fix(node/fs/exists): fix promisified exists (#2409)

Author: kt3k

node/_fs/_fs_exists.ts

@@ -1,18 +1,30 @@
 // Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
 import { fromFileUrl } from "../path.ts";
 
-type ExitsCallback = (exists: boolean) => void;
+type ExistsCallback = (exists: boolean) => void;
 
 /**
  * TODO: Also accept 'path' parameter as a Node polyfill Buffer type once these
  * are implemented. See https://github.com/denoland/deno/issues/3403
  * Deprecated in node api
  */
-export function exists(path: string | URL, callback: ExitsCallback): void {
+export function exists(path: string | URL, callback: ExistsCallback): void {
   path = path instanceof URL ? fromFileUrl(path) : path;
   Deno.lstat(path).then(() => callback(true), () => callback(false));
 }
 
+// The callback of fs.exists doesn't have standard callback signature.
+// We need to provide special implementation for promisify.
+// See https://github.com/nodejs/node/pull/13316
+const kCustomPromisifiedSymbol = Symbol.for("nodejs.util.promisify.custom");
+Object.defineProperty(exists, kCustomPromisifiedSymbol, {
+  value: (path: string | URL) => {
+    return new Promise((resolve) => {
+      exists(path, (exists) => resolve(exists));
+    });
+  },
+});
+
 /**
  * TODO: Also accept 'path' parameter as a Node polyfill Buffer or URL type once these
  * are implemented. See https://github.com/denoland/deno/issues/3403

node/_fs/_fs_exists_test.ts

@@ -5,8 +5,9 @@ import {
   assertStringIncludes,
 } from "../../testing/asserts.ts";
 import { exists, existsSync } from "./_fs_exists.ts";
+import { promisify } from "../util.ts";
 
-Deno.test("existsFile", async function () {
+Deno.test("[std/node/fs] exists", async function () {
   const availableFile = await new Promise((resolve) => {
     const tmpFilePath = Deno.makeTempFileSync();
     exists(tmpFilePath, (exists: boolean) => {
@@ -21,13 +22,24 @@ Deno.test("existsFile", async function () {
   assertEquals(notAvailableFile, false);
 });
 
-Deno.test("existsSyncFile", function () {
+Deno.test("[std/node/fs] existsSync", function () {
   const tmpFilePath = Deno.makeTempFileSync();
   assertEquals(existsSync(tmpFilePath), true);
   Deno.removeSync(tmpFilePath);
   assertEquals(existsSync("./notAvailable.txt"), false);
 });
 
+Deno.test("[std/node/fs] promisify(exists)", async () => {
+  const tmpFilePath = await Deno.makeTempFile();
+  try {
+    const existsPromisified = promisify(exists);
+    assert(await existsPromisified(tmpFilePath));
+    assert(!await existsPromisified("./notAvailable.txt"));
+  } finally {
+    await Deno.remove(tmpFilePath);
+  }
+});
+
 Deno.test("[std/node/fs] exists callback isn't called twice if error is thrown", async () => {
   // This doesn't use `assertCallbackErrorUncaught()` because `exists()` doesn't return a standard node callback, which is what it expects.
   const tempFile = await Deno.makeTempFile();