Revert "[Github] Fetch all commits in PR for code formatting checks (#69766)"

This reverts commit 4aa12afb96.

This change introduced failures upon checking out the PR source code.
Pulling this out of tree while I investigate further.

.github/workflows/pr-code-format.yml

@@ -7,37 +7,17 @@ jobs:
   code_formatter:
     runs-on: ubuntu-latest
     steps:
-      # Get changed files before checking out the repository to force the action
-      # to analyze the diff from the Github API rather than looking at the
-      # shallow clone and erroring out, which is significantly more prone to
-      # failure.
+      - name: Fetch LLVM sources
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 2
+
       - name: Get changed files
         id: changed-files
         uses: tj-actions/changed-files@v39
         with:
           separator: ","
-
-      - name: Calculate number of commits to fetch
-        run: echo "PR_FETCH_DEPTH=$(( ${{ github.event.pull_request.commits }} + 1 ))" >> "${GITHUB_ENV}"
-
-      - name: Fetch PR sources
-        uses: actions/checkout@v4
-        with:
-          ref: ${{ github.event.pull_request.head.ref }}
-          fetch-depth: ${{ env.PR_FETCH_DEPTH }}
-          path: pr-sources
-
-      # We need to make sure that we aren't executing/using any code from the
-      # PR for security reasons as we're using pull_request_target. Checkout
-      # the target branch with the necessary files.
-      - name: Fetch LLVM Sources
-        uses: actions/checkout@v4
-        with:
-          sparse-checkout: |
-            llvm/utils/git/requirements_formatting.txt
-            llvm/utils/git/code-format-helper.py
-          sparse-checkout-cone-mode: false
-          path: llvm-sources
+          fetch_depth: 100 # Fetches only the last 10 commits
 
       - name: "Listed files"
         run: |
@@ -54,21 +34,21 @@ jobs:
         with:
           python-version: '3.11'
           cache: 'pip'
-          cache-dependency-path: 'llvm-sources/llvm/utils/git/requirements_formatting.txt'
+          cache-dependency-path: 'llvm/utils/git/requirements_formatting.txt'
 
       - name: Install python dependencies
-        run: pip install -r llvm-sources/llvm/utils/git/requirements_formatting.txt
+        run: pip install -r llvm/utils/git/requirements_formatting.txt
 
       - name: Run code formatter
         env:
           GITHUB_PR_NUMBER: ${{ github.event.pull_request.number }}
-          PR_DEPTH: ${{ github.event.pull_request.commits }}
+          START_REV: ${{ github.event.pull_request.base.sha }}
+          END_REV: ${{ github.event.pull_request.head.sha }}
           CHANGED_FILES: ${{ steps.changed-files.outputs.all_changed_files }}
-        working-directory: ./pr-sources
         run: |
-          python ../llvm-sources/llvm/utils/git/code-format-helper.py \
+          python llvm/utils/git/code-format-helper.py \
             --token ${{ secrets.GITHUB_TOKEN }} \
             --issue-number $GITHUB_PR_NUMBER \
-            --start-rev HEAD~$PR_DEPTH \
-            --end-rev HEAD \
+            --start-rev $START_REV \
+            --end-rev $END_REV \
             --changed-files "$CHANGED_FILES"