.github: add workflow to check commit history

Author: peterbarker

.github/workflows/test_size.yml

@@ -325,3 +325,36 @@ jobs:
           else
             echo "No differences found." >> $GITHUB_STEP_SUMMARY
           fi
+
+      - 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