Build impl with javac 11 to work around compiler bugs

.github/workflows/build-project.yaml

@@ -33,10 +33,11 @@ jobs:
           key: "${{ runner.os }}-minecraft-${{ env.CACHE_REV }}-${{ hashFiles('**/*.gradle*') }}"
           restore-keys: |
             ${{ runner.os }}-minecraft-${{ env.CACHE_REV }}-
-      - name: Set up JDK 1.8
-        uses: actions/setup-java@v1
+      - name: Set up JDK 11
+        uses: actions/setup-java@v2
         with:
-          java-version: 1.8
+          distribution: adopt
+          java-version: 11
       - name: Validate Gradle Wrapper
         uses: gradle/wrapper-validation-action@v1
       - name: Setup workspace

.github/workflows/deploy.yaml

@@ -28,10 +28,11 @@ jobs:
           key: "${{ runner.os }}-minecraft-${{ env.CACHE_REV }}-${{ hashFiles('**/*.gradle*') }}"
           restore-keys: |
             ${{ runner.os }}-minecraft-${{ env.CACHE_REV }}-
-      - name: Set up JDK 1.8
-        uses: actions/setup-java@v1
+      - name: Set up JDK 11
+        uses: actions/setup-java@v2
         with:
-          java-version: 1.8
+          distribution: adopt
+          java-version: 11
       - name: Validate Gradle Wrapper
         uses: gradle/wrapper-validation-action@v1
       - name: Setup workspace
@@ -108,10 +109,11 @@ jobs:
           key: "${{ runner.os }}-minecraft-${{ env.CACHE_REV }}-${{ hashFiles('**/*.gradle*') }}"
           restore-keys: |
             ${{ runner.os }}-minecraft-${{ env.CACHE_REV }}-
-      - name: Set up JDK 1.8
-        uses: actions/setup-java@v1
+      - name: Set up JDK 11
+        uses: actions/setup-java@v2
         with:
-          java-version: 1.8
+          distribution: adopt
+          java-version: 11
         # We don't need to run tests again, so we just publish
       - name: Setup workspace
         run: |

build.gradle.kts

@@ -271,6 +271,9 @@ allprojects {
     java {
         sourceCompatibility = JavaVersion.VERSION_1_8
         targetCompatibility = JavaVersion.VERSION_1_8
+        if (!JavaVersion.current().isJava11Compatible) {
+            toolchain.languageVersion.set(JavaLanguageVersion.of(11))
+        }
     }
 
     tasks.withType<AbstractArchiveTask> {
@@ -284,9 +287,7 @@ allprojects {
         withType(JavaCompile::class).configureEach {
             options.compilerArgs.addAll(listOf("-Xmaxerrs", "1000"))
             options.encoding = "UTF-8"
-            if (JavaVersion.current().isJava10Compatible) {
-                options.release.set(8)
-            }
+            options.release.set(8)
             if (project.name != "testplugins" && System.getProperty("idea.sync.active") != null) {
                 options.annotationProcessorPath = emptyAnnotationProcessors // hack so IntelliJ doesn't try to run Mixin AP
             }