Prohibit explicit usage of kotlin.Metadata as annotation

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/checkers/ExplicitMetadataChecker.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.resolve.jvm.checkers
+
+import org.jetbrains.kotlin.descriptors.annotations.KotlinTarget
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.psi.KtAnnotationEntry
+import org.jetbrains.kotlin.resolve.AdditionalAnnotationChecker
+import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.BindingTrace
+import org.jetbrains.kotlin.resolve.jvm.diagnostics.ErrorsJvm
+
+object ExplicitMetadataChecker : AdditionalAnnotationChecker {
+    private val METADATA_FQ_NAME = FqName("kotlin.Metadata")
+
+    override fun checkEntries(entries: List<KtAnnotationEntry>, actualTargets: List<KotlinTarget>, trace: BindingTrace) {
+        for (entry in entries) {
+            val descriptor = trace.get(BindingContext.ANNOTATION, entry) ?: continue
+            if (descriptor.fqName == METADATA_FQ_NAME) {
+                trace.report(ErrorsJvm.EXPLICIT_METADATA_IS_DISALLOWED.on(entry))
+            }
+        }
+    }
+}

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/DefaultErrorMessagesJvm.java

@@ -141,6 +141,7 @@ public class DefaultErrorMessagesJvm implements DefaultErrorMessages.Extension {
         MAP.put(JVM_DEFAULT_THROUGH_INHERITANCE, "Inheritance from an interface with '@JvmDefault' members is only allowed with -Xjvm-default option");
         MAP.put(USAGE_OF_JVM_DEFAULT_THROUGH_SUPER_CALL, "Super calls of '@JvmDefault' members are only allowed with -Xjvm-default option");
         MAP.put(NON_JVM_DEFAULT_OVERRIDES_JAVA_DEFAULT, "Non-@JvmDefault interface method cannot override default Java method. Please annotate this method with @JvmDefault");
+        MAP.put(EXPLICIT_METADATA_IS_DISALLOWED, "Explicit @Metadata is disallowed");
     }
 
     @NotNull

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/diagnostics/ErrorsJvm.java

@@ -123,6 +123,8 @@ public interface ErrorsJvm {
 
     DiagnosticFactory0<KtDeclaration> NON_JVM_DEFAULT_OVERRIDES_JAVA_DEFAULT = DiagnosticFactory0.create(WARNING, DECLARATION_SIGNATURE);
 
+    DiagnosticFactory0<KtAnnotationEntry> EXPLICIT_METADATA_IS_DISALLOWED = DiagnosticFactory0.create(ERROR);
+
     enum NullabilityInformationSource {
         KOTLIN {
             @NotNull

compiler/frontend.java/src/org/jetbrains/kotlin/resolve/jvm/platform/JvmPlatformConfigurator.kt

@@ -71,7 +71,8 @@ object JvmPlatformConfigurator : PlatformConfigurator(
 
     additionalAnnotationCheckers = listOf(
         RepeatableAnnotationChecker,
-        FileClassAnnotationsChecker
+        FileClassAnnotationsChecker,
+        ExplicitMetadataChecker
     ),
 
     identifierChecker = JvmSimpleNameBacktickChecker,

compiler/testData/diagnostics/testsWithStdLib/annotations/explicitMetadata.kt

@@ -0,0 +1,11 @@
+// !DIAGNOSTICS: -INVISIBLE_MEMBER -INVISIBLE_REFERENCE -EXPOSED_PARAMETER_TYPE
+
+<!EXPLICIT_METADATA_IS_DISALLOWED!>@Metadata<!>
+class A
+
+<!EXPLICIT_METADATA_IS_DISALLOWED!>@Metadata(xs = "_")<!>
+annotation class B(val m: Metadata)
+
+<!WRONG_ANNOTATION_TARGET, EXPLICIT_METADATA_IS_DISALLOWED!>@Metadata(xi = 0)<!>
+@B(Metadata())
+fun f() {}

compiler/testData/diagnostics/testsWithStdLib/annotations/explicitMetadata.txt

@@ -0,0 +1,18 @@
+package
+
+@kotlin.Metadata(xi = 0) @B(m = kotlin.Metadata) public fun f(): kotlin.Unit
+
+@kotlin.Metadata public final class A {
+    public constructor A()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+@kotlin.Metadata(xs = "_") public final annotation class B : kotlin.Annotation {
+    public constructor B(/*0*/ m: kotlin.Metadata)
+    public final val m: kotlin.Metadata
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestWithStdLibGenerated.java

@@ -171,6 +171,11 @@ public class DiagnosticsTestWithStdLibGenerated extends AbstractDiagnosticsTestW
             runTest("compiler/testData/diagnostics/testsWithStdLib/annotations/defaultValueMustBeConstant.kt");
         }
 
+        @TestMetadata("explicitMetadata.kt")
+        public void testExplicitMetadata() throws Exception {
+            runTest("compiler/testData/diagnostics/testsWithStdLib/annotations/explicitMetadata.kt");
+        }
+
         @TestMetadata("JvmSyntheticOnDelegate.kt")
         public void testJvmSyntheticOnDelegate() throws Exception {
             runTest("compiler/testData/diagnostics/testsWithStdLib/annotations/JvmSyntheticOnDelegate.kt");

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsTestWithStdLibUsingJavacGenerated.java

@@ -171,6 +171,11 @@ public class DiagnosticsTestWithStdLibUsingJavacGenerated extends AbstractDiagno
             runTest("compiler/testData/diagnostics/testsWithStdLib/annotations/defaultValueMustBeConstant.kt");
         }
 
+        @TestMetadata("explicitMetadata.kt")
+        public void testExplicitMetadata() throws Exception {
+            runTest("compiler/testData/diagnostics/testsWithStdLib/annotations/explicitMetadata.kt");
+        }
+
         @TestMetadata("JvmSyntheticOnDelegate.kt")
         public void testJvmSyntheticOnDelegate() throws Exception {
             runTest("compiler/testData/diagnostics/testsWithStdLib/annotations/JvmSyntheticOnDelegate.kt");