bundle-size: Use mergeSha when showing code changes

Uses the [new `mergeSha` field](https://github.com/ampproject/amphtml/pull/33165/files#diff-c141453bcbdbe03ca8414e5b4d425c5b7323e43d524b614455ce13770633509eR191), which resolves ampproject/amphtml#33165 (comment).

bundle-size/api.js

@@ -101,6 +101,7 @@ function erroredCheckOutput(partialBaseSha) {
  *
  * @param {string} headSha commit being checked
  * @param {string} baseSha baseline commit for comparison
+ * @param {string} mergeSha merge commit combining the head and base
  * @param {!Array<string>} bundleSizeDeltas text description of all bundle size
  *   changes.
  * @param {!Array<string>} missingBundleSizes text description of missing bundle
@@ -110,15 +111,19 @@ function erroredCheckOutput(partialBaseSha) {
 function extraBundleSizesSummary(
   headSha,
   baseSha,
+  mergeSha,
   bundleSizeDeltasRequireApproval,
   bundleSizeDeltasAutoApproved,
   missingBundleSizes
 ) {
+  const compareUrl =
+    mergeSha ||
+    `https://github.com/ampproject/amphtml/compare/${baseSha}..${headSha}`;
   let output =
     '## Commit details\n' +
     `**Head commit:** ${headSha}\n` +
     `**Base commit:** ${baseSha}\n` +
-    `**Code changes:** https://github.com/ampproject/amphtml/compare/${baseSha}..${headSha}\n`;
+    `**Code changes:** ${compareUrl}\n`;
 
   if (bundleSizeDeltasRequireApproval.length) {
     output +=
@@ -248,14 +253,22 @@ exports.installApiRouter = (app, router, db, githubUtils) => {
    *
    * @param {!object} check GitHub Check database object.
    * @param {string} baseSha commit SHA of the base commit being compared to.
+   * @param {string} mergeSha commit SHA of the merge commit that combines the head and base.
    * @param {!Map<string, number>} prBundleSizes the bundle sizes of various
    *   dist files in the pull request in KB.
    * @param {boolean} lastAttempt true if this is the last retry.
    * @return {boolean} true if succeeded; false otherwise.
    */
-  async function tryReport(check, baseSha, prBundleSizes, lastAttempt = false) {
+  async function tryReport(
+    check,
+    baseSha,
+    mergeSha,
+    prBundleSizes,
+    lastAttempt = false
+  ) {
     const partialHeadSha = check.head_sha.substr(0, 7);
     const partialBaseSha = baseSha.substr(0, 7);
+    const partialMergeSha = mergeSha.substr(0, 7);
     const github = await app.auth(check.installation_id);
     const githubOptions = {
       owner: check.owner,
@@ -375,6 +388,7 @@ exports.installApiRouter = (app, router, db, githubUtils) => {
     const reportMarkdown = extraBundleSizesSummary(
       partialHeadSha,
       partialBaseSha,
+      partialMergeSha,
       bundleSizeDeltasRequireApproval,
       bundleSizeDeltasAutoApproved,
       missingBundleSizes
@@ -454,13 +468,21 @@ exports.installApiRouter = (app, router, db, githubUtils) => {
 
   router.post('/commit/:headSha/report', async (request, response) => {
     const {headSha} = request.params;
-    const {baseSha, bundleSizes} = request.body;
+    // mergeSha is new, and not all reports will have it.
+    const {baseSha, mergeSha = '', bundleSizes} = request.body;
 
     if (typeof baseSha !== 'string' || !/^[0-9a-f]{40}$/.test(baseSha)) {
       return response
         .status(400)
         .end('POST request to /report must have commit SHA field "baseSha"');
     }
+    if (typeof mergeSha !== 'string' || !/^[0-9a-f]{40}$|^$/.test(mergeSha)) {
+      return response
+        .status(400)
+        .end(
+          'POST request to /report with "mergeSha" field must be a valid commit SHA'
+        );
+    }
     if (
       !bundleSizes ||
       Object.values(bundleSizes).some(value => typeof value !== 'number') ||
@@ -486,7 +508,12 @@ exports.installApiRouter = (app, router, db, githubUtils) => {
     }
 
     try {
-      let reportSuccess = await tryReport(check, baseSha, bundleSizes);
+      let reportSuccess = await tryReport(
+        check,
+        baseSha,
+        mergeSha,
+        bundleSizes
+      );
       if (reportSuccess) {
         response.end();
       } else {
@@ -501,6 +528,7 @@ exports.installApiRouter = (app, router, db, githubUtils) => {
           reportSuccess = await tryReport(
             check,
             baseSha,
+            mergeSha,
             bundleSizes,
             /* lastAttempt */ retriesLeft == 0
           );

bundle-size/test/api.test.js

@@ -651,6 +651,88 @@ describe('bundle-size api', () => {
       );
     });
 
+    test('update check on bundle-size report with mergeSha (report/_delayed_-base = 12.34KB/12.23KB)', async () => {
+      await db('checks').insert({
+        head_sha: '26ddec3fbbd3c7bd94e05a701c8b8c3ea8826faa',
+        owner: 'ampproject',
+        repo: 'amphtml',
+        pull_request_id: 19603,
+        installation_id: 123456,
+        check_run_id: 555555,
+        approving_teams: null,
+        report_markdown: null,
+      });
+
+      baseBundleSizeFixture.content = Buffer.from(
+        '{"dist/v0.js":12.23}'
+      ).toString('base64');
+
+      let notFoundCount = 2;
+      github.repos.getContent.mockImplementation(params => {
+        if (
+          params.path.endsWith('5f27002526a808c5c1ad5d0f1ab1cec471af0a33.json')
+        ) {
+          if (notFoundCount > 0) {
+            notFoundCount--;
+            return Promise.reject({status: 404});
+          }
+          return Promise.resolve({data: baseBundleSizeFixture});
+        }
+        const fixture = params.path.replace(/^.+\/(.+)$/, '$1');
+        return Promise.resolve({data: getFixture(fixture)});
+      });
+
+      await request(probot.server)
+        .post('/v0/commit/26ddec3fbbd3c7bd94e05a701c8b8c3ea8826faa/report')
+        .send({
+          ...jsonPayload,
+          mergeSha: '9f6fd877fc27c679ad318699ac25a3fb4e228fca',
+        })
+        .set('Content-Type', 'application/json')
+        .set('Accept', 'application/json')
+        .expect(202);
+
+      await expect(
+        db('checks')
+          .where({
+            head_sha: '26ddec3fbbd3c7bd94e05a701c8b8c3ea8826faa',
+          })
+          .first()
+      ).resolves.toMatchObject({
+        head_sha: '26ddec3fbbd3c7bd94e05a701c8b8c3ea8826faa',
+        owner: 'ampproject',
+        repo: 'amphtml',
+        pull_request_id: 19603,
+        installation_id: 123456,
+        check_run_id: 555555,
+        approving_teams: 'ampproject/wg-performance,ampproject/wg-runtime',
+        report_markdown:
+          '## Commit details\n' +
+          '**Head commit:** 26ddec3\n' +
+          '**Base commit:** 5f27002\n' +
+          '**Code changes:** 9f6fd87\n\n' +
+          '## Bundle size changes that require approval\n' +
+          '* `dist/v0.js`: Δ +0.11KB\n' +
+          '## Bundle sizes missing from this PR\n' +
+          '* `dist/amp4ads-v0.js`: (11.22 KB) missing in `master`\n' +
+          '* `dist/v0/amp-accordion-0.1.js`: (1.11 KB) missing in `master`\n' +
+          '* `dist/v0/amp-ad-0.1.js`: (4.56 KB) missing in `master`',
+      });
+
+      expect(github.pulls.listRequestedReviewers).toHaveBeenCalled();
+      expect(github.pulls.listReviews).toHaveBeenCalled();
+      expect(github.pulls.requestReviewers).toHaveBeenCalled();
+      expect(github.checks.update).toHaveBeenCalledWith(
+        expect.objectContaining({
+          conclusion: 'action_required',
+          output: expect.objectContaining({
+            title:
+              'Approval required from one of [@ampproject/wg-performance, @ampproject/wg-runtime]',
+          }),
+        })
+      );
+    });
+
     test('update check on bundle-size report on missing base size', async () => {
       await db('checks').insert({
         head_sha: '26ddec3fbbd3c7bd94e05a701c8b8c3ea8826faa',