Module augmentation causes import to be tree-shaken (is removed from output)

[matthew-dean]

🔎 Search Terms

"module augmentation" tree-shaking

🕗 Version & Regression Information

• I was unable to test this on prior versions because: I'm using the satisfies keyword

⏯ Playground Link

https://github.com/jesscss/jess/blob/dev-freeze/packages/css-parser/src/cssParser.ts#L2

💻 Code

// chevrotain.d.ts
declare module 'chevrotain' {
  interface CstParser {
    // things that augment this type
  }
}


// cssParser.ts
import { CstParser, EOF } from 'chevrotain'

class CssParser extends CstParser {
 // class implementation
}

// outputs
import { EOF } from 'chevrotain'

🙁 Actual behavior

Augmenting the module seems to remove it from being considered "used" when compiling.

🙂 Expected behavior

Augmenting the module should have no effect on tree-shaking imports.

Additional information about the issue

I thought maybe this was an expected behavior, and I'd just never encountered it before? But I could find nothing in TypeScript documentation about this.

Also, interestingly, the import is not tree-shaken from the exported .d.ts file, only the .js file. 🤷‍♂️

[jakebailey]

You didn't mention that you were using a patched version of TypeScript via ts-patch. If you disable ts-patch, then things work as expected.

Before:

$ (cd packages/css-parser; pnpm compile)
$ grep 'CstParser' packages/css-parser/lib/cssParser.js
export class CssParser extends CstParser {

After removing ts-patch, cleaning the repo, and reinstalling:

$ git diff package.json
diff --git a/package.json b/package.json
index 93f9a2e..85e0d09 100644
--- a/package.json
+++ b/package.json
@@ -47,8 +46,7 @@
     "ci": "pnpm run -r ci && pnpm run lint",
     "lint:fix": "eslint --fix '**/*.{js,ts}'",
     "lint": "eslint '**/*.{js,ts}'",
-    "preinstall": "npx only-allow pnpm",
-    "prepare": "ts-patch install -s"
+    "preinstall": "npx only-allow pnpm"
   },
   "repository": {
     "type": "git",
$ (cd packages/css-parser; pnpm compile)
$ grep 'CstParser' packages/css-parser/lib/cssParser.js
import { CstParser, EOF } from 'chevrotain';
export class CssParser extends CstParser {

This can only be a bug in ts-patch or some plugin you're using, which we can't support.

[typescript-bot]

This issue has been marked as "External" and has seen no recent activity. It has been automatically closed for house-keeping purposes.

[matthew-dean]

@jakebailey Derp. That's not something that occurred to me, as I'm only using ts-macros and no macros were involved. I appreciate your time in investigating.