Add support for empty results in getChangedFiles (#37877)

* Add support for empty results in getChangedFiles

* Add comment

---------

Co-authored-by: Mike Harder <[email protected]>

Author: danieljurek

.github/shared/src/changed-files.js

@@ -33,7 +33,11 @@ export async function getChangedFiles(options = {}) {
   // filter based on status with a single call to `git diff`.
   const result = await simpleGit(cwd).diff(["--name-only", baseCommitish, headCommitish, ...paths]);
 
-  const files = result.trim().split("\n");
+  const files = result
+    .trim()
+    .split("\n")
+    // ignore empty lines (e.g. when no files are changed)
+    .filter((s) => s.length > 0);
   logger?.info("Changed Files:");
   for (const file of files) {
     logger?.info(`  ${file}`);

.github/shared/test/changed-files.test.js

@@ -57,6 +57,12 @@ describe("changedFiles", () => {
     ]);
   });
 
+  it("getChangedFiles returns empty array when no files are changed", async () => {
+    vi.mocked(simpleGit.simpleGit().diff).mockResolvedValue("");
+    await expect(getChangedFiles()).resolves.toEqual([]);
+    expect(simpleGit.simpleGit().diff).toHaveBeenCalledWith(["--name-only", "HEAD^", "HEAD"]);
+  });
+
   const files = [
     "cspell.json",
     "cspell.yaml",