Apply automatic Ruff fixes to pull requests

.github/workflows/autofix.yml

@@ -0,0 +1,36 @@
+# Ruff rewrites quote styles and capitalises docstrings without any help
+# from a person, so a contributor should never have to. This hands those
+# fixes to the autofix.ci app, which commits them to the pull request
+# branch, forks included. The existing lint gate still reports any
+# findings that ruff cannot fix.
+#
+# The filename and the workflow name are both fixed by autofix.ci, which
+# uses them to identify the workflow it trusts. Renaming either one stops
+# the app from accepting the patch.
+name: autofix.ci # needed to securely identify the workflow
+
+on:
+  pull_request:
+  push:
+    branches: [develop, master]
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+jobs:
+  autofix:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7
+        with:
+          persist-credentials: false
+      - uses: astral-sh/setup-uv@20cfd1bf945f4377ade1205e4dbc17946fc9a30d # v10.0.1
+        with:
+          python-version: '3.13'
+      - run: uvx --with tox-uv tox -e ruff-fix
+      - uses: autofix-ci/action@c5b2d67aa2274e7b5a18224e8171550871fc7e4a # v1.3.4

.github/workflows/ci.yml

@@ -85,7 +85,13 @@ jobs:
           activate-environment: true
       - name: Install tox
         run: uv pip install '.[tox]'
+      - name: Apply Ruff fixes to pull requests
+        if: github.event_name == 'pull_request'
+        run: tox -e ruff-fix
       - name: Lint
+        env:
+          RUFF_OUTPUT_FORMAT: >-
+            ${{ github.event_name == 'pull_request' && 'github' || 'full' }}
         run: tox -e lint
 
   type-check:

CONTRIBUTING.md

@@ -142,3 +142,16 @@ Include:
 - Steps to reproduce
 - Expected versus actual behaviour
 - The statsd server you are sending to, if the problem is on the wire
+
+## Automatic formatting
+
+Pull requests apply Ruff fixes before the lint check. With the autofix.ci
+app installed for this repository, those fixes are committed to the pull
+request branch, including forks. Findings Ruff cannot fix still fail CI.
+Push builds check the committed files without applying fixes.
+
+Apply the same fixes locally with:
+
+```console
+uvx --with tox-uv tox -e ruff-fix
+```

tox.ini

@@ -37,6 +37,7 @@ commands =
     coverage lcov -o {toxworkdir}/coverage.lcov
 
 [testenv:lint]
+pass_env = RUFF_OUTPUT_FORMAT
 description = Lint with ruff
 skip_install = true
 deps = ruff>=0.15.0
@@ -79,3 +80,13 @@ deps = .[docs]
 changedir = docs
 commands =
     sphinx-build -W -b html -d {envtmpdir}/doctrees . {envtmpdir}/html
+
+
+[testenv:ruff-fix]
+labels = fix
+description = Apply the available Ruff fixes
+skip_install = true
+deps = ruff>=0.15.0
+commands =
+    ruff check --fix --exit-zero statsd tests conftest.py
+    ruff format statsd tests conftest.py