[FIR] Introduce a feature flag for context-sensitive enum resolution

The feature was previously enabled unconditionally in K2 which
triggered a bug when an enum has an entry with the same name as itself.

#KT-58897 Fixed
#KT-52774

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

@@ -35846,6 +35846,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
                 runTest("compiler/testData/diagnostics/tests/when/whenOnNothing.kt");
             }
 
+            @Test
+            @TestMetadata("whenOverEnumWithSameNameAsEntry.kt")
+            public void testWhenOverEnumWithSameNameAsEntry() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/when/whenOverEnumWithSameNameAsEntry.kt");
+            }
+
             @Test
             @TestMetadata("WhenTypeDisjunctions.kt")
             public void testWhenTypeDisjunctions() throws Exception {

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

@@ -35846,6 +35846,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
                 runTest("compiler/testData/diagnostics/tests/when/whenOnNothing.kt");
             }
 
+            @Test
+            @TestMetadata("whenOverEnumWithSameNameAsEntry.kt")
+            public void testWhenOverEnumWithSameNameAsEntry() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/when/whenOverEnumWithSameNameAsEntry.kt");
+            }
+
             @Test
             @TestMetadata("WhenTypeDisjunctions.kt")
             public void testWhenTypeDisjunctions() throws Exception {

compiler/fir/analysis-tests/testData/resolve/unqualifiedEnum/correctJava.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContextSensitiveEnumResolutionInWhen
 // FILE: JavaEnum.java
 
 public enum JavaEnum {

compiler/fir/analysis-tests/testData/resolve/unqualifiedEnum/incorrectJava.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContextSensitiveEnumResolutionInWhen
 // FILE: JavaEnum.java
 
 public enum JavaEnum {

compiler/fir/analysis-tests/testData/resolve/unqualifiedEnum/nested.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContextSensitiveEnumResolutionInWhen
 enum class Outer {
     FIRST, SECOND;
 }

compiler/fir/analysis-tests/testData/resolve/unqualifiedEnum/notInsideBranches.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContextSensitiveEnumResolutionInWhen
 enum class Some {
     FIRST,
     SECOND;

compiler/fir/analysis-tests/testData/resolve/unqualifiedEnum/priority.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContextSensitiveEnumResolutionInWhen
 // FILE: first.kt
 
 package first

compiler/fir/analysis-tests/testData/resolve/unqualifiedEnum/typeAlias.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContextSensitiveEnumResolutionInWhen
 enum class Some {
     FIRST,
     SECOND;

compiler/fir/analysis-tests/testData/resolve/unqualifiedEnum/unqualifiedEnum.kt

@@ -1,3 +1,4 @@
+// LANGUAGE: +ContextSensitiveEnumResolutionInWhen
 package test
 
 enum class Sample {

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

@@ -35846,6 +35846,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
                 runTest("compiler/testData/diagnostics/tests/when/whenOnNothing.kt");
             }
 
+            @Test
+            @TestMetadata("whenOverEnumWithSameNameAsEntry.kt")
+            public void testWhenOverEnumWithSameNameAsEntry() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/when/whenOverEnumWithSameNameAsEntry.kt");
+            }
+
             @Test
             @TestMetadata("WhenTypeDisjunctions.kt")
             public void testWhenTypeDisjunctions() throws Exception {

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

@@ -35942,6 +35942,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
                 runTest("compiler/testData/diagnostics/tests/when/whenOnNothing.kt");
             }
 
+            @Test
+            @TestMetadata("whenOverEnumWithSameNameAsEntry.kt")
+            public void testWhenOverEnumWithSameNameAsEntry() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/when/whenOverEnumWithSameNameAsEntry.kt");
+            }
+
             @Test
             @TestMetadata("WhenTypeDisjunctions.kt")
             public void testWhenTypeDisjunctions() throws Exception {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/BodyResolveContext.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.fir.resolve.transformers.body.resolve
 
+import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.ClassKind
 import org.jetbrains.kotlin.fir.FirSession
 import org.jetbrains.kotlin.fir.PrivateForInline
@@ -15,6 +16,7 @@ import org.jetbrains.kotlin.fir.declarations.utils.isCompanion
 import org.jetbrains.kotlin.fir.declarations.utils.isInner
 import org.jetbrains.kotlin.fir.expressions.FirCallableReferenceAccess
 import org.jetbrains.kotlin.fir.expressions.FirWhenExpression
+import org.jetbrains.kotlin.fir.languageVersionSettings
 import org.jetbrains.kotlin.fir.resolve.*
 import org.jetbrains.kotlin.fir.resolve.calls.ImplicitExtensionReceiverValue
 import org.jetbrains.kotlin.fir.resolve.calls.ImplicitReceiverValue
@@ -534,19 +536,28 @@ class BodyResolveContext(
     inline fun <T> withWhenSubjectType(
         subjectType: ConeKotlinType?,
         sessionHolder: SessionHolder,
-        f: () -> T
+        f: () -> T,
     ): T {
         val session = sessionHolder.session
-        val subjectClassSymbol = (subjectType as? ConeClassLikeType)
+
-            ?.lookupTag?.toFirRegularClassSymbol(session)?.takeIf { it.fir.classKind == ClassKind.ENUM_CLASS }
+        val withContextSensitiveResolution =
-        val whenSubjectImportingScope = subjectClassSymbol?.let {
+            session.languageVersionSettings.supportsFeature(LanguageFeature.ContextSensitiveEnumResolutionInWhen)
-            FirWhenSubjectImportingScope(it.classId, session, sessionHolder.scopeSession)
+
+        if (withContextSensitiveResolution) {
+            val subjectClassSymbol = (subjectType as? ConeClassLikeType)
+                ?.lookupTag?.toFirRegularClassSymbol(session)?.takeIf { it.fir.classKind == ClassKind.ENUM_CLASS }
+            val whenSubjectImportingScope = subjectClassSymbol?.let {
+                FirWhenSubjectImportingScope(it.classId, session, sessionHolder.scopeSession)
+            }
+            whenSubjectImportingScopes.add(whenSubjectImportingScope)
         }
-        whenSubjectImportingScopes.add(whenSubjectImportingScope)
+
         return try {
             f()
         } finally {
-            whenSubjectImportingScopes.removeLast()
+            if (withContextSensitiveResolution) {
+                whenSubjectImportingScopes.removeLast()
+            }
         }
     }
 

compiler/testData/codegen/box/fir/unqualifiedEnum.kt

@@ -1,6 +1,7 @@
 // TARGET_BACKEND: JVM_IR
 // IGNORE_BACKEND_K1: JVM_IR
 // WITH_STDLIB
+// LANGUAGE: +ContextSensitiveEnumResolutionInWhen
 
 enum class Rainbow {
     RED,

compiler/testData/diagnostics/tests/when/whenOverEnumWithSameNameAsEntry.kt

@@ -0,0 +1,12 @@
+// FIR_IDENTICAL
+// KT-58897
+
+enum class A {
+    A,
+    B,
+}
+
+fun test2(a: A) = when (a) {
+    A.A -> "A"
+    A.B -> "B"
+}

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

@@ -36744,6 +36744,12 @@ public class DiagnosticTestGenerated extends AbstractDiagnosticTest {
                 runTest("compiler/testData/diagnostics/tests/when/whenOnNothing.kt");
             }
 
+            @Test
+            @TestMetadata("whenOverEnumWithSameNameAsEntry.kt")
+            public void testWhenOverEnumWithSameNameAsEntry() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/when/whenOverEnumWithSameNameAsEntry.kt");
+            }
+
             @Test
             @TestMetadata("WhenTypeDisjunctions.kt")
             public void testWhenTypeDisjunctions() throws Exception {

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

@@ -348,6 +348,7 @@ enum class LanguageFeature(
     ForbidInferringTypeVariablesIntoEmptyIntersection(sinceVersion = null, kind = BUG_FIX), // KT-51221
     IntrinsicConstEvaluation(sinceVersion = null, kind = UNSTABLE_FEATURE), // KT-49303
     DisableCheckingChangedProgressionsResolve(sinceVersion = null, kind = OTHER), // KT-49276
+    ContextSensitiveEnumResolutionInWhen(sinceVersion = null, kind = UNSTABLE_FEATURE), // KT-52774
     ;
 
     init {