[K2] Disallow named functions as expressions

^KT-62573 Fixed
^KT-59945 Fixed

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDataClassConverters.kt

@@ -3056,6 +3056,18 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.SINGLE_ANONYMOUS_FUNCTION_WITH_NAME.errorFactory) { firDiagnostic ->
+        SingleAnonymousFunctionWithNameErrorImpl(
+            firDiagnostic as KtPsiDiagnostic,
+            token,
+        )
+    }
+    add(FirErrors.SINGLE_ANONYMOUS_FUNCTION_WITH_NAME.warningFactory) { firDiagnostic ->
+        SingleAnonymousFunctionWithNameWarningImpl(
+            firDiagnostic as KtPsiDiagnostic,
+            token,
+        )
+    }
     add(FirErrors.ANONYMOUS_FUNCTION_PARAMETER_WITH_DEFAULT_VALUE) { firDiagnostic ->
         AnonymousFunctionParameterWithDefaultValueImpl(
             firDiagnostic as KtPsiDiagnostic,

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -2164,6 +2164,14 @@ sealed interface KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         override val diagnosticClass get() = AnonymousFunctionWithName::class
     }
 
+    interface SingleAnonymousFunctionWithNameError : KtFirDiagnostic<KtFunction> {
+        override val diagnosticClass get() = SingleAnonymousFunctionWithNameError::class
+    }
+
+    interface SingleAnonymousFunctionWithNameWarning : KtFirDiagnostic<KtFunction> {
+        override val diagnosticClass get() = SingleAnonymousFunctionWithNameWarning::class
+    }
+
     interface AnonymousFunctionParameterWithDefaultValue : KtFirDiagnostic<KtParameter> {
         override val diagnosticClass get() = AnonymousFunctionParameterWithDefaultValue::class
     }

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -2592,6 +2592,16 @@ internal class AnonymousFunctionWithNameImpl(
     token: KtLifetimeToken,
 ) : KtAbstractFirDiagnostic<KtFunction>(firDiagnostic, token), KtFirDiagnostic.AnonymousFunctionWithName
 
+internal class SingleAnonymousFunctionWithNameErrorImpl(
+    firDiagnostic: KtPsiDiagnostic,
+    token: KtLifetimeToken,
+) : KtAbstractFirDiagnostic<KtFunction>(firDiagnostic, token), KtFirDiagnostic.SingleAnonymousFunctionWithNameError
+
+internal class SingleAnonymousFunctionWithNameWarningImpl(
+    firDiagnostic: KtPsiDiagnostic,
+    token: KtLifetimeToken,
+) : KtAbstractFirDiagnostic<KtFunction>(firDiagnostic, token), KtFirDiagnostic.SingleAnonymousFunctionWithNameWarning
+
 internal class AnonymousFunctionParameterWithDefaultValueImpl(
     firDiagnostic: KtPsiDiagnostic,
     token: KtLifetimeToken,

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java

@@ -9212,6 +9212,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
                 runTest("compiler/testData/diagnostics/tests/declarationChecks/kt2643MultiDeclInControlFlow.kt");
             }
 
+            @Test
+            @TestMetadata("kt47245.kt")
+            public void testKt47245() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/declarationChecks/kt47245.kt");
+            }
+
             @Test
             @TestMetadata("kt559.kt")
             public void testKt559() throws Exception {

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java

@@ -9212,6 +9212,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
                 runTest("compiler/testData/diagnostics/tests/declarationChecks/kt2643MultiDeclInControlFlow.kt");
             }
 
+            @Test
+            @TestMetadata("kt47245.kt")
+            public void testKt47245() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/declarationChecks/kt47245.kt");
+            }
+
             @Test
             @TestMetadata("kt559.kt")
             public void testKt559() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java

@@ -9206,6 +9206,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
                 runTest("compiler/testData/diagnostics/tests/declarationChecks/kt2643MultiDeclInControlFlow.kt");
             }
 
+            @Test
+            @TestMetadata("kt47245.kt")
+            public void testKt47245() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/declarationChecks/kt47245.kt");
+            }
+
             @Test
             @TestMetadata("kt559.kt")
             public void testKt559() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java

@@ -9212,6 +9212,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
                 runTest("compiler/testData/diagnostics/tests/declarationChecks/kt2643MultiDeclInControlFlow.kt");
             }
 
+            @Test
+            @TestMetadata("kt47245.kt")
+            public void testKt47245() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/declarationChecks/kt47245.kt");
+            }
+
             @Test
             @TestMetadata("kt559.kt")
             public void testKt559() throws Exception {

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt

@@ -1096,6 +1096,7 @@ object DIAGNOSTICS_LIST : DiagnosticList("FirErrors") {
 
         val FUNCTION_DECLARATION_WITH_NO_NAME by error<KtFunction>(PositioningStrategy.DECLARATION_SIGNATURE)
         val ANONYMOUS_FUNCTION_WITH_NAME by error<KtFunction>()
+        val SINGLE_ANONYMOUS_FUNCTION_WITH_NAME by deprecationError<KtFunction>(LanguageFeature.ProhibitSingleNamedFunctionAsExpression)
 
         // TODO: val ANONYMOUS_FUNCTION_WITH_NAME by error1<PsiElement, Name>(SourceElementPositioningStrategies.DECLARATION_NAME)
         val ANONYMOUS_FUNCTION_PARAMETER_WITH_DEFAULT_VALUE by error<KtParameter>(PositioningStrategy.PARAMETER_DEFAULT_VALUE)

compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt

@@ -24,6 +24,7 @@ import org.jetbrains.kotlin.config.LanguageFeature.ProhibitInlineModifierOnPrima
 import org.jetbrains.kotlin.config.LanguageFeature.ProhibitInvisibleAbstractMethodsInSuperclasses
 import org.jetbrains.kotlin.config.LanguageFeature.ProhibitNonReifiedArraysAsReifiedTypeArguments
 import org.jetbrains.kotlin.config.LanguageFeature.ProhibitScriptTopLevelInnerClasses
+import org.jetbrains.kotlin.config.LanguageFeature.ProhibitSingleNamedFunctionAsExpression
 import org.jetbrains.kotlin.config.LanguageFeature.ProhibitUseSiteTargetAnnotationsOnSuperTypes
 import org.jetbrains.kotlin.config.LanguageFeature.RestrictRetentionForExpressionAnnotations
 import org.jetbrains.kotlin.config.LanguageFeature.RestrictionOfValReassignmentViaBackingField
@@ -551,6 +552,7 @@ object FirErrors {
     val NON_MEMBER_FUNCTION_NO_BODY by error1<KtFunction, FirCallableSymbol<*>>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
     val FUNCTION_DECLARATION_WITH_NO_NAME by error0<KtFunction>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
     val ANONYMOUS_FUNCTION_WITH_NAME by error0<KtFunction>()
+    val SINGLE_ANONYMOUS_FUNCTION_WITH_NAME by deprecationError0<KtFunction>(ProhibitSingleNamedFunctionAsExpression)
     val ANONYMOUS_FUNCTION_PARAMETER_WITH_DEFAULT_VALUE by error0<KtParameter>(SourceElementPositioningStrategies.PARAMETER_DEFAULT_VALUE)
     val USELESS_VARARG_ON_PARAMETER by warning0<KtParameter>()
     val MULTIPLE_VARARG_PARAMETERS by error0<KtParameter>(SourceElementPositioningStrategies.PARAMETER_VARARG_MODIFIER)

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/CommonExpressionCheckers.kt

@@ -129,7 +129,8 @@ object CommonExpressionCheckers : ExpressionCheckers() {
     override val blockCheckers: Set<FirBlockChecker>
         get() = setOf(
             FirForLoopChecker,
-            FirConflictsExpressionChecker
+            FirConflictsExpressionChecker,
+            FirSingleNamedFunctionChecker
         )
 
     override val checkNotNullCallCheckers: Set<FirCheckNotNullCallChecker>

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/expression/FirSingleNamedFunctionChecker.kt

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2010-2023 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.fir.analysis.checkers.expression
+
+import org.jetbrains.kotlin.config.LanguageFeature
+import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.diagnostics.reportOn
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
+import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
+import org.jetbrains.kotlin.fir.expressions.FirBlock
+import org.jetbrains.kotlin.fir.expressions.impl.FirSingleExpressionBlock
+
+object FirSingleNamedFunctionChecker : FirBlockChecker() {
+    override fun check(expression: FirBlock, context: CheckerContext, reporter: DiagnosticReporter) {
+        if (expression is FirSingleExpressionBlock && expression.statement is FirSimpleFunction) {
+            reporter.reportOn(
+                expression.statement.source,
+                FirErrors.SINGLE_ANONYMOUS_FUNCTION_WITH_NAME,
+                context
+            )
+        }
+    }
+}

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrorsDefaultMessages.kt

@@ -570,6 +570,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SENSELESS_NULL_IN
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SETTER_PROJECTED_OUT
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SETTER_VISIBILITY_INCONSISTENT_WITH_PROPERTY_VISIBILITY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SINGLETON_IN_SUPERTYPE
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SINGLE_ANONYMOUS_FUNCTION_WITH_NAME
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SMARTCAST_IMPOSSIBLE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SPREAD_OF_NULLABLE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.SUBCLASS_OPT_IN_INAPPLICABLE
@@ -1783,6 +1784,7 @@ object FirErrorsDefaultMessages : BaseDiagnosticRendererFactory() {
         map.put(NON_MEMBER_FUNCTION_NO_BODY, "Function ''{0}'' must have a body.", DECLARATION_NAME)
         map.put(FUNCTION_DECLARATION_WITH_NO_NAME, "Function declaration must have a name.")
         map.put(ANONYMOUS_FUNCTION_WITH_NAME, "Anonymous functions with names are prohibited.")
+        map.put(SINGLE_ANONYMOUS_FUNCTION_WITH_NAME, "Anonymous functions with names are prohibited.")
 
         map.put(
             ANONYMOUS_FUNCTION_PARAMETER_WITH_DEFAULT_VALUE,

compiler/testData/diagnostics/tests/declarationChecks/kt47245.fir.kt

@@ -0,0 +1,6 @@
+// !COMPILER_VERSION 2.0
+// SKIP_KT_DUMP
+
+fun test() {
+    for (i in 0..0) <!SINGLE_ANONYMOUS_FUNCTION_WITH_NAME_WARNING!>fun x() {}<!>
+}

compiler/testData/diagnostics/tests/declarationChecks/kt47245.kt

@@ -0,0 +1,6 @@
+// !COMPILER_VERSION 2.0
+// SKIP_KT_DUMP
+
+fun test() {
+    for (i in 0..0) fun x() {}
+}

compiler/testData/diagnostics/tests/declarationChecks/namedFunAsLastExpressionInBlock.fir.kt

@@ -1,5 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_ANONYMOUS_PARAMETER -UNUSED_VARIABLE
 // !CHECK_TYPE
+// !COMPILER_VERSION 2.0
 fun foo(block: () -> (() -> Int)) {}
 
 fun test() {
@@ -26,15 +27,15 @@ fun test() {
     <!SYNTAX!><!>fun named7() = 1
 
     val x3 = when (1) {
-        0 -> fun named8(): Int {return 1}
+        0 -> <!SINGLE_ANONYMOUS_FUNCTION_WITH_NAME_WARNING!>fun named8(): Int {return 1}<!>
-        else -> fun named9() = 1
+        else -> <!SINGLE_ANONYMOUS_FUNCTION_WITH_NAME_WARNING!>fun named9() = 1<!>
     }
 
     val x31 = when (1) {
         0 -> {
             fun named10(): Int {return 1}
         }
-        else -> fun named11() = 1
+        else -> <!SINGLE_ANONYMOUS_FUNCTION_WITH_NAME_WARNING!>fun named11() = 1<!>
     }
 
     val x4 = {

compiler/testData/diagnostics/tests/declarationChecks/namedFunAsLastExpressionInBlock.kt

@@ -1,5 +1,6 @@
 // !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_ANONYMOUS_PARAMETER -UNUSED_VARIABLE
 // !CHECK_TYPE
+// !COMPILER_VERSION 2.0
 fun foo(block: () -> (() -> Int)) {}
 
 fun test() {

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/DiagnosticTestGenerated.java

@@ -9212,6 +9212,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/declarationChecks/kt2643MultiDeclInControlFlow.kt");
             }
 
+            @Test
+            @TestMetadata("kt47245.kt")
+            public void testKt47245() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/declarationChecks/kt47245.kt");
+            }
+
             @Test
             @TestMetadata("kt559.kt")
             public void testKt559() throws Exception {

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

@@ -314,6 +314,7 @@ enum class LanguageFeature(
     ProhibitImplementingVarByInheritedVal(KOTLIN_2_1, kind = BUG_FIX), // KT-56779
     PrioritizedEnumEntries(KOTLIN_2_1, kind = UNSTABLE_FEATURE), // KT-58920
     ProhibitInlineModifierOnPrimaryConstructorParameters(KOTLIN_2_1, kind = BUG_FIX), // KT-59664
+    ProhibitSingleNamedFunctionAsExpression(KOTLIN_2_1, kind = BUG_FIX), // KT-62573
 
     // End of 2.* language features --------------------------------------------------