Introduce warning for private inline functions which return anonymous objects without specified supertypes (KT-33917)

compiler/fir/analysis-tests/tests/org/jetbrains/kotlin/fir/FirOldFrontendDiagnosticsTestGenerated.java

@@ -12431,6 +12431,11 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirOldFronte
             runTest("compiler/testData/diagnostics/tests/inline/recursion.kt");
         }
 
+        @TestMetadata("returnedAnonymousObjects.kt")
+        public void testReturnedAnonymousObjects() throws Exception {
+            runTest("compiler/testData/diagnostics/tests/inline/returnedAnonymousObjects.kt");
+        }
+
         @TestMetadata("returns.kt")
         public void testReturns() throws Exception {
             runTest("compiler/testData/diagnostics/tests/inline/returns.kt");

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

@@ -1129,6 +1129,7 @@ public interface Errors {
     DiagnosticFactory1<PsiElement, CallableDescriptor> PROTECTED_CALL_FROM_PUBLIC_INLINE_ERROR = DiagnosticFactory1.create(ERROR);
     DiagnosticFactory2<KtElement, KtExpression, DeclarationDescriptor> INVALID_DEFAULT_FUNCTIONAL_PARAMETER_FOR_INLINE = DiagnosticFactory2.create(ERROR);
     DiagnosticFactory2<KtElement, KtExpression, DeclarationDescriptor> NOT_SUPPORTED_INLINE_PARAMETER_IN_INLINE_PARAMETER_DEFAULT_VALUE = DiagnosticFactory2.create(ERROR);
+    DiagnosticFactory0<PsiElement> PRIVATE_INLINE_FUNCTIONS_RETURNING_ANONYMOUS_OBJECTS = DiagnosticFactory0.create(WARNING);
 
     DiagnosticFactory0<PsiElement> NON_LOCAL_SUSPENSION_POINT = DiagnosticFactory0.create(ERROR);
     DiagnosticFactory1<PsiElement, CallableDescriptor> ILLEGAL_SUSPEND_FUNCTION_CALL = DiagnosticFactory1.create(ERROR);

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

@@ -1016,6 +1016,8 @@ public class DefaultErrorMessages {
         MAP.put(PROTECTED_CALL_FROM_PUBLIC_INLINE_ERROR, "Protected function call from public-API inline function is prohibited", NAME);
         MAP.put(INVALID_DEFAULT_FUNCTIONAL_PARAMETER_FOR_INLINE, "Invalid default value for inline parameter: ''{0}''. Only lambdas, anonymous functions, and callable references are supported", ELEMENT_TEXT, SHORT_NAMES_IN_TYPES);
         MAP.put(NOT_SUPPORTED_INLINE_PARAMETER_IN_INLINE_PARAMETER_DEFAULT_VALUE, "Usage of inline parameter ''{0}'' in default value for another inline parameter is not supported", ELEMENT_TEXT, SHORT_NAMES_IN_TYPES);
+        MAP.put(PRIVATE_INLINE_FUNCTIONS_RETURNING_ANONYMOUS_OBJECTS, "Return type of the private inline function can't be anonymous. It will be approximated to Any in 1.5." +
+                                                                      "See https://youtrack.jetbrains.com/issue/KT-33917 for more details");
         //Inline non locals
         MAP.put(NON_LOCAL_RETURN_NOT_ALLOWED, "Can''t inline ''{0}'' here: it may contain non-local returns. Add ''crossinline'' modifier to parameter declaration ''{0}''", ELEMENT_TEXT);
         MAP.put(INLINE_CALL_CYCLE, "The ''{0}'' invocation is a part of inline cycle", NAME);

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

@@ -39,7 +39,8 @@ private val DEFAULT_DECLARATION_CHECKERS = listOf(
     MissingDependencySupertypeChecker.ForDeclarations,
     FunInterfaceDeclarationChecker(),
     DeprecatedSinceKotlinAnnotationChecker,
-    ContractDescriptionBlockChecker
+    ContractDescriptionBlockChecker,
+    PrivateInlineFunctionsReturningAnonymousObjectsChecker
 )
 
 private val DEFAULT_CALL_CHECKERS = listOf(

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

@@ -0,0 +1,36 @@
+/*
+ * 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.checkers
+
+import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.diagnostics.Errors
+import org.jetbrains.kotlin.psi.KtDeclaration
+import org.jetbrains.kotlin.psi.KtNamedFunction
+import org.jetbrains.kotlin.psi.psiUtil.isPrivate
+import org.jetbrains.kotlin.resolve.DescriptorUtils
+import org.jetbrains.kotlin.types.typeUtil.isAnyOrNullableAny
+
+object PrivateInlineFunctionsReturningAnonymousObjectsChecker : DeclarationChecker {
+    override fun check(declaration: KtDeclaration, descriptor: DeclarationDescriptor, context: DeclarationCheckerContext) {
+        if (context.languageVersionSettings.supportsFeature(LanguageFeature.ForbidAnonymousReturnTypesInPrivateInlineFunctions))
+            return
+
+        if (descriptor !is SimpleFunctionDescriptor || !descriptor.isInline || !declaration.isPrivate() || declaration !is KtNamedFunction)
+            return
+
+        val returnTypeConstructor = descriptor.returnType?.constructor ?: return
+
+        if (returnTypeConstructor.supertypes.singleOrNull { it.isAnyOrNullableAny() } == null) return
+
+        val nameIdentifier = declaration.nameIdentifier ?: return
+        val returnTypeDeclarationDescriptor = returnTypeConstructor.declarationDescriptor ?: return
+
+        if (DescriptorUtils.isAnonymousObject(returnTypeDeclarationDescriptor)) {
+            context.trace.report(Errors.PRIVATE_INLINE_FUNCTIONS_RETURNING_ANONYMOUS_OBJECTS.on(nameIdentifier))
+        }
+    }
+}

compiler/testData/diagnostics/tests/inline/returnedAnonymousObjects.fir.kt

@@ -0,0 +1,11 @@
+private inline fun foo(crossinline f: () -> Int) = object {
+    fun bar(): Int = f()
+}
+
+fun test(b: Boolean) {
+    var x = foo { 1 }
+    if (b) {
+        x = foo { 2 }
+    }
+    x.bar()
+}

compiler/testData/diagnostics/tests/inline/returnedAnonymousObjects.kt

@@ -0,0 +1,11 @@
+private inline fun <!PRIVATE_INLINE_FUNCTIONS_RETURNING_ANONYMOUS_OBJECTS!>foo<!>(crossinline f: () -> Int) = object {
+    fun bar(): Int = f()
+}
+
+fun test(b: Boolean) {
+    var x = foo { 1 }
+    if (b) {
+        x = foo { 2 }
+    }
+    x.bar()
+}

compiler/testData/diagnostics/tests/inline/returnedAnonymousObjects.txt

@@ -0,0 +1,4 @@
+package
+
+private inline fun foo(/*0*/ crossinline f: () -> kotlin.Int): foo.<no name provided>
+public fun test(/*0*/ b: kotlin.Boolean): kotlin.Unit

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

@@ -12438,6 +12438,11 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTestWithFirVali
                 runTest("compiler/testData/diagnostics/tests/inline/recursion.kt");
             }
 
+            @TestMetadata("returnedAnonymousObjects.kt")
+            public void testReturnedAnonymousObjects() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inline/returnedAnonymousObjects.kt");
+            }
+
             @TestMetadata("returns.kt")
             public void testReturns() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/inline/returns.kt");

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

@@ -12433,6 +12433,11 @@ public class DiagnosticsUsingJavacTestGenerated extends AbstractDiagnosticsUsing
                 runTest("compiler/testData/diagnostics/tests/inline/recursion.kt");
             }
 
+            @TestMetadata("returnedAnonymousObjects.kt")
+            public void testReturnedAnonymousObjects() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/inline/returnedAnonymousObjects.kt");
+            }
+
             @TestMetadata("returns.kt")
             public void testReturns() throws Exception {
                 runTest("compiler/testData/diagnostics/tests/inline/returns.kt");

compiler/util/src/org/jetbrains/kotlin/config/LanguageVersionSettings.kt

@@ -137,6 +137,7 @@ enum class LanguageFeature(
     ProhibitUsingNullableTypeParameterAgainstNotNullAnnotated(KOTLIN_1_5, kind = BUG_FIX),
     InferenceCompatibility(KOTLIN_1_5, kind = BUG_FIX),
     RequiredPrimaryConstructorDelegationCallInEnums(KOTLIN_1_5, kind = BUG_FIX),
+    ForbidAnonymousReturnTypesInPrivateInlineFunctions(KOTLIN_1_5, kind = BUG_FIX),
 
     // Temporarily disabled, see KT-27084/KT-22379
     SoundSmartcastFromLoopConditionForLoopAssignedVariables(sinceVersion = null, kind = BUG_FIX),