Fix "isolatedDeclarations" QuickFix about typescript HOT 2 OPEN

It's not quite clear to me if the duplicate identifier error itself is a bug— assignments of initializers that aren't function expressions are allowed to merge with the existing sybol declaration during binding: https://www.typescriptlang.org/play/?noUnusedLocals=true&install-plugin=typescript-playground-link-shortener#code/CYUwxgNghgTiAEAzArgOzAFwJYHtVJxwAoBKALngDcctgBuAWAChRJYFUoBbEAZwAcoYBIkLwA3s3jSqseKmRcKUVAE9GTGbJhJUASVCpsiLCBjK1GrZTmJUAUQAe-OL165UF9cwC+zUTgAdApc8AC88ACMGijo2Hi6BiBGWCZmpBJ+TAGBdkkpaToReYbGpjAxhLkOzq7uCREZYQB8mRpAA

from typescript.

After some discussion within the team, we decided that this is in fact a bug.

In JS, this code makes m a static method of f:

function f() { }
f.m = () => 1

Which is a little questionable since m isn't strictly speaking on the prototype the way most methods usually are. So it's not clear that it's worthwhile to mark it as such.

But it's definitely a bad idea in TS where you can have namespaces, because it results in a duplicate 'declaration':

function f() { }
declare namespace f {
  export function m(): number
}
f.m = () => 1

both export function m and f.m = end up counting as declarations.

The narrow fix is to avoid binding f.m = () => 1 as a method in TS.
The wider fix is, I think, to stop binding f.m = () => 1 as a method even in JS. f.prototype.m = () => 1 should continue to be bound as a method but I think it's fine to represent f.m as binding a property (whose type happens to be a function).

Both fixes boil down to deleting or conditionalising code in bindPotentiallyNewExpandoMemberToNamespace. The wider fix should make sure to continue binding prototype assignments as methods, so an additional parameter is probably needed if that's the way we want to go.

from typescript.