Re-export module namespace as global

[evmar]

We're attempting to migrate users within Google to new @types typings, which move most typings into modules, and having a ton of trouble. The basic problem is that a module (e.g. CodeMirror) used to declare a global complex interface:

declare function CodeMirror(...);
declare namespace CodeMirror { ... }

and now they are modules:

export = CodeMirror;

and other typings refer to them as modules (so we can't just undo that export statement) but we also have tons of older user code that doesn't refer to them as modules. Ideally we'd be able to make it work both ways while we migrate users incrementally.

I appreciate that you don't want the language to make this convenient, but I'm having difficulty finding any way to make it work temporarily while we migrate.

Some things I tried:

1. Aliasing the module into the global namespace

declare global {
  import CodeMirror = require('codemirror');
}

(and other variants) fails with "Imports are not permitted in module augmentations.".

2. Making the module global first, then aliasing it into a module namespace.
   If you wrap the file contents with a "declare global {", then I couldn't figure out a way to repackage that global as a module again. The export = CodeMirror; fails with "Cannot find name 'CodeMirror'." despite the global CodeMirror being declared in the same file.

Do you have any advice? Note that "export as namespace" doesn't help because our user code is already modules, not scripts.

[mhegazy]

I am not sure i understand the issue, so this might be useless to you, but if CodeMirror is supposed to be accessed as a global, why not add export as namespace CodeMirror in the declaration file? if it is not, how was that code working in the first place?

[evmar]

The declaration file does have "export as namespace CodeMirror", but that does not help. The to-be-upgraded user code is already written as modules (so it doesn't see the global codemirror) but does not have an import of CodeMirror (so it doesn't get the module one either).

[evmar]

Smaller repro of the problem.

1. Say the new version of foo.d.ts that we're trying to upgrade to has this:

export = Foo;
export as namespace Foo;

declare function Foo(x: number);
declare namespace Foo {
  namespace Bar {
    var baz: number;
    interface IF { a: number }
  }
}

2. Suppose the upgrade includes other code that writes import * as foo from 'foo'.

3. Finally, suppose there are many users like

export {}  // is a module already
Foo.Bar.baz;  // expects a global Foo
let x: Foo.Bar.IF;  // that includes namespace elements

Currently these don't compile together as written, and we want to eventually migrate all the various different code that looks like #3 to use an import statement. But in the interim we can temporarily modify #1, and I can't find an invocation that works in a way that allows us to incrementally migrate #3.

[blakeembrey]

How about something like this? Have a file that declares all the globals (assuming I'm reading the requirement right).

import * as _foo from 'foo'

declare global {
  var foo: typeof _foo;
}

[evmar]

Thanks for looking! That works to re-export the foo value, but loses the namespace members.
E.g. if inside Bar there is an interface XXX, then with your amendment the user code still cannot do let x: Foo.Bar.XXX;. I'm gonna modify the above snippet to make this more obvious.

[blakeembrey]

@evmar If you can't do that, it means the definition was written incorrectly and it's not really accessible anyway. Those definitions would need to be fixed up. Do you have an example of what doesn't work and I can point out where to fix it up for use as an external module?

[evmar]

Here's an example of the nested namespaces in the d.ts:
https://github.com/DefinitelyTyped/DefinitelyTyped/blob/8e2708ca2118472ca8a3071c21bfe7a5250b911d/codemirror/index.d.ts#L1154
How are they wrong? Can you suggest how I should fix them up?

[blakeembrey]

That looks fine, you should be able to access that by CoreMirror.MergeView .MergeViewEditorConfiguration (where CodeMirror is whatever you declared globally in declare global).

Wasn't meant to imply they were definitely wrong, but if you need to access types and you can't it means that type was accidentally hidden in the definition (e.g. by not exporting it). I've seen that done a lot and was all I meant by "wrong". E.g.

// Wrong (`Bar` is never exported).
declare namespace X {}
declare interface Bar {}
export = X

// Better (`Bar` is part of the exported namespace, can be accessed externally).
declare namespace X {
  export interface Bar {}
}
export = X

[evmar]

@blakeembrey if you try the example snippet I posted above, you'll see it doesn't work with your declare global suggestion. The problem is that the var foo: typeof _foo; only exports the value but not the namespace.

I believe the TS syntax for aliasing the value+type+namespace is the import = syntax I wrote as option 1 in the original report, which also fails for other reasons.

[blakeembrey]

@evmar It should work, I've used it a dozen times - a lot of modules in @types are written in this style. If you can link me to what explicitly you're writing, I can test it for you. For example, it works fine for me:

Edit: To prove that it is using the namespace I provided, here it is using Foo:

[evmar]

Edit: I wrote a long comment here but it was wrong because I have failed at cut and paste, let me get back to you.

[evmar]

I had a combination of failing other piece, but the critical part was that to augment this module, it appears you must

import cm = require('./foo');
declare module "./foo" {
  ... stuff here ...
}

and not do

declare global {
  namespace Foo {
    ... stuff here ...
  }
}

---

So, to summarize, to make a typings module into a global:

1. leave original module unchanged

2. add file

import m = require('mymod');
declare global {
  var mymod: typeof m;
}

3. if you want to augment, you must augment the import module, not the global one, so change clients that looked like

namespace mymod {
  ...
}

to instead say

import m = require('mymod');
declare module 'mymod' {
  ...
}

Thanks for your help, Blake!

[YowaiCoder]

import * as _foo from 'foo'
declare global {
  var foo: typeof _foo;
}

It doesn't work with let something: foo.SomeType, claim Cannot find namespace 'foo'.

[olee]

Same problem - it doesn't reexport the namespace types.