CI: check the presence of the changelog line in every pull request

Checking it only in the merge queue leads to deferred failures once the
decision to merge has been taken already.

Author: samueltardieu

.github/workflows/clippy_mq.yml

@@ -15,37 +15,7 @@ defaults:
     shell: bash
 
 jobs:
-  changelog:
-    runs-on: ubuntu-latest
-
-    steps:
-    - name: Checkout
-      uses: actions/checkout@v4
-      with:
-        ref: ${{ github.ref }}
-        # Unsetting this would make so that any malicious package could get our Github Token
-        persist-credentials: false
-
-    # Run
-    - name: Check Changelog
-      run: |
-        MESSAGE=$(git log --format=%B -n 1)
-        PR=$(echo "$MESSAGE" | grep -o "#[0-9]*" | head -1 | sed -e 's/^#//')
-        body=$(curl -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" -s "https://api.github.com/repos/rust-lang/rust-clippy/pulls/$PR" | \
-          python -c "import sys, json; print(json.load(sys.stdin)['body'])")
-        output=$(grep "^changelog:\s*\S" <<< "$body" | sed "s/changelog:\s*//g") || {
-          echo "ERROR: PR body must contain 'changelog: ...'"
-          exit 1
-        }
-        if [[ "$output" = "none" ]]; then
-          echo "WARNING: changelog is 'none'"
-        else
-          echo "changelog: $output"
-        fi
-      env:
-        PYTHONIOENCODING: 'utf-8'
   base:
-    needs: changelog
     strategy:
       matrix:
         include:
@@ -119,7 +89,6 @@ jobs:
         OS: ${{ runner.os }}
 
   metadata_collection:
-    needs: changelog
     runs-on: ubuntu-latest
 
     steps:
@@ -138,7 +107,6 @@ jobs:
       run: cargo collect-metadata
 
   integration_build:
-    needs: changelog
     runs-on: ubuntu-latest
 
     steps:
@@ -228,7 +196,7 @@ jobs:
         INTEGRATION: ${{ matrix.integration }}
 
   conclusion:
-    needs: [ changelog, base, metadata_collection, integration_build, integration ]
+    needs: [ base, metadata_collection, integration_build, integration ]
     # We need to ensure this job does *not* get skipped if its dependencies fail,
     # because a skipped job is considered a success by GitHub. So we have to
     # overwrite `if:`. We use `!cancelled()` to ensure the job does still not get run

.github/workflows/clippy_pr_changelog.yml

@@ -0,0 +1,56 @@
+name: Clippy changelog check
+
+on:
+  pull_request:
+    types: [opened, reopened, edited]
+
+concurrency:
+  # For a given workflow, if we push to the same PR, cancel all previous builds on that PR.
+  # If the push is not attached to a PR, we will cancel all builds on the same branch.
+  group: "${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}"
+  cancel-in-progress: true
+
+jobs:
+  changelog:
+    runs-on: ubuntu-latest
+
+    defaults:
+      run:
+        shell: bash
+
+    steps:
+    # Run
+    - name: Check Changelog
+      run: |
+        body=$(curl -H "Authorization: token ${{ secrets.GITHUB_TOKEN }}" -s "https://api.github.com/repos/rust-lang/rust-clippy/pulls/$PR_NUMBER" | \
+          python -c "import sys, json; print(json.load(sys.stdin)['body'])")
+        output=$(grep "^changelog:\s*\S" <<< "$body" | sed "s/changelog:\s*//g") || {
+          echo "ERROR: pull request message must contain 'changelog: ...'. Add it " \
+               "and push (or force-push) the pull request to trigger a new check."
+          exit 1
+        }
+        echo "changelog: $output"
+      env:
+        PYTHONIOENCODING: 'utf-8'
+        PR_NUMBER: '${{ github.event.number }}'
+
+  # We need to have the "conclusion" job also on PR CI, to make it possible
+  # to add PRs to a merge queue.
+  conclusion_changelog:
+    needs: [ changelog ]
+    # We need to ensure this job does *not* get skipped if its dependencies fail,
+    # because a skipped job is considered a success by GitHub. So we have to
+    # overwrite `if:`. We use `!cancelled()` to ensure the job does still not get run
+    # when the workflow is canceled manually.
+    #
+    # ALL THE PREVIOUS JOBS NEED TO BE ADDED TO THE `needs` SECTION OF THIS JOB!
+    if: ${{ !cancelled() }}
+    runs-on: ubuntu-latest
+    steps:
+      # Manually check the status of all dependencies. `if: failure()` does not work.
+      - name: Conclusion
+        run: |
+          # Print the dependent jobs to see them in the CI log
+          jq -C <<< '${{ toJson(needs) }}'
+          # Check if all jobs that we depend on (in the needs array) were successful.
+          jq --exit-status 'all(.result == "success")' <<< '${{ toJson(needs) }}'