Prettier removes Promise<void> type and other annotations in TypeScript arrow functions

[danielbjornadal]

Summary

Prettier removes Promise type annotations in TypeScript arrow functions, even with "arrowParens": "always" configured, making it impossible to satisfy TypeScript's requirement for generic type parameters on Promises.

Steps To Reproduce:

1. Create a new TypeScript file with an interface containing Promise return types
2. Configure Prettier with "arrowParens": "always"
3. Save the file and observe Prettier's formatting
4. Note that TypeScript shows an error: "Generic type 'Promise' requires 1 type argument(s)"

Expected result

Prettier should preserve the Promise type annotation when formatting TypeScript files, especially when "arrowParens": "always" is set.

Example:

interface Example {
  myFunction: (param: string) => Promise<void>;
}

Actual result

Prettier removes the type parameter, resulting in invalid TypeScript:

interface Example {
  myFunction: (param: string) => Promise;
}

This causes TypeScript to error with "Generic type 'Promise' requires 1 type argument(s)".

Additional information

The only current workarounds are // @ts-ignore or // prettier-ignore

Neither solution is ideal for maintaining clean, type-safe code.

VS Code Version: 1.95.3

Prettier Extension Version: 11.0.0

OS and version: Ubuntu 24.04

Prettier Log Output

[INFO] Prettier Options:
{
  "plugins": ["@trivago/prettier-plugin-sort-imports"],
  "importOrder": [...],
  "importOrderSeparation": true,
  "importOrderSortSpecifiers": true,
  "printWidth": 120,
  "arrowParens": "always"
}
[INFO] Prettier Resolution: Prettier Path: /Users/[username]/project/node_modules/prettier
[INFO] Formatting file:///Users/[username]/project/src/types.ts
[INFO] Formatting completed in 0.1s

[madaxen86]

Same issue here.
Temporary workaround is to remove the plugins. No matter what plugins I think, cause I had
"@trivago/prettier-plugin-sort-imports",
"prettier-plugin-tailwindcss",
The error occurred no matter which I disabled, as long as one is active.

[IanMitchell]

I also have noticed this. I have a repo with a reproduction here: https://github.com/ianmitchell/tailwind-example

If you open the repro and navigate to the page.tsx file and save, the extension will change the Promise<number> function return signature to Promise. This doesn't happen when prettier is invoked via the CLI.

If I can do anything else to help debug this, happy to help!

[jjram19]

+1 here

[davidy3k]

+1 here

[pawel-halat]

I meet in the same issue after packages.json libraries update. Restarting Prettier VScode extension worked for me.

[madaxen86]

I had to remove this line of my vscode settings.json
"prettier.prettierPath": "/usr/local/lib/node_modules/prettier/index.cjs",
Now it works again.

[solastley]

+1 here

Only way to fix was to remove this plugin:

"plugins": ["@trivago/prettier-plugin-sort-imports"],

which we'd love to keep using...

[sd-hoag]

+1 here

Only way to fix was to remove this plugin:

"plugins": ["@trivago/prettier-plugin-sort-imports"],

which we'd love to keep using...

Exact same situation here. Just added the plugin to a new repo and observed the behavior

[sd-hoag]

+1 here
Only way to fix was to remove this plugin:

"plugins": ["@trivago/prettier-plugin-sort-imports"],

which we'd love to keep using...

Exact same situation here. Just added the plugin to a new repo and observed the behavior

Reinstalling the VSCode Prettier extentions appears to have solved this for me

[vinnymac]

For me Prettier 3.3.2 or lower does not exhibit this behavior. I narrowed it down to 3.3.3+ that does, which makes me wonder what changed in 3.3.3 that could have broken compatibility when using plugins and generics at the same time.

Uninstalling and reinstalling the extension did not help, but disabling plugins also prevents the generics from being removed, so long as 0 plugins are configured.

Related discussion on SO here

[cedeber]

I don't have this issue in vscode, but only in the CLI. But same for me, removing the only plugin I had (prettier-plugin-tailwindcss) was solving the issue in the cli. For information though, weirdly I was used to use pnpm instead of npm and had no issue with pnpm. Not sure why it has to be different but maybe it helps.

Update: I went back to prettier 3.4.2 and it solved the issue. Then I installed 3.5.0 again and it works. Looks like a npm install issue?

[mgoulet101]

FWIW, I ran into this same issue after I updated my project typescript dependency from v4.9 to v5.7 and found my way here. The recommendation from @pawel-halat worked for me. I restarted my extensions and the problem went away. I was just about to give up and disable with a prettier-ignore comment.

@cedeber , it might have worked for you because you effectively restarted the extension by switching versions.

[quark-zju]

FWIW, prettier-plugin-sort-imports seems to have this problem. I switched to prettier-plugin-organize-imports and it works fine.