From 441d392c35b7574f13f7b2fedd504c1d9d6e72af Mon Sep 17 00:00:00 2001
From: arcwiser <arcwiser@users.noreply.github.com>
Date: Mon, 12 Oct 2026 23:53:47 +1100
Subject: [PATCH] fix(tools): batch pr_overlap fetch refspecs

---
 tools/pr_overlap.py            |  4 +++-
 tools/tests/test_pr_overlap.py | 16 ++++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/tools/pr_overlap.py b/tools/pr_overlap.py
index 183d01311..819c38e0c 100644
--- a/tools/pr_overlap.py
+++ b/tools/pr_overlap.py
@@ -13,6 +13,7 @@ DEPENDS = re.compile(r'Depends on:[ \t]*((?:#\d+\b(?:(?:[ \t]*,[ \t]*(?:and[ \t]
 PLAIN_DEPENDS = re.compile(r'Depends on[ \t]+(#\d+\b(?:(?:[ \t]*,[ \t]*(?:and[ \t]+)?|[ \t]+and[ \t]+)#\d+\b)*)')
 HUNK = re.compile(r"^@@ -(\d+)(?:,(\d+))?", re.M)
 MARKER = "<!-- pr-overlap -->"
+FETCH_REFS = 100
 
 
 def git(*args):
@@ -51,7 +52,8 @@ def open_prs(base):
 
 def fetch(base, prs):
     refspecs = [f"+refs/heads/{base}:refs/pr/base"] + [f"+{pr['sha']}:{pr['ref']}" for pr in prs.values()]
-    git("fetch", "--no-tags", "-q", f"https://github.com/{REPO}.git", *refspecs)
+    for start in range(0, len(refspecs), FETCH_REFS):
+        git("fetch", "--no-tags", "-q", f"https://github.com/{REPO}.git", *refspecs[start:start + FETCH_REFS])
 
 
 def merge(*args):
diff --git a/tools/tests/test_pr_overlap.py b/tools/tests/test_pr_overlap.py
index 31488bb0c..f250ca15d 100644
--- a/tools/tests/test_pr_overlap.py
+++ b/tools/tests/test_pr_overlap.py
@@ -69,6 +69,22 @@ class FetchTests(unittest.TestCase):
             "+refs/heads/main:refs/pr/base", f"+{'a' * 40}:refs/pr/7", f"+{'b' * 40}:refs/pr/9",
         )
 
+    def test_batches_large_sets_of_pull_request_heads(self):
+        prs = {
+            number: {
+                "ref": f"refs/pr/{number}", "sha": f"{number:040x}",
+                "author": "contributor", "depends": set(),
+            }
+            for number in range(250)
+        }
+        with patch.object(pr_overlap, "REPO", "owner/project", create=True), \
+                patch.object(pr_overlap, "git", return_value="") as git:
+            pr_overlap.fetch("main", prs)
+        self.assertEqual(git.call_count, 3)
+        self.assertEqual([len(call.args) - 4 for call in git.call_args_list], [100, 100, 51])
+        self.assertEqual(git.call_args_list[0].args[4], "+refs/heads/main:refs/pr/base")
+        self.assertEqual(git.call_args_list[-1].args[-1], "+00000000000000000000000000000000000000f9:refs/pr/249")
+
 
 if __name__ == "__main__":
     unittest.main()