Add diff-features workflow (#3109)

* Add diff-features workflow

* Revert "fix(test-builder): preserve CSS functions when extracting values (#3092)"

This reverts commit a5da0a9.

* ci(diff-features): merge into test workflow

* Reapply "fix(test-builder): preserve CSS functions when extracting values (#3092)"

This reverts commit 79ed751.

Author: caugner

.github/workflows/test.yml

@@ -10,7 +10,6 @@ permissions:
 
 env:
   FORCE_COLOR: 3
-  BCD_DIR: ./browser-compat-data
 
 jobs:
   test:
@@ -23,6 +22,8 @@ jobs:
           #   runs-on: macos-latest
     name: Test (${{ matrix.name }})
     runs-on: ${{ matrix.runs-on }}
+    env:
+      BCD_DIR: ./browser-compat-data
     steps:
       - name: Clone collector
         uses: actions/checkout@v6
@@ -54,3 +55,56 @@ jobs:
           NODE_ENV: production
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v5
+
+  diff-features:
+    if: github.event_name == 'pull_request'
+    name: Diff features
+    runs-on: ubuntu-latest
+    concurrency:
+      group: ${{ github.workflow }}-${{ github.event.pull_request.number }}-diff-features
+      cancel-in-progress: true
+    steps:
+      - name: Clone collector (base)
+        uses: actions/checkout@v6
+        with:
+          ref: ${{ github.base_ref }}
+          path: base
+          persist-credentials: false
+          submodules: true
+      - name: Clone collector (PR)
+        uses: actions/checkout@v6
+        with:
+          path: pr
+          persist-credentials: false
+          submodules: true
+      - name: Clone browser-compat-data
+        uses: actions/checkout@v6
+        with:
+          repository: mdn/browser-compat-data
+          path: bcd
+          persist-credentials: false
+      - name: Setup NodeJS
+        uses: actions/setup-node@v6
+        with:
+          node-version-file: pr/.nvmrc
+      - name: Install
+        run: |
+          cd bcd && npm ci | sed "s/^/[bcd] /" &
+          cd base && npm ci | sed "s/^/[base] /" &
+          cd pr && npm ci | sed "s/^/[pr] /" &
+          wait
+      - name: Build tests
+        run: |
+          cd base && npm run build:tests | sed "s/^/[base] /" &
+          cd pr && npm run build:tests | sed "s/^/[pr] /" &
+          wait
+      - name: Feature coverage
+        run: |
+          cd base && npm run feature-coverage -- -l > ../base-features.txt | sed "s/^/[base] /" &
+          cd pr && npm run feature-coverage -- -l > ../pr-features.txt | sed "s/^/[pr] /" &
+          wait
+        env:
+          BCD_DIR: ../bcd
+      - name: Diff
+        run: git diff --color=always --no-index base-features.txt pr-features.txt || true
+