on-tag.yml

name: Create shortened tags

# Only triggered on git tag push
on:
  push:
    tags: [ '*' ]

jobs:
  shorten:
    name: Short tags
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v1

      - name: Make sure that current tag is merged to master
        run: |
          cd "$GITHUB_WORKSPACE"

          git switch master

          # Returns 1 if it's not, and therefore terminates the workflow
          git merge-base --is-ancestor "$GITHUB_SHA" HEAD

      - name: Create, or update the short-name branch
        run: |
          cd "$GITHUB_WORKSPACE"

          git config user.name "$GITHUB_ACTOR"
          git config user.email "$GITHUB_ACTOR@users.noreply.github.com"

          TAG=$(echo "$GITHUB_REF" | awk -F/ '{print $NF}')
          SHORT=$(echo "${TAG#v}" | cut -d. -f-2)

          # Do nothing on test tags
          if [[ "$SHORT" = "0.0" ]]; then
            exit 0
          fi

          git branch -f "$SHORT" "$TAG"

          REMOTE="https://$GITHUB_ACTOR:${{ secrets.GITHUB_TOKEN }}@github.com/$GITHUB_REPOSITORY.git"
          git push --force "$REMOTE" "$SHORT"