[llvm] [CI] Make premerge_advisor_explain write comments (PR #166605)

[David Spickett via llvm-commits]

================
@@ -4,20 +4,58 @@
 """Script for getting explanations from the premerge advisor."""
 
 import argparse
-import os
 import platform
 import sys
+import json
 
 import requests
+import github
+import github.PullRequest
 
 import generate_test_report_lib
 
 PREMERGE_ADVISOR_URL = (
     "http://premerge-advisor.premerge-advisor.svc.cluster.local:5000/explain"
 )
+COMMENT_TAG = "<!--PREMERGE ADVISOR COMMENT: {platform}-->"
 
 
-def main(commit_sha: str, build_log_files: list[str]):
+def get_comment_id(platform: str, pr: github.PullRequest.PullRequest) -> int | None:
+    platform_comment_tag = COMMENT_TAG.format(platform=platform)
+    for comment in pr.as_issue().get_comments():
+        if platform_comment_tag in comment.body:
+            return comment.id
+    return None
+
+
+def get_comment(
+    github_token: str,
+    pr_number: int,
+    body: str,
+) -> dict[str, str]:
+    repo = github.Github(github_token).get_repo("llvm/llvm-project")
+    pr = repo.get_issue(pr_number).as_pull_request()
+    comment = {"body": body}
+    comment_id = get_comment_id(platform.system(), pr)
+    if comment_id:
+        comment["id"] = comment_id
+
+
+def main(
+    commit_sha: str,
+    build_log_files: list[str],
+    github_token: str,
+    pr_number: int,
+    return_code: int,
+):
+    if return_code == 0:
+        with open("comment", "w") as comment_file_handle:
+            comment = get_comment(
+                ":white_check_mark: With the latest revision this PR passed "
+                "the premerge checks."
+            )
+            if comment["id"]:
----------------
DavidSpickett wrote:

That's great, thanks.

I didn't realise we needed to write out an empty file even when there's no comment to make so I'm glad you've included that detail.

https://github.com/llvm/llvm-project/pull/166605