feat: require approval at current PR head for merge (#471)

Add merge_approval_gate assessment so gitea_merge_pr fails closed when visible APPROVED reviews do not pin the live head SHA. Expose approval_at_current_head and stale_approval_block_reason in review feedback. Document re-review requirement in canonical merge workflow. Closes #471. Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
2026-07-08 00:37:54 -04:00
parent a1de4ab8f9
commit 89582a0f2a
7 changed files with 184 additions and 1 deletions
@@ -0,0 +1,61 @@
+"""Merge approval must pin the current PR head SHA (#471).
+
+Formal APPROVED reviews that predate the live PR head must not satisfy
+``gitea_merge_pr`` eligibility. Pure assessment helpers are isolated here
+for hermetic unit tests apart from MCP HTTP calls.
+"""
+
+from __future__ import annotations
+
+
+def assess_merge_approval_head(
+    *,
+    current_head_sha: str | None,
+    latest_by_reviewer: dict,
+) -> dict:
+    """Return whether a visible approval applies to the live PR head.
+
+    Args:
+        current_head_sha: Current PR head commit SHA.
+        latest_by_reviewer: Map of reviewer login → review entry dicts with
+            ``verdict``, ``dismissed``, and ``reviewed_head_sha`` keys.
+
+    Returns:
+        dict with ``approval_at_current_head``, ``latest_approved_head_sha``,
+        and ``stale_approval_block_reason`` (set when merge must fail closed).
+    """
+    current = (current_head_sha or "").strip()
+    approved_entries = [
+        entry
+        for entry in (latest_by_reviewer or {}).values()
+        if (entry.get("verdict") or "").upper() == "APPROVED"
+        and not entry.get("dismissed")
+    ]
+    at_current = any(
+        (entry.get("reviewed_head_sha") or "").strip() == current
+        for entry in approved_entries
+        if current
+    )
+    latest_approved = None
+    if approved_entries:
+        latest_entry = sorted(
+            approved_entries,
+            key=lambda entry: (
+                entry.get("submitted_at") or "",
+                entry.get("reviewed_head_sha") or "",
+            ),
+        )[-1]
+        latest_approved = (latest_entry.get("reviewed_head_sha") or "").strip() or None
+    reason = None
+    if approved_entries and not at_current:
+        reason = (
+            f"stale approval: approved SHA '{latest_approved}' does not match "
+            f"current live PR head SHA '{current or '(unknown)'}' (fail closed); "
+            "required next action: re-review PR at current head before merge"
+        )
+
+    return {
+        "approval_at_current_head": at_current,
+        "latest_approved_head_sha": latest_approved,
+        "stale_approval_block_reason": reason,
+    }