[FIR] Properly set sources of intersection overrides

Otherwise, they may point to one of
the base intersected functions, and
if we start reporting diagnostics on
them, they'll appear on base
functions.

compiler/fir/providers/src/org/jetbrains/kotlin/fir/scopes/impl/FirFakeOverrideGenerator.kt

@@ -121,9 +121,9 @@ object FirFakeOverrideGenerator {
         newModality: Modality? = null,
         newVisibility: Visibility? = null,
         deferredReturnTypeCalculation: CallableCopyDeferredReturnTypeCalculation? = null,
-        newSource: KtSourceElement? = null,
+        newSource: KtSourceElement? = derivedClassLookupTag?.toSymbol(session)?.source ?: baseFunction.source,
     ): FirSimpleFunction = buildSimpleFunction {
-        source = newSource ?: derivedClassLookupTag?.toSymbol(session)?.source ?: baseFunction.source
+        source = newSource
         moduleData = session.nullableModuleData ?: baseFunction.moduleData
         this.origin = origin
         name = baseFunction.name
@@ -401,8 +401,9 @@ object FirFakeOverrideGenerator {
         newModality: Modality? = null,
         newVisibility: Visibility? = null,
         deferredReturnTypeCalculation: CallableCopyDeferredReturnTypeCalculation? = null,
+        newSource: KtSourceElement? = derivedClassLookupTag?.toSymbol(session)?.source ?: baseProperty.source,
     ): FirProperty = buildProperty {
-        source = derivedClassLookupTag?.toSymbol(session)?.source ?: baseProperty.source
+        source = newSource
         moduleData = session.nullableModuleData ?: baseProperty.moduleData
         this.origin = origin
         name = baseProperty.name

compiler/fir/providers/src/org/jetbrains/kotlin/fir/scopes/impl/FirTypeIntersectionScopeContext.kt

@@ -358,6 +358,7 @@ class FirTypeIntersectionScopeContext(
             newDispatchReceiverType = dispatchReceiverType,
             deferredReturnTypeCalculation = deferredReturnTypeCalculation,
             newReturnType = if (!forClassUseSiteScope && deferredReturnTypeCalculation == null) intersectReturnTypes(mostSpecific) else null,
+            newSource = dispatchReceiverType.toSymbol(session)?.source,
         ).apply {
             originalForIntersectionOverrideAttr = keyFir
         }
@@ -385,7 +386,8 @@ class FirTypeIntersectionScopeContext(
                 deferredReturnTypeCalculation = deferredReturnTypeCalculation,
                 // If any of the properties are vars and the types are not equal, these declarations are conflicting
                 // anyway and their uses should result in an overload resolution error.
-                newReturnType = returnType
+                newReturnType = returnType,
+                newSource = dispatchReceiverType.toSymbol(session)?.source,
             )
         }
     }