improve diff files filtering logic (#222)

src/review.ts

@@ -98,20 +98,46 @@ export const codeReview = async (
     core.info(`Will review from commit: ${highest_reviewed_commit_id}`)
   }
 
-  // get the list of files changed between the highest reviewed commit
-  // and the latest (head) commit
-  // use octokit.pulls.compareCommits to get the list of files changed
-  // between the highest reviewed commit and the latest (head) commit
-  const diff = await octokit.repos.compareCommits({
+  // Fetch the diff between the highest reviewed commit and the latest commit of the PR branch
+  const incrementalDiff = await octokit.repos.compareCommits({
     owner: repo.owner,
     repo: repo.repo,
     base: highest_reviewed_commit_id,
     head: context.payload.pull_request.head.sha
   })
 
-  const {files, commits} = diff.data
+  // Fetch the diff between the target branch's base commit and the latest commit of the PR branch
+  const targetBranchDiff = await octokit.repos.compareCommits({
+    owner: repo.owner,
+    repo: repo.repo,
+    base: context.payload.pull_request.base.sha,
+    head: context.payload.pull_request.head.sha
+  })
+
+  const incrementalFiles = incrementalDiff.data.files
+  const targetBranchFiles = targetBranchDiff.data.files
+
+  if (!incrementalFiles || !targetBranchFiles) {
+    core.warning(`Skipped: files data is missing`)
+    return
+  }
+  // Filter out any file that is not changed compared to the target branch
+  const files = incrementalFiles.filter(incrementalChange =>
+    targetBranchFiles.some(
+      changeRelativeToTargetBranch =>
+        changeRelativeToTargetBranch.filename === incrementalChange.filename
+    )
+  )
+
   if (!files) {
-    core.warning(`Skipped: diff.data.files is null`)
+    core.warning(`Skipped: files is null`)
+    return
+  }
+
+  const commits = incrementalDiff.data.commits
+
+  if (!commits) {
+    core.warning(`Skipped: commits is null`)
     return
   }