Fix false "not rebaseable" by retrying when GitHub returns null

GitHub's API computes rebaseable asynchronously and returns null while
pending. The code already retried for unknown mergeableState but treated
null rebaseable as false, causing eligible PRs to be skipped.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: JBlaak

src/Github/Api/getPullRequestService.ts

@@ -7,7 +7,7 @@ export interface GetPullRequestService {
 
 export interface ApiGetPullRequest {
     draft: boolean;
-    rebaseable: boolean;
+    rebaseable: boolean | null;
     mergeableState: MergeableState;
     labels: string[];
 }

src/Github/__tests__/githubPullRequestInfoProvider.test.ts

@@ -91,4 +91,45 @@ describe('The pull request info is retried', () => {
         /* Then */
         expect(result.mergeableState).toBe('unknown');
     });
+
+    it('when rebaseable is null', async () => {
+        /* Given */
+        getPullRequestService.results.push({
+            draft: false,
+            rebaseable: null,
+            mergeableState: 'behind',
+            labels: [],
+        });
+
+        getPullRequestService.results.push({
+            draft: false,
+            rebaseable: true,
+            mergeableState: 'behind',
+            labels: [],
+        });
+
+        /* When */
+        const result = await provider.pullRequestInfoFor('owner', 'repo', 3);
+
+        /* Then */
+        expect(result.rebaseable).toBe(true);
+    });
+
+    it('when rebaseable is null after max retries, defaults to false', async () => {
+        /* Given */
+        for (let i = 0; i < 10; i++) {
+            getPullRequestService.results.push({
+                draft: false,
+                rebaseable: null,
+                mergeableState: 'behind',
+                labels: [],
+            });
+        }
+
+        /* When */
+        const result = await provider.pullRequestInfoFor('owner', 'repo', 3);
+
+        /* Then */
+        expect(result.rebaseable).toBe(false);
+    });
 });

src/Github/githubPullRequestInfoProvider.ts

@@ -11,43 +11,47 @@ export class GithubPullRequestInfoProvider {
         repoName: string,
         pullRequestNumber: number,
     ): Promise<PullRequestInfo> {
-        return promiseRetry<PullRequestInfo>(
-            async (attemptNumber): Promise<PullRequestInfo> => {
-                try {
-                    const {draft, rebaseable, mergeableState, labels} = await this.getPullRequestService.getPullRequest(
-                        ownerName,
-                        repoName,
-                        pullRequestNumber,
-                    );
+        return promiseRetry<PullRequestInfo>(async (attemptNumber): Promise<PullRequestInfo> => {
+            try {
+                const {draft, rebaseable, mergeableState, labels} = await this.getPullRequestService.getPullRequest(
+                    ownerName,
+                    repoName,
+                    pullRequestNumber,
+                );
 
-                    if (attemptNumber < 10 && !draft) {
-                        if (mergeableState === 'unknown' || !mergeableStates.includes(mergeableState)) {
-                            debug(`mergeableState for pull request #${pullRequestNumber} is 'unknown', retrying.`);
-                            throw Error("mergeableState is 'unknown'");
-                        }
+                if (attemptNumber < 10 && !draft) {
+                    if (mergeableState === 'unknown' || !mergeableStates.includes(mergeableState)) {
+                        debug(`mergeableState for pull request #${pullRequestNumber} is 'unknown', retrying.`);
+                        throw Error("mergeableState is 'unknown'");
                     }
+                    if (rebaseable === null) {
+                        debug(
+                            `rebaseable for pull request #${pullRequestNumber} is null (not yet computed), retrying.`,
+                        );
+                        throw Error('rebaseable is null');
+                    }
+                }
 
-                    debug(`rebaseable value for pull request #${pullRequestNumber}: ${String(rebaseable)}`);
-                    debug(`mergeableState for pull request #${pullRequestNumber}: ${mergeableState}`);
+                debug(`rebaseable value for pull request #${pullRequestNumber}: ${String(rebaseable)}`);
+                debug(`mergeableState for pull request #${pullRequestNumber}: ${mergeableState}`);
 
-                    return {
-                        ownerName: ownerName,
-                        repoName: repoName,
-                        number: pullRequestNumber,
-                        draft: draft,
-                        rebaseable: rebaseable,
-                        mergeableState: mergeableState,
-                        labels: labels,
-                    };
-                } catch (error) {
-                    debug(
-                        `Fetching mergeableState for pull request #${pullRequestNumber} failed: "${String(
-                            error,
-                        )}", retrying.`,
-                    );
-                    throw error;
-                }
-            },
-        );
+                return {
+                    ownerName: ownerName,
+                    repoName: repoName,
+                    number: pullRequestNumber,
+                    draft: draft,
+                    rebaseable: rebaseable ?? false,
+                    mergeableState: mergeableState,
+                    labels: labels,
+                };
+            } catch (error) {
+                debug(
+                    `Fetching mergeableState for pull request #${pullRequestNumber} failed: "${String(
+                        error,
+                    )}", retrying.`,
+                );
+                throw error;
+            }
+        });
     }
 }