fix(git): handle missing remote branch comparisons (#3881)

Author: tatoalo

packages/workspace-server/src/services/git/service.test.ts

@@ -0,0 +1,87 @@
+import type { GhExecResult } from "@posthog/git/gh";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const execGhMock = vi.hoisted(() => vi.fn());
+
+vi.mock("@posthog/git/gh", () => ({ execGh: execGhMock }));
+
+import { GitService } from "./service";
+
+function ghResult(overrides: Partial<GhExecResult> = {}): GhExecResult {
+  return {
+    stdout: "",
+    stderr: "",
+    exitCode: 0,
+    ...overrides,
+  };
+}
+
+describe("GitService", () => {
+  beforeEach(() => {
+    execGhMock.mockReset();
+  });
+
+  it("returns no changed files when the remote branch does not exist yet", async () => {
+    execGhMock
+      .mockResolvedValueOnce(ghResult({ stdout: "main\n" }))
+      .mockResolvedValueOnce(
+        ghResult({
+          stderr: "gh: Not Found (HTTP 404)\n",
+          exitCode: 1,
+        }),
+      );
+
+    await expect(
+      new GitService().getBranchChangedFiles("posthog/code", "feature/new"),
+    ).resolves.toEqual([]);
+  });
+
+  it("returns changed files from a successful comparison", async () => {
+    execGhMock
+      .mockResolvedValueOnce(ghResult({ stdout: "main\n" }))
+      .mockResolvedValueOnce(
+        ghResult({
+          stdout: JSON.stringify({
+            files: [
+              {
+                filename: "src/example.ts",
+                status: "added",
+                additions: 3,
+                deletions: 0,
+                sha: "abc123",
+              },
+            ],
+          }),
+        }),
+      );
+
+    await expect(
+      new GitService().getBranchChangedFiles("posthog/code", "feature/new"),
+    ).resolves.toEqual([
+      {
+        path: "src/example.ts",
+        status: "added",
+        originalPath: undefined,
+        linesAdded: 3,
+        linesRemoved: 0,
+        sha: "abc123",
+        patch: undefined,
+      },
+    ]);
+  });
+
+  it("preserves non-404 comparison failures", async () => {
+    execGhMock
+      .mockResolvedValueOnce(ghResult({ stdout: "main\n" }))
+      .mockResolvedValueOnce(
+        ghResult({
+          stderr: "gh: authentication failed (HTTP 401)\n",
+          exitCode: 1,
+        }),
+      );
+
+    await expect(
+      new GitService().getBranchChangedFiles("posthog/code", "feature/new"),
+    ).rejects.toThrow("Failed to fetch branch files");
+  });
+});

packages/workspace-server/src/services/git/service.ts

@@ -1236,6 +1236,9 @@ export class GitService extends TypedEventEmitter<GitCloneEvents> {
     ]);
 
     if (result.exitCode !== 0) {
+      if (/HTTP 404\b/.test(`${result.stderr} ${result.error ?? ""}`)) {
+        return [];
+      }
       throw new Error(
         `Failed to fetch branch files: ${result.stderr || result.error || "Unknown error"}`,
       );