github: Adds commit workflow

Signed-off-by: Thomas Parrott <[email protected]>

.github/workflows/commits.yml

@@ -0,0 +1,42 @@
+name: Commits
+on:
+  - pull_request
+
+permissions:
+  contents: read
+
+jobs:
+  dco-check:
+    permissions:
+      pull-requests: read  # for tim-actions/get-pr-commits to get list of commits from the PR
+    name: Signed-off-by (DCO) and branch target
+    runs-on: ubuntu-22.04
+    steps:
+    - name: Get PR Commits
+      id: 'get-pr-commits'
+      uses: tim-actions/get-pr-commits@master
+      with:
+        token: ${{ secrets.GITHUB_TOKEN }}
+
+    - name: Check that all commits are signed-off
+      uses: tim-actions/dco@master
+      with:
+        commits: ${{ steps.get-pr-commits.outputs.commits }}
+
+    - name: Check branch target
+      env:
+        TARGET: ${{ github.event.pull_request.base.ref }}
+        TITLE: ${{ github.event.pull_request.title }}
+      if: ${{ github.actor != 'dependabot[bot]' }}
+      run: |
+        set -x
+        TARGET_FROM_PR_TITLE="$(echo "${TITLE}" | sed -n 's/.*(\(\(latest\|[0-9]\.[0-9]\)-\(edge\|candidate\)\))$/\1/p')"
+        if [ -z "${TARGET_FROM_PR_TITLE}" ]; then
+          TARGET_FROM_PR_TITLE="latest-edge"
+        else
+          echo "Branch target overridden from PR title"
+        fi
+        [ "${TARGET}" = "${TARGET_FROM_PR_TITLE}" ] && exit 0
+
+        echo "Invalid branch target: ${TARGET} != ${TARGET_FROM_PR_TITLE}"
+        exit 1