Report error if fun interface method has JVM name getFunctionDelegate

This is needed so that it wouldn't clash with the corresponding member
from the kotlin/jvm/internal/FunctionAdapter interface, which all fun
interface wrappers will implement to get proper equals/hashCode. The
workaround is to rename the fun interface method.

 #KT-33455

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

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * 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.*
+import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.psi.KtNamedDeclaration
+import org.jetbrains.kotlin.resolve.checkers.DeclarationChecker
+import org.jetbrains.kotlin.resolve.checkers.DeclarationCheckerContext
+import org.jetbrains.kotlin.resolve.jvm.diagnostics.ErrorsJvm
+
+object FunctionDelegateMemberNameClashChecker : DeclarationChecker {
+    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+        if (descriptor !is CallableMemberDescriptor) return
+        val container = descriptor.containingDeclaration
+        if (container !is ClassDescriptor || !container.isFun) return
+        if (descriptor.extensionReceiverParameter != null || descriptor.valueParameters.isNotEmpty()) return
+
+        if (descriptor is FunctionDescriptor && descriptor.name.asString() == "getFunctionDelegate" ||
+            descriptor is PropertyDescriptor && descriptor.name.asString() == "functionDelegate"
+        ) {
+            val reportOn = (declaration as? KtNamedDeclaration)?.nameIdentifier ?: declaration
+            context.trace.report(ErrorsJvm.FUNCTION_DELEGATE_MEMBER_NAME_CLASH.on(reportOn))
+        }
+    }
+}

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

@@ -156,6 +156,9 @@ public class DefaultErrorMessagesJvm implements DefaultErrorMessages.Extension {
         String spreadOnPolymorphicSignature = "Spread operator is prohibited for arguments to signature-polymorphic calls";
         MAP.put(SPREAD_ON_SIGNATURE_POLYMORPHIC_CALL, spreadOnPolymorphicSignature);
         MAP.put(SPREAD_ON_SIGNATURE_POLYMORPHIC_CALL_ERROR, spreadOnPolymorphicSignature);
+
+        MAP.put(FUNCTION_DELEGATE_MEMBER_NAME_CLASH,
+                "Functional interface member cannot have this name on JVM because it clashes with an internal member getFunctionDelegate");
     }
 
     @NotNull

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

@@ -137,6 +137,8 @@ public interface ErrorsJvm {
     DiagnosticFactory0<PsiElement> SPREAD_ON_SIGNATURE_POLYMORPHIC_CALL = DiagnosticFactory0.create(WARNING);
     DiagnosticFactory0<PsiElement> SPREAD_ON_SIGNATURE_POLYMORPHIC_CALL_ERROR = DiagnosticFactory0.create(ERROR);
 
+    DiagnosticFactory0<PsiElement> FUNCTION_DELEGATE_MEMBER_NAME_CLASH = DiagnosticFactory0.create(ERROR);
+
     @SuppressWarnings("UnusedDeclaration")
     Object _initializer = new Object() {
         {

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

@@ -39,7 +39,8 @@ object JvmPlatformConfigurator : PlatformConfiguratorBase(
         BadInheritedJavaSignaturesChecker,
         JvmMultifileClassStateChecker,
         SynchronizedOnInlineMethodChecker,
-        DefaultCheckerInTailrec
+        DefaultCheckerInTailrec,
+        FunctionDelegateMemberNameClashChecker,
     ),
 
     additionalCallCheckers = listOf(