Fetch PR Body before updating

src/github.ts

@@ -1,7 +1,7 @@
 import * as core from '@actions/core';
 import * as octokit from '@octokit/rest';
 import similarity from 'string-similarity';
-import { CreateIssueCommentParams, PullRequestUpdateParams, UpdateLabelParams } from './types';
+import { CreateIssueCommentParams, PullRequestParams, PullRequestUpdateParams, UpdateLabelParams } from './types';
 import { BOT_BRANCH_PATTERNS, DEFAULT_BRANCH_PATTERNS, MARKER_REGEX } from './constants';
 
 export class GitHub {
@@ -68,6 +68,25 @@ export class GitHub {
     }
   };
 
+  /** Get the PR description. */
+  getPRDescription = async (pr: PullRequestParams): Promise<string | null> => {
+    try {
+      const { owner, repo, number } = pr;
+      const { data } = await this.client.pulls.get({
+        owner,
+        repo,
+        // eslint-disable-next-line @typescript-eslint/naming-convention
+        pull_number: number,
+      });
+      return data.body;
+    } catch (error) {
+      console.error(error);
+      // eslint-disable-next-line i18n-text/no-en
+      core.setFailed((error as Error)?.message ?? 'Failed to fetch latest PR description');
+      throw error;
+    }
+  };
+
   /** Get a comment based on story title and PR title similarity. */
   getPRTitleComment = (storyTitle: string, prTitle: string): string => {
     const matchRange: number = similarity.compareTwoStrings(storyTitle, prTitle);

src/main.ts

@@ -97,7 +97,6 @@ async function run(): Promise<void> {
       base: { ref: baseBranch },
       head: { ref: headBranch },
       number: prNumber = 0,
-      body: prBody = '',
       additions = 0,
       title = '',
     } = pullRequest as PullRequestParams;
@@ -149,6 +148,11 @@ async function run(): Promise<void> {
 
       await gh.addLabels({ ...commonPayload, labels });
 
+      const pr = pullRequest as PullRequestParams;
+      pr.owner = owner;
+      pr.repo = repo;
+      const prBody = await gh.getPRDescription(pr);
+
       if (GitHub.shouldUpdatePRDescription(prBody)) {
         console.log('Updating PR description…', prBody);
 

src/types.ts

@@ -14,7 +14,7 @@ export interface PullRequestUpdateParams extends UpdateParams {
   body?: string;
 }
 
-export interface PullRequestParams {
+export interface PullRequestParams extends UpdateParams {
   number: number;
   // eslint-disable-next-line @typescript-eslint/naming-convention
   html_url?: string;