.github: add workflow to check commit history

Author: peterbarker

.github/workflows/test_commitlist.yml

@@ -0,0 +1,51 @@
+name: test commit list
+
+on: push
+
+concurrency:
+  group: ci-${{github.workflow}}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-22.04
+    container: ardupilot/ardupilot-dev-${{ matrix.toolchain }}:v0.1.3
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.base.ref }}
+          path: base_branch
+          submodules: 'recursive'
+
+      - name: Check commitlist ${{ github.event.pull_request.base.ref }}..HEAD
+        shell: bash
+        run: |
+          set -ex
+          git config --global --add safe.directory ${GITHUB_WORKSPACE}
+
+          # create file to inspect
+          COMMITLIST=/tmp/commitlist.txt
+          git log --format="%s" ${{ github.event.pull_request.base.ref }}..HEAD >$COMMITLIST
+
+          echo "Commit list:"
+          cat $COMMITLIST
+
+          # fixup commits should never be merged:
+          if grep -F 'fixup!' $COMMITLIST; then
+             echo "Fixup commits found"
+             exit 1
+          fi
+
+          # No Merge commits to be merged:
+          if grep 'Merge branch.*into' $COMMITLIST; then
+             echo "Merge commits found"
+             exit 1
+          fi
+
+          # require a ":" to appear somewhere in the message:
+          while IFS= read x; do
+              if ! [[ "$x" == *":"* ]] ; then
+                 echo "Commit message ($x) missing subsystem tag on front"
+                 exit 1
+              fi
+          done < $COMMITLIST