Compiler fails to detect a constructed file type.

[AlekseyTs]

file class C1 {}

class C2 : C1 {}

file class C3<T> {}

class C4 : C3<int> {}

Observed:

error CS9053: File-local type 'C1' cannot be used as a base type of non-file-local type 'C2'.

Expected an additional error for base type of C4.

The type is SourceMemberContainerTypeSymbol check is the likely source of the problem:

        public static bool HasFileLocalTypes(this TypeSymbol type)
        {
            var foundType = type.VisitType(predicate: (type, _, _) => type is SourceMemberContainerTypeSymbol { IsFileLocal: true }, arg: (object?)null);
            return foundType is not null;
        }

There are several more places in the code base that might have similar issues.

[AlekseyTs]

CC @RikkiGibson