chore(ci): add prettier formatter

[MikeMcC399]

• closes "Test Whitespace and line endings" workflow uses unmaintained eclint #2526

Description

Add Prettier for source code formatting of js, mjs, json, md, yml files using prettier npm module.

In .prettierrc.json, set default

• singleQuote = true

Execute npx prettier --write . to reformat all affected files.

Add a GitHub Actions workflow prettier.yml

Remove workflow eclint.yml

Motivation and Context

The npm module eclint, last published in Oct 2018, is archived since Oct 2020 and is therefore unsupported and unmaintained. It is used in the GitHub Actions workflow eclint.yml "Test Whitespace and line endings".

Prettier is a widely-used, mature, code formatter (91 Mio downloads / week, 4.9k GitHub stars).

Prettier parses an EditorConfig file and so can work with the existing .editorconfig in the repo.

In .prettierrc.json, set configuration options only where they differ from Prettier defaults:

Option	Prettier default	docker-node setting
singleQuote	false	true

Set the printWidth for versions.json to 38 to force the variant arrays to continue to be vertically formatted.

Testing Details

npm install prettier@latest -g
npx prettier --check .

Types of changes

• Documentation
• Version change (Update, remove or add more Node.js versions)
• Variant change (Update, remove or add more variants, or versions of variants)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Other (none of the above)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• All new and existing tests passed.

[MikeMcC399]

This PR enables the unsupported eclint to be replaced with prettier using minimal configuration.

I'd like feedback about whether this is a reasonable approach.

If the end-result is acceptable, the PR could either be merged in one go, or each of the files / file types could be separated out for finer-grained review and testing in a set of stacked PRs. Theoretically none of the formatting changes should have any effect on execution, but testing is usually better than just assuming!

In JavaScript, quotes and semicolons were being used inconsistently. This change sets the standard to single quotes, and usage of semicolons. This is the same setting that the nodejs/node repo uses, although it is enforced there through ESLint, not through Prettier.

[nschonni]

2 things that could be done as separate PRs:

1. Create a package.json to easier manage the versions of Prettier, and a script reference to locally debug the CI
2. Adding Depenabot for the NPM deps if a package.json is added.

[MikeMcC399]

2 things that could be done as separate PRs:

1. Create a package.json to easier manage the versions of Prettier, and a script reference to locally debug the CI
2. Adding Depenabot for the NPM deps if a package.json is added.

I do believe this is the way to go, and I'm happy you're suggesting it. I did already consider it when I looked at using ESLint instead of, or together with, Prettier. It would also allow other npm dependencies called only in CI to be managed through Dependabot's version updates.

[MikeMcC399]

I will leave this open for one week for review. Also I'm seeing that there is a security release planned for Jul 27, 2026, so I would wait until after that date before merging to avoid any risk of disrupting it.

[nschonni]

I think if you rebase this for the conflicts from the Action bump, it doesn't need to wait till after the Security release. All this is non-breaking formatting things

[MikeMcC399]

I think if you rebase this for the conflicts from the Action bump, it doesn't need to wait till after the Security release. All this is non-breaking formatting things

OK. I'll do that. I was just being super cautious!

[github-actions]

Created PR on the official-images repo (docker-library/official-images#21889). See https://github.com/docker-library/faq#an-images-source-changed-in-git-now-what if you are wondering when it will be available on the Docker Hub.