[GHF] Bot should reopen PR after revert (pytorch#112614)

Fixes pytorch/test-infra#4692
Test plan, see malfet/deleteme#58 (comment) / https://github.com/malfet/deleteme/actions/runs/6723011476
Pull Request resolved: pytorch#112614
Approved by: https://github.com/seemethere, https://github.com/ezyang
ghstack dependencies: pytorch#112613

.github/scripts/github_utils.py

@@ -174,3 +174,8 @@ def gh_fetch_merge_base(org: str, repo: str, base: str, head: str) -> str:
         warnings.warn(f"Failed to get merge base for {base}...{head}: {error}")
 
     return merge_base
+
+
+def gh_update_pr_state(org: str, repo: str, pr_num: int, state: str = "open") -> None:
+    url = f"{GITHUB_API_URL}/repos/{org}/{repo}/pulls/{pr_num}"
+    gh_fetch_url(url, method="PATCH", data={"state": state})

.github/scripts/trymerge.py

@@ -30,6 +30,7 @@
     gh_fetch_url,
     gh_post_commit_comment,
     gh_post_pr_comment,
+    gh_update_pr_state,
     GitHubComment,
 )
 
@@ -1803,6 +1804,7 @@ def post_comment(msg: str) -> None:
     if not dry_run:
         pr.add_numbered_label("reverted")
         gh_post_commit_comment(pr.org, pr.project, commit_sha, revert_msg)
+        gh_update_pr_state(pr.org, pr.project, pr.pr_num)
 
 
 def prefix_with_github_url(suffix_str: str) -> str: