Specify which files had merge conflicts while cherry-picking (#1934)

When cherry-picking, the bot issues a comment "Cherry-pick was attempted
but there were merge conflicts in the following file(s). Please resolve
manually." But there can be an improvement for the users and specify
which files had the conflicts.

actions/cherry_picker/cherrypick_with_commits.py

@@ -72,7 +72,7 @@
         failure_commits_str += "\n\nThe failed commits are NOT included in the PR. Please resolve manually.\ncc: @bazelbuild/triage"
         issue_comment_body += failure_commits_str
 elif len(failed_commits):
-    issue_comment_body = "Failed commmits (likely due to merge conflicts): "
+    issue_comment_body = "Failed commits (likely due to merge conflicts): "
     for fail_commit in failed_commits:
         issue_comment_body += f"https://github.com/{input_data['api_repo_name']}/commit/{fail_commit}, "
     issue_comment_body = issue_comment_body[::-1].replace(" ,", ".", 1)[::-1] + "\nPlease resolve manually.\ncc: @bazelbuild/triage"

actions/cherry_picker/functions.py

@@ -144,15 +144,16 @@ def run_cherry_pick(is_prod, commit_id, target_branch_name):
             cherrypick_status = subprocess.run(['git', 'cherry-pick', '-m', '1', commit_id])
 
         lockfile_names = {"src/test/tools/bzlmod/MODULE.bazel.lock", "MODULE.bazel.lock"}
-        unmerged_all_files = str(subprocess.Popen(["git", "diff", "--name-only", "--diff-filter=U"], stdout=subprocess.PIPE).communicate()[0].decode()).split("\n")
+        unmerged_all_files = str(subprocess.Popen(["git", "diff", "--name-only", "--diff-filter=U"], stdout=subprocess.PIPE).communicate()[0].decode()).strip().split("\n")
         unmerged_rest = [j for i,j in enumerate(unmerged_all_files) if j not in lockfile_names and j != ""]
 
         if cherrypick_status.returncode != 0:
             if len(unmerged_rest) == 0 and ("src/test/tools/bzlmod/MODULE.bazel.lock" in changed_files or "MODULE.bazel.lock" in changed_files):
                 update_lockfile(changed_files, True)
             else:
                 subprocess.run(['git', 'cherry-pick', '--skip'])
-                raise Exception("Cherry-pick was attempted, but there may be merge conflict(s). Please resolve manually.\ncc: @bazelbuild/triage")
+                unmerged_files_names = "`" + "`\n`".join(unmerged_all_files) + "`"
+                raise Exception(f"Cherry-pick was attempted but there were merge conflicts in the following file(s). Please resolve manually.\n\n{unmerged_files_names}\n\ncc: @bazelbuild/triage")
         elif cherrypick_status.returncode == 0 and ("src/test/tools/bzlmod/MODULE.bazel.lock" in changed_files or "MODULE.bazel.lock" in changed_files):
             update_lockfile(changed_files, False)