fix: Skip reviewer runs for unchanged PR diffs (#1335)

* fix: skip unchanged reviewer diffs

* fix: queue active reviewer pushes

---------

Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>

agent/webapp.py

@@ -9,6 +9,7 @@ import uuid
 from collections.abc import AsyncIterator
 from contextlib import asynccontextmanager
 from typing import Any
+from urllib.parse import quote
 
 import httpx
 from fastapi import BackgroundTasks, FastAPI, HTTPException, Request
@@ -1877,6 +1878,58 @@ async def _fetch_open_pr_for_branch(
     return pr if isinstance(pr, dict) else None
 
 
+def _normalized_diff_hash(diff_text: str) -> str:
+    normalized = "\n".join(
+        line.rstrip() for line in diff_text.replace("\r\n", "\n").replace("\r", "\n").split("\n")
+    ).strip()
+    return hashlib.sha256(normalized.encode("utf-8")).hexdigest()
+
+
+async def _fetch_compare_diff(
+    repo_config: dict[str, str], base_ref: str, head_ref: str, *, token: str
+) -> str | None:
+    owner = repo_config.get("owner", "")
+    repo = repo_config.get("name", "")
+    if not owner or not repo or not base_ref or not head_ref:
+        return None
+
+    base = quote(base_ref, safe="")
+    head = quote(head_ref, safe="")
+    headers = {
+        "Accept": "application/vnd.github.diff",
+        "Authorization": f"Bearer {token}",
+        "X-GitHub-Api-Version": "2022-11-28",
+    }
+    async with httpx.AsyncClient() as http_client:
+        try:
+            response = await http_client.get(
+                f"https://api.github.com/repos/{owner}/{repo}/compare/{base}...{head}",
+                headers=headers,
+            )
+            response.raise_for_status()
+        except httpx.HTTPError:
+            logger.exception(
+                "Failed to fetch compare diff for %s/%s %s...%s", owner, repo, base_ref, head_ref
+            )
+            return None
+    return response.text
+
+
+async def _is_pr_diff_unchanged_since_last_review(
+    repo_config: dict[str, str],
+    *,
+    base_ref: str,
+    last_reviewed_sha: str,
+    head_sha: str,
+    token: str,
+) -> bool:
+    previous_diff = await _fetch_compare_diff(repo_config, base_ref, last_reviewed_sha, token=token)
+    current_diff = await _fetch_compare_diff(repo_config, base_ref, head_sha, token=token)
+    if previous_diff is None or current_diff is None:
+        return False
+    return _normalized_diff_hash(previous_diff) == _normalized_diff_hash(current_diff)
+
+
 async def _get_thread_metadata_safe(thread_id: str) -> dict[str, Any] | None:
     """Fetch a thread's metadata; return ``None`` if the thread doesn't exist."""
     langgraph_client = get_client(url=LANGGRAPH_URL)
@@ -2025,6 +2078,26 @@ async def process_github_push_event(payload: dict[str, Any]) -> None:
     if isinstance(last_reviewed_sha, str) and last_reviewed_sha == head_sha:
         logger.info("Push to %s ignored: head_sha unchanged from last_reviewed_sha", head_ref)
         return
+    thread_active = await is_thread_active(thread_id)
+    if (
+        not thread_active
+        and isinstance(last_reviewed_sha, str)
+        and last_reviewed_sha
+        and await _is_pr_diff_unchanged_since_last_review(
+            repo_config,
+            base_ref=base_ref,
+            last_reviewed_sha=last_reviewed_sha,
+            head_sha=head_sha,
+            token=app_token,
+        )
+    ):
+        await set_reviewer_thread_metadata(thread_id, last_reviewed_sha=head_sha)
+        logger.info(
+            "Push to %s ignored: PR diff unchanged since last reviewed SHA %s",
+            head_ref,
+            last_reviewed_sha,
+        )
+        return
 
     langgraph_client = get_client(url=LANGGRAPH_URL)
     if not await _ensure_thread_exists_for_metadata(thread_id, langgraph_client):
@@ -2065,7 +2138,6 @@ async def process_github_push_event(payload: dict[str, Any]) -> None:
         last_reviewed_sha=last_reviewed_sha if isinstance(last_reviewed_sha, str) else "",
     )
 
-    thread_active = await is_thread_active(thread_id)
     if thread_active:
         logger.info("Reviewer thread %s busy, queuing push re-review", thread_id)
         await queue_message_for_thread(thread_id, re_review_prompt)

tests/test_reviewer_watch.py

@@ -74,6 +74,117 @@ async def test_push_event_skips_when_thread_not_watching() -> None:
     fake_client.runs.create.assert_not_called()
 
 
+@pytest.mark.asyncio
+async def test_push_event_skips_when_pr_diff_unchanged_since_last_review() -> None:
+    payload = _push_payload(ref="refs/heads/feat-x", after="newsha")
+    pr = {
+        "number": 7,
+        "html_url": "https://github.com/lc/repo/pull/7",
+        "title": "T",
+        "head": {"sha": "newsha", "ref": "feat-x"},
+        "base": {"sha": "basesha", "ref": "main"},
+    }
+    fake_client = MagicMock()
+    fake_client.runs.create = AsyncMock()
+    set_metadata = AsyncMock()
+
+    with (
+        patch("agent.webapp._is_repo_allowed_for_reviewer", return_value=True),
+        patch(
+            "agent.webapp.get_github_app_installation_token_with_expiry",
+            new_callable=AsyncMock,
+            return_value=("t", None),
+        ),
+        patch(
+            "agent.webapp._fetch_open_pr_for_branch",
+            new_callable=AsyncMock,
+            return_value=pr,
+        ),
+        patch(
+            "agent.webapp._get_thread_metadata_safe",
+            new_callable=AsyncMock,
+            return_value={
+                "kind": "reviewer",
+                "watch": True,
+                "last_reviewed_sha": "oldsha",
+            },
+        ),
+        patch(
+            "agent.webapp._fetch_compare_diff",
+            new_callable=AsyncMock,
+            side_effect=["same diff", "same diff"],
+        ),
+        patch("agent.webapp.set_reviewer_thread_metadata", new=set_metadata),
+        patch("agent.webapp.is_thread_active", new_callable=AsyncMock, return_value=False),
+        patch("agent.webapp.get_client", return_value=fake_client),
+    ):
+        await webapp.process_github_push_event(payload)
+
+    fake_client.runs.create.assert_not_called()
+    set_metadata.assert_awaited_once()
+    assert set_metadata.await_args.kwargs["last_reviewed_sha"] == "newsha"
+
+
+@pytest.mark.asyncio
+async def test_push_event_queues_when_thread_active_even_if_pr_diff_unchanged() -> None:
+    payload = _push_payload(ref="refs/heads/feat-x", after="newsha")
+    pr = {
+        "number": 7,
+        "html_url": "https://github.com/lc/repo/pull/7",
+        "title": "T",
+        "head": {"sha": "newsha", "ref": "feat-x"},
+        "base": {"sha": "basesha", "ref": "main"},
+    }
+    fake_client = MagicMock()
+    fake_client.runs.create = AsyncMock()
+    fetch_compare_diff = AsyncMock()
+    queue_message = AsyncMock()
+
+    with (
+        patch("agent.webapp._is_repo_allowed_for_reviewer", return_value=True),
+        patch(
+            "agent.webapp.get_github_app_installation_token_with_expiry",
+            new_callable=AsyncMock,
+            return_value=("t", None),
+        ),
+        patch(
+            "agent.webapp._fetch_open_pr_for_branch",
+            new_callable=AsyncMock,
+            return_value=pr,
+        ),
+        patch(
+            "agent.webapp._get_thread_metadata_safe",
+            new_callable=AsyncMock,
+            return_value={
+                "kind": "reviewer",
+                "watch": True,
+                "last_reviewed_sha": "oldsha",
+            },
+        ),
+        patch("agent.webapp._fetch_compare_diff", new=fetch_compare_diff),
+        patch(
+            "agent.webapp._ensure_thread_exists_for_metadata",
+            new_callable=AsyncMock,
+            return_value=True,
+        ),
+        patch(
+            "agent.webapp.persist_encrypted_github_token",
+            new_callable=AsyncMock,
+            return_value="enc",
+        ),
+        patch("agent.webapp.set_reviewer_thread_metadata", new_callable=AsyncMock),
+        patch("agent.webapp.is_thread_active", new_callable=AsyncMock, return_value=True),
+        patch("agent.webapp.queue_message_for_thread", new=queue_message),
+        patch("agent.webapp.get_client", return_value=fake_client),
+    ):
+        await webapp.process_github_push_event(payload)
+
+    fetch_compare_diff.assert_not_called()
+    fake_client.runs.create.assert_not_called()
+    queue_message.assert_awaited_once()
+    assert "newsha" in queue_message.await_args.args[1]
+
+
 @pytest.mark.asyncio
 async def test_push_event_triggers_re_review_run_when_watching() -> None:
     payload = _push_payload(ref="refs/heads/feat-x", after="newsha")
@@ -113,6 +224,11 @@ async def test_push_event_triggers_re_review_run_when_watching() -> None:
                 "last_reviewed_sha": "oldsha",
             },
         ),
+        patch(
+            "agent.webapp._fetch_compare_diff",
+            new_callable=AsyncMock,
+            side_effect=["old diff", "new diff"],
+        ),
         patch(
             "agent.webapp._ensure_thread_exists_for_metadata",
             new_callable=AsyncMock,