[FIR] fix publication race in fakeOverrideSubstitution

Problem: fakeOverrideSubstitution was set to null before the return
type was published, so another thread can see a state where
fakeOverrideSubstitution is null and a return type is implicit
simultaneously

^KT-60385
^KT-59758 Fixed

compiler/fir/providers/src/org/jetbrains/kotlin/fir/scopes/FakeOverrideTypeCalculator.kt

@@ -26,19 +26,21 @@ abstract class FakeOverrideTypeCalculator {
 
     abstract class AbstractFakeOverrideTypeCalculator : FakeOverrideTypeCalculator() {
         override fun computeReturnType(declaration: FirCallableDeclaration): FirResolvedTypeRef? {
-            val fakeOverrideSubstitution = declaration.attributes.fakeOverrideSubstitution
-                ?: return declaration.getResolvedTypeRef()
+            val fakeOverrideSubstitution = declaration.attributes.fakeOverrideSubstitution ?: return declaration.getResolvedTypeRef()
+
+            // TODO: drop synchronized in KT-60385
             synchronized(fakeOverrideSubstitution) {
                 if (declaration.attributes.fakeOverrideSubstitution == null) {
                     return declaration.returnTypeRef as FirResolvedTypeRef
                 }
+
                 val (substitutor, baseSymbol) = fakeOverrideSubstitution
                 val baseDeclaration = baseSymbol.fir as FirCallableDeclaration
                 val baseReturnType = computeReturnType(baseDeclaration)?.type ?: return null
-                declaration.attributes.fakeOverrideSubstitution = null
                 val coneType = substitutor.substituteOrSelf(baseReturnType)
                 val returnType = declaration.returnTypeRef.resolvedTypeFromPrototype(coneType)
                 declaration.replaceReturnTypeRef(returnType)
+                declaration.attributes.fakeOverrideSubstitution = null
                 return returnType
             }
         }

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

@@ -31,6 +31,7 @@ import org.jetbrains.kotlin.fir.symbols.impl.FirSyntheticPropertySymbol
 import org.jetbrains.kotlin.fir.symbols.lazyResolveToPhase
 import org.jetbrains.kotlin.fir.types.FirImplicitTypeRef
 import org.jetbrains.kotlin.fir.types.FirResolvedTypeRef
+import org.jetbrains.kotlin.fir.types.FirTypeRef
 import org.jetbrains.kotlin.fir.types.builder.buildErrorTypeRef
 import org.jetbrains.kotlin.fir.visitors.FirTransformer
 
@@ -231,9 +232,13 @@ open class ReturnTypeCalculatorWithJump(
         if (declaration.isSubstitutionOrIntersectionOverride) {
             val fakeOverrideSubstitution = declaration.attributes.fakeOverrideSubstitution
                 ?: return declaration.returnTypeRef as FirResolvedTypeRef
+
+            // TODO: drop synchronized in KT-60385
             synchronized(fakeOverrideSubstitution) {
-                (declaration.returnTypeRef as? FirResolvedTypeRef)?.let { return it }
-                declaration.attributes.fakeOverrideSubstitution = null
+                if (declaration.attributes.fakeOverrideSubstitution == null) {
+                    return declaration.returnTypeRef as FirResolvedTypeRef
+                }
+
                 val (substitutor, baseSymbol) = fakeOverrideSubstitution
                 val baseDeclaration = baseSymbol.fir as FirCallableDeclaration
                 val baseReturnTypeRef = tryCalculateReturnType(baseDeclaration)
@@ -245,6 +250,8 @@ open class ReturnTypeCalculatorWithJump(
                     declaration.getter?.replaceReturnTypeRef(returnType)
                     declaration.setter?.valueParameters?.firstOrNull()?.replaceReturnTypeRef(returnType)
                 }
+
+                declaration.attributes.fakeOverrideSubstitution = null
                 return returnType
             }
         }