pr-label.yml

# Automatically add a label to PRs based on the [Label] prefix in the title
#
# Usage:
#   - PR title must start with a [Label] prefix in brackets
#   - Example: "[BugFix] Fix memory leak" will add the "bug" label
#   - Fails if no valid prefix is found
#   - Labels are ONLY ADDED, never removed (preserves manual labels)
#   - Matching is case-insensitive
#
# Supported prefixes -> label:
#   [BE]                                -> BE
#   [BugFix], [Fix]                     -> bug
#   [Feature]                           -> Feature
#   [Doc], [Docs], [Documentation]      -> documentation
#   [Refactor], [Refactoring]           -> Refactor
#   [CI]                                -> CI
#   [Test], [Tests]                     -> Test
#   [Compile]                           -> Compile
#   [Performance], [Perf]              -> Performance
#   [Deprecation], [Deprecated]         -> Deprecation
#   [Setup]                             -> setup
#   [Distributed], [Dist], [DTensor]    -> Distributed
#   [Benchmark], [Benchmarks], [Bench]  -> Benchmarks
#   [Typing], [Type]                    -> Typing
#   [BC-breaking], [BC]                 -> BC-breaking
#   [Formatting], [Format]             -> Formatting
#   [Quality]                           -> Quality
#   [Release]                           -> release
#   [Versioning]                        -> versioning
#------------------------------------------------------------

name: PR Label

on:
  # Using pull_request_target to have write access for PRs from forks
  # This is safe because we only read PR metadata (title), not code from the fork
  pull_request_target:
    types: [opened, edited, synchronize, reopened]

jobs:
  add-label:
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write
    steps:
      - name: Parse and apply label from PR title
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          PR_TITLE: ${{ github.event.pull_request.title }}
          PR_NUMBER: ${{ github.event.pull_request.number }}
          REPO: ${{ github.repository }}
        run: |
          set -euo pipefail

          post_help_comment() {
            local reason="$1"
            local current_title="$2"
            cat > /tmp/pr_comment.md << 'COMMENT_EOF'
          ## PR Title Label Error

          REASON_PLACEHOLDER

          **Current title:** `TITLE_PLACEHOLDER`

          ### Supported Prefixes

          Your PR title must start with **exactly** one of these prefixes (case-insensitive):

          | Prefix | Label Applied | Example |
          |--------|---------------|---------|
          | `[BE]` | BE | `[BE] Improve internal plumbing` |
          | `[BugFix]` or `[Fix]` | bug | `[BugFix] Fix memory leak in TensorDict` |
          | `[Feature]` | Feature | `[Feature] Add new storage backend` |
          | `[Doc]` or `[Docs]` | documentation | `[Doc] Update installation guide` |
          | `[Refactor]` | Refactor | `[Refactor] Clean up module imports` |
          | `[CI]` | CI | `[CI] Fix workflow permissions` |
          | `[Test]` or `[Tests]` | Test | `[Test] Add unit tests for nn module` |
          | `[Compile]` | Compile | `[Compile] Fix torch.compile issue` |
          | `[Performance]` or `[Perf]` | Performance | `[Perf] Optimize tensor operations` |
          | `[Deprecation]` | Deprecation | `[Deprecation] Mark old function` |
          | `[Setup]` | setup | `[Setup] Update build configuration` |
          | `[Distributed]`, `[Dist]`, or `[DTensor]` | Distributed | `[DTensor] Add cross-mesh transfer` |
          | `[Benchmark]` or `[Bench]` | Benchmarks | `[Benchmark] Add compile benchmark` |
          | `[Typing]` or `[Type]` | Typing | `[Typing] Add type stubs` |
          | `[BC-breaking]` or `[BC]` | BC-breaking | `[BC-breaking] Remove deprecated API` |
          | `[Formatting]` or `[Format]` | Formatting | `[Format] Fix code style` |
          | `[Quality]` | Quality | `[Quality] Improve error messages` |
          | `[Release]` | release | `[Release] Publish release artifacts` |
          | `[Versioning]` | versioning | `[Versioning] Bump release version` |

          **Note:** Matching is case-insensitive. Common variations (singular/plural) are supported.
          COMMENT_EOF
            sed -i 's/^ *//' /tmp/pr_comment.md
            COMMENT_REASON="$reason" COMMENT_TITLE="$current_title" python3 - <<'PY'
          import os
          from pathlib import Path

          path = Path("/tmp/pr_comment.md")
          comment = path.read_text()
          comment = comment.replace("REASON_PLACEHOLDER", os.environ["COMMENT_REASON"])
          comment = comment.replace("TITLE_PLACEHOLDER", os.environ["COMMENT_TITLE"])
          path.write_text(comment)
          PY
            gh pr comment "$PR_NUMBER" --repo "$REPO" --body-file /tmp/pr_comment.md
          }

          echo "PR Title: $PR_TITLE"

          # Check if title starts with [...]
          if [[ ! "$PR_TITLE" =~ ^\[([^\]]+)\] ]]; then
            echo "::error::PR title must start with [Label]. Got: '$PR_TITLE'"
            post_help_comment "PR title must start with a label prefix in brackets (e.g., \`[BugFix]\`)." "$PR_TITLE"
            exit 1
          fi

          # Extract the prefix
          PREFIX="${BASH_REMATCH[1]}"

          echo "Extracted prefix: $PREFIX"

          # Case-insensitive matching: lowercase the prefix once
          PREFIX_LOWER="${PREFIX,,}"

          # Map prefixes to GitHub label names
          case "$PREFIX_LOWER" in
            be)                        LABEL="BE" ;;
            bugfix|fix|bug)            LABEL="bug" ;;
            feature|features)          LABEL="Feature" ;;
            doc|docs|documentation)    LABEL="documentation" ;;
            refactor|refactoring)      LABEL="Refactor" ;;
            ci)                        LABEL="CI" ;;
            test|tests)                LABEL="Test" ;;
            compile)                   LABEL="Compile" ;;
            performance|perf)          LABEL="Performance" ;;
            deprecation|deprecated)    LABEL="Deprecation" ;;
            setup)                     LABEL="setup" ;;
            distributed|dist|dtensor)  LABEL="Distributed" ;;
            benchmark|benchmarks|bench) LABEL="Benchmarks" ;;
            typing|type)               LABEL="Typing" ;;
            bc-breaking|bc)            LABEL="BC-breaking" ;;
            formatting|format)         LABEL="Formatting" ;;
            quality)                   LABEL="Quality" ;;
            release)                   LABEL="release" ;;
            versioning)                LABEL="versioning" ;;
            *)
              echo "::error::Unknown or invalid prefix '[$PREFIX]'."
              post_help_comment "Unknown or invalid prefix \`[$PREFIX]\`." "$PR_TITLE"
              exit 1
              ;;
          esac

          echo "Mapped to label: $LABEL"

          # Add the label to the PR (never remove existing labels)
          gh pr edit "$PR_NUMBER" --repo "$REPO" --add-label "$LABEL"

          echo "Successfully added label '$LABEL' to PR #$PR_NUMBER"