Enforce no formatting changes for PRs via CI

Now PRs will run two diff-shades jobs, "preview-changes" which formats
all projects with preview=True, and "assert-no-changes" which formats
all projects with preview=False. The latter also fails if any changes
were made.

Also the workflow_dispatch feature was dropped since it was
complicating everything for little gain.

.github/workflows/diff_shades.yml

@@ -3,54 +3,61 @@ name: diff-shades
 on:
   push:
     branches: [main]
-    paths-ignore: ["docs/**", "tests/**", "**.md", "**.rst"]
+    paths: ["src/**", "setup.*", "pyproject.toml", ".github/workflows/*"]
 
   pull_request:
-    paths-ignore: ["docs/**", "tests/**", "**.md", "**.rst"]
-
-  workflow_dispatch:
-    inputs:
-      baseline:
-        description: >
-          The baseline revision. Pro-tip, use `.pypi` to use the latest version
-          on PyPI or `.XXX` to use a PR.
-        required: true
-        default: main
-      baseline-args:
-        description: "Custom Black arguments (eg. -l 79)"
-        required: false
-      target:
-        description: >
-          The target revision to compare against the baseline. Same tip applies here.
-        required: true
-      target-args:
-        description: "Custom Black arguments (eg. -S)"
-        required: false
+    paths: ["src/**", "setup.*", "pyproject.toml", ".github/workflows/*"]
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}
   cancel-in-progress: true
 
 jobs:
+  configure:
+    runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.set-config.outputs.matrix }}
+
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-python@v3
+
+      - name: Install diff-shades and support dependencies
+        run: |
+          python -m pip install click packaging urllib3
+          python -m pip install https://github.com/ichard26/diff-shades/archive/stable.zip
+
+      - name: Calculate run configuration & metadata
+        id: set-config
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+        run: >
+          python scripts/diff_shades_gha_helper.py config ${{ github.event_name }} ${{ matrix.mode }}
+
   analysis:
-    name: analysis / linux
+    name: analysis / ${{ matrix.mode }}
+    needs: configure
     runs-on: ubuntu-latest
     env:
       # Clang is less picky with the C code it's given than gcc (and may
       # generate faster binaries too).
       CC: clang-12
+    strategy:
+      fail-fast: false
+      matrix:
+        include: ${{ fromJson(needs.configure.outputs.matrix )}}
 
     steps:
       - name: Checkout this repository (full clone)
         uses: actions/checkout@v3
         with:
+          # The baseline revision could be rather old so a full clone is ideal.
           fetch-depth: 0
 
       - uses: actions/setup-python@v3
 
       - name: Install diff-shades and support dependencies
         run: |
-          python -m pip install pip --upgrade
           python -m pip install https://github.com/ichard26/diff-shades/archive/stable.zip
           python -m pip install click packaging urllib3
           python -m pip install -r .github/mypyc-requirements.txt
@@ -59,92 +66,87 @@ jobs:
           git config user.name "diff-shades-gha"
           git config user.email "diff-shades-gha@example.com"
 
-      - name: Calculate run configuration & metadata
-        id: config
-        env:
-          GITHUB_TOKEN: ${{ github.token }}
-        run: >
-          python helper.py config ${{ github.event_name }}
-          ${{ github.event.inputs.baseline }} ${{ github.event.inputs.target }}
-          --baseline-args "${{ github.event.inputs.baseline-args }}"
-
       - name: Attempt to use cached baseline analysis
         id: baseline-cache
         uses: actions/cache@v2.1.7
         with:
-          path: ${{ steps.config.outputs.baseline-analysis }}
-          key: ${{ steps.config.outputs.baseline-cache-key }}
+          path: ${{ matrix.baseline-analysis }}
+          key: ${{ matrix.baseline-cache-key }}
 
       - name: Build and install baseline revision
         if: steps.baseline-cache.outputs.cache-hit != 'true'
         env:
           GITHUB_TOKEN: ${{ github.token }}
         run: >
-          ${{ steps.config.outputs.baseline-setup-cmd }}
+          ${{ matrix.baseline-setup-cmd }}
           && python setup.py --use-mypyc bdist_wheel
           && python -m pip install dist/*.whl && rm build dist -r
 
       - name: Analyze baseline revision
         if: steps.baseline-cache.outputs.cache-hit != 'true'
         run: >
           diff-shades analyze -v --work-dir projects-cache/
-          ${{ steps.config.outputs.baseline-analysis }} -- ${{ github.event.inputs.baseline-args }}
+          ${{ matrix.baseline-analysis }} ${{ matrix.force-flag }}
 
       - name: Build and install target revision
         env:
           GITHUB_TOKEN: ${{ github.token }}
         run: >
-          ${{ steps.config.outputs.target-setup-cmd }}
+          ${{ matrix.target-setup-cmd }}
           && python setup.py --use-mypyc bdist_wheel
           && python -m pip install dist/*.whl
 
       - name: Analyze target revision
         run: >
           diff-shades analyze -v --work-dir projects-cache/
-          ${{ steps.config.outputs.target-analysis }} --repeat-projects-from
-          ${{ steps.config.outputs.baseline-analysis }} -- ${{ github.event.inputs.target-args }}
+          ${{ matrix.target-analysis }} --repeat-projects-from
+          ${{ matrix.baseline-analysis }} ${{ matrix.force-flag }}
 
       - name: Generate HTML diff report
         run: >
-          diff-shades --dump-html diff.html compare --diff --quiet
-          ${{ steps.config.outputs.baseline-analysis }} ${{ steps.config.outputs.target-analysis }}
+          diff-shades --dump-html diff.html compare --diff
+          ${{ matrix.baseline-analysis }} ${{ matrix.target-analysis }}
 
       - name: Upload diff report
         uses: actions/upload-artifact@v2
         with:
-          name: diff.html
+          name: ${{ matrix.mode }}-diff.html
           path: diff.html
 
       - name: Upload baseline analysis
         uses: actions/upload-artifact@v2
         with:
-          name: ${{ steps.config.outputs.baseline-analysis }}
-          path: ${{ steps.config.outputs.baseline-analysis }}
+          name: ${{ matrix.baseline-analysis }}
+          path: ${{ matrix.baseline-analysis }}
 
       - name: Upload target analysis
         uses: actions/upload-artifact@v2
         with:
-          name: ${{ steps.config.outputs.target-analysis }}
-          path: ${{ steps.config.outputs.target-analysis }}
+          name: ${{ matrix.target-analysis }}
+          path: ${{ matrix.target-analysis }}
 
       - name: Generate summary file (PR only)
-        if: github.event_name == 'pull_request'
+        if: github.event_name == 'pull_request' && matrix.mode == 'preview-changes'
         run: >
           python helper.py comment-body
-          ${{ steps.config.outputs.baseline-analysis }} ${{ steps.config.outputs.target-analysis }}
-          ${{ steps.config.outputs.baseline-sha }} ${{ steps.config.outputs.target-sha }}
+          ${{ matrix.baseline-analysis }} ${{ matrix.target-analysis }}
+          ${{ matrix.baseline-sha }} ${{ matrix.target-sha }}
           ${{ github.event.pull_request.number }}
 
       - name: Upload summary file (PR only)
-        if: github.event_name == 'pull_request'
+        if: github.event_name == 'pull_request' && matrix.mode == 'preview-changes'
         uses: actions/upload-artifact@v2
         with:
           name: .pr-comment.json
           path: .pr-comment.json
 
-        # This is last so the diff-shades-comment workflow can still work even if we
-        # end up detecting failed files and failing the run.
-      - name: Check for failed files in both analyses
+      - name: Verify zero changes
+        if: matrix.mode == 'assert-no-changes'
+        run: diff-shades compare --check ${{ matrix.baseline-analysis }} ${{ matrix.target-analysis }}
+
+      - name: Check for failed files for target revision
+        # Even if the previous step failed, we should still check for failed files.
+        if: always()
         run: >
-          diff-shades show-failed --check --show-log ${{ steps.config.outputs.baseline-analysis }};
-          diff-shades show-failed --check --show-log ${{ steps.config.outputs.target-analysis }}
+          diff-shades show-failed --check --show-log ${{ matrix.target-analysis }}
+          --check-allow 'sqlalchemy:test/orm/test_relationship_criteria.py'

docs/contributing/gauging_changes.md

@@ -15,46 +15,50 @@ internally and will be removed from the _Black_ repository in the future.
 
 ## diff-shades
 
-diff-shades is a tool that runs _Black_ across a list of Git cloneable OSS 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.
+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].
 
 ### CI integration
 
 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