🐛 Properly detect MERGE_HEAD in GinChaperon

Close #146

denops/gin/command/chaperon/util.ts

@@ -1,5 +1,6 @@
 import * as fs from "jsr:@std/fs@^1.0.0";
 import * as path from "jsr:@std/path@^1.0.0";
+import { findGitdir } from "../../git/finder.ts";
 
 const beginMarker = `${"<".repeat(7)} `;
 const endMarker = `${">".repeat(7)} `;
@@ -29,8 +30,9 @@ export type AliasHead = typeof validAliasHeads[number];
 export async function getInProgressAliasHead(
   worktree: string,
 ): Promise<AliasHead | undefined> {
+  const gitdir = await findGitdir(worktree);
   for (const head of validAliasHeads) {
-    if (await fs.exists(path.join(worktree, ".git", head))) {
+    if (await fs.exists(path.join(gitdir, head))) {
       return head;
     }
   }

denops/gin/git/finder.ts

@@ -5,6 +5,7 @@ import { decodeUtf8 } from "../util/text.ts";
 
 const ttl = 30000; // seconds
 const cacheWorktree = new Cache<string, string | Error>(ttl);
+const cacheGitdir = new Cache<string, string | Error>(ttl);
 
 /**
  * Find a root path of a git working directory.
@@ -33,6 +34,30 @@ export async function findWorktree(cwd: string): Promise<string> {
   return result;
 }
 
+/**
+ * Find a .git directory of a git working directory.
+ *
+ * @param cwd - A current working directory.
+ * @returns A root path of a git working directory.
+ */
+export async function findGitdir(cwd: string): Promise<string> {
+  const path = await Deno.realPath(cwd);
+  const result = cacheGitdir.get(path) ?? await (async () => {
+    let result: string | Error;
+    try {
+      result = await revParse(path, ["--git-dir"]);
+    } catch (e) {
+      result = e;
+    }
+    cacheGitdir.set(path, result);
+    return result;
+  })();
+  if (result instanceof Error) {
+    throw result;
+  }
+  return result;
+}
+
 async function revParse(cwd: string, args: string[]): Promise<string> {
   const terms = cwd.split(SEPARATOR);
   if (terms.includes(".git")) {

denops/gin/git/finder_test.ts

@@ -1,11 +1,12 @@
 import { assertEquals, assertRejects } from "jsr:@std/assert@^1.0.0";
 import { sandbox } from "jsr:@lambdalisue/sandbox@^2.0.0";
 import $ from "jsr:@david/dax@^0.42.0";
-import { findWorktree } from "./finder.ts";
+import { join } from "jsr:@std/path@^1.0.0";
+import { findGitdir, findWorktree } from "./finder.ts";
 import { ExecuteError } from "./process.ts";
 
 Deno.test({
-  name: "find() returns a root path of a git working directory",
+  name: "findWorktree() returns a root path of a git working directory",
   fn: async () => {
     await using sbox = await prepare();
     Deno.chdir("a/b/c");
@@ -18,7 +19,8 @@ Deno.test({
 });
 
 Deno.test({
-  name: "find() throws an error if the path is not in a git working directory",
+  name:
+    "findWorktree() throws an error if the path is not in a git working directory",
   fn: async () => {
     await assertRejects(async () => {
       await findWorktree("/");
@@ -32,6 +34,55 @@ Deno.test({
   sanitizeOps: false,
 });
 
+Deno.test({
+  name: "findGitdir() returns a root path of a git working directory",
+  fn: async () => {
+    await using sbox = await prepare();
+    Deno.chdir("a/b/c");
+    assertEquals(await findGitdir("."), join(sbox.path, ".git"));
+    // An internal cache will be used for the following call
+    assertEquals(await findGitdir("."), join(sbox.path, ".git"));
+  },
+  sanitizeResources: false,
+  sanitizeOps: false,
+});
+
+Deno.test({
+  name: "findGitdir() returns a worktree path of a git working directory",
+  fn: async () => {
+    await using sbox = await prepare();
+    await $`git worktree add -b test test main`;
+    Deno.chdir("test");
+    assertEquals(
+      await findGitdir("."),
+      join(sbox.path, ".git", "worktrees", "test"),
+    );
+    // An internal cache will be used for the following call
+    assertEquals(
+      await findGitdir("."),
+      join(sbox.path, ".git", "worktrees", "test"),
+    );
+  },
+  sanitizeResources: false,
+  sanitizeOps: false,
+});
+
+Deno.test({
+  name:
+    "findGitdir() throws an error if the path is not in a git working directory",
+  fn: async () => {
+    await assertRejects(async () => {
+      await findGitdir("/");
+    }, ExecuteError);
+    // An internal cache will be used for the following call
+    await assertRejects(async () => {
+      await findGitdir("/");
+    }, ExecuteError);
+  },
+  sanitizeResources: false,
+  sanitizeOps: false,
+});
+
 async function prepare(): ReturnType<typeof sandbox> {
   const sbox = await sandbox();
   await $`git init`;