Simplify space checker (#472)

Author: vkucera

.github/workflows/space-checker.yml

@@ -11,25 +11,17 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0 # needed to get the full history
-      - name: Fetch upstream
-        run: |
-          # Fetch the main upstream branch to find the common ancestor
-          git config --global user.name "Nemo" # required on some servers
-          git remote add upstream https://github.com/AliceO2Group/Run3Analysisvalidation.git || exit 1
-          git fetch upstream ${{ env.MAIN_BRANCH }} || exit 1
       - name: Find bad spacing
         run: |
           # Find tabs and trailing whitespaces in modified text files and show where they are
           status_tab=0
           status_trail=0
-          # Get the common ancestor of the current branch and the main upstream branch
-          BASE_COMMIT=$(git merge-base HEAD upstream/${{ env.MAIN_BRANCH }})
-          echo "Diffing against: $BASE_COMMIT"
           # loop over changed files
-          for f in $(git diff --diff-filter d --name-only "$BASE_COMMIT"); do
+          # Diff against the common ancestor of the source branch and the main branch.
+          for f in $(git diff --diff-filter d --name-only origin/${{ env.MAIN_BRANCH }}...); do
             # ignore binary files
             file -bi "$f" | grep -q "charset=binary" && continue
             echo "Scanning file: $f"
@@ -54,7 +46,7 @@ jobs:
             # shellcheck disable=2028
             echo "::warning::Fix the errors in your editor (or with a command)
             Command tips:
-            - Get list of files you changed: git diff --diff-filter d --name-only \$(git merge-base HEAD upstream/${{ env.MAIN_BRANCH }})
+            - Get list of files you changed: git diff --diff-filter d --name-only ${{ env.MAIN_BRANCH }}...
             - Replace each tab with two spaces: sed -i 's/\\t/  /g' <files>
             - Remove trailing whitespaces: sed -i 's/[[:space:]]*$//' <files>"
             echo "::warning::To avoid these errors, configure your editor to: