No error for invalid module augmentation in '.d.ts' file

[ghost]

TypeScript Version: 2.9.0-dev.20180519

Code

// @Filename: /a.d.ts
export {};
declare module "invalid" {}

// @Filename: /b.ts
export {};
declare module "invalid" {}

Expected behavior:

Error in both files.

Actual behavior:

Only error in b.ts.

[ghost]

There is a comment in checker.ts, // do not validate names of augmentations that are defined in ambient context, added in #8200.

[mhegazy]

thanks for the reference.. i vaguely remember this issue. i guess it is by design then.