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

[joaomoreno]

Pushed a bunch of fixes. We're down to 23 errors.

[jrieken]

Down to 9 errors - This is some left for @bpasero in glob.ts and there is some more tweaking needed for the Event and CancellationToken story... Getting closer

[jrieken]

Almost done. This is what's left 👇

[bpasero]

I own the simple pieces of glob, not this crazy stuff. Assigning to @chrmarti. I tried to fix it and had to give up, this is just beyond my skills.

E.g I really do not think we should add properties to functions like here 7852430

[roblourens]

I don't understand the preferences editor one. It's on a line using the IConstructorSignature type helper, and the bottom line is Type 'BrandedService' is missing the following properties from type 'IInstantiationService': createInstance, invokeFunction, createChild

like it thinks a BrandedService is being referenced as an IInstantiationService. But it should be the other way around, the IInstantiationService in the constructor's argument list should just have to fulfill BrandedService.

[mjbvz]

@roblourens I can't decipher this either but have added a workaround: 91fc43d

[chrmarti]

@mjbvz Fixed the last ones, back to you.