chore: fix PRlinter dequeuing PRs because of CodeCov

tools/@aws-cdk/prlint/github.ts

@@ -41,25 +41,17 @@ export interface GitHubFile {
  * Returns `success` if they all return a positive result, `failure` if
  * one of them failed for some reason, and `waiting` if the result isn't available
  * yet.
+ *
+ * 'failure' takes precedence over 'waiting' if there's any reason for it.
  */
 export function summarizeRunConclusions(conclusions: Array<CheckRun['conclusion'] | undefined>): 'success' | 'failure' | 'waiting' {
-  for (const concl of conclusions) {
-    switch (concl) {
-      case null:
-      case undefined:
-      case 'action_required':
-        return 'waiting';
-
-      case 'failure':
-      case 'cancelled':
-      case 'timed_out':
-        return 'failure';
+  if (conclusions.some(c => ['failure', 'cancelled', 'timed_out'].includes(c ?? ''))) {
+    return 'failure';
+  }
 
-      case 'neutral':
-      case 'skipped':
-      case 'success':
-        break;
-    }
+  if (conclusions.some(c => c === 'action_required' || c === null || c === undefined)) {
+    return 'waiting';
   }
+
   return 'success';
 }

tools/@aws-cdk/prlint/lint.ts

@@ -267,7 +267,26 @@ export class PullRequestLinter extends PullRequestLinterBase {
 
             switch (summary) {
               case 'failure': return TestResult.failure('CodeCov is indicating a drop in code coverage');
-              case 'waiting': return TestResult.failure('Still waiting for CodeCov results (make sure the build is passing first)');
+              // If we don't know the result of the CodeCov results yet, we pretend that there isn't a problem.
+              //
+              // It would be safer to ask for changes until we're confident that CodeCov has passed, but if we do
+              // that the following sequence of events happens:
+              //
+              // 1. PR is ready to be merged (approved, everything passes)
+              // 2. Mergify enqueues it and merges from main
+              // 3. CodeCov needs to run again
+              // 4. PR linter requests changes because CodeCov result is uncertain
+              // 5. Mergify dequeues the PR because PR linter requests changes
+              //
+              // This looks very confusing and noisy, and also will never fix itself, so the PR ends up unmerged.
+              //
+              // The better solution would probably be not to do a "Request Changes" review, but leave a comment
+              // and create a GitHub "status" on the PR to say 'success/pending/failure', and make it required.
+              // (https://github.com/aws/aws-cdk/issues/33136)
+              //
+              // For now, not doing anything with a 'waiting' status is a smaller delta, and the race condition posed by it is
+              // unlikely to happen given that there are much slower jobs that the merge is blocked on anyway.
+              case 'waiting': return TestResult.success();
               case 'success': return TestResult.success();
             }
           },

tools/@aws-cdk/prlint/test/lint.test.ts

@@ -1183,7 +1183,7 @@ describe('for any PR', () => {
   };
 
   const ARBITRARY_FILES: GitHubFile[] = [{
-    filename: 'packages/aws-cdk-lib/region-info/build-tools/metadata.ts',
+    filename: 'README.md',
   }];
 
   test('deletes old comments', async () => {
@@ -1212,7 +1212,8 @@ describe('for any PR', () => {
     }));
   });
 
-  test('missing CodeCov runs lead to a failure', async () => {
+  test('missing CodeCov run does not lead to request changes', async () => {
+    // Not ideal, but https://github.com/aws/aws-cdk/issues/33136
     // GIVEN
     const prLinter = configureMock(ARBITRARY_PR, ARBITRARY_FILES);
     prLinter.octomock.checks.listForRef.mockReturnValue({ data: [] });
@@ -1221,9 +1222,7 @@ describe('for any PR', () => {
     const result = await prLinter.validatePullRequestTarget();
 
     // THEN
-    expect(result.requestChanges?.failures).toContainEqual(
-      expect.stringContaining('Still waiting for CodeCov results'),
-    );
+    expect(result.requestChanges).toBeUndefined();
   });
 
   test('failing CodeCov runs lead to a failure', async () => {