Add diff in output of --check (for CI use cases)

[muescha]

Edit 2025-03-06 by @lydell: This is a very long thread. It starts out with me asking for use cases for this feature. People then provide use cases over and over. It is clear that this is a wanted feature. There is no need to add more comments about that, but do react with 👍 on this post. There is a pull request #12598 for this feature, but it is (in my opinion) a bit lacking: #12598 (comment). I’m not a maintainer anymore, but it seems to me like a good PR for this would be merged.

---

More people submit PR for documents in Markdown files or other things via Github web editor. If they make a mistake then the CI fails but there is no chance to inform the user whats wrong.

I see some infos should be with the --debug-check but currently there is no output with this option.

Environments:

• Prettier Version: 1.18.2
• Running Prettier via: cli
• Runtime: node?
• Operating System: linux

Steps to reproduce:

prettier "**/*.{md,css,scss,yaml,yml,ts}" "--check"

Expected behavior:

Show each error and the changes like with --debug-check here in #4415

Actual behavior:

Show nothing about the errors:

> @ prettier /home/circleci/project
> prettier "**/*.{md,css,scss,yaml,yml,ts}" "--check"

Checking formatting...
docs/contributing/environment.md
Code style issues found in the above file(s). Forgot to run Prettier?

Also there are no more infos available with this commands:

prettier "**/*.{md,css,scss,yaml,yml,ts}" "--debug-check"
prettier "**/*.{md,css,scss,yaml,yml,ts}" "--debug-check" "--check"

[dylannz-sailthru]

"Forgot to run Prettier?" is really not a very helpful message...

[thorn0]

The message contains the file names. What else do you need to run Prettier on those files? ¯\_(ツ)_/¯

[lydell]

Edit 2025: People seem to read this comment, and then skip the entire thread. Things have changed during the last 5 years. #6885 (comment)

---

I personally like the output of --check very much.

CI: "Forgot to run Prettier?"

Me: "Oh yeah, I guess I did!" Runs Prettier.

CI: "All good!"

[muescha]

I like to point again to:

more people submit PR for documents in Markdown files or other things via Github web editor.

That means they have no local IDE installed. That's why they can not run prettier on the file.

[muescha]

Expected behavior would be a detailed error message or a diff

[error] src/index.js: ast(input) !== ast(prettier(input))
[error] Index:
[error] ===================================================================
[error] ---
[error] +++
[error] @@ -17,6 +17,6 @@
[error]                    "method": false,
[error]                    "key": {
[error] -                    "type": "StringLiteral",
[error] -                    "value": "asd"
[error] +                    "type": "Identifier",
[error] +                    "name": "asd"
[error]                    },
[error]                    "computed": false,
[error]
[error] Index:
[error] ===================================================================
[error] ---
[error] +++
[error] @@ -1,1 +1,1 @@
[error] -const test = { "asd": 1 };
[error] +const test = { asd: 1 };
[error]

[alexander-akait]

Why not run prettier \"{**/*,*}.{js,json,md,yml,css}\" --list-different" using npm/yarn script?

[muescha]

thx. I would try on monday the output of --list-different

[lydell]

--list-different also just lists file names – I don’t think it’ll make any difference for @muescha.

@muescha I think this proposal might be solving your problem the wrong way. Forcing people to click into a CI build log, find diffs of expected output and then manually applying them does no sound very friendly. I think we could try several other things:

• Encourage people to clone the project rather than using the web editor.
• Use --prose-wrap preserve or --prose-wrap never to reduce chance of needing to run Prettier.
• Running Prettier in the web editor via https://github.com/prettier/prettier-chrome-extension.
• A bot that automatically runs Prettier on PRs.
• You could pull people’s branches, run Prettier yourself and push to their PR (contributions from maintainers is generally enabled).
• Not use Prettier for markdown files if you get a lot of contributions to them via the web editor.

[muescha]

• Encourage people to clone the project rather than using the web editor.

thats much overhead :(

• Use --prose-wrap preserve or --prose-wrap never to reduce chance of needing to run Prettier.

it should run normal prettier

• Running Prettier in the web editor via prettier/prettier-chrome-extension.

this is only the solution for one user, and not for all

• A bot that automatically runs Prettier on PRs.

this changes the PR - the user should have information about the problems

• You could pull people’s branches, run Prettier yourself and push to their PR (contributions from maintainers is generally enabled).

to much overhead to checkout a branch etc

• Not use Prettier for markdown files if you get a lot of contributions to them via the web editor.

also prettier is a good help

the only thing is that there should be an more verbose error message :/

[lydell]

Thanks for the responses!

You didn’t seem to respond to this one, though:

Forcing people to click into a CI build log, find diffs of expected output and then manually applying them does no sound very friendly.

Thoughts?