@types's definition doesn't match its own type

[falsandtru]

DefinitelyTyped/DefinitelyTyped#40731 broke the following global declaration.

cc @rbuckton

TypeScript Version: 3.7.x-dev.20191207

Search Terms:

Code

https://github.com/falsandtru/spica/blob/v0.0.289/global.test.d.ts and @types/power-assert@1.5.1

import assert from 'power-assert';

type Assert = typeof assert;

declare global {
  const assert: Assert;
}

Expected behavior:
pass
Actual behavior:
TypeScript error: global.test.d.ts(6,9): Error TS2403: Subsequent variable declarations must have the same type. Variable 'assert' must be of type 'typeof assert', but here has type 'typeof assert'.
Playground Link:

Related Issues: #32808

[rbuckton]

I see a couple things that could be problems that I didn't notice in the DT pull request:

• Both power-assert/index.d.ts and power-assert/t3.7/index.d.ts have export as namespace assert;
• The power-assert/ts3.7/index.d.ts imports power-assert/index.d.ts explicitly, so both of the export as namespace assert declarations exist and could possibly collide.

Also, you are declaring assert using typeof, which only gets the type-side of the declaration and not necessarily the namespace aspects of the declaration. You might try using the --allowUmdGlobalAccess flag, which would allow you to access the assert global namespace rather than redeclaring it via a global augmentation, but I'm not sure if you'll run into an issue due to the above collision.

We may need to change the DT definitions so that you aren't including both the root index.d.ts and ts3.7/index.d.ts.

[rbuckton]

I just checked this and the issue is due to the duplicate definitions of export as namespace in the root and ts3.7 versions.

[falsandtru]

The power-assert/ts3.7/index.d.ts imports power-assert/index.d.ts explicitly, so both of the export as namespace assert declarations exist and could possibly collide.

I think so too. Looks like the compiler can't distinguish them.

[rbuckton]

The issue is that the declarations collide. I tested the following locally, which seems to fix the issue:

1. Create a _common.d.ts file and copy the everything from index.d.ts into it except for the export as namespace declaration.
2. Replace the source of index.d.ts, with the following:

   import assert = require("./_common");
   export = assert;
   export as namespace assert;

3. Replace the import declaration in ts3.7/index.d.ts with this:

   import module = require("../_common");

Then TS won't attempt to load both files and the error goes away.

@falsandtru: This requires a DT PR to address. Do you want to do that or should I?

[rbuckton]

Alternatively, just reproduce the contents of index.d.ts in ts3.7/index.d.ts (with the adjustments for asserts conditions) and not have the import at all.

[falsandtru]

I feel the first workaround is too complex. I want to choose the second. I'll make a PR. However, I think this is a bug anyway.

[rbuckton]

If we choose to address this bug, it will likely be by reporting a duplicate identifier error on each of the export as namespace assert declarations.

[rbuckton]

@falsandtru: Once you've made a PR, can you post a link to it here so that I can more easily review it?

[falsandtru]

Sure.

[falsandtru]

DefinitelyTyped/DefinitelyTyped#40903 is available.

[falsandtru]

This problem is caused by the program written on this repository. When you resolve the problem you have to fix code on this repository. So this issue is not external.