fix(ci): sweep PRs with unknown mergeability — stuck merge-ref is the target pathology

steipete · steipete · commit e5c9cdfbf59c · 2026-07-18T21:14:24.000+01:00
Live verification showed dropped-CI PRs report mergeable=null and
mergeable_state=unknown indefinitely: the stuck merge-ref computation is
the same failure that dropped their CI, and close/reopen is what
un-sticks it. The pending-mergeability skip therefore made the primary
repair population permanently unsweepable (three real dropped PRs skipped
across three consecutive sweeps). Keep skipping computed conflicts; a
not-yet-computed conflict costs at most one budgeted re-fire.
diff --git a/scripts/github/pr-ci-sweeper.mjs b/scripts/github/pr-ci-sweeper.mjs
@@ -37,15 +37,14 @@ export function classifyPrForSweep({ pr, ciRuns, botCloseCount, now }) {
     return { action: "skip", reason: "recently-updated" };
   }
   // A conflicted PR legitimately has no merge ref; CI cannot attach until the
-  // author resolves, so re-firing would loop forever.
+  // author resolves, so re-firing would loop forever. Null/unknown mergeability
+  // is NOT skipped: live testing showed dropped-CI PRs stay mergeable=null
+  // indefinitely (the stuck merge-ref computation IS the pathology), and
+  // close/reopen is what un-sticks it. A not-yet-computed conflict costs at
+  // most one budgeted re-fire before the recomputed false skips it.
   if (pr.mergeable === false) {
     return { action: "skip", reason: "merge-conflict" };
   }
-  // Pending computation resolves by the next hourly sweep; do not close/reopen
-  // on an unknown merge state.
-  if (pr.mergeable === null || pr.mergeable === undefined) {
-    return { action: "skip", reason: "mergeability-pending" };
-  }
   // Closing a PR silently cancels enabled auto-merge and reopening does not
   // restore it; leave those PRs (e.g. generated locale refreshes) to a human.
   if (pr.auto_merge) {
@@ -203,7 +202,7 @@ export async function runPrCiSweeper({ github, context, core, dryRun = false, ap
       fresh.state !== "open" ||
       fresh.head.sha !== pr.head.sha ||
       fresh.auto_merge ||
-      fresh.mergeable !== true
+      fresh.mergeable === false
     ) {
       core.info(`pr-ci-sweeper: #${pr.number} changed during sweep; leaving it alone`);
       continue;
diff --git a/test/scripts/pr-ci-sweeper.test.ts b/test/scripts/pr-ci-sweeper.test.ts
@@ -113,9 +113,9 @@ describe("classifyPrForSweep", () => {
       expected: { action: "skip", reason: "refire-budget-exhausted" },
     },
     {
-      name: "skips while mergeability is still computing",
+      name: "re-fires on unknown mergeability (stuck merge-ref IS the pathology)",
       input: { pr: pr({ mergeable: null }), ciRuns: [], botCloseCount: 0, now: NOW },
-      expected: { action: "skip", reason: "mergeability-pending" },
+      expected: { action: "refire", reason: "ci-run-missing" },
     },
   ];
 
