VS Code: "editor.showUnused": true not working in `*.d.ts` files

[gilluminate]

I was asked by the VS Code team to move this bug report upstream to the TypeScript project.

• searched existing issues to avoid creating duplicates

• tested using the latest insiders build to make sure issue has not already been fixed

• issue occurs when all extensions are disabled

• VSCode Version: 1.37.1

• VSCode Insiders Version: 1.38.0-insider

• OS Version: MacOS Mojave 10.14.6

• TypeScript Version: 3.7.0-dev.20190828

Search Terms:
"VS Code", "d.ts", "unused", "editor.showUnused"

Steps to Reproduce:

1. Ensure editor.showUnused is set to true for user, workspace, and folder.
2. Create a file with extension .d.ts
3. Add valid import statement such as
   import { User } from 'types/users';

Actual behavior: Import statement is not faded even though it hasn't been used.
Expected behavior: Import statement should be faded out as per setting.

Additional steps:

1. convert filename to have only the .ts extension (drop the .d)
   Note: import line is dimmed as expected. The issue appears to only be affected by .d.ts files.

Related Issues:
Possibly:
#32196
#30260

[andrewbranch]

It seems this is by design since #9452 (4789ff0). I personally think it would be nice to recognize unused identifiers, but should probably be excluded from being errors with --noUnusedLocals.