ci (check-whitespace): suggest fixes for errors

Make the errors more visible by adding them to the job summary and
display the git commands that will usually fix the problem.

Signed-off-by: Chris. Webster <chris@webstech.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.github/workflows/check-whitespace.yml

@@ -20,31 +20,50 @@ jobs:
     - name: git log --check
       id: check_out
       run: |
-        log=
+        problems=()
         commit=
-        while read dash etc
+        commitText=
+        lastcommit=
+        while read dash sha etc
         do
           case "${dash}" in
           "---")
-            commit="${etc}"
+            if test -z "${commit}"
+            then
+              lastcommit=${sha}
+            fi
+            commit="${sha}"
+            commitText="${sha} ${etc}"
             ;;
           "")
             ;;
           *)
             if test -n "${commit}"
             then
-              log="${log}\n${commit}"
+              problems+=("" "--- ${commitText}")
               echo ""
-              echo "--- ${commit}"
+              echo "--- ${commitText}"
+              commit=
             fi
-            commit=
-            log="${log}\n${dash} ${etc}"
-            echo "${dash} ${etc}"
+            problems+=("${dash} ${sha} ${etc}")
+            echo "${problems[-1]}"
             ;;
           esac
         done <<< $(git log --check --pretty=format:"---% h% s" ${{github.event.pull_request.base.sha}}..)
 
-        if test -n "${log}"
+        if test ${#problems[*]} -gt 0
         then
+          if test -z "${commit}"
+          then
+            lastcommit=${{github.event.pull_request.base.sha}}
+          fi
+          echo "A whitespace issue was found in one or more of the commits." >$GITHUB_STEP_SUMMARY
+          echo "" >>$GITHUB_STEP_SUMMARY
+          echo "Run \`git rebase --whitespace=fix ${lastcommit}\` and \`git push --force\` to correct the problem." >>$GITHUB_STEP_SUMMARY
+          for i in "${problems[@]}"
+          do
+            echo "${i}" >>$GITHUB_STEP_SUMMARY
+          done
+
           exit 2
         fi