From 377c5d30b03fec06e6ce51c1bd7427412937b0f4 Mon Sep 17 00:00:00 2001
From: Joey Perrott <josephperrott@gmail.com>
Date: Mon, 7 Dec 2020 10:27:13 -0800
Subject: [PATCH] fix(rerun-ci): Fixes the rerun-ci tooling to request a rerun
 from CircleCI

Previously, rerunning CI with the tooling would simply request a new run of the workflow
on the branch.  Instead, we should request a rerun via the API to allow only running
the failing jobs rather than rerunning the successful jobs.
---
 functions/src/plugins/rerun-circleci.ts | 90 ++++++++++++++++++++++---
 1 file changed, 79 insertions(+), 11 deletions(-)

diff --git a/functions/src/plugins/rerun-circleci.ts b/functions/src/plugins/rerun-circleci.ts
index a9ec332..38da121 100644
--- a/functions/src/plugins/rerun-circleci.ts
+++ b/functions/src/plugins/rerun-circleci.ts
@@ -50,25 +50,24 @@ export class RerunCircleCITask extends Task {
     const pullRequest: Github.PullRequestsGetResponse = context.payload.pull_request;
     const sender: Github.PullRequestsGetResponseUser = context.payload.sender;
     const {owner, repo} = context.repo();
-    const circleCiUrl = `https://circleci.com/api/v2/project/gh/${owner}/${repo}/pipeline?circle-token=${CIRCLE_CI_TOKEN}`;
+    const id = this.getCircleCiWorkflowIdForPullRequest(context);
+    const url = `https://circleci.com/api/v2/workflow/${id}/rerun?circle-token=${CIRCLE_CI_TOKEN}`;
     try {
-      const response = await fetch(circleCiUrl, {
+      const response = await (await fetch(url, {
         method: 'POST',
         headers: {
           'Content-Type': 'application/json',
         },
         body: JSON.stringify({
-          branch: `pull/${pullRequest.number}/head`,
+          // Always rerun only the steps which failed.
+          from_failed: true
         })
-      });
-      // Properly handled failures in the CircleCI requests are returned with an HTTP response code
-      // of 200 and json response with a `:message` key mapping to the failure message.  If
-      // `:message` is not defined, the API request was successful.
-      const errMessage = (await response.json())[':message'];
-      if (errMessage) {
-        throw Error(errMessage);
-      }
+      })).json();
+
+      assertNoErrorsInCircleCiResponse(response);
+
     } catch (err) {
+      this.logError(err);
       const error: TypeError = err;
       context.github.issues.createComment({
         body: `@${sender.login} the CircleCI rerun you requested failed.  See details below:
@@ -98,4 +97,73 @@ ${error.message}
     const repositoryConfig = await this.getAppConfig(context);
     return repositoryConfig.rerunCircleCI;
   }
+
+  /**
+   * Get the CircleCI workflow id of the first discovered CircleCI status in the statuses.  Since
+   * only one workflow is run on each PR, all CircleCI statuses will track back to the same
+   * workflow id.
+   */
+  private async getCircleCiWorkflowIdForPullRequest(context: Context) {
+    /** The target url of the discovered CircleCI status. */
+    let targetUrl: string;
+    /** The pull request which triggered the bot action. */
+    const pullRequest: Github.PullRequestsGetResponse = context.payload.pull_request;
+    /** The owner and repository name. */
+    const {owner, repo} = context.repo();
+    /** The list of statuses for the latest ref of the PR. */
+    const {statuses} = (await context.github.repos.getCombinedStatusForRef({
+      owner, repo, ref: pullRequest.head.ref
+    })).data;
+
+    for (const status of statuses) {
+      if (status.context.startsWith('ci/circleci:')) {
+        targetUrl = status.target_url;
+        break;
+      }
+    }
+
+    if (targetUrl === undefined) {
+      throw Error('No status for a CircleCI workflow was found on the pull request to be rerun.');
+    }
+
+    /**
+     * The matcher results of the regex to select the job ID of the job which the status represents.
+     */
+    const jobIdMatcher = targetUrl.match(`https://circleci.com/gh/${owner}/${repo}/(\d+)\?`);
+
+    if (jobIdMatcher === null) {
+      throw Error('Unable to determine the job ID for the CircleCI job creating the status');
+    }
+
+    /** The job ID. */
+    const job = jobIdMatcher[0];
+    /** The full url of the API request to CircleCI. */
+    const url = `https://circleci.com/api/v2/project/gh/${owner}/${repo}/job/${job}?circle-token=${CIRCLE_CI_TOKEN}`;
+    /** The API response from the CircleCI request. */
+    const response = (await (await fetch(url, {
+      method: 'GET',
+      headers: {
+        'Content-Type': 'application/json',
+      }
+    })).json());
+
+    assertNoErrorsInCircleCiResponse(response);
+
+    return response.latest_workflow.id;
+  }
+}
+
+
+
+/**
+ * Checks the provided response from CircleCI's API to determine if it is an error message.
+ *
+ * Properly handled failures in the CircleCI requests are returned with an HTTP response code of 200
+ * and json response with a `:message` key mapping to the failure message.  If `:message` is not
+ * defined, the API request was successful.
+ */
+function assertNoErrorsInCircleCiResponse(response: any) {
+  if (response[':message'] !== undefined) {
+    throw Error(response[':message']);
+  }
 }