Keep moved file paths and diffs intact in commit history (#8509)

* fix(server): keep commit file paths when a file moves up a directory

* test(git): open moved commit files through their listed path

Verify commit history and diff lookup agree for files moved up a directory, with and without content edits.

Co-authored-by: hadan8977 <zc-huang23@mails.tsinghua.edu.cn>

* refactor(git): clarify compact rename handling and test cases

Co-authored-by: hadan8977 <zc-huang23@mails.tsinghua.edu.cn>

---------

Co-authored-by: hadan8977 <zc-huang23@mails.tsinghua.edu.cn>
Co-authored-by: paseo-bot[bot] <266920839+paseo-bot[bot]@users.noreply.github.com>

packages/server/src/utils/checkout-git.commits.test.ts

@@ -3,7 +3,7 @@ import { mkdirSync, mkdtempSync, realpathSync, rmSync, writeFileSync } from "fs"
 import { tmpdir } from "os";
 import { join } from "path";
 import { afterEach, describe, expect, it } from "vitest";
-import { listCheckoutCommits } from "./checkout-git.js";
+import { getCommitFileDiff, listCheckoutCommits } from "./checkout-git.js";
 import { writePaseoWorktreeMetadata } from "./worktree-metadata.js";
 
 const tempDirs: string[] = [];
@@ -332,6 +332,50 @@ describe("listCheckoutCommits", () => {
     ]);
   });
 
+  it.each([
+    {
+      label: "without edits",
+      content: "one\ntwo\nthree\nfour\nfive\n",
+      additions: 0,
+      deletions: 0,
+    },
+    { label: "with edits", content: "one\nTWO\nthree\nfour\nfive\n", additions: 1, deletions: 1 },
+  ])(
+    "opens a file moved up out of a directory $label",
+    async ({ content, additions, deletions }) => {
+      const { repoDir } = initRepoOnMain();
+      git(["checkout", "-b", "feature"], repoDir);
+      mkdirSync(join(repoDir, "src", "nested"), { recursive: true });
+      commitFile(repoDir, "src/nested/a.txt", "one\ntwo\nthree\nfour\nfive\n", "Add nested file");
+      git(["mv", "src/nested/a.txt", "src/a.txt"], repoDir);
+      writeFileSync(join(repoDir, "src/a.txt"), content);
+      git(["add", "src/a.txt"], repoDir);
+      commit(repoDir, "Move file up");
+
+      const { commits } = await listCheckoutCommits({ cwd: repoDir });
+
+      const movedCommit = commits[0]!;
+      const movedFile = movedCommit.files[0]!;
+      expect(movedCommit.files).toEqual([
+        {
+          path: "src/a.txt",
+          additions,
+          deletions,
+          status: "renamed",
+        },
+      ]);
+      expect(
+        await getCommitFileDiff({ cwd: repoDir, sha: movedCommit.sha, path: movedFile.path }),
+      ).toMatchObject({
+        path: "src/a.txt",
+        isNew: false,
+        isDeleted: false,
+        additions,
+        deletions,
+      });
+    },
+  );
+
   it("derives status for modified and deleted files", async () => {
     const { repoDir } = initRepoOnMain();
     git(["checkout", "-b", "feature"], repoDir);

packages/server/src/utils/checkout-git.ts

@@ -636,6 +636,11 @@ function normalizeNumstatPath(pathField: string): string {
   const braceRenameMatch = pathField.match(/^(.*)\{(.*) => (.*)\}(.*)$/);
   if (braceRenameMatch) {
     const [, prefix, , renamed, suffix] = braceRenameMatch;
+    // Moving out of a directory prints `src/{nested => }/a.ts`, so an empty
+    // destination leaves a separator from each side behind.
+    if (!renamed) {
+      return unquoteGitPath(`${prefix}${suffix.slice(1)}`);
+    }
     return unquoteGitPath(`${prefix}${renamed}${suffix}`);
   }