chore: prlinter should use HEAD instead of base commit (#25779)

The `sha` for the `pull_request_target` event is for the base branch (i.e. `main`) so we were checking the status from the last commit to `main`. We should instead get the `sha` from the event payload which contains the `head` sha.

This also fixes an issue processing the status event where we were trying to parse the latest commit from the status URL, but that value is always equal to `{sha}`. Instead get it from the `head` info.

Added some debug logs to help us see what is getting processed. 

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: corymhall

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

@@ -2,7 +2,7 @@ import * as core from '@actions/core';
 import * as github from '@actions/github';
 import { Octokit } from '@octokit/rest';
 import * as linter from './lint';
-import { StatusEvent } from '@octokit/webhooks-definitions/schema';
+import { StatusEvent, PullRequestEvent } from '@octokit/webhooks-definitions/schema';
 
 async function run() {
   const token: string = process.env.GITHUB_TOKEN!;
@@ -11,25 +11,28 @@ async function run() {
   try {
     switch (github.context.eventName) {
       case 'status':
-        const pr = await linter.PullRequestLinter.getPRFromCommit(client, 'aws', 'aws-cdk', github.context.payload.sha);
+        const statusPayload = github.context.payload as StatusEvent;
+        const pr = await linter.PullRequestLinter.getPRFromCommit(client, 'aws', 'aws-cdk', statusPayload.sha);
         if (pr) {
           const prLinter = new linter.PullRequestLinter({
             client,
             owner: 'aws',
             repo: 'aws-cdk',
             number: pr.number,
           });
+          console.log('validating status event');
           await prLinter.validateStatusEvent(pr, github.context.payload as StatusEvent);
         }
         break;
       default:
+        const payload = github.context.payload as PullRequestEvent;
         const prLinter = new linter.PullRequestLinter({
           client,
           owner: github.context.repo.owner,
           repo: github.context.repo.repo,
           number: github.context.issue.number,
         });
-        await prLinter.validatePullRequestTarget(github.context.sha);
+        await prLinter.validatePullRequestTarget(payload.pull_request.head.sha);
     }
   } catch (error: any) {
     core.setFailed(error.message);

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

@@ -183,6 +183,7 @@ export class PullRequestLinter {
     const prs = await client.search.issuesAndPullRequests({
       q: sha,
     });
+    console.log('Found PRs: ', prs);
     const foundPr = prs.data.items.find(pr => pr.state === 'open');
     if (foundPr) {
       // need to do this because the list PR response does not have
@@ -192,9 +193,9 @@ export class PullRequestLinter {
         repo,
         pull_number: foundPr.number,
       })).data;
-      const latestCommit = pr.statuses_url.split('/').pop();
+      console.log(`PR: ${foundPr.number}: `, pr);
       // only process latest commit
-      if (latestCommit === sha) {
+      if (pr.head.sha === sha) {
         return pr;
       }
     }