chore(ci): Add labels to PRs based on LoC / num files changed (mdn#31729

)

* chore(ci): Add labels to PRs based on LoC / num files changed

* chore(ci): Make label-by-size depend on label by path, only run on opened & syncd PRs against main

.github/pull-request-size.yml

@@ -0,0 +1,42 @@
+# Configuration for PR Size Labeler
+
+# List of files to exclude from size calculation
+# Files matching these patterns will not be considered when calculating PR size
+exclude_files:
+  - "files/en-us/_redirects.txt"
+  - "files/en-us/_wikihistory.json"
+
+# Configuration for labeling based on the size of the Pull Request
+# Each entry defines a size label, along with thresholds for diff and file count
+label_configs:
+  # Configuration for 'extra small' PRs
+  - size: xs
+    diff: 10 # Threshold for the total lines of code changed (additions + deletions)
+    files: 1 # Threshold for the total number of files changed
+    labels: ["size/xs"] # Labels to be applied for this size
+
+  # Configuration for 'small' PRs
+  - size: s
+    diff: 25
+    files: 5
+    labels: ["size/s"]
+
+  # Configuration for 'medium' PRs
+  - size: m
+    diff: 100
+    files: 10
+    # Additional labels can be added, e.g.;
+    # labels: ["size/m", "pairing-wanted"]
+    labels: ["size/m"]
+
+  # Configuration for 'large' PRs
+  - size: l
+    diff: 250
+    files: 25
+    labels: ["size/l"]
+
+  # Configuration for 'extra large' PRs
+  - size: xl
+    diff: 500
+    files: 50
+    labels: ["size/xl"]

.github/workflows/pr-labeler.yml

@@ -1,13 +1,36 @@
-name: "Pull request labeler"
+name: Pull request labeler
+
 on:
-  - pull_request_target
+  pull_request:
+    types: [opened, synchronize]
+    branches:
+      - "main"
 
 jobs:
-  triage:
+  # Docs: https://github.com/actions/labeler
+  label-by-path:
     # do not run on forks
     if: github.repository == 'mdn/content'
     runs-on: ubuntu-latest
     steps:
       - uses: actions/labeler@v4
         with:
           repo-token: "${{ secrets.GITHUB_TOKEN }}"
+
+  # Docs: https://github.com/cbrgm/pr-size-labeler-action
+  label-by-size:
+    # do not run on forks
+    if: github.repository == 'mdn/content'
+    needs: label-by-path
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Label PR based on size
+        uses: cbrgm/pr-size-labeler-action@main
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          github_repository: ${{ github.repository }} # Repository name
+          github_pr_number: ${{ github.event.number }} # Pull request number
+          config_file_path: ".github/pull-request-size.yml" # Path to pr-size-labeler config