Use fallback reviewers for bot (apache#33155)

scripts/ci/pr-bot/findPrsNeedingAttention.ts

@@ -114,13 +114,16 @@ async function assignToNewReviewers(
   reviewersToExclude.push(pull.user.login);
   const reviewersForLabels: { [key: string]: string[] } =
     reviewerConfig.getReviewersForLabels(labelObjects, reviewersToExclude);
+  const fallbackReviewers =
+    reviewerConfig.getFallbackReviewers();
   for (const labelObject of labelObjects) {
     const label = labelObject.name;
     let availableReviewers = reviewersForLabels[label];
     if (availableReviewers && availableReviewers.length > 0) {
       let reviewersState = await stateClient.getReviewersForLabelState(label);
       let chosenReviewer = await reviewersState.assignNextCommitter(
-        availableReviewers
+        availableReviewers,
+        fallbackReviewers
       );
       reviewerStateToUpdate[label] = reviewersState;
       prState.reviewersAssignedForLabels[label] = chosenReviewer;

scripts/ci/pr-bot/processNewPrs.ts

@@ -217,8 +217,11 @@ async function processPull(
         );
         const availableReviewers =
           reviewerConfig.getReviewersForLabel(labelOfReviewer);
+        const fallbackReviewers =
+          reviewerConfig.getFallbackReviewers();
         const chosenCommitter = await reviewersState.assignNextCommitter(
-          availableReviewers
+          availableReviewers,
+          fallbackReviewers
         );
         prState.reviewersAssignedForLabels[labelOfReviewer] = chosenCommitter;
         prState.committerAssigned = true;

scripts/ci/pr-bot/shared/reviewersForLabel.ts

@@ -75,7 +75,10 @@ export class ReviewersForLabel {
   // Given the up to date list of available reviewers (excluding the author),
   // returns the next reviewer up based on who has reviewed least recently.
   // Updates this object to reflect their assignment.
-  async assignNextCommitter(availableReviewers: string[]): Promise<string> {
+  async assignNextCommitter(
+    availableReviewers: string[],
+    fallbackReviewers: string[]
+  ): Promise<string> {
     let earliestDate = Date.now();
     let earliestCommitter: string = "";
 
@@ -94,7 +97,9 @@ export class ReviewersForLabel {
     }
 
     if (!earliestCommitter) {
-      throw new Error(`No committers available for label ${this.label}`);
+      console.log(`No committers available for label ${this.label}`);
+      console.log(`Using fallbackReviewers label instead of ${this.label}`);
+      return this.assignNextCommitter(fallbackReviewers, fallbackReviewers);
     }
     this.dateOfLastReviewAssignment[earliestCommitter] = Date.now();
     return earliestCommitter;