Fix excess property checking for intersections with index signatures

Author: ahejlsberg

src/compiler/checker.ts

@@ -20693,6 +20693,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     isNonGenericObjectType(target) && !isArrayOrTupleType(target) && source.flags & TypeFlags.Intersection && getApparentType(source).flags & TypeFlags.StructuredType && !some((source as IntersectionType).types, t => !!(getObjectFlags(t) & ObjectFlags.NonInferrableType)))) {
                     inPropertyCheck = true;
                     result &= propertiesRelatedTo(source, target, reportErrors, /*excludedProperties*/ undefined, IntersectionState.None);
+                    if (result) {
+                        result &= indexSignaturesRelatedTo(source, target, /*sourceIsPrimitive*/ false, reportErrors, IntersectionState.None);
+                    }
                     inPropertyCheck = false;
                 }
             }
@@ -21861,7 +21864,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return result;
         }
 
-        function membersRelatedToIndexInfo(source: Type, targetInfo: IndexInfo, reportErrors: boolean): Ternary {
+        function membersRelatedToIndexInfo(source: Type, targetInfo: IndexInfo, reportErrors: boolean, intersectionState: IntersectionState): Ternary {
             let result = Ternary.True;
             const keyType = targetInfo.keyType;
             const props = source.flags & TypeFlags.Intersection ? getPropertiesOfUnionOrIntersectionType(source as IntersectionType) : getPropertiesOfObjectType(source);
@@ -21875,7 +21878,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     const type = exactOptionalPropertyTypes || propType.flags & TypeFlags.Undefined || keyType === numberType || !(prop.flags & SymbolFlags.Optional)
                         ? propType
                         : getTypeWithFacts(propType, TypeFacts.NEUndefined);
-                    const related = isRelatedTo(type, targetInfo.type, RecursionFlags.Both, reportErrors);
+                    const related = isRelatedTo(type, targetInfo.type, RecursionFlags.Both, reportErrors, /*headMessage*/ undefined, intersectionState);
                     if (!related) {
                         if (reportErrors) {
                             reportError(Diagnostics.Property_0_is_incompatible_with_index_signature, symbolToString(prop));
@@ -21936,7 +21939,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             }
             if (!(intersectionState & IntersectionState.Source) && isObjectTypeWithInferableIndex(source)) {
                 // Intersection constituents are never considered to have an inferred index signature
-                return membersRelatedToIndexInfo(source, targetInfo, reportErrors);
+                return membersRelatedToIndexInfo(source, targetInfo, reportErrors, intersectionState);
             }
             if (reportErrors) {
                 reportError(Diagnostics.Index_signature_for_type_0_is_missing_in_type_1, typeToString(targetInfo.keyType), typeToString(source));