sys: Avoid array copy in getDirectories

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

Author: andersk

src/compiler/sys.ts

@@ -1350,7 +1350,7 @@ namespace ts {
                 }
             }
 
-            function getAccessibleFileSystemEntries(path: string): FileSystemEntries {
+            function getAccessibleFileSystemEntries(path: string): { files: string[]; directories: string[] } {
                 perfLogger.logEvent("ReadDir: " + (path || "."));
                 try {
                     const entries = _fs.readdirSync(path || ".", { withFileTypes: true });
@@ -1393,7 +1393,7 @@ namespace ts {
                     return { files, directories };
                 }
                 catch (e) {
-                    return emptyFileSystemEntries;
+                    return { files: [], directories: [] };
                 }
             }
 
@@ -1424,7 +1424,7 @@ namespace ts {
             }
 
             function getDirectories(path: string): string[] {
-                return getAccessibleFileSystemEntries(path).directories.slice();
+                return getAccessibleFileSystemEntries(path).directories;
             }
 
             function realpath(path: string): string {