FIR/FE1.0: keep flexibility when approximating local types

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

@@ -16973,6 +16973,18 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                     runTest("compiler/testData/diagnostics/tests/inference/substitutions/delegationAndInference.kt");
                 }
 
+                @Test
+                @TestMetadata("hideFlexibleLocalTypeInPublicPosition.kt")
+                public void testHideFlexibleLocalTypeInPublicPosition() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/substitutions/hideFlexibleLocalTypeInPublicPosition.kt");
+                }
+
+                @Test
+                @TestMetadata("hideFlexibleLocalTypeInPublicPosition_before.kt")
+                public void testHideFlexibleLocalTypeInPublicPosition_before() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/substitutions/hideFlexibleLocalTypeInPublicPosition_before.kt");
+                }
+
                 @Test
                 @TestMetadata("hideLocalTypeForReturnTypeOfSingleExpressionFunction.kt")
                 public void testHideLocalTypeForReturnTypeOfSingleExpressionFunction() throws Exception {
@@ -16985,6 +16997,12 @@ public class FirOldFrontendDiagnosticsTestGenerated extends AbstractFirDiagnosti
                     runTest("compiler/testData/diagnostics/tests/inference/substitutions/hideNullableLocalTypeInPublicPosition.kt");
                 }
 
+                @Test
+                @TestMetadata("hideNullableLocalTypeInPublicPosition_before.kt")
+                public void testHideNullableLocalTypeInPublicPosition_before() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/substitutions/hideNullableLocalTypeInPublicPosition_before.kt");
+                }
+
                 @Test
                 @TestMetadata("kt32189returnTypeWithTypealiasSubtitution.kt")
                 public void testKt32189returnTypeWithTypealiasSubtitution() throws Exception {

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

@@ -16973,6 +16973,18 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                     runTest("compiler/testData/diagnostics/tests/inference/substitutions/delegationAndInference.kt");
                 }
 
+                @Test
+                @TestMetadata("hideFlexibleLocalTypeInPublicPosition.kt")
+                public void testHideFlexibleLocalTypeInPublicPosition() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/substitutions/hideFlexibleLocalTypeInPublicPosition.kt");
+                }
+
+                @Test
+                @TestMetadata("hideFlexibleLocalTypeInPublicPosition_before.kt")
+                public void testHideFlexibleLocalTypeInPublicPosition_before() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/substitutions/hideFlexibleLocalTypeInPublicPosition_before.kt");
+                }
+
                 @Test
                 @TestMetadata("hideLocalTypeForReturnTypeOfSingleExpressionFunction.kt")
                 public void testHideLocalTypeForReturnTypeOfSingleExpressionFunction() throws Exception {
@@ -16985,6 +16997,12 @@ public class FirOldFrontendDiagnosticsWithLightTreeTestGenerated extends Abstrac
                     runTest("compiler/testData/diagnostics/tests/inference/substitutions/hideNullableLocalTypeInPublicPosition.kt");
                 }
 
+                @Test
+                @TestMetadata("hideNullableLocalTypeInPublicPosition_before.kt")
+                public void testHideNullableLocalTypeInPublicPosition_before() throws Exception {
+                    runTest("compiler/testData/diagnostics/tests/inference/substitutions/hideNullableLocalTypeInPublicPosition_before.kt");
+                }
+
                 @Test
                 @TestMetadata("kt32189returnTypeWithTypealiasSubtitution.kt")
                 public void testKt32189returnTypeWithTypealiasSubtitution() throws Exception {

compiler/fir/providers/src/org/jetbrains/kotlin/fir/types/TypeUtils.kt

@@ -12,7 +12,6 @@ import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.descriptors.Visibility
 import org.jetbrains.kotlin.fakeElement
 import org.jetbrains.kotlin.fir.FirSession
-import org.jetbrains.kotlin.fir.copyWithNewSourceKind
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.isEnumClass
 import org.jetbrains.kotlin.fir.declarations.utils.isExpect
@@ -381,39 +380,50 @@ private fun FirTypeRef.hideLocalTypeIfNeeded(
     session: FirSession,
     isInlineFunction: Boolean = false
 ): FirTypeRef {
-    if (!shouldHideLocalType(containingCallableVisibility, isInlineFunction)) return this
+    if (this !is FirResolvedTypeRef || !shouldHideLocalType(containingCallableVisibility, isInlineFunction)) return this
+    return withReplacedConeType(type.approximateToOnlySupertype(session))
+}
 
-    val coneType = coneTypeSafe<ConeClassLikeType>() ?: return this
-    val firClass = (coneType.lookupTag as? ConeClassLookupTagWithFixedSymbol)?.symbol?.fir
+private fun ConeKotlinType.approximateToOnlySupertype(session: FirSession): ConeKotlinType? {
+    if (this is ConeFlexibleType) {
+        val lower = lowerBound.approximateToOnlySupertype(session)?.coneLowerBoundIfFlexible()
+        val upper = upperBound.approximateToOnlySupertype(session)?.coneUpperBoundIfFlexible()
+        if (lower == null && upper == null) {
+            return null
+        }
+        return coneFlexibleOrSimpleType(session.typeContext, lower ?: lowerBound, upper ?: upperBound)
+    }
+
+    if (this !is ConeClassLikeType) {
+        return null
+    }
+    val firClass = (lookupTag as? ConeClassLookupTagWithFixedSymbol)?.symbol?.fir
     if (firClass !is FirAnonymousObject) {
         // NB: local classes are acceptable here, but reported by EXPOSED_* checkers as errors
-        return this
+        return null
     }
     if (firClass.superTypeRefs.size > 1) {
         // NB: don't approximate so members can be resolved. The error is reported by FirAmbiguousAnonymousTypeChecker.
-        return this
+        return null
     }
     val superType = firClass.superTypeRefs.single()
-    if (superType is FirResolvedTypeRef) {
-        val newKind = source?.kind
-        var result = superType
-        val resultTypeArguments = result.type.typeArguments
-
-        result = result.withReplacedConeType(result.type.withNullability(coneType.nullability, session.typeContext))
-        if (resultTypeArguments.isNotEmpty() && resultTypeArguments.size == coneType.typeArguments.size) {
-            val substitution = mutableMapOf<FirTypeParameterSymbol, ConeKotlinType>()
-            for (index in resultTypeArguments.indices) {
-                val key = resultTypeArguments[index]
-                val value = coneType.typeArguments[index]
-                val symbol = (key as? ConeTypeParameterType)?.lookupTag?.typeParameterSymbol ?: continue
-                substitution[symbol] = value.type!!
-            }
-            result = result.withReplacedConeType(ConeSubstitutorByMap(substitution, session).substituteOrSelf(result.type))
-        }
-
-        return if (newKind is KtFakeSourceElementKind) result.copyWithNewSourceKind(newKind) else result
+    if (superType !is FirResolvedTypeRef) {
+        return null
     }
-    return this
+    val result = superType.type.withNullability(nullability, session.typeContext)
+    val resultTypeArguments = result.typeArguments
+    if (resultTypeArguments.isNotEmpty() && resultTypeArguments.size == typeArguments.size) {
+        val substitution = mutableMapOf<FirTypeParameterSymbol, ConeKotlinType>()
+        for (index in resultTypeArguments.indices) {
+            // TODO: this is not correct (should use firClass' arguments as keys); see comment in KT-51418
+            val key = resultTypeArguments[index]
+            val value = typeArguments[index]
+            val symbol = (key as? ConeTypeParameterType)?.lookupTag?.typeParameterSymbol ?: continue
+            substitution[symbol] = value.type!!
+        }
+        return ConeSubstitutorByMap(substitution, session).substituteOrSelf(result)
+    }
+    return result
 }
 
 fun shouldHideLocalType(containingCallableVisibility: Visibility?, isInlineFunction: Boolean): Boolean {