fix(reference): read linked worktree commit provenance (#677)

Signed-off-by: RudyCelekli <47457359+rudycelekli@users.noreply.github.com>

src/application/ReferenceSourceVcsAdapter.ts

@@ -1,6 +1,6 @@
 import fs from "node:fs";
-import { lstat } from "node:fs/promises";
-import { join } from "node:path";
+import { lstat, readFile } from "node:fs/promises";
+import { join, resolve } from "node:path";
 
 import { resolveRef } from "isomorphic-git";
 
@@ -31,7 +31,7 @@ export const readReferenceSourceVcs = async (
       : { kind: "unknown", head: null, dirty: null };
   }
   try {
-    const head = await resolveRef({ fs, dir: root, ref: "HEAD" });
+    const head = await resolveSourceHead(root);
     if (isAborted(signal)) return { kind: "unknown", head: null, dirty: null };
     return { kind: "git", head, dirty: null };
   } catch (cause: unknown) {
@@ -41,6 +41,42 @@ export const readReferenceSourceVcs = async (
   }
 };
 
+const resolveSourceHead = async (root: string): Promise<string> => {
+  const dotgit = join(root, ".git");
+  if (!(await lstat(dotgit)).isFile())
+    return resolveRef({ fs, dir: root, ref: "HEAD" });
+  const pointer = (await readFile(dotgit, "utf8")).replace(/\r?\n$/u, "");
+  if (!pointer.startsWith("gitdir: ") || pointer.length === 8)
+    throw new Error("Invalid Git directory pointer");
+  const gitdir = resolve(root, pointer.slice(8));
+  let commonDirectory: string;
+  try {
+    commonDirectory = resolve(
+      gitdir,
+      (await readFile(join(gitdir, "commondir"), "utf8")).replace(
+        /\r?\n$/u,
+        "",
+      ),
+    );
+  } catch (cause: unknown) {
+    if (errorCode(cause) !== "ENOENT") throw cause;
+    return resolveRef({ fs, dir: root, gitdir, ref: "HEAD" });
+  }
+  const head = (await readFile(join(gitdir, "HEAD"), "utf8")).trim();
+  if (!head.startsWith("ref: "))
+    return resolveRef({ fs, dir: root, gitdir, ref: "HEAD" });
+  const ref = head.slice(5);
+  const privateRef = ["refs/bisect/", "refs/rewritten/", "refs/worktree/"].some(
+    (prefix) => ref.startsWith(prefix),
+  );
+  return resolveRef({
+    fs,
+    dir: root,
+    gitdir: privateRef ? gitdir : commonDirectory,
+    ref,
+  });
+};
+
 const errorCode = (cause: unknown): string | undefined =>
   typeof cause === "object" && cause !== null && "code" in cause
     ? String(cause.code)