Fix deleted diff syntax highlighting

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

@@ -81,6 +81,49 @@ describe("checkout git utilities", () => {
     expect(message).toBe("update file");
   });
 
+  it("preserves removed-line syntax highlighting with structured diffs", async () => {
+    const originalContent = `/*
+comment line 1
+comment line 2
+comment line 3
+comment line 4
+comment line 5
+comment line 6
+old comment line
+comment line 8
+*/
+const x = 1;
+`;
+    const updatedContent = `/*
+comment line 1
+comment line 2
+comment line 3
+comment line 4
+comment line 5
+comment line 6
+new comment line
+comment line 8
+*/
+const x = 1;
+`;
+
+    writeFileSync(join(repoDir, "example.ts"), originalContent);
+    execSync("git add example.ts", { cwd: repoDir });
+    execSync("git -c commit.gpgsign=false commit -m 'add multiline comment fixture'", {
+      cwd: repoDir,
+    });
+
+    writeFileSync(join(repoDir, "example.ts"), updatedContent);
+
+    const diff = await getCheckoutDiff(repoDir, { mode: "uncommitted", includeStructured: true });
+    const file = diff.structured?.find((entry) => entry.path === "example.ts");
+    const removedLine = file?.hunks[0]?.lines.find((line) => line.type === "remove");
+    const addedLine = file?.hunks[0]?.lines.find((line) => line.type === "add");
+
+    expect(addedLine?.tokens).toEqual([{ text: "new comment line", style: "comment" }]);
+    expect(removedLine?.tokens).toEqual([{ text: "old comment line", style: "comment" }]);
+  });
+
   it("returns lightweight checkout status for normal repos", async () => {
     const status = await getCheckoutStatusLite(repoDir);
     expect(status.isGit).toBe(true);

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

@@ -304,6 +304,23 @@ async function listCheckoutFileChanges(cwd: string, ref: string): Promise<Checko
   return Array.from(byPath.values());
 }
 
+async function readGitFileContentAtRef(
+  cwd: string,
+  ref: string,
+  path: string,
+): Promise<string | null> {
+  try {
+    const { stdout } = await execFileAsync("git", ["show", `${ref}:${path}`], {
+      cwd,
+      env: READ_ONLY_GIT_ENV,
+      maxBuffer: SMALL_OUTPUT_MAX_BUFFER,
+    });
+    return stdout;
+  } catch {
+    return null;
+  }
+}
+
 async function tryResolveMergeBase(cwd: string, baseRef: string): Promise<string | null> {
   try {
     const { stdout } = await execGit(`git merge-base ${baseRef} HEAD`, {
@@ -1239,6 +1256,7 @@ export async function getCheckoutDiff(
 
   const trackedChanges = changes.filter((change) => !change.isUntracked);
   const untrackedChanges = changes.filter((change) => change.isUntracked === true);
+  const trackedChangeByPath = new Map(trackedChanges.map((change) => [change.path, change]));
 
   const trackedNumstatByPath =
     trackedChanges.length > 0
@@ -1294,7 +1312,18 @@ export async function getCheckoutDiff(
 
   if (compare.includeStructured) {
     const parsedTrackedFiles =
-      trackedDiffText.length > 0 ? await parseAndHighlightDiff(trackedDiffText, cwd) : [];
+      trackedDiffText.length > 0
+        ? await parseAndHighlightDiff(trackedDiffText, cwd, {
+            getOldFileContent: async (file) => {
+              const change = trackedChangeByPath.get(file.path);
+              if (!change || change.isNew) {
+                return null;
+              }
+              const refPath = change.oldPath ?? change.path;
+              return readGitFileContentAtRef(cwd, refForDiff, refPath);
+            },
+          })
+        : [];
     const parsedTrackedByPath = new Map(parsedTrackedFiles.map((file) => [file.path, file]));
 
     for (const change of trackedChanges) {