modification causes before submitting a PR. Think about if the change seems disruptive
enough to cause frustration to projects that are already "black formatted".
-## black-primer
-
-`black-primer` is a tool built for CI (and humans) to have _Black_ `--check` a number of
-Git accessible projects in parallel. (configured in `primer.json`) _(A PR will be
-accepted to add Mercurial support.)_
-
-### Run flow
-
-- Ensure we have a `black` + `git` in PATH
-- Load projects from `primer.json`
-- Run projects in parallel with `--worker` workers (defaults to CPU count / 2)
- - Checkout projects
- - Run black and record result
- - Clean up repository checkout _(can optionally be disabled via `--keep`)_
-- Display results summary to screen
-- Default to cleaning up `--work-dir` (which defaults to tempfile schemantics)
-- Return
- - 0 for successful run
- - \< 0 for environment / internal error
- - \> 0 for each project with an error
-
-### Speed up runs 🏎
-
-If you're running locally yourself to test black on lots of code try:
-
-- Using `-k` / `--keep` + `-w` / `--work-dir` so you don't have to re-checkout the repo
- each run
-
-### CLI arguments
-
-```{program-output} black-primer --help
-
-```
-
## diff-shades
-diff-shades is a tool similar to black-primer, it also runs _Black_ across a list of Git
-cloneable OSS projects recording the results. The intention is to eventually fully
-replace black-primer with diff-shades as it's much more feature complete and supports
-our needs better.
-
-The main highlight feature of diff-shades is being able to compare two revisions of
-_Black_. This is incredibly useful as it allows us to see what exact changes will occur,
-say merging a certain PR. Black-primer's results would usually be filled with changes
-caused by pre-existing code in Black drowning out the (new) changes we want to see. It
-operates similarly to black-primer but crucially it saves the results as a JSON file
-which allows for the rich comparison features alluded to above.
+diff-shades is a tool that runs _Black_ across a list of open-source projects recording
+the results. The main highlight feature of diff-shades is being able to compare two
+revisions of _Black_. This is incredibly useful as it allows us to see what exact
+changes will occur, say merging a certain PR.
For more information, please see the [diff-shades documentation][diff-shades].
diff-shades is also the tool behind the "diff-shades results comparing ..." /
"diff-shades reports zero changes ..." comments on PRs. The project has a GitHub Actions
-workflow which runs diff-shades twice against two revisions of _Black_ according to
-these rules:
+workflow that analyzes and compares two revisions of _Black_ according to these rules:
| | Baseline revision | Target revision |
| --------------------- | ----------------------- | ---------------------------- |
| On PRs | latest commit on `main` | PR commit with `main` merged |
| On pushes (main only) | latest PyPI version | the pushed commit |
-Once finished, a PR comment will be posted embedding a summary of the changes and links
-to further information. If there's a pre-existing diff-shades comment, it'll be updated
-instead the next time the workflow is triggered on the same PR.
+For pushes to main, there's only one analysis job named `preview-changes` where the
+preview style is used for all projects.
-The workflow uploads 3-4 artifacts upon completion: the two generated analyses (they
-have the .json file extension), `diff.html`, and `.pr-comment.json` if triggered by a
-PR. The last one is downloaded by the `diff-shades-comment` workflow and shouldn't be
-downloaded locally. `diff.html` comes in handy for push-based or manually triggered
-runs. And the analyses exist just in case you want to do further analysis using the
-collected data locally.
+For PRs they get one more analysis job: `assert-no-changes`. It's similar to
+`preview-changes` but runs with the stable code style. It will fail if changes were
+made. This makes sure code won't be reformatted again and again within the same year in
+accordance to Black's stability policy.
-Note that the workflow will only fail intentionally if while analyzing a file failed to
+Additionally for PRs, a PR comment will be posted embedding a summary of the preview
+changes and links to further information. If there's a pre-existing diff-shades comment,
+it'll be updated instead the next time the workflow is triggered on the same PR.
+
+```{note}
+The `preview-changes` job will only fail intentionally if while analyzing a file failed to
format. Otherwise a failure indicates a bug in the workflow.
+```
-```{tip}
-Maintainers with write access or higher can trigger the workflow manually from the
-Actions tab using the `workflow_dispatch` event. Simply select "diff-shades"
-from the workflows list on the left, press "Run workflow", and fill in which revisions
-and command line arguments to use.
+The workflow uploads several artifacts upon completion:
-Once finished, check the logs or download the artifacts for local use.
-```
+- The raw analyses (.json)
+- HTML diffs (.html)
+- `.pr-comment.json` (if triggered by a PR)
+
+The last one is downloaded by the `diff-shades-comment` workflow and shouldn't be
+downloaded locally. The HTML diffs come in handy for push-based where there's no PR to
+post a comment. And the analyses exist just in case you want to do further analysis
+using the collected data locally.
[diff-shades]: https://github.com/ichard26/diff-shades#readme