+          keyword == eCSSKeyword_revert_layer) {
         return false;
       } else if (keyword == eCSSKeyword_none) {
         if (haveImage)
@@ -14262,7 +14280,8 @@ bool CSSParserImpl::ParseBoxPositionValues(nsCSSValuePair &aOut,
     if (eCSSUnit_Inherit == xValue.GetUnit() ||
         eCSSUnit_Initial == xValue.GetUnit() ||
         eCSSUnit_Unset == xValue.GetUnit() ||
-        eCSSUnit_Revert == xValue.GetUnit()) {  // both are inherit, initial, unset, or revert
+        eCSSUnit_Revert == xValue.GetUnit() ||
+        eCSSUnit_RevertLayer == xValue.GetUnit()) {
       yValue = xValue;
       return true;
     }
@@ -15094,6 +15113,7 @@ CSSParserImpl::ParseBorderSide(const nsCSSPropertyID aPropIDs[],
     case eCSSUnit_Initial:
     case eCSSUnit_Unset:
     case eCSSUnit_Revert:
+    case eCSSUnit_RevertLayer:
       extraValue = values[0];
       // Set value of border-image properties to initial/inherit/unset/revert
       AppendValue(eCSSProperty_border_image_source, extraValue);
@@ -15860,7 +15880,8 @@ CSSParserImpl::ParseFont()
     if (eCSSUnit_Inherit == family.GetUnit() ||
         eCSSUnit_Initial == family.GetUnit() ||
         eCSSUnit_Unset == family.GetUnit() ||
-        eCSSUnit_Revert == family.GetUnit()) {
+        eCSSUnit_Revert == family.GetUnit() ||
+        eCSSUnit_RevertLayer == family.GetUnit()) {
       AppendValue(eCSSProperty__x_system_font, nsCSSValue(eCSSUnit_None));
       AppendValue(eCSSProperty_font_family, family);
       AppendValue(eCSSProperty_font_style, family);
@@ -15929,7 +15950,8 @@ CSSParserImpl::ParseFont()
       eCSSUnit_Inherit == values[kFontStyleIndex].GetUnit() ||
       eCSSUnit_Initial == values[kFontStyleIndex].GetUnit() ||
       eCSSUnit_Unset == values[kFontStyleIndex].GetUnit() ||
-      eCSSUnit_Revert == values[kFontStyleIndex].GetUnit() ) { // illegal data
+      eCSSUnit_Revert == values[kFontStyleIndex].GetUnit() ||
+      eCSSUnit_RevertLayer == values[kFontStyleIndex].GetUnit() ) { // illegal data
     return false;
   }
   if ((found & (1 << kFontStyleIndex)) == 0) {
@@ -15988,7 +16010,8 @@ CSSParserImpl::ParseFont()
     if (eCSSUnit_Inherit != family.GetUnit() &&
         eCSSUnit_Initial != family.GetUnit() &&
         eCSSUnit_Unset != family.GetUnit() &&
-        eCSSUnit_Revert != family.GetUnit()) {
+        eCSSUnit_Revert != family.GetUnit() &&
+        eCSSUnit_RevertLayer != family.GetUnit()) {
       AppendValue(eCSSProperty__x_system_font, nsCSSValue(eCSSUnit_None));
       AppendValue(eCSSProperty_font_family, family);
       AppendValue(eCSSProperty_font_style, values[kFontStyleIndex]);
@@ -16034,7 +16057,8 @@ CSSParserImpl::ParseFontSynthesis(nsCSSValue& aValue)
       eCSSUnit_Initial == aValue.GetUnit() ||
       eCSSUnit_Inherit == aValue.GetUnit() ||
       eCSSUnit_Unset == aValue.GetUnit() ||
-      eCSSUnit_Revert == aValue.GetUnit() )
+      eCSSUnit_Revert == aValue.GetUnit() ||
+      eCSSUnit_RevertLayer == aValue.GetUnit() )
   {
     return true;
   }
@@ -16657,6 +16681,9 @@ CSSParserImpl::ParseFamily(nsCSSValue& aValue)
       case eCSSKeyword_revert:
         aValue.SetRevertValue(mLevel);
         return true;
+      case eCSSKeyword_revert_layer:
+        aValue.SetRevertLayerValue();
+        return true;
       case eCSSKeyword__moz_use_system_font:
         if (!IsParsingCompoundProperty()) {
           aValue.SetSystemFontValue();
@@ -16691,6 +16718,7 @@ CSSParserImpl::ParseFamily(nsCSSValue& aValue)
         case eCSSKeyword_initial:
         case eCSSKeyword_default:
         case eCSSKeyword_revert:
+        case eCSSKeyword_revert_layer:
         case eCSSKeyword__moz_use_system_font:
           return false;
         case eCSSKeyword_unset:
@@ -18340,7 +18368,8 @@ bool CSSParserImpl::ParseTransformOrigin(bool aPerspective)
   if (position.mXValue.GetUnit() == eCSSUnit_Inherit ||
       position.mXValue.GetUnit() == eCSSUnit_Initial ||
       position.mXValue.GetUnit() == eCSSUnit_Unset ||
-      position.mXValue.GetUnit() == eCSSUnit_Revert) {
+      position.mXValue.GetUnit() == eCSSUnit_Revert ||
+      position.mXValue.GetUnit() == eCSSUnit_RevertLayer) {
     MOZ_ASSERT(position.mXValue == position.mYValue,
                "inherit/initial/unset/revert only half?");
     AppendValue(prop, position.mXValue);
@@ -18564,14 +18593,15 @@ CSSParserImpl::ParseTransitionProperty()
       }
       if (cur->mValue.GetUnit() == eCSSUnit_Ident) {
         nsDependentString str(cur->mValue.GetStringBufferValue());
-        // Exclude 'none', 'inherit', 'initial', 'unset', and 'revert'
-        // according to the same rules as for 'counter-reset' in CSS 2.1.
+        // Exclude CSS-wide keywords and 'none' according to the same rules
+        // as for 'counter-reset' in CSS 2.1.
         if (str.LowerCaseEqualsLiteral("none") ||
             str.LowerCaseEqualsLiteral("inherit") ||
             str.LowerCaseEqualsLiteral("initial") ||
             (str.LowerCaseEqualsLiteral("unset") &&
              nsLayoutUtils::UnsetValueEnabled()) ||
-            str.LowerCaseEqualsLiteral("revert")) {
+            str.LowerCaseEqualsLiteral("revert") ||
+            str.LowerCaseEqualsLiteral("revert-layer")) {
           return false;
         }
       }
@@ -19484,8 +19514,7 @@ CSSParserImpl::ParseValueWithVariables(CSSVariableDeclarations::Type* aType,
     }
   }
 
-  // Look for 'initial', 'inherit', 'unset', or 'revert' as the first
-  // non-white space token.
+  // Look for CSS-wide keywords as the first non-white space token.
   CSSVariableDeclarations::Type type = CSSVariableDeclarations::eTokenStream;
   if (mToken.mType == eCSSToken_Ident) {
     if (mToken.mIdent.LowerCaseEqualsLiteral("initial")) {
@@ -19496,6 +19525,8 @@ CSSParserImpl::ParseValueWithVariables(CSSVariableDeclarations::Type* aType,
       type = CSSVariableDeclarations::eUnset;
     } else if (mToken.mIdent.LowerCaseEqualsLiteral("revert")) {
       type = CSSVariableDeclarations::eRevert;
+    } else if (mToken.mIdent.LowerCaseEqualsLiteral("revert-layer")) {
+      type = CSSVariableDeclarations::eRevertLayer;
     }
   }
 

layout/style/nsCSSProps.h

@@ -44,7 +44,7 @@
 // 'inherit' and 'initial'
 #define VARIANT_OPACITY         0x008000  // Take floats and percents as input, output float.
 #define VARIANT_AUTO            0x010000  // A
-#define VARIANT_INHERIT         0x020000  // H eCSSUnit_Initial, eCSSUnit_Inherit, eCSSUnit_Unset, eCSSUnit_Revert
+#define VARIANT_INHERIT         0x020000  // H eCSSUnit_Initial, eCSSUnit_Inherit, eCSSUnit_Unset, eCSSUnit_Revert, eCSSUnit_RevertLayer
 #define VARIANT_NONE            0x040000  // O
 #define VARIANT_NORMAL          0x080000  // M
 #define VARIANT_SYSFONT         0x100000  // eCSSUnit_System_Font
@@ -364,7 +364,7 @@ public:
     }
 
     template<typename T,
-             typename = typename std::enable_if<std::is_enum<T>::value>::type>
+             typename = typename std::enable_if_t<std::is_enum_v<T>>>
     KTableEntry(nsCSSKeyword aKeyword, T aValue)
       : mKeyword(aKeyword)
       , mValue(static_cast<int16_t>(aValue))
@@ -451,7 +451,7 @@ public:
   static nsCSSKeyword ValueToKeywordEnum(int32_t aValue,
                                          const KTableEntry aTable[]);
   template<typename T,
-           typename = typename std::enable_if<std::is_enum<T>::value>::type>
+           typename = typename std::enable_if_t<std::is_enum_v<T>>>
   static nsCSSKeyword ValueToKeywordEnum(T aValue,
                                          const KTableEntry aTable[])
   {
@@ -463,7 +463,7 @@ public:
   static const nsAFlatCString& ValueToKeyword(int32_t aValue,
                                               const KTableEntry aTable[]);
   template<typename T,
-           typename = typename std::enable_if<std::is_enum<T>::value>::type>
+           typename = typename std::enable_if_t<std::is_enum_v<T>>>
   static const nsAFlatCString& ValueToKeyword(T aValue,
                                               const KTableEntry aTable[])
   {

layout/style/nsCSSValue.cpp

@@ -192,6 +192,9 @@ nsCSSValue::nsCSSValue(const nsCSSValue& aCopy)
   else if (eCSSUnit_Revert == mUnit) {
     mValue.mCascadeOrigin = aCopy.mValue.mCascadeOrigin;
   }
+  else if (eCSSUnit_RevertLayer == mUnit) {
+    mValue.mInt = aCopy.mValue.mInt;
+  }
   else if (UnitHasArrayValue()) {
     mValue.mArray = aCopy.mValue.mArray;
     mValue.mArray->AddRef();
@@ -316,6 +319,9 @@ bool nsCSSValue::operator==(const nsCSSValue& aOther) const
     else if (eCSSUnit_Revert == mUnit) {
       return mValue.mCascadeOrigin == aOther.mValue.mCascadeOrigin;
     }
+    else if (eCSSUnit_RevertLayer == mUnit) {
+      return mValue.mInt == aOther.mValue.mInt;
+    }
     else if (UnitHasArrayValue()) {
       return *mValue.mArray == *aOther.mValue.mArray;
     }
@@ -593,6 +599,31 @@ nsCSSValue::SetCascadeOriginValue(mozilla::SheetType aValue, nsCSSUnit aUnit)
   mValue.mCascadeOrigin = aValue;
 }
 
+static const int32_t kRevertLayerMask = 0x000fffff;
+static const int32_t kRevertLayerImportant = 0x00100000;
+static const int32_t kRevertLayerOriginShift = 21;
+
+mozilla::SheetType
+nsCSSValue::GetRevertLayerOriginValue() const
+{
+  MOZ_ASSERT(mUnit == eCSSUnit_RevertLayer, "not a revert-layer value");
+  return mozilla::SheetType(uint32_t(mValue.mInt) >> kRevertLayerOriginShift);
+}
+
+bool
+nsCSSValue::GetRevertLayerImportanceValue() const
+{
+  MOZ_ASSERT(mUnit == eCSSUnit_RevertLayer, "not a revert-layer value");
+  return (mValue.mInt & kRevertLayerImportant) != 0;
+}
+
+int32_t
+nsCSSValue::GetRevertLayerLayerIndexValue() const
+{
+  MOZ_ASSERT(mUnit == eCSSUnit_RevertLayer, "not a revert-layer value");
+  return mValue.mInt & kRevertLayerMask;
+}
+
 void nsCSSValue::SetArrayValue(nsCSSValue::Array* aValue, nsCSSUnit aUnit)
 {
   Reset();
@@ -663,7 +694,9 @@ void nsCSSValue::SetPairValue(const nsCSSValuePair* aValue)
              aValue->mXValue.GetUnit() != eCSSUnit_Unset &&
              aValue->mYValue.GetUnit() != eCSSUnit_Unset &&
              aValue->mXValue.GetUnit() != eCSSUnit_Revert &&
-             aValue->mYValue.GetUnit() != eCSSUnit_Revert,
+             aValue->mYValue.GetUnit() != eCSSUnit_Revert &&
+             aValue->mXValue.GetUnit() != eCSSUnit_RevertLayer &&
+             aValue->mYValue.GetUnit() != eCSSUnit_RevertLayer,
              "missing or inappropriate pair value");
   Reset();
   mUnit = eCSSUnit_Pair;
@@ -683,7 +716,9 @@ void nsCSSValue::SetPairValue(const nsCSSValue& xValue,
              xValue.GetUnit() != eCSSUnit_Unset &&
              yValue.GetUnit() != eCSSUnit_Unset &&
              xValue.GetUnit() != eCSSUnit_Revert &&
-             yValue.GetUnit() != eCSSUnit_Revert,
+             yValue.GetUnit() != eCSSUnit_Revert &&
+             xValue.GetUnit() != eCSSUnit_RevertLayer &&
+             yValue.GetUnit() != eCSSUnit_RevertLayer,
              "inappropriate pair value");
   Reset();
   mUnit = eCSSUnit_Pair;
@@ -709,7 +744,10 @@ void nsCSSValue::SetTripletValue(const nsCSSValueTriplet* aValue)
              aValue->mZValue.GetUnit() != eCSSUnit_Unset &&
              aValue->mXValue.GetUnit() != eCSSUnit_Revert &&
              aValue->mYValue.GetUnit() != eCSSUnit_Revert &&
-             aValue->mZValue.GetUnit() != eCSSUnit_Revert,
+             aValue->mZValue.GetUnit() != eCSSUnit_Revert &&
+             aValue->mXValue.GetUnit() != eCSSUnit_RevertLayer &&
+             aValue->mYValue.GetUnit() != eCSSUnit_RevertLayer &&
+             aValue->mZValue.GetUnit() != eCSSUnit_RevertLayer,
              "missing or inappropriate triplet value");
   Reset();
   mUnit = eCSSUnit_Triplet;
@@ -735,7 +773,10 @@ void nsCSSValue::SetTripletValue(const nsCSSValue& xValue,
              zValue.GetUnit() != eCSSUnit_Unset &&
              xValue.GetUnit() != eCSSUnit_Revert &&
              yValue.GetUnit() != eCSSUnit_Revert &&
-             zValue.GetUnit() != eCSSUnit_Revert,
+             zValue.GetUnit() != eCSSUnit_Revert &&
+             xValue.GetUnit() != eCSSUnit_RevertLayer &&
+             yValue.GetUnit() != eCSSUnit_RevertLayer &&
+             zValue.GetUnit() != eCSSUnit_RevertLayer,
              "inappropriate triplet value");
   Reset();
   mUnit = eCSSUnit_Triplet;
@@ -851,6 +892,26 @@ nsCSSValue::SetRevertValue(mozilla::SheetType aValue)
   SetCascadeOriginValue(aValue, eCSSUnit_Revert);
 }
 
+void
+nsCSSValue::SetRevertLayerValue()
+{
+  SetRevertLayerValue(mozilla::SheetType::Unknown, false, 0);
+}
+
+void
+nsCSSValue::SetRevertLayerValue(mozilla::SheetType aLevel,
+                                bool aIsImportant,
+                                int32_t aLayerIndex)
+{
+  MOZ_ASSERT(aLayerIndex >= 0 && aLayerIndex <= kRevertLayerMask,
+             "cascade layer index is out of range");
+  Reset();
+  mUnit = eCSSUnit_RevertLayer;
+  mValue.mInt = (uint32_t(aLevel) << kRevertLayerOriginShift) |
+                (aIsImportant ? kRevertLayerImportant : 0) |
+                (aLayerIndex & kRevertLayerMask);
+}
+
 void nsCSSValue::SetNoneValue()
 {
   Reset();
@@ -2234,6 +2295,7 @@ nsCSSValue::AppendToString(nsCSSPropertyID aProperty, nsAString& aResult,
     case eCSSUnit_Initial:      aResult.AppendLiteral("initial");  break;
     case eCSSUnit_Unset:        aResult.AppendLiteral("unset");    break;
     case eCSSUnit_Revert:       aResult.AppendLiteral("revert");   break;
+    case eCSSUnit_RevertLayer:  aResult.AppendLiteral("revert-layer"); break;
     case eCSSUnit_None:         aResult.AppendLiteral("none");     break;
     case eCSSUnit_Normal:       aResult.AppendLiteral("normal");   break;
     case eCSSUnit_System_Font:  aResult.AppendLiteral("-moz-use-system-font"); break;
@@ -2511,6 +2573,7 @@ nsCSSValue::SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
 
     // Cascade Origin: nothing extra to measure.
     case eCSSUnit_Revert:
+    case eCSSUnit_RevertLayer:
       break;
 
     // Float: nothing extra to measure.
@@ -2836,7 +2899,8 @@ nsCSSRect::AppendToString(nsCSSPropertyID aProperty, nsAString& aResult,
              mTop.GetUnit() != eCSSUnit_Inherit &&
              mTop.GetUnit() != eCSSUnit_Initial &&
              mTop.GetUnit() != eCSSUnit_Unset &&
-             mTop.GetUnit() != eCSSUnit_Revert,
+             mTop.GetUnit() != eCSSUnit_Revert &&
+             mTop.GetUnit() != eCSSUnit_RevertLayer,
              "parser should have used a bare value");
 
   if (eCSSProperty_border_image_slice == aProperty ||
@@ -3007,6 +3071,7 @@ nsCSSValuePairList::AppendToString(nsCSSPropertyID aProperty,
         item->mXValue.GetUnit() != eCSSUnit_Initial &&
         item->mXValue.GetUnit() != eCSSUnit_Unset &&
         item->mXValue.GetUnit() != eCSSUnit_Revert &&
+        item->mXValue.GetUnit() != eCSSUnit_RevertLayer &&
         item->mYValue.GetUnit() != eCSSUnit_Null) {
       aResult.Append(char16_t(' '));
       item->mYValue.AppendToString(aProperty, aResult, aSerialization);
@@ -3443,6 +3508,8 @@ nsCSSValueTokenStream::nsCSSValueTokenStream()
   : mPropertyID(eCSSProperty_UNKNOWN)
   , mShorthandPropertyID(eCSSProperty_UNKNOWN)
   , mLevel(SheetType::Count)
+  , mIsImportant(false)
+  , mLayerIndex(0)
 {
   MOZ_COUNT_CTOR(nsCSSValueTokenStream);
 }

layout/style/nsCSSValue.h

@@ -490,6 +490,7 @@ enum nsCSSUnit {
   eCSSUnit_GridTemplateAreas   = 44,   // (GridTemplateAreasValue*)
                                        // for grid-template-areas
   eCSSUnit_Revert       = 45,     // (SheetType) value is the current cascade origin
+  eCSSUnit_RevertLayer  = 46,     // (int32_t) packed cascade layer rollback data
 
   eCSSUnit_Pair         = 50,     // (nsCSSValuePair*) pair of values
   eCSSUnit_Triplet      = 51,     // (nsCSSValueTriplet*) triplet of values
@@ -939,6 +940,9 @@ public:
     MOZ_ASSERT(mUnit == eCSSUnit_Revert, "not a cascade origin value");
     return mValue.mCascadeOrigin;
   }
+  mozilla::SheetType GetRevertLayerOriginValue() const;
+  bool GetRevertLayerImportanceValue() const;
+  int32_t GetRevertLayerLayerIndexValue() const;
 
   void Reset()  // sets to null
   {
@@ -951,7 +955,7 @@ private:
 public:
   void SetIntValue(int32_t aValue, nsCSSUnit aUnit);
   template<typename T,
-           typename = typename std::enable_if<std::is_enum<T>::value>::type>
+           typename = typename std::enable_if_t<std::is_enum_v<T>>>
   void SetIntValue(T aValue, nsCSSUnit aUnit)
   {
     static_assert(mozilla::EnumTypeFitsWithin<T, int32_t>::value,
@@ -994,6 +998,10 @@ public:
   void SetInitialValue();
   void SetUnsetValue();
   void SetRevertValue(mozilla::SheetType aValue);
+  void SetRevertLayerValue();
+  void SetRevertLayerValue(mozilla::SheetType aLevel,
+                           bool aIsImportant,
+                           int32_t aLayerIndex);
   void SetNoneValue();
   void SetAllValue();
   void SetNormalValue();
@@ -1837,6 +1845,8 @@ public:
            mShorthandPropertyID == aOther.mShorthandPropertyID &&
            mTokenStream.Equals(aOther.mTokenStream) &&
            mLevel == aOther.mLevel &&
+           mIsImportant == aOther.mIsImportant &&
+           mLayerIndex == aOther.mLayerIndex &&
            (mBaseURI == aOther.mBaseURI ||
             (mBaseURI && aOther.mBaseURI &&
              NS_SUCCEEDED(mBaseURI->Equals(aOther.mBaseURI, &eq)) &&
@@ -1886,6 +1896,8 @@ public:
   uint32_t mLineNumber;
   uint32_t mLineOffset;
   mozilla::SheetType mLevel;
+  bool mIsImportant;
+  int32_t mLayerIndex;
 
 private:
   nsCSSValueTokenStream(const nsCSSValueTokenStream& aOther) = delete;

layout/style/nsRuleData.cpp

@@ -28,6 +28,9 @@ nsRuleData::GetPoisonOffset()
 nsRuleData::nsRuleData(uint32_t aSIDs, nsCSSValue* aValueStorage,
                        nsPresContext* aContext, nsStyleContext* aStyleContext)
   : mSIDs(aSIDs),
+    mIsImportantRule(false),
+    mLevel(mozilla::SheetType::Unknown),
+    mLayerIndex(0),
     mPresContext(aContext),
     mStyleContext(aStyleContext),
     mValueStorage(aValueStorage)

layout/style/nsRuleData.h

@@ -31,6 +31,7 @@ struct nsRuleData
   mozilla::RuleNodeCacheConditions mConditions;
   bool mIsImportantRule;
   mozilla::SheetType mLevel;
+  int32_t mLayerIndex;
   nsPresContext* const mPresContext;
   nsStyleContext* const mStyleContext;
 

layout/style/nsRuleNode.cpp

@@ -188,9 +188,10 @@ nsRuleNode::ChildrenHashHashKey(const void *aKey)
 {
   const nsRuleNode::Key *key =
     static_cast<const nsRuleNode::Key*>(aKey);
-  // Disagreement on importance and level for the same rule is extremely
-  // rare, so hash just on the rule.
-  return PLDHashTable::HashVoidPtrKeyStub(key->mRule);
+  return PLDHashTable::HashVoidPtrKeyStub(key->mRule) ^
+         (uint32_t(key->mLayerIndex) << 4) ^
+         (uint32_t(key->mLevel) << 1) ^
+         (key->mIsImportantRule ? 1 : 0);
 }
 
 /* static */ bool
@@ -2270,18 +2271,19 @@ already_AddRefed<nsRuleNode>
 nsRuleNode::CreateRootNode(nsPresContext* aPresContext)
 {
   return do_AddRef(new (aPresContext)
-    nsRuleNode(aPresContext, nullptr, nullptr, SheetType::Unknown, false));
+    nsRuleNode(aPresContext, nullptr, nullptr, SheetType::Unknown, false, 0));
 }
 
 nsRuleNode::nsRuleNode(nsPresContext* aContext, nsRuleNode* aParent,
                        nsIStyleRule* aRule, SheetType aLevel,
-                       bool aIsImportant)
+                       bool aIsImportant, int32_t aLayerIndex)
   : mPresContext(aContext),
     mParent(aParent),
     mRule(aRule),
     mNextSibling(nullptr),
     mDependentBits((uint32_t(aLevel) << NS_RULE_NODE_LEVEL_SHIFT) |
                    (aIsImportant ? NS_RULE_NODE_IS_IMPORTANT : 0)),
+    mLayerIndex(aLayerIndex),
     mNoneBits(aParent ? aParent->mNoneBits & NS_RULE_NODE_HAS_ANIMATION_DATA :
                         0),
     mRefCnt(0)
@@ -2295,6 +2297,8 @@ nsRuleNode::nsRuleNode(nsPresContext* aContext, nsRuleNode* aParent,
 
   NS_ASSERTION(IsRoot() || GetLevel() == aLevel, "not enough bits");
   NS_ASSERTION(IsRoot() || IsImportantRule() == aIsImportant, "yikes");
+  NS_ASSERTION(IsRoot() || GetLayerIndex() == aLayerIndex,
+               "bad layer index");
   aContext->StyleSet()->RuleNodeUnused(this, /* aMayGC = */ false);
 
   // nsStyleSet::GetContext depends on there being only one animation
@@ -2319,7 +2323,7 @@ nsRuleNode::~nsRuleNode()
 
 nsRuleNode*
 nsRuleNode::Transition(nsIStyleRule* aRule, SheetType aLevel,
-                       bool aIsImportantRule)
+                       bool aIsImportantRule, int32_t aLayerIndex)
 {
 #ifdef DEBUG
   {
@@ -2330,7 +2334,7 @@ nsRuleNode::Transition(nsIStyleRule* aRule, SheetType aLevel,
 #endif
 
   nsRuleNode* next = nullptr;
-  nsRuleNode::Key key(aRule, aLevel, aIsImportantRule);
+  nsRuleNode::Key key(aRule, aLevel, aIsImportantRule, aLayerIndex);
 
   if (HaveChildren() && !ChildrenAreHashed()) {
     int32_t numKids = 0;
@@ -2357,12 +2361,14 @@ nsRuleNode::Transition(nsIStyleRule* aRule, SheetType aLevel,
       next = entry->mRuleNode;
     } else {
       next = entry->mRuleNode = new (mPresContext)
-        nsRuleNode(mPresContext, this, aRule, aLevel, aIsImportantRule);
+        nsRuleNode(mPresContext, this, aRule, aLevel, aIsImportantRule,
+                   aLayerIndex);
     }
   } else if (!next) {
     // Create the new entry in our list.
     next = new (mPresContext)
-      nsRuleNode(mPresContext, this, aRule, aLevel, aIsImportantRule);
+      nsRuleNode(mPresContext, this, aRule, aLevel, aIsImportantRule,
+                 aLayerIndex);
     next->mNextSibling = ChildrenList();
     SetChildrenList(next);
   }
@@ -2545,7 +2551,8 @@ ExamineCSSValue(const nsCSSValue& aValue,
       ++aInheritedCount;
     } else if (aValue.GetUnit() == eCSSUnit_Unset) {
       ++aUnsetCount;
-    } else if (aValue.GetUnit() == eCSSUnit_Revert) {
+    } else if (aValue.GetUnit() == eCSSUnit_Revert ||
+               aValue.GetUnit() == eCSSUnit_RevertLayer) {
       ++aRevertCount;
     }
   }
@@ -3021,7 +3028,11 @@ nsRuleNode::ResolveVariableReferences(const nsStyleStructID aSID,
                "Token stream should have a defined level");
 
     AutoRestore<SheetType> saveLevel(aRuleData->mLevel);
+    AutoRestore<bool> saveImportant(aRuleData->mIsImportantRule);
+    AutoRestore<int32_t> saveLayerIndex(aRuleData->mLayerIndex);
     aRuleData->mLevel = tokenStream->mLevel;
+    aRuleData->mIsImportantRule = tokenStream->mIsImportant;
+    aRuleData->mLayerIndex = tokenStream->mLayerIndex;
 
     // Note that ParsePropertyWithVariableReferences relies on the fact
     // that the nsCSSValue in aRuleData for the property we are re-parsing
@@ -3045,6 +3056,114 @@ nsRuleNode::ResolveVariableReferences(const nsStyleStructID aSID,
   return anyTokenStreams;
 }
 
+static nsCSSPropertyID
+PropertyAtIndexInStruct(nsStyleStructID aSID, size_t aIndex)
+{
+  for (int32_t prop = 0; prop < eCSSProperty_COUNT_no_shorthands; prop++) {
+    nsCSSPropertyID property = nsCSSPropertyID(prop);
+    if (nsCSSProps::kSIDTable[property] == aSID &&
+        nsCSSProps::PropertyIndexInStruct(property) == aIndex) {
+      return property;
+    }
+  }
+  MOZ_ASSERT_UNREACHABLE("no property for style struct index");
+  return eCSSProperty_UNKNOWN;
+}
+
+/* static */ bool
+nsRuleNode::ResolveRevertLayerValues(const nsStyleStructID aSID,
+                                     nsRuleData* aRuleData,
+                                     nsStyleContext* aContext,
+                                     nsRuleNode* aStartRuleNode)
+{
+  MOZ_ASSERT(aSID != eStyleStruct_Variables);
+
+  size_t nprops = nsCSSProps::PropertyCountInStruct(aSID);
+  bool resolvedAny = false;
+
+  for (size_t pass = 0; pass <= nprops; pass++) {
+    bool resolvedThisPass = false;
+    bool needsVariableResolution = false;
+
+    for (size_t index = 0; index < nprops; index++) {
+      nsCSSValue* target = aRuleData->mValueStorage + index;
+      if (target->GetUnit() != eCSSUnit_RevertLayer) {
+        continue;
+      }
+
+      nsCSSPropertyID property = PropertyAtIndexInStruct(aSID, index);
+      if (property == eCSSProperty_UNKNOWN) {
+        continue;
+      }
+
+      AutoTArray<nsCSSValue, 64> tempValues;
+      tempValues.SetLength(nprops);
+      for (size_t i = 0; i < nprops; i++) {
+        tempValues[i].SetDummyValue();
+      }
+      tempValues[index] = *target;
+
+      nsRuleData tempRuleData(nsCachedStyleData::GetBitForSID(aSID),
+                              tempValues.Elements(),
+                              aStartRuleNode->mPresContext, aContext);
+      tempRuleData.mValueOffsets[aSID] = 0;
+
+      uint32_t bit = nsCachedStyleData::GetBitForSID(aSID);
+      for (nsRuleNode* ruleNode = aStartRuleNode; ruleNode;
+           ruleNode = ruleNode->GetParent()) {
+        if (ruleNode->mNoneBits & bit) {
+          break;
+        }
+
+        nsIStyleRule* rule = ruleNode->mRule;
+        if (rule) {
+          tempRuleData.mLevel = ruleNode->GetLevel();
+          tempRuleData.mIsImportantRule = ruleNode->IsImportantRule();
+          tempRuleData.mLayerIndex = ruleNode->GetLayerIndex();
+          rule->MapRuleInfoInto(&tempRuleData);
+        }
+
+        if (tempValues[index].GetUnit() != eCSSUnit_RevertLayer) {
+          break;
+        }
+      }
+
+      if (tempValues[index].GetUnit() == eCSSUnit_RevertLayer) {
+        tempValues[index].SetRevertValue(
+          target->GetRevertLayerOriginValue());
+      } else if (tempValues[index].GetUnit() == eCSSUnit_TokenStream) {
+        needsVariableResolution = true;
+      }
+
+      *target = tempValues[index];
+      aRuleData->mConditions.SetUncacheable();
+      resolvedThisPass = true;
+      resolvedAny = true;
+    }
+
+    if (!resolvedThisPass) {
+      break;
+    }
+
+    if (needsVariableResolution &&
+        ResolveVariableReferences(aSID, aRuleData, aContext)) {
+      resolvedAny = true;
+      continue;
+    }
+  }
+
+  for (size_t index = 0; index < nprops; index++) {
+    nsCSSValue* target = aRuleData->mValueStorage + index;
+    if (target->GetUnit() == eCSSUnit_RevertLayer) {
+      target->SetRevertValue(target->GetRevertLayerOriginValue());
+      aRuleData->mConditions.SetUncacheable();
+      resolvedAny = true;
+    }
+  }
+
+  return resolvedAny;
+}
+
 const void*
 nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
                          nsStyleContext* aContext)
@@ -3118,6 +3237,7 @@ nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
     if (rule) {
       ruleData.mLevel = ruleNode->GetLevel();
       ruleData.mIsImportantRule = ruleNode->IsImportantRule();
+      ruleData.mLayerIndex = ruleNode->GetLayerIndex();
       rule->MapRuleInfoInto(&ruleData);
     }
 
@@ -3154,6 +3274,11 @@ nsRuleNode::WalkRuleTree(const nsStyleStructID aSID,
     recomputeDetail = ResolveVariableReferences(aSID, &ruleData, aContext);
   }
 
+  if (aSID != eStyleStruct_Variables &&
+      ResolveRevertLayerValues(aSID, &ruleData, aContext, this)) {
+    recomputeDetail = true;
+  }
+
   // If needed, unset the properties that don't have a flag that allows
   // them to be set for this style context.  (For example, only some
   // properties apply to :first-line and :first-letter.)
@@ -4889,6 +5014,7 @@ nsRuleNode::SetGenericFont(nsPresContext* aPresContext,
       if (rule) {
         ruleData.mLevel = ruleNode->GetLevel();
         ruleData.mIsImportantRule = ruleNode->IsImportantRule();
+        ruleData.mLayerIndex = ruleNode->GetLayerIndex();
         rule->MapRuleInfoInto(&ruleData);
       }
     }
@@ -4902,6 +5028,8 @@ nsRuleNode::SetGenericFont(nsPresContext* aPresContext,
     }
 
     ResolveVariableReferences(eStyleStruct_Font, &ruleData, aContext);
+    ResolveRevertLayerValues(eStyleStruct_Font, &ruleData, aContext,
+                             context->RuleNode());
 
     RuleNodeCacheConditions dummy;
     nsRuleNode::SetFont(aPresContext, context,
@@ -11081,6 +11209,8 @@ nsRuleNode::ComputeVariablesData(void* aStartStruct,
   CSSVariableResolver resolver(&variables->mVariables);
   resolver.Resolve(&parentVariables->mVariables,
                    aRuleData->mVariables);
+  aRuleData->mVariables->ResolveRevertLayerFallbacks(&parentVariables->mVariables,
+                                                     &variables->mVariables);
   conditions.SetUncacheable();
 
   COMPUTE_END_INHERITED(Variables, variables)
@@ -11473,6 +11603,7 @@ nsRuleNode::HasAuthorSpecifiedRules(nsStyleContext* aStyleContext,
       if (rule) {
         ruleData.mLevel = ruleNode->GetLevel();
         ruleData.mIsImportantRule = ruleNode->IsImportantRule();
+        ruleData.mLayerIndex = ruleNode->GetLayerIndex();
 
         rule->MapRuleInfoInto(&ruleData);
 
@@ -11485,11 +11616,13 @@ nsRuleNode::HasAuthorSpecifiedRules(nsStyleContext* aStyleContext,
             nsCSSUnit unit = values[i]->GetUnit();
             if (unit != eCSSUnit_Null &&
                 unit != eCSSUnit_Revert &&
+                unit != eCSSUnit_RevertLayer &&
                 unit != eCSSUnit_Dummy &&
                 unit != eCSSUnit_DummyInherit) {
               if (unit == eCSSUnit_Inherit ||
                   (i >= inheritedOffset && unit == eCSSUnit_Unset) ||
-                  (i >= inheritedOffset && unit == eCSSUnit_Revert)) {
+                  (i >= inheritedOffset && unit == eCSSUnit_Revert) ||
+                  (i >= inheritedOffset && unit == eCSSUnit_RevertLayer)) {
                 haveExplicitUAInherit = true;
                 values[i]->SetDummyInheritValue();
               } else {
@@ -11504,7 +11637,8 @@ nsRuleNode::HasAuthorSpecifiedRules(nsStyleContext* aStyleContext,
             if (values[i]->GetUnit() != eCSSUnit_Null &&
                 values[i]->GetUnit() != eCSSUnit_Dummy && // see above
                 values[i]->GetUnit() != eCSSUnit_DummyInherit &&
-                values[i]->GetUnit() != eCSSUnit_Revert) {
+                values[i]->GetUnit() != eCSSUnit_Revert &&
+                values[i]->GetUnit() != eCSSUnit_RevertLayer) {
               // If author colors are not allowed, only claim to have
               // author-specified rules if we're looking at a non-color
               // property or if we're looking at the background color and it's
@@ -11596,6 +11730,7 @@ nsRuleNode::ComputePropertiesOverridingAnimation(
     if (rule) {
       ruleData.mLevel = ruleNode->GetLevel();
       ruleData.mIsImportantRule = ruleNode->IsImportantRule();
+      ruleData.mLayerIndex = ruleNode->GetLayerIndex();
 
       // Transitions are the only non-!important level overriding
       // animations in the cascade ordering.  They also don't actually

layout/style/nsRuleNode.h

@@ -441,16 +441,20 @@ private:
   struct Key {
     nsIStyleRule* mRule;
     mozilla::SheetType mLevel;
+    int32_t mLayerIndex;
     bool mIsImportantRule;
 
-    Key(nsIStyleRule* aRule, mozilla::SheetType aLevel, bool aIsImportantRule)
-      : mRule(aRule), mLevel(aLevel), mIsImportantRule(aIsImportantRule)
+    Key(nsIStyleRule* aRule, mozilla::SheetType aLevel,
+        bool aIsImportantRule, int32_t aLayerIndex)
+      : mRule(aRule), mLevel(aLevel), mLayerIndex(aLayerIndex),
+        mIsImportantRule(aIsImportantRule)
     {}
 
     bool operator==(const Key& aOther) const
     {
       return mRule == aOther.mRule &&
              mLevel == aOther.mLevel &&
+             mLayerIndex == aOther.mLayerIndex &&
              mIsImportantRule == aOther.mIsImportantRule;
     }
 
@@ -469,7 +473,7 @@ private:
   static const PLDHashTableOps ChildrenHashOps;
 
   Key GetKey() const {
-    return Key(mRule, GetLevel(), IsImportantRule());
+    return Key(mRule, GetLevel(), IsImportantRule(), GetLayerIndex());
   }
 
   // The children of this node are stored in either a hashtable or list
@@ -528,6 +532,8 @@ private:
   uint32_t mDependentBits; // Used to cache the fact that we can look up
                            // cached data under a parent rule.
 
+  int32_t mLayerIndex;
+
   uint32_t mNoneBits; // Used to cache the fact that the branch to this
                       // node specifies no non-inherited data for a
                       // given struct type.  (This usually implies that
@@ -585,6 +591,10 @@ protected:
   static bool ResolveVariableReferences(const nsStyleStructID aSID,
                                         nsRuleData* aRuleData,
                                         nsStyleContext* aContext);
+  static bool ResolveRevertLayerValues(const nsStyleStructID aSID,
+                                       nsRuleData* aRuleData,
+                                       nsStyleContext* aContext,
+                                       nsRuleNode* aStartRuleNode);
 
   const void*
     WalkRuleTree(const nsStyleStructID aSID, nsStyleContext* aContext);
@@ -792,7 +802,8 @@ protected:
 
 private:
   nsRuleNode(nsPresContext* aPresContext, nsRuleNode* aParent,
-             nsIStyleRule* aRule, mozilla::SheetType aLevel, bool aIsImportant);
+             nsIStyleRule* aRule, mozilla::SheetType aLevel,
+             bool aIsImportant, int32_t aLayerIndex);
   ~nsRuleNode();
 
 public:
@@ -805,7 +816,7 @@ public:
 
   // Transition never returns null; on out of memory it'll just return |this|.
   nsRuleNode* Transition(nsIStyleRule* aRule, mozilla::SheetType aLevel,
-                         bool aIsImportantRule);
+                         bool aIsImportantRule, int32_t aLayerIndex);
   nsRuleNode* GetParent() const { return mParent; }
   bool IsRoot() const { return mParent == nullptr; }
 
@@ -825,6 +836,10 @@ public:
     NS_ASSERTION(!IsRoot(), "can't call on root");
     return (mDependentBits & NS_RULE_NODE_IS_IMPORTANT) != 0;
   }
+  int32_t GetLayerIndex() const {
+    NS_ASSERTION(!IsRoot(), "can't call on root");
+    return mLayerIndex;
+  }
 
   /**
    * Has this rule node at some time in its lifetime been the mRuleNode

layout/style/nsRuleWalker.h

@@ -28,7 +28,8 @@ public:
 
 protected:
   void DoForward(nsIStyleRule* aRule) {
-    mCurrent = mCurrent->Transition(aRule, mLevel, mImportance);
+    mCurrent = mCurrent->Transition(aRule, mLevel, mImportance,
+                                    mLayerIndex);
     NS_POSTCONDITION(mCurrent, "Transition messed up");
   }
 
@@ -61,10 +62,16 @@ public:
                  "important rules");
     mLevel = aLevel;
     mImportance = aImportance;
+    mLayerIndex = 0;
     mCheckForImportantRules = aCheckForImportantRules;
   }
   mozilla::SheetType GetLevel() const { return mLevel; }
   bool GetImportance() const { return mImportance; }
+  void SetLayerIndex(int32_t aLayerIndex) {
+    MOZ_ASSERT(aLayerIndex >= 0, "negative cascade layer index");
+    mLayerIndex = aLayerIndex;
+  }
+  int32_t GetLayerIndex() const { return mLayerIndex; }
   bool GetCheckForImportantRules() const { return mCheckForImportantRules; }
 
   bool AuthorStyleDisabled() const { return mAuthorStyleDisabled; }
@@ -87,6 +94,7 @@ private:
   nsRuleNode* mCurrent; // Our current position.  Never null.
   nsRuleNode* mRoot; // The root of the tree we're walking.
   mozilla::SheetType mLevel;
+  int32_t mLayerIndex;
   bool mImportance;
   bool mCheckForImportantRules; // If true, check for important rules as
                                 // we walk and set to false if we find
@@ -97,6 +105,10 @@ public:
   nsRuleWalker(nsRuleNode* aRoot, bool aAuthorStyleDisabled)
     : mCurrent(aRoot)
     , mRoot(aRoot)
+    , mLevel(mozilla::SheetType::Unknown)
+    , mLayerIndex(0)
+    , mImportance(false)
+    , mCheckForImportantRules(false)
     , mAuthorStyleDisabled(aAuthorStyleDisabled)
   {
     NS_ASSERTION(mCurrent, "Caller screwed up and gave us null node");

layout/style/nsStyleSet.cpp

@@ -847,14 +847,14 @@ ReplaceAnimationRule(nsRuleNode *aOldRuleNode,
              "wrong level");
 
   if (aNewAnimRule) {
-    n = n->Transition(aNewAnimRule, SheetType::Animation, false);
+    n = n->Transition(aNewAnimRule, SheetType::Animation, false, 0);
     n->SetIsAnimationRule();
   }
 
   for (uint32_t i = moreSpecificNodes.Length(); i-- != 0; ) {
     nsRuleNode *oldNode = moreSpecificNodes[i];
     n = n->Transition(oldNode->GetRule(), oldNode->GetLevel(),
-                      oldNode->IsImportantRule());
+                      oldNode->IsImportantRule(), oldNode->GetLayerIndex());
   }
 
   return n;
@@ -1124,6 +1124,7 @@ FileRulesFromAllChildProcessors(
         if (i > 0) {
           aRuleWalker->SetLevel(aLevel, false, true);
         }
+        aRuleWalker->SetLayerIndex(i);
         nsCOMPtr<nsIStyleRuleProcessor> processor = (*processors)[i];
         (*aCollectorFunc)(processor, aData);
         TrackRuleNodeForCurrentOrigin(aRuleWalker,
@@ -1307,6 +1308,7 @@ nsStyleSet::FileRules(nsIStyleRuleProcessor::EnumFunc aCollectorFunc,
   if (haveAnyImportantDocRules) {
     for (uint32_t i = lastDocRNs.Length(); i-- != 0; ) {
       aRuleWalker->SetLevel(SheetType::Doc, true, false);
+      aRuleWalker->SetLayerIndex(i);
       nsRuleNode* startRN = lastDocRNs[i];
       nsRuleNode* endRN = i == 0 ? lastSVGAttrAnimationRN : lastDocRNs[i - 1];
       if (haveImportantDocRules[i]) {
@@ -1352,6 +1354,7 @@ nsStyleSet::FileRules(nsIStyleRuleProcessor::EnumFunc aCollectorFunc,
   if (haveAnyImportantUserRules) {
     for (uint32_t i = lastUserRNs.Length(); i-- != 0;) {
       aRuleWalker->SetLevel(SheetType::User, true, false);
+      aRuleWalker->SetLayerIndex(i);
       nsRuleNode* startRN = lastUserRNs[i];
       nsRuleNode* endRN = i == 0 ? lastAgentRN : lastUserRNs[i - 1];
       if (haveImportantUserRules[i]) {
@@ -1373,6 +1376,7 @@ nsStyleSet::FileRules(nsIStyleRuleProcessor::EnumFunc aCollectorFunc,
   if (haveAnyImportantAgentRules) {
     for (uint32_t i = lastAgentRNs.Length(); i-- != 0;) {
       aRuleWalker->SetLevel(SheetType::Agent, true, false);
+      aRuleWalker->SetLayerIndex(i);
       nsRuleNode* startRN = lastAgentRNs[i];
       nsRuleNode* endRN = i == 0 ? lastRestrictionRN : lastAgentRNs[i - 1];
       if (haveImportantAgentRules[i]) {
@@ -1585,6 +1589,7 @@ nsStyleSet::ResolveStyleByAddingRules(nsStyleContext* aBaseContext,
 struct RuleNodeInfo {
   nsIStyleRule* mRule;
   SheetType mLevel;
+  int32_t mLayerIndex;
   bool mIsImportant;
   bool mIsAnimationRule;
 };
@@ -1657,6 +1662,7 @@ nsStyleSet::RuleNodeWithReplacement(Element* aElement,
     RuleNodeInfo* curRule = rules.AppendElement();
     curRule->mRule = ruleNode->GetRule();
     curRule->mLevel = ruleNode->GetLevel();
+    curRule->mLayerIndex = ruleNode->GetLayerIndex();
     curRule->mIsImportant = ruleNode->IsImportantRule();
     curRule->mIsAnimationRule = ruleNode->IsAnimationRule();
   }
@@ -1771,6 +1777,7 @@ nsStyleSet::RuleNodeWithReplacement(Element* aElement,
       }
 
       if (!doReplace) {
+        ruleWalker.SetLayerIndex(ruleInfo.mLayerIndex);
         ruleWalker.ForwardOnPossiblyCSSRule(ruleInfo.mRule);
         if (ruleInfo.mIsAnimationRule) {
           ruleWalker.CurrentNode()->SetIsAnimationRule();

layout/style/test/mochitest.ini

@@ -245,6 +245,7 @@ support-files =
 support-files = redundant_font_download.sjs
 [test_rem_unit.html]
 [test_restyles_in_smil_animation.html]
+[test_revert_layer.html]
 [test_root_node_display.html]
 [test_rule_insertion.html]
 [test_rule_serialization.html]

layout/style/test/test_css_supports.html

@@ -37,6 +37,7 @@ function runTest()
     "(unknown:) or (color: green)",
     "(unknown) or (color: green)",
     "(font: 16px serif)",
+    "(all: revert-layer)",
     "(color:) or (color: green)",
     "not (@page)",
     "not ({ something @with [ balanced ] brackets })",
@@ -69,6 +70,7 @@ function runTest()
     "not ({ something @with (unbalanced brackets })",
     "(color: green) or an-extension(that is [unbalanced)",
     "not(unknown: unknown)",
+    "not (all: revert-layer)",
     "(color: green) or(color: blue)",
     "(color: green;)",
     "(font-family: 'Helvetica\n",
@@ -87,7 +89,9 @@ function runTest()
     ["font", "16px serif"],
     ["font", "16px /* comment */ serif"],
     ["font", "16px\nserif"],
-    ["color", "\\0067reen"]
+    ["color", "\\0067reen"],
+    ["all", "revert-layer"],
+    ["color", "revert-layer"]
   ];
 
   var failingDeclarations = [

layout/style/test/test_revert_layer.html

@@ -0,0 +1,127 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test CSS revert-layer cascade behavior</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<div id="display"></div>
+<pre id="test">
+<script type="application/javascript">
+
+SimpleTest.waitForExplicitFinish();
+
+let fixtureCount = 0;
+
+function runFixture(css, callback) {
+  const id = "revert-layer-fixture-" + (++fixtureCount);
+  const style = document.createElement("style");
+  style.textContent = css.replace(/__ID__/g, id);
+  document.head.appendChild(style);
+
+  const element = document.createElement("div");
+  element.id = id;
+  document.getElementById("display").appendChild(element);
+
+  try {
+    callback(element, getComputedStyle(element));
+  } finally {
+    element.remove();
+    style.remove();
+  }
+}
+
+ok(CSS.supports("color", "revert-layer"), "revert-layer parses as a CSS-wide keyword");
+ok(CSS.supports("all", "revert-layer"), "all accepts revert-layer");
+ok(!CSS.supports("not (all: revert-layer)"), "supports negation sees revert-layer support");
+
+runFixture(`
+  @layer { #__ID__ { color: rgb(0, 128, 0); } }
+  @layer { #__ID__ { color: red; color: revert-layer; } }
+`, function(element, cs) {
+  is(cs.color, "rgb(0, 128, 0)", "revert-layer rolls back to a previous explicit layer");
+});
+
+runFixture(`
+  @layer { #__ID__ { color: rgb(0, 128, 0); } }
+  #__ID__ { color: red; color: revert-layer; }
+`, function(element, cs) {
+  is(cs.color, "rgb(0, 128, 0)", "revert-layer rolls back from the implicit outer layer");
+});
+
+runFixture(`
+  @layer {
+    #__ID__ { color: rgb(0, 128, 0); width: 5px; height: 6px; }
+  }
+  @layer {
+    #__ID__ { color: red; width: 50px; height: 60px; }
+    #__ID__ { all: revert-layer; }
+  }
+`, function(element, cs) {
+  is(cs.color, "rgb(0, 128, 0)", "all: revert-layer rolls color back");
+  is(cs.width, "5px", "all: revert-layer rolls width back");
+  is(cs.height, "6px", "all: revert-layer rolls height back");
+});
+
+runFixture(`
+  @layer { #__ID__ { height: 7px; } }
+  @layer { #__ID__ { block-size: revert-layer; } }
+`, function(element, cs) {
+  is(cs.height, "7px", "revert-layer on a logical alias rolls back the physical property");
+});
+
+runFixture(`
+  @layer { #__ID__ { color: rgb(0, 128, 0) !important; } }
+  @layer { #__ID__ { color: red !important; color: revert-layer !important; } }
+`, function(element, cs) {
+  is(cs.color, "rgb(0, 128, 0)", "important revert-layer uses reversed layer order");
+});
+
+runFixture(`
+  @layer { #__ID__ { color: rgb(0, 128, 0); } }
+`, function(element, cs) {
+  element.style.color = "revert-layer";
+  is(cs.color, "rgb(0, 128, 0)", "normal style attribute revert-layer rolls back to author rules");
+});
+
+runFixture(`
+  @layer { #__ID__ { color: rgb(0, 128, 0) !important; } }
+`, function(element, cs) {
+  element.style.setProperty("color", "revert-layer", "important");
+  is(cs.color, "rgb(0, 128, 0)",
+     "important style attribute revert-layer does not skip author important rules");
+});
+
+runFixture(`
+  @layer {
+    #__ID__ { --x:PASS; margin: 1px; padding-left: 1px; }
+  }
+  @layer {
+    #__ID__ {
+      --x: var(--unknown, revert-layer);
+      margin: var(--unknown, revert-layer);
+      padding-left: var(--unknown, revert-layer);
+    }
+  }
+`, function(element, cs) {
+  is(cs.getPropertyValue("--x"), "PASS", "custom property var() fallback can resolve to revert-layer");
+  is(cs.marginLeft, "1px", "shorthand var() fallback can resolve to revert-layer");
+  is(cs.paddingLeft, "1px", "longhand var() fallback can resolve to revert-layer");
+});
+
+runFixture(`
+  @layer { #__ID__ { --x:PASS; } }
+  @layer { #__ID__ { --x: var(--unknown-a, revert-layer); } }
+  @layer { #__ID__ { --x: var(--unknown-b, revert-layer); } }
+`, function(element, cs) {
+  is(cs.getPropertyValue("--x"), "PASS",
+     "custom property fallback continues past lower declarations that also resolve to revert-layer");
+});
+
+SimpleTest.finish();
+
+</script>
+</pre>
+</body>
+</html>

mfbt/EnumTypeTraits.h

@@ -56,13 +56,13 @@ template<typename T, typename Storage>
 struct EnumTypeFitsWithin
   : public detail::EnumFitsWithinHelper<
       sizeof(T),
-      std::is_signed<typename std::underlying_type<T>::type>::value,
+      std::is_signed_v<typename std::underlying_type_t<T>>,
       sizeof(Storage),
-      std::is_signed<Storage>::value
+      std::is_signed_v<Storage>
     >
 {
-  static_assert(std::is_enum<T>::value, "must provide an enum type");
-  static_assert(std::is_integral<Storage>::value, "must provide an integral type");
+  static_assert(std::is_enum_v<T>, "must provide an enum type");
+  static_assert(std::is_integral_v<Storage>, "must provide an integral type");
 };
 
 } // namespace mozilla

mfbt/EnumeratedRange.h

@@ -31,7 +31,7 @@ template<typename EnumTypeT>
 class EnumeratedIterator
 {
 public:
-  typedef typename std::underlying_type<EnumTypeT>::type IntTypeT;
+  typedef typename std::underlying_type_t<EnumTypeT> IntTypeT;
 
   template<typename EnumType>
   explicit EnumeratedIterator(EnumType aCurrent)

mfbt/Maybe.h

@@ -115,7 +115,7 @@ public:
    */
   template<typename U,
            typename =
-             typename std::enable_if<std::is_convertible<U, T>::value>::type>
+             typename std::enable_if_t<std::is_convertible_v<U, T>>>
   MOZ_IMPLICIT
   Maybe(const Maybe<U>& aOther)
     : mIsSome(false)
@@ -139,7 +139,7 @@ public:
    */
   template<typename U,
            typename =
-             typename std::enable_if<std::is_convertible<U, T>::value>::type>
+             typename std::enable_if_t<std::is_convertible_v<U, T>>>
   MOZ_IMPLICIT
   Maybe(Maybe<U>&& aOther)
     : mIsSome(false)
@@ -168,7 +168,7 @@ public:
 
   template<typename U,
            typename =
-             typename std::enable_if<std::is_convertible<U, T>::value>::type>
+             typename std::enable_if_t<std::is_convertible_v<U, T>>>
   Maybe& operator=(const Maybe<U>& aOther)
   {
     if (aOther.isSome()) {
@@ -203,7 +203,7 @@ public:
 
   template<typename U,
            typename =
-             typename std::enable_if<std::is_convertible<U, T>::value>::type>
+             typename std::enable_if_t<std::is_convertible_v<U, T>>>
   Maybe& operator=(Maybe<U>&& aOther)
   {
     if (aOther.isSome()) {
@@ -539,8 +539,8 @@ class Maybe<T&> {
  * reference value, you need to use emplace() instead.
  */
 template<typename T,
-         typename U = typename std::remove_cv<
-           typename std::remove_reference<T>::type>::type>
+         typename U = typename std::remove_cv_t<
+           typename std::remove_reference_t<T>>>
 Maybe<U>
 Some(T&& aValue)
 {
@@ -574,7 +574,7 @@ ToMaybe(T* aPtr)
 template<typename T> bool
 operator==(const Maybe<T>& aLHS, const Maybe<T>& aRHS)
 {
-  static_assert(!std::is_reference<T>::value,
+  static_assert(!std::is_reference_v<T>,
                 "operator== is not defined for Maybe<T&>, compare values or "
                 "addresses explicitly instead");
   if (aLHS.isNothing() != aRHS.isNothing()) {

mfbt/Saturate.h

@@ -40,7 +40,7 @@ public:
   explicit SaturateOp(T& aValue)
     : mValue(aValue)
   {
-    // We should actually check for |std::is_scalar<T>::value| to be
+    // We should actually check for |std::is_scalar_v<T>| to be
     // true, but this type trait is not available everywhere. Relax
     // this assertion if you want to use floating point values as well.
     static_assert(IsIntegral<T>::value,

old-configure.in

@@ -2135,6 +2135,16 @@ if test -z "$XULRUNNER_STUB_NAME"; then
 fi
 AC_SUBST(XULRUNNER_STUB_NAME)
 
+dnl ========================================================
+
+dnl there are a lot of tests on MOZ_ENABLE_GTK below, that are more convenient
+dnl to keep that way than testing against MOZ_WIDGET_TOOLKIT
+case "$MOZ_WIDGET_TOOLKIT" in
+gtk*)
+    MOZ_ENABLE_GTK=1
+    ;;
+esac
+
 dnl ========================================================
 dnl = NPAPI support
 dnl ========================================================
@@ -2153,6 +2163,22 @@ fi
 
 AC_SUBST(MOZ_ENABLE_NPAPI)
 
+if test -n "$MOZ_ENABLE_GTK" ; then
+    MOZ_ENABLE_NPAPI_GTK2=1
+
+    MOZ_ARG_DISABLE_BOOL(npapi-gtk2,
+    [  --disable-npapi-gtk2     Disable GTK2 support for NPAPI plugins ],
+        MOZ_ENABLE_NPAPI_GTK2=,
+        MOZ_ENABLE_NPAPI_GTK2=1)
+
+    if test "$MOZ_ENABLE_NPAPI" -a "$MOZ_ENABLE_NPAPI_GTK2"
+    then
+        AC_DEFINE(MOZ_ENABLE_NPAPI_GTK2)
+    fi
+
+    AC_SUBST(MOZ_ENABLE_NPAPI_GTK2)
+fi
+
 dnl ========================================================
 dnl =
 dnl = Toolkit Options
@@ -2192,13 +2218,9 @@ cocoa)
 
 esac
 
-dnl there are a lot of tests on MOZ_ENABLE_GTK below, that are more convenient
-dnl to keep that way than testing against MOZ_WIDGET_TOOLKIT
-case "$MOZ_WIDGET_TOOLKIT" in
-gtk*)
-    MOZ_ENABLE_GTK=1
-    ;;
-esac
+if test "$MOZ_WIDGET_TOOLKIT" = gtk2 -a -z "$MOZ_ENABLE_NPAPI_GTK2"; then
+  AC_MSG_ERROR([--disable-npapi-gtk2 cannot be used with GTK2 browser builds.])
+fi
 
 if test "$COMPILE_ENVIRONMENT"; then
   if test "$MOZ_WIDGET_TOOLKIT" = gtk3; then
@@ -2210,8 +2232,9 @@ if test "$COMPILE_ENVIRONMENT"; then
     dnl are suppressed by widget/gtk/compat-gtk3/gdk/gdkversionmacros.h.
     AC_DEFINE_UNQUOTED(GDK_VERSION_MAX_ALLOWED,$GDK_VERSION_MAX_ALLOWED)
     GLIB_VERSION_MAX_ALLOWED=GLIB_VERSION_2_32
-    dnl We want to check GTK2 packages if NPAPI is enabled, even if building with GTK3.
-    if test "$MOZ_ENABLE_NPAPI"; then
+    dnl GTK2 NPAPI plugin support needs GTK2 packages, even when the browser
+    dnl itself is built against GTK3.
+    if test "$MOZ_ENABLE_NPAPI" -a "$MOZ_ENABLE_NPAPI_GTK2"; then
       MOZ_CHECK_GTK2=1
     fi
   fi
@@ -2229,7 +2252,7 @@ if test "$COMPILE_ENVIRONMENT"; then
 
     if test "$MOZ_CHECK_GTK2"; then
       PKG_CHECK_MODULES(MOZ_GTK2, gtk+-2.0 >= $GTK2_VERSION gtk+-unix-print-2.0 glib-2.0 >= $GLIB_VERSION gobject-2.0 $GDK_PACKAGES, ,
-                               [AC_MSG_ERROR([ * * * Could not find gtk+-2.0. Required for NPAPI plugins. To build without NPAPI, add --disable-npapi to your .mozconfig and clobber.])])
+                               [AC_MSG_ERROR([ * * * Could not find gtk+-2.0. Required for GTK2 browser builds and GTK2 NPAPI plugin support. To build a GTK3 browser with NPAPI but without GTK2 NPAPI plugin support, add --disable-npapi-gtk2 to your .mozconfig and clobber.])])
     MOZ_GTK2_CFLAGS="-I${_topsrcdir}/widget/gtk/compat $MOZ_GTK2_CFLAGS"
     fi
   fi

toolkit/moz.configure

@@ -445,8 +445,6 @@ option('--disable-skia', help='Disable use of Skia')
 
 @depends('--disable-skia', target)
 def skia(value, target):
-    if value.origin == 'default' and target.endianness == 'big':
-        return None
     if value:
         return True
 

widget/cocoa/nsChildView.mm

@@ -3727,7 +3727,7 @@ NSEvent* gLastDragMouseDownEvent = nil;
 
   NSSize viewSize = [self bounds].size;
   gfx::IntSize backingSize = gfx::IntSize::Truncate(viewSize.width * scale, viewSize.height * scale);
-#if defined(MAC_OS_X_VERSION_10_7) && (MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_7)
+#ifdef USE_SKIA
   LayoutDeviceIntRegion region = [self nativeDirtyRegionWithBoundingRect:aRect];
 
   bool painted = mGeckoChild->PaintWindowInContext(cgContext, region, backingSize);

widget/gtk/mozgtk/moz.build

@@ -3,4 +3,7 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-DIRS += ['stub', 'gtk2', 'gtk3']
+DIRS += ['stub', 'gtk3']
+
+if CONFIG['MOZ_ENABLE_NPAPI_GTK2']:
+    DIRS += ['gtk2']

widget/gtk/mozgtk/stub/moz.build

@@ -7,9 +7,12 @@ SOURCES += [
     '../mozgtk.c',
 ]
 
-for var in ('COMMON_SYMBOLS', 'GTK2_SYMBOLS', 'GTK3_SYMBOLS'):
+for var in ('COMMON_SYMBOLS', 'GTK3_SYMBOLS'):
     DEFINES[var] = True
 
+if CONFIG['MOZ_ENABLE_NPAPI_GTK2']:
+    DEFINES['GTK2_SYMBOLS'] = True
+
 SharedLibrary('mozgtk_stub')
 
 SONAME = 'mozgtk'

widget/moz.build

@@ -52,7 +52,8 @@ if toolkit in ('cocoa', 'gtk2', 'gtk3'):
 if 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']:
     DIRS += ['gtk']
 
-    if CONFIG['MOZ_X11'] and CONFIG['MOZ_ENABLE_NPAPI']:
+    if (CONFIG['MOZ_X11'] and CONFIG['MOZ_ENABLE_NPAPI'] and
+            CONFIG['MOZ_ENABLE_NPAPI_GTK2']):
         DIRS += ['gtkxtbin']
 
 XPIDL_SOURCES += [