Many organisations have a CI step that runs a linter or formatter on all the code and fails if tool made changes.

The idea is to catch cases where contributors failed to run the tool on save.

On large code bases this can be time consuming.

The trick to make CI in large codebases fast, or how to make any system fast, is to only test what’s changed.

In CI you only need to lint the files that have changed, or run the tests that depend on code that has changed etc.

This way the time it takes to execute the tests scales with the amount of changes, and not with the total amount of code.

The difficulty with that is trust, if there’s any chance it will miss things by accident then I’d rather eat the slow runs.

Test runners that run new/changed tests first though are cool. Faster feedback on error but still comprehensive.

Adding on to the other comment about CI setups, when I benchmarked removing eslint-plugin-prettier from my work’s ESLint configuration we saw a 37.5% speedup. On our fairly slow CI agents that ended up being pretty significant (~34s per run).

I _wanted_ to drop the plugin and have Prettier automatically run on as a pre-commit hook (as you suggested) but in the end I lost :) We wound up keeping the plugin and eating the slower pipeline time.

Of course there’s more overhead than just Prettier in this case—the ESLint plugin itself will be contributing towards the added runtime!—but depending on your codebase and CI machines, Prettier can definitely slow things down quite a bit. CI taking over a minute or two is a big drag on developer productivity imo.

Ideal world is that everyone is on board with code formatting as a pre-commit task that only touches modified files so it doesn’t bloat CI unnecessarily, but it’s not always possible :(

What we did to avoid that bottleneck was just turn off the prettier eslint rule in CI and just run the `prettier --check` command they recommend in their docs.

We also have it set to only run in changed files which helps a lot.

We generally don't link pre-commit hooks for standards though, hence the CI focus. Too easy to circumvent, and I'd rather pay for an external machine to check it when it matters (pre-merge by doing it on PR commits) than block my devs when it doesn't (every time they commit to a non-main branch).

I’ve done some research on this in the past. The reason that is so slow is because the eslint plugin runs prettier, does a diff between the result of prettier and the real file and then converts each diff entry into a eslint issues. Most of the pain comes from this remarshaling cost

I ran into the same issue and have been separating the prettier and eslint steps ever since: https://cpojer.net/posts/fastest-frontend-tooling-in-2022#es...

it's very common to have a lint/format step that make sure all files are well-formatted in Pull request.

This is such a waste of electricity IMO. Just occasionally batch-fix all files for syntax. Semantic linting can run in CI, as it's about catching bugs. But formatting is for long-term consistency and doesn't need to be done on every commit.

Occasionally batch-fixing syntax makes "git blame" far less useful.

Yup, but you need to reference the commit ID, meaning that you always need to create two commits, one for the reformatting, and a second one for updating the .git-blame-ignore-revs file. Additionally, you may not use git rebase, or any other workflow that modifies the history, or the references will be broken. Third, the git config needs to be set per-project (can't be set globally), so all developers need to manually adjust their config, for this feature to be useful.

If you value a clean commit history, then simply reformat as part of the code change. With autoformatting on save (e.g. through prettier), that's a complete non-issue anyways.

Until you change the formatting rules and the whole codebase is in one diff. This seems to happen at least once a year from my observations.

you may have to force approve edits by the formatter then, since they’re pretty annoying when included in changes for code review.

only in node.js, it's a waste of electricity.

in other language, formatters are pretty damn fast. never heard anyone complain about gofmt or cargo fmt

I'm not a lint fascist, but enforcing them gave our team: - less time reviewing: no more "you forgot to indent here" - less git conflicts: because of differences in trailing comas, line breaks, ... - less (to no more) code style debates: the linter is the benevolant dictator - less time making our code clean, thinking about line breaks: just get it done, the linter and CI will handle formatting !

Or, better still, just remove prettier and free yourself to write more expressive code again.

I believe you don't see the big picture.

What you just described is running on thousands of machines several times a day.