enable strictFunctionTypes in VS Code codebase

[mjbvz]

Problem

For an example service defined in VS Code core:

export class MyService {
  constructor(
    private readonly value: string,
    @ITextModelService private readonly textModelResolverService: ITextModelService
  ) { }
}

It is currently possible to use the instantiation service to create an instance of MyService that passes undefined for value:

instantiationService.createInstance(MyService, undefined);

This does not produce any compile errors. It does bypass our strict null checking however and can cause unexpected runtime behavior.

Proposed fix

Enable strictFunctionTypes in our code base

There are about 800 or so errors related to this in our code base today. While some of these errors are simple, many are rather cryptic and some may prove difficult to fix

[mjbvz]

As a first step, I've created a branch that attempts to make the typings for createInstance more strict: dev/mjbvz/stricter-createInstance. This revealed about 100 potential type errors in our the code.

To investigate these errors

1. git checkout dev/mjbvz/stricter-createInstance
2. Open effected file and see if you need to fix the error. See f2d4172 for an example of the type of bug this can detect. 073e8bb shows how to use the new createInstance typing with a constructor for a generic type
3. Consider pushing the fix to master instead of to this branch!
4. Be sure to check off the file in the list

File List

• src/vs/workbench/services/extensions/common/extensionHostProcessManager.ts @sandy081
• src/vs/workbench/contrib/terminal/browser/terminalProcessManager.ts @Tyriar
• src/vs/workbench/contrib/markers/browser/markersTreeViewer.ts @sandy081