fix: handle linkDir existence

As nodeModulesDirForPackageInner is asynchronous and contains
several `await` calls, the file can be created after the first
check for existence.

The error thrown is not an instance of Deno.errors.AlreadyExists,
as tested on macOS (OS error 66) and linux (OS error 39)

.vscode/settings.json

@@ -12,5 +12,9 @@
     "https://deno.": false,
     "https://deno.l": false,
     "https://deno.lan": false
+  },
+  "editor.defaultFormatter": "denoland.vscode-deno",
+  "[typescript]": {
+    "editor.defaultFormatter": "denoland.vscode-deno"
   }
 }

deps.ts

@@ -7,7 +7,7 @@ export {
   resolve,
   toFileUrl,
 } from "https://deno.land/[email protected]/path/mod.ts";
-export { copy } from "https://deno.land/[email protected]/fs/mod.ts";
+export { copy, exists } from "https://deno.land/[email protected]/fs/mod.ts";
 export { basename, extname } from "https://deno.land/[email protected]/path/mod.ts";
 export * as JSONC from "https://deno.land/[email protected]/encoding/jsonc.ts";
 export { encode as base32Encode } from "https://deno.land/[email protected]/encoding/base32.ts";

src/loader_native.ts

@@ -3,6 +3,7 @@ import {
   DenoDir,
   dirname,
   esbuild,
+  exists,
   fromFileUrl,
   join,
 } from "../deps.ts";
@@ -120,23 +121,18 @@ export class NativeLoader implements Loader {
 
     // check if the package is already linked, if so, return the link and skip
     // a bunch of work
-    try {
-      await Deno.stat(linkDir);
-      this.#linkDirCache.set(npmPackageId, linkDir);
-      return linkDir;
-    } catch {
-      // directory does not yet exist
-    }
+    if (await exists(linkDir)) return linkDir;
 
     // create a temporary directory, recursively hardlink the package contents
     // into it, and then rename it to the final location
     const tmpDir = await Deno.makeTempDir();
+
     await linkRecursive(packageDir, tmpDir);
     try {
       await Deno.mkdir(linkDirParent, { recursive: true });
       await Deno.rename(tmpDir, linkDir);
     } catch (err) {
-      if (err instanceof Deno.errors.AlreadyExists) {
+      if (err instanceof Deno.errors.AlreadyExists || await exists(linkDir)) {
         // ignore
       } else {
         throw err;