Improve error message for invalid global expression

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• I've read the contributing guidelines and wholeheartedly agree

I've found a bug, and:

• The documentation does not mention anything about my problem
• There are no open or closed issues that are related to my problem

Description

Hello!

I'm trying to use the {{is_default_branch}} template to enable or disable specific tagging. This is my code:

      - name: Extract Docker metadata
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ghcr.io/${{ github.repository_owner }}/messenger
          tags: |
            # Set version from releases. By default uses git tag which is has prefix "messenger"
            type=semver,pattern={{version}},value=${{ needs.release.outputs.version }}

            # Only on default branch (master) add MAJOR.MINOR and MAJOR and 'latest'
            type=semver,pattern={{major}}.{{minor}},value=${{ needs.release.outputs.version }},enable={{is_default_branch}}
            type=semver,pattern={{major}},value=${{ needs.release.outputs.version }},enable={{is_default_branch}}
            type=raw,value=latest,enable={{is_default_branch}}

            # Only on prereleases add beta-latest
            type=raw,value=beta-latest,enable={{is_prerelease}}
          labels: |
            org.opencontainers.image.created={{commit_date 'YYYY-MM-DDTHH:mm:ss.SSS[Z]'}}

The build fails on my CI because: "Error: Invalid value for enable attribute: " - sadly I can't figure this one out after hours of searching on google and trying to maybe set the context right.

Expected behaviour

is_default_branch to have a value

Actual behaviour

is_default_branch must be undefined or null since this code in src/meta.ts checks for the value:

# src/meta.ts
    for (const tag of this.tags) {
      const enabled = this.setGlobalExp(tag.attrs['enable']);
      if (!['true', 'false'].includes(enabled)) {
        throw new Error(`Invalid value for enable attribute: ${enabled}`);
      }

Repository URL

No response

Workflow run URL

No response

YAML workflow

name: Release and Publish Messenger

on:
  # Trigger on PR merge since direct pushes are prohibited
  push:
    branches:
      - beta
      - master
    paths:
      - 'messenger/**'
      - '.github/workflows/release-messenger.yml'
  # Trigger from UI
  workflow_dispatch:
jobs:
  # Create tag and release on github with correct version from conventional commits
  release:
    permissions:
      contents: write
    name: Create release
    runs-on: ubuntu-latest
    outputs:
      published: ${{ steps.semantic.outputs.new_release_published }}
      version: ${{ steps.semantic.outputs.new_release_version }}
      major: ${{ steps.semantic.outputs.new_release_major_version }}
      minor: ${{ steps.semantic.outputs.new_release_minor_version }}
      patch: ${{ steps.semantic.outputs.new_release_patch_version }}
      notes: ${{ steps.semantic.outputs.new_release_notes }}
      tag: ${{ steps.semantic.outputs.new_release_git_tag }}
      head: ${{ steps.semantic.outputs.new_release_git_head }}
    steps:
      - name: Checkout repository
        uses: actions/checkout@v4
        with:
          fetch-depth: 0
      - name: Execute Semantic Release
        id: semantic
        uses: cycjimmy/semantic-release-action@v4
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        with:
          working_directory: ./messenger
          # needed by commit-analyzer as dependency, this action installs it for us with this option
          extra_plugins: |
            conventional-changelog-conventionalcommits@9.1.0
  build-and-push:
    name: Build and Push Ponton Docker Image
    runs-on: ubuntu-latest
    needs: release
    if: needs.release.outputs.published == 'true'
    permissions:
      contents: read
      packages: write
    steps:
      - name: Checkout repository at released tag
        uses: actions/checkout@v4
        with:
          ref: ${{ needs.release.outputs.head }}
          fetch-depth: 0
          fetch-tags: true
      - name: Read Ponton version
        id: ponton
        run: |
          PONTON_VERSION="$(cat messenger/VERSION)"
          echo "ponton_version=${PONTON_VERSION}" >> "$GITHUB_OUTPUT"

      - name: Compose combined image tag
        id: tag
        run: |
          echo "combined=${{ steps.ponton.outputs.ponton_version }}-${{ needs.release.outputs.version }}" >> "$GITHUB_OUTPUT"

      # For multiarch builds (x86, arm)
      - name: Set up QEMU
        uses: docker/setup-qemu-action@v3

      - name: Set up Docker Buildx
        uses: docker/setup-buildx-action@v3

      - name: Log in to GitHub Container Registry
        uses: docker/login-action@v3
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      # Generate tags/labels. We pass the release version explicitly.
      - name: Extract Docker metadata
        id: meta
        uses: docker/metadata-action@v5
        with:
          images: ghcr.io/${{ github.repository_owner }}/messenger
          tags: |
            # Set version from releases. By default uses git tag which is has prefix "messenger"
            type=semver,pattern={{version}},value=${{ needs.release.outputs.version }}

            # Only on default branch (master) add MAJOR.MINOR and MAJOR and 'latest'
            type=semver,pattern={{major}}.{{minor}},value=${{ needs.release.outputs.version }},enable={{is_default_branch}}
            type=semver,pattern={{major}},value=${{ needs.release.outputs.version }},enable={{is_default_branch}}
            type=raw,value=latest,enable={{is_default_branch}}

            # Only on prereleases add beta-latest
            type=raw,value=beta-latest,enable={{is_prerelease}}
          labels: |
            org.opencontainers.image.created={{commit_date 'YYYY-MM-DDTHH:mm:ss.SSS[Z]'}}
      - name: Build and push Docker image
        uses: docker/build-push-action@v5
        with:
          context: ./messenger
          file: ./messenger/Dockerfile
          push: true
          platforms: linux/amd64
          tags: |
            # Combined Ponton + SemRel tag (always)
            ghcr.io/${{ github.repository_owner }}/messenger:${{ steps.tag.outputs.combined }}
            # Tags from metadata-action 
            ${{ steps.meta.outputs.tags }}
          labels: ${{ steps.meta.outputs.labels }}
          cache-from: type=gha
          cache-to: type=gha,mode=max

      - name: Output image details
        run: |
          cat <<'EOF'
          Docker image pushed
          Semantic-release version: ${{ needs.release.outputs.version }}
          Ponton version: ${{ steps.ponton.outputs.ponton_version }}
          Combined Version: ${{ steps.tag.outputs.combined }}
          All tags:
          $(echo "${{ steps.meta.outputs.tags }}" | sed 's/^/  - /')
            - ${{ steps.tag.outputs.combined }}
          EOF

Workflow logs

No response

BuildKit logs

Additional info

No response

Start in src/meta.ts at setGlobalExp and the validation of the tags' enable attribute. Reproduce the workflow's is_default_branch and is_prerelease expressions, then trace why the value is empty. Done means the expression handling or error reporting clearly reflects the supported behavior for these tag attributes.