"sufficiently overlaps" on class instance depends on class statics

[evmar]

Bug Report

🔎 Search Terms

sufficiently overlaps class namespace

🕗 Version & Regression Information

TS 4.2, TS v4.3.0-dev.20210420

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about compatibility

⏯ Playground Link

Playground link with relevant code

💻 Code

class C1 { foo() {} }
new C1() as Record<string, unknown>;  // error, as expected

class C2 { foo() {} }
namespace C2 { export const unrelated = 3; }
new C2() as Record<string, unknown>;  // allowed!?

🙁 Actual behavior

The existence of the field in the C2 namespace somehow affects the assignability calculation of the instance.

🙂 Expected behavior

I would expect these namespace-level properties to not get involved (?) in the assignability of instances.

Either both succeed or both fail.

[ayazhafiz]

This is due to the check

        function isObjectTypeWithInferableIndex(type: Type): boolean {
            return type.flags & TypeFlags.Intersection ? every((<IntersectionType>type).types, isObjectTypeWithInferableIndex) :
                !!(type.symbol && (type.symbol.flags & (SymbolFlags.ObjectLiteral | SymbolFlags.TypeLiteral | SymbolFlags.Enum | SymbolFlags.ValueModule)) !== 0 &&
                !typeHasCallOrConstructSignatures(type)) || !!(getObjectFlags(type) & ObjectFlags.ReverseMapped && isObjectTypeWithInferableIndex((type as ReverseMappedType).source));
        }

which yields true for C2 since it's a ValueModule. This then enables the check

                if (!(intersectionState & IntersectionState.Source) && isObjectTypeWithInferableIndex(source)) {
                    // Intersection constituents are never considered to have an inferred index signature
                    let related = eachPropertyRelatedTo(source, targetType, kind, reportErrors);
                    if (related && kind === IndexKind.String) {
                        const numberIndexType = getIndexTypeOfType(source, IndexKind.Number);
                        if (numberIndexType) {
                            related &= indexTypeRelatedTo(numberIndexType, targetType, reportErrors);
                        }
                    }
                    return related;
                }

in indexTypesRelatedTo in the checker.

Admission of ValueModules as an inferable index object type was added in b949245. One solution is to say a ValueModule that is merged with class/function declaration never has a inferable index type, but Im not sure this is desirable.