fix permission errors are swallowed by fs.exists (#3493)

std/fs/exists.ts

@@ -1,12 +1,20 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-
+const { lstat, lstatSync, DenoError, ErrorKind } = Deno;
 /**
  * Test whether or not the given path exists by checking with the file system
  */
 export async function exists(filePath: string): Promise<boolean> {
-  return Deno.lstat(filePath)
+  return lstat(filePath)
     .then((): boolean => true)
-    .catch((): boolean => false);
+    .catch((err: Error): boolean => {
+      if (err instanceof DenoError) {
+        if (err.kind === ErrorKind.NotFound) {
+          return false;
+        }
+      }
+
+      throw err;
+    });
 }
 
 /**
@@ -14,9 +22,14 @@ export async function exists(filePath: string): Promise<boolean> {
  */
 export function existsSync(filePath: string): boolean {
   try {
-    Deno.lstatSync(filePath);
+    lstatSync(filePath);
     return true;
-  } catch {
-    return false;
+  } catch (err) {
+    if (err instanceof DenoError) {
+      if (err.kind === ErrorKind.NotFound) {
+        return false;
+      }
+    }
+    throw err;
   }
 }