Report diagnostic on virtual tailrec function

#KT-18541 Fixed

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/Errors.java

@@ -585,6 +585,8 @@ public interface Errors {
     DiagnosticFactory0<KtParameter> VALUE_PARAMETER_WITH_NO_TYPE_ANNOTATION = DiagnosticFactory0.create(ERROR);
 
     DiagnosticFactory0<KtNamedFunction> NO_TAIL_CALLS_FOUND = DiagnosticFactory0.create(WARNING, DECLARATION_SIGNATURE);
+    DiagnosticFactory0<KtNamedFunction> TAILREC_ON_VIRTUAL_MEMBER = DiagnosticFactory0.create(WARNING, DECLARATION_SIGNATURE);
+    DiagnosticFactory0<KtNamedFunction> TAILREC_ON_VIRTUAL_MEMBER_ERROR = DiagnosticFactory0.create(ERROR, DECLARATION_SIGNATURE);
 
     DiagnosticFactory0<KtParameter>
             ANONYMOUS_FUNCTION_PARAMETER_WITH_DEFAULT_VALUE = DiagnosticFactory0.create(ERROR, PARAMETER_DEFAULT_VALUE);

compiler/frontend/src/org/jetbrains/kotlin/diagnostics/rendering/DefaultErrorMessages.java

@@ -620,6 +620,9 @@ public class DefaultErrorMessages {
         MAP.put(ILLEGAL_SELECTOR, "The expression cannot be a selector (occur after a dot)");
 
         MAP.put(NO_TAIL_CALLS_FOUND, "A function is marked as tail-recursive but no tail calls are found");
+        MAP.put(TAILREC_ON_VIRTUAL_MEMBER, "Tailrec on open members is deprecated");
+        MAP.put(TAILREC_ON_VIRTUAL_MEMBER_ERROR, "Tailrec is not allowed on open members");
+
         MAP.put(VALUE_PARAMETER_WITH_NO_TYPE_ANNOTATION, "A type annotation is required on a value parameter");
         MAP.put(BREAK_OR_CONTINUE_OUTSIDE_A_LOOP, "'break' and 'continue' are only allowed inside a loop");
         MAP.put(BREAK_OR_CONTINUE_IN_WHEN, "'break' and 'continue' are not allowed in 'when' statements. Consider using labels to continue/break from the outer loop");

compiler/frontend/src/org/jetbrains/kotlin/resolve/PlatformConfiguratorBase.kt

@@ -31,7 +31,8 @@ private val DEFAULT_DECLARATION_CHECKERS = listOf(
     AnnotationClassTargetAndRetentionChecker(),
     ReservedMembersAndConstructsForInlineClass(),
     ResultClassInReturnTypeChecker(),
-    LocalVariableTypeParametersChecker()
+    LocalVariableTypeParametersChecker(),
+    TailrecFunctionChecker
 )
 
 private val DEFAULT_CALL_CHECKERS = listOf(

compiler/frontend/src/org/jetbrains/kotlin/resolve/checkers/TailrecFunctionChecker.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2010-2019 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.checkers
+
+import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.descriptors.FunctionDescriptor
+import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.psi.KtNamedFunction
+import org.jetbrains.kotlin.resolve.isEffectivelyFinal
+
+object TailrecFunctionChecker : DeclarationChecker {
+    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+        if (declaration !is KtNamedFunction || descriptor !is FunctionDescriptor || !descriptor.isTailrec) return
+
+        if (descriptor.isEffectivelyFinal(false)) return
+
+        if (!context.languageVersionSettings.supportsFeature(LanguageFeature.ProhibitTailrecOnVirtualMember)) {
+            context.trace.report(Errors.TAILREC_ON_VIRTUAL_MEMBER.on(declaration))
+        } else {
+            context.trace.report(Errors.TAILREC_ON_VIRTUAL_MEMBER_ERROR.on(declaration))
+        }
+    }
+}

compiler/frontend/src/org/jetbrains/kotlin/resolve/inline/InlineAnalyzerExtension.kt

@@ -28,6 +28,7 @@ import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.BindingTrace
 import org.jetbrains.kotlin.resolve.calls.components.hasDefaultValue
 import org.jetbrains.kotlin.resolve.descriptorUtil.declaresOrInheritsDefaultValue
+import org.jetbrains.kotlin.resolve.isEffectivelyFinal
 
 class InlineAnalyzerExtension(
     private val reasonableInlineRules: Iterable<ReasonableInlineRule>,
@@ -159,7 +160,8 @@ class InlineAnalyzerExtension(
             }
         }
 
-        if (callableDescriptor.isEffectivelyFinal()) {
+        //TODO: actually it should be isEffectivelyFinal(false), but looks like it requires committee decision: KT-34372)
+        if (callableDescriptor.isEffectivelyFinal(true)) {
             if (overridesAnything) {
                 trace.report(Errors.OVERRIDE_BY_INLINE.on(functionOrProperty))
             }
@@ -168,12 +170,6 @@ class InlineAnalyzerExtension(
         trace.report(Errors.DECLARATION_CANT_BE_INLINED.on(functionOrProperty))
     }
 
-    private fun CallableMemberDescriptor.isEffectivelyFinal(): Boolean =
-        modality == Modality.FINAL ||
-                containingDeclaration.let { containingDeclaration ->
-                    containingDeclaration is ClassDescriptor && containingDeclaration.modality == Modality.FINAL
-                }
-
     private fun checkHasInlinableAndNullability(functionDescriptor: FunctionDescriptor, function: KtFunction, trace: BindingTrace) {
         var hasInlineArgs = false
         function.valueParameters.zip(functionDescriptor.valueParameters).forEach { (parameter, descriptor) ->

compiler/frontend/src/org/jetbrains/kotlin/resolve/ktDescriptorUtil.kt

@@ -5,7 +5,10 @@
 
 package org.jetbrains.kotlin.resolve
 
+import org.jetbrains.kotlin.descriptors.CallableMemberDescriptor
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
+import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.types.DeferredType
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.typeUtil.contains
@@ -24,3 +27,11 @@ fun FunctionDescriptor.isFunctionForExpectTypeFromCastFeature(): Boolean {
 
     return true
 }
+
+
+internal fun CallableMemberDescriptor.isEffectivelyFinal(ignoreEnumClassFinality: Boolean): Boolean =
+    modality == Modality.FINAL ||
+            containingDeclaration.let { parent ->
+                (ignoreEnumClassFinality || !DescriptorUtils.isEnumClass(parent)) &&
+                        parent is ClassDescriptor && parent.modality == Modality.FINAL
+            }