workflows/check-by-name: Slim down and prepare for --base

.github/workflows/check-by-name.yml

@@ -75,92 +75,13 @@ jobs:
           ref: ${{ env.mergedSha }}
           # Fetches the merge commit and its parents
           fetch-depth: 2
-      - name: Determining PR git hashes
+      - name: Checking out base branch
         run: |
-          # For pull_request_target this is the same as $GITHUB_SHA
-          echo "baseSha=$(git rev-parse HEAD^1)" >> "$GITHUB_ENV"
-
-          echo "headSha=$(git rev-parse HEAD^2)" >> "$GITHUB_ENV"
+          base=$(mktemp -d)
+          git worktree add "$base" "$(git rev-parse HEAD^1)"
+          echo "base=$base" >> "$GITHUB_ENV"
       - uses: cachix/install-nix-action@7ac1ec25491415c381d9b62f0657c7a028df52a7 # v24
       - name: Fetching the tool
         run: pkgs/test/nixpkgs-check-by-name/scripts/fetch-tool.sh "$GITHUB_BASE_REF" result
       - name: Running nixpkgs-check-by-name
-        run: |
-          echo "Checking whether the check succeeds on the base branch $GITHUB_BASE_REF"
-          git checkout -q "$baseSha"
-          if baseOutput=$(result/bin/nixpkgs-check-by-name . 2>&1); then
-            baseSuccess=1
-          else
-            baseSuccess=
-          fi
-          printf "%s\n" "$baseOutput"
-
-          echo "Checking whether the check would succeed after merging this pull request"
-          git checkout -q "$mergedSha"
-          if mergedOutput=$(result/bin/nixpkgs-check-by-name . 2>&1); then
-            mergedSuccess=1
-            exitCode=0
-          else
-            mergedSuccess=
-            exitCode=1
-          fi
-          printf "%s\n" "$mergedOutput"
-
-          resultToEmoji() {
-            if [[ -n "$1" ]]; then
-              echo ":heavy_check_mark:"
-            else
-              echo ":x:"
-            fi
-          }
-
-          # Print a markdown summary in GitHub actions
-          {
-            echo "| Nixpkgs version | Check result |"
-            echo "| --- | --- |"
-            echo "| Latest base commit | $(resultToEmoji "$baseSuccess") |"
-            echo "| After merging this PR | $(resultToEmoji "$mergedSuccess") |"
-            echo ""
-
-            if [[ -n "$baseSuccess" ]]; then
-              if [[ -n "$mergedSuccess" ]]; then
-                echo "The check succeeds on both the base branch and after merging this PR"
-              else
-                echo "The check succeeds on the base branch, but would fail after merging this PR:"
-                echo "\`\`\`"
-                echo "$mergedOutput"
-                echo "\`\`\`"
-                echo ""
-              fi
-            else
-              if [[ -n "$mergedSuccess" ]]; then
-                echo "The check fails on the base branch, but this PR fixes it, nicely done!"
-              else
-                echo "The check fails on both the base branch and after merging this PR, unknown if only this PRs changes would satisfy the check, the base branch needs to be fixed first."
-                echo ""
-                echo "Failure on the base branch:"
-                echo "\`\`\`"
-                echo "$baseOutput"
-                echo "\`\`\`"
-                echo ""
-                echo "Failure after merging this PR:"
-                echo "\`\`\`"
-                echo "$mergedOutput"
-                echo "\`\`\`"
-                echo ""
-              fi
-            fi
-
-            echo "### Details"
-            echo "- nixpkgs-check-by-name tool:"
-            echo "  - Channel: $channel"
-            echo "  - Nixpkgs commit: [$rev](https://github.com/${GITHUB_REPOSITORY}/commit/$rev)"
-            echo "  - Store path: \`$(realpath result)\`"
-            echo "- Tested Nixpkgs:"
-            echo "  - Base branch: $GITHUB_BASE_REF"
-            echo "  - Latest base branch commit: [$baseSha](https://github.com/${GITHUB_REPOSITORY}/commit/$baseSha)"
-            echo "  - Latest PR commit: [$headSha](https://github.com/${GITHUB_REPOSITORY}/commit/$headSha)"
-            echo "  - Merge commit: [$mergedSha](https://github.com/${GITHUB_REPOSITORY}/commit/$mergedSha)"
-          } >> "$GITHUB_STEP_SUMMARY"
-
-          exit "$exitCode"
+        run: result/bin/nixpkgs-check-by-name .