fix: backfill files by commit for rebased PRs

Fixes googleapis#2140

src/github.ts

@@ -469,14 +469,36 @@ export class GitHub {
     }
     const history = response.repository.ref.target.history;
     const commits = (history.nodes || []) as GraphQLCommit[];
+    // Count the number of pull requests associated with each merge commit. This is
+    // used in the next step to make sure we only find pull requests with a
+    // merge commit that contain 1 merged commit.
+    const mergeCommitCount: Record<string, number> = {};
+    for (const commit of commits) {
+      for (const pr of commit.associatedPullRequests.nodes) {
+        if (pr.mergeCommit?.oid) {
+          mergeCommitCount[pr.mergeCommit.oid] ??= 0;
+          mergeCommitCount[pr.mergeCommit.oid]++;
+        }
+      }
+    }
     const commitData: Commit[] = [];
     for (const graphCommit of commits) {
       const commit: Commit = {
         sha: graphCommit.sha,
         message: graphCommit.message,
       };
       const pullRequest = graphCommit.associatedPullRequests.nodes.find(pr => {
-        return pr.mergeCommit && pr.mergeCommit.oid === graphCommit.sha;
+        return (
+          // Only match the pull request with a merge commit if there is a
+          // single merged commit in the PR. This means merge commits and squash
+          // merges will be matched, but rebase merged PRs will only be matched
+          // if they contain a single commit. This is so PRs that are rebased
+          // and merged will have files backfilled from each commit instead of
+          // the whole PR.
+          pr.mergeCommit &&
+          pr.mergeCommit.oid === graphCommit.sha &&
+          mergeCommitCount[pr.mergeCommit.oid] === 1
+        );
       });
       if (pullRequest) {
         const files = (pullRequest.files?.nodes || []).map(node => node.path);

test/fixtures/commits-since-rebase.json

@@ -0,0 +1,88 @@
+{
+  "repository": {
+    "ref": {
+      "target": {
+        "history": {
+          "nodes": [
+            {
+              "associatedPullRequests": {
+                "nodes": [
+                  {
+                    "number": 7,
+                    "title": "feat: feature that will be rebase merged",
+                    "baseRefName": "main",
+                    "headRefName": "feature-branch-rebase-merge",
+                    "labels": {
+                      "nodes": []
+                    },
+                    "body": "",
+                    "mergeCommit": {
+                      "oid": "b29149f890e6f76ee31ed128585744d4c598924c"
+                    },
+                    "files": {
+                      "nodes": []
+                    }
+                  }
+                ]
+              },
+              "sha": "b29149f890e6f76ee31ed128585744d4c598924c",
+              "message": "feat: feature-branch-rebase-merge commit 1"
+            },
+            {
+              "associatedPullRequests": {
+                "nodes": [
+                  {
+                    "number": 7,
+                    "title": "feat: feature that will be rebase merged",
+                    "baseRefName": "main",
+                    "headRefName": "feature-branch-rebase-merge",
+                    "labels": {
+                      "nodes": []
+                    },
+                    "body": "",
+                    "mergeCommit": {
+                      "oid": "b29149f890e6f76ee31ed128585744d4c598924c"
+                    },
+                    "files": {
+                      "nodes": []
+                    }
+                  }
+                ]
+              },
+              "sha": "27d7d7232e2e312d1380e906984f0823f5decf61",
+              "message": "feat: feature-branch-rebase-merge commit 2"
+            },
+            {
+              "associatedPullRequests": {
+                "nodes": [
+                  {
+                    "number": 6,
+                    "title": "feat: other pr",
+                    "baseRefName": "main",
+                    "headRefName": "feature-branch-other",
+                    "labels": {
+                      "nodes": []
+                    },
+                    "body": "",
+                    "mergeCommit": {
+                      "oid": "2b4e0b3be2e231cd87cc44c411bd8f84b4587ab5"
+                    },
+                    "files": {
+                      "nodes": []
+                    }
+                  }
+                ]
+              },
+              "sha": "2b4e0b3be2e231cd87cc44c411bd8f84b4587ab5",
+              "message": "fix: feature-branch-other"
+            }
+          ],
+          "pageInfo": {
+            "hasNextPage": false,
+            "endCursor": "e6daec403626c9987c7af0d97b34f324cd84320a 12"
+          }
+        }
+      }
+    }
+  }
+}

test/github.ts

@@ -546,6 +546,39 @@ describe('GitHub', () => {
       snapshot(commitsSinceSha);
       req.done();
     });
+
+    it('backfills commit files for pull requests rebased and merged', async () => {
+      const graphql = JSON.parse(
+        readFileSync(resolve(fixturesPath, 'commits-since-rebase.json'), 'utf8')
+      );
+      req
+        .post('/graphql')
+        .reply(200, {
+          data: graphql,
+        })
+        .get(
+          '/repos/fake/fake/commits/b29149f890e6f76ee31ed128585744d4c598924c'
+        )
+        .reply(200, {files: [{filename: 'abc'}]})
+        .get(
+          '/repos/fake/fake/commits/27d7d7232e2e312d1380e906984f0823f5decf61'
+        )
+        .reply(200, {files: [{filename: 'def'}]});
+      const targetBranch = 'main';
+      const commitsSinceSha = await github.commitsSince(
+        targetBranch,
+        commit => {
+          // this commit is the 3rd most recent
+          return commit.sha === '2b4e0b3be2e231cd87cc44c411bd8f84b4587ab5';
+        },
+        {backfillFiles: true}
+      );
+      expect(commitsSinceSha.length).to.eql(2);
+      expect(commitsSinceSha[0].files).to.eql(['abc']);
+      expect(commitsSinceSha[1].files).to.eql(['def']);
+      snapshot(commitsSinceSha);
+      req.done();
+    });
   });
 
   describe('mergeCommitIterator', () => {