ci: enforce formatting with prettier

Author: PierreJeanjacquot

.mise/locks/npm-prettier/3.9.8/aube-lock.yaml

@@ -0,0 +1,24 @@
+lockfileVersion: '9.0'
+
+settings:
+  autoInstallPeers: true
+  excludeLinksFromLockfile: false
+
+importers:
+
+  .:
+    dependencies:
+      prettier:
+        specifier: 3.9.8
+        version: 3.9.8
+
+packages:
+
+  prettier@3.9.8:
+    resolution: {integrity: sha512-WRFq3Wn3WId7LLROfMLdH7xaFr2jR62wU8nLO6rQUOLOxNZUviyJQs1M0iIhLexSFy+L+w0ch66wtoO2jRjG0A==}
+    engines: {node: '>=14'}
+    hasBin: true
+
+snapshots:
+
+  prettier@3.9.8: {}

.mise/locks/npm-prettier/3.9.8/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "mise-npm-install",
+  "private": true,
+  "dependencies": {
+    "prettier": "3.9.8"
+  }
+}

.prettierignore

@@ -0,0 +1,5 @@
+# generated files
+## release-please
+*/CHANGELOG.md
+## mise
+.mise/

.prettierrc.json

@@ -0,0 +1,3 @@
+{
+  "proseWrap": "never"
+}

CONTRIBUTING.md

@@ -7,16 +7,26 @@ Each shared reusable workflow is backed by a Component directory `<name>/` that
 After editing any `.github/workflows/<name>.yml` for a workflow listed in `release-please-config.json`, run:
 
 ```sh
-bash scripts/compute-workflow-sha256.sh
+mise run update-checksums
 ```
 
-This regenerates `<name>/workflow-sha256`, a checksum of the workflow file. Commit the resulting diff alongside your workflow change — this is what makes the change visible to release-please for that Component.
+This formats the repository (see [Formatting](#formatting)), then runs `scripts/compute-workflow-sha256.sh`, which regenerates `<name>/workflow-sha256`, a checksum of the workflow file. Commit the resulting diff alongside your workflow change — this is what makes the change visible to release-please for that Component.
 
 CI enforces this on every pull request via `bash scripts/compute-workflow-sha256.sh --check`, which fails if any `workflow-sha256` file is out of date.
 
+## Formatting
+
+Files are formatted with [Prettier](https://prettier.io), using its default settings. Generated files (release-please changelogs, mise files) are excluded via `.prettierignore`. Format the repository with:
+
+```sh
+mise run format
+```
+
+Formatting can rewrite workflow files, which changes their checksum. After editing a workflow, run `mise run update-checksums` instead of `mise run format` alone, so `workflow-sha256` files are computed from the formatted content.
+
 ## Linting
 
-Workflows are linted with [actionlint](https://github.com/rhysd/actionlint), which also runs [shellcheck](https://github.com/koalaman/shellcheck) on inline `run:` scripts. Shell scripts committed to the repository (`*.sh`, e.g. under `scripts/`) are linted with shellcheck directly. Both tools are pinned in `mise.toml` and `mise.lock`. Install them with [mise](https://mise.jdx.dev):
+Workflows are linted with [actionlint](https://github.com/rhysd/actionlint), which also runs [shellcheck](https://github.com/koalaman/shellcheck) on inline `run:` scripts. Shell scripts committed to the repository (`*.sh`, e.g. under `scripts/`) are linted with shellcheck directly. Formatting is checked with `prettier --check`. All tools are pinned in `mise.toml` and `mise.lock`. Install them with [mise](https://mise.jdx.dev):
 
 ```sh
 mise install --locked

mise.lock

@@ -5,6 +5,17 @@ lockfile = true
 [tools]
 "aqua:actionlint" = "1.7.12"
 "aqua:koalaman/shellcheck" = "0.11.0"
+"npm:prettier" = "3.9.8"
+
+[tasks.format]
+run = "prettier --write ."
+
+[tasks."update-checksums"]
+run = "scripts/compute-workflow-sha256.sh"
+depends = ["format"]
+
+[tasks."lint:format"]
+run = "prettier --check ."
 
 [tasks."lint:actionlint"]
 run = "actionlint"
@@ -14,4 +25,4 @@ shell = "bash -euo pipefail -c"
 run = "git ls-files -z --cached --others --exclude-standard '*.sh' | xargs -0 -r shellcheck"
 
 [tasks.lint]
-depends = [ "lint:actionlint", "lint:shellcheck" ]
+depends = [ "lint:format", "lint:actionlint", "lint:shellcheck" ]