Try to set branches in env

Author: vkucera

.github/workflows/o2-linter.yml

@@ -3,6 +3,8 @@
 name: O2 linter
 
 "on": [pull_request_target, push]
+env:
+  BRANCH_MAIN: master
 permissions: {}
 
 concurrency:
@@ -16,29 +18,35 @@ jobs:
     permissions:
       pull-requests: write
     steps:
+      - name: Set branches
+        run: |
+          if [[ "${{ github.event_name }}" == "push" ]]; then
+            branch_head="${{ github.ref }}"
+            branch_base="${{ env.BRANCH_MAIN }}"
+          else
+            branch_head="refs/pull/${{ github.event.pull_request.number }}/merge"
+            branch_base="${{ github.event.pull_request.base.ref }}"
+          fi
+          echo BRANCH_HEAD="$branch_head" >> "$GITHUB_ENV"
+          echo BRANCH_BASE="$branch_base" >> "$GITHUB_ENV"
       - name: Checkout Code
         uses: actions/checkout@v4
-        env:
-          branch_head: ${{ github.event_name == 'push' && github.ref || 'refs/pull/'github.event.number'/merge' }}
         with:
-          ref: ${{ env.branch_head }}
+          ref: ${{ env.BRANCH_HEAD }}
           fetch-depth: 0 # needed to get the full history
       - name: Run tests
         id: linter
-        env:
-          branch_head: ${{ github.event_name == 'push' && github.ref || 'refs/pull/'github.event.number'/merge' }}
-          branch_base: ${{ github.event_name == 'push' && 'master' || github.event.pull_request.base.ref }}
         run: |
           # Diff against the common ancestor of the source branch and the target branch.
-          echo "Diffing ${{ env.branch_head }} against ${{ env.branch_base }}."
-          readarray -t files < <(git diff --diff-filter d --name-only origin/${{ env.branch_base }}...)
+          echo "Diffing ${{ env.BRANCH_HEAD }} against ${{ env.BRANCH_BASE }}."
+          readarray -t files < <(git diff --diff-filter d --name-only origin/${{ env.BRANCH_BASE }}...)
           if [ ${#files[@]} -eq 0 ]; then
               echo "::notice::No files to lint."
               echo "linter_ran=0" >> "$GITHUB_OUTPUT"
               exit 0
           fi
           echo "linter_ran=1" >> "$GITHUB_OUTPUT"
-          [ ${{ github.event_name }} == 'pull_request_target' ] && options="-g"
+          [[ "${{ github.event_name }}" == "pull_request_target" ]] && options="-g"
           # shellcheck disable=SC2086 # Ignore unquoted options.
           python3 Scripts/o2_linter.py $options "${files[@]}"
           echo "Tip: If you allow actions in your fork repository, O2 linter will run when you push commits."