vfs: address aduh95 review feedback

Simplify srcIsDir checks in cp-sync.js and cp.js to one-liner with
optional chaining and nullish coalescing. Use isPromise() instead of
duck-typing in memory provider. Use FunctionPrototypeSymbolHasInstance
instead of instanceof in vfs.js.

Author: mcollina

lib/internal/fs/cp/cp-sync.js

@@ -239,13 +239,7 @@ function onLink(destStat, src, dest, verbatimSymlinks) {
   }
   // internalModuleStat is a C++ call that can't see VFS files.
   const { vfsState } = require('internal/fs/utils');
-  let srcIsDir;
-  const vfsStat = vfsState.handlers?.statSync(src);
-  if (vfsStat) {
-    srcIsDir = vfsStat.isDirectory();
-  } else {
-    srcIsDir = fsBinding.internalModuleStat(src) === 1;
-  }
+  const srcIsDir = vfsState.handlers?.statSync(src)?.isDirectory() ?? fsBinding.internalModuleStat(src) === 1;
 
   if (srcIsDir && isSrcSubdir(resolvedSrc, resolvedDest)) {
     throw new ERR_FS_CP_EINVAL({

lib/internal/fs/cp/cp.js

@@ -357,12 +357,7 @@ async function onLink(destStat, src, dest, opts) {
 
   // internalModuleStat is a C++ call that can't see VFS files.
   const { vfsState } = require('internal/fs/utils');
-  let srcIsDir;
-  if (vfsState.handlers !== null && vfsState.handlers.statSync(src)) {
-    srcIsDir = (await stat(src)).isDirectory();
-  } else {
-    srcIsDir = fsBinding.internalModuleStat(src) === 1;
-  }
+  const srcIsDir = vfsState.handlers?.statSync(src)?.isDirectory() ?? fsBinding.internalModuleStat(src) === 1;
 
   if (srcIsDir && isSrcSubdir(resolvedSrc, resolvedDest)) {
     throw new ERR_FS_CP_EINVAL({

lib/internal/vfs/providers/memory.js

@@ -10,6 +10,7 @@ const {
 } = primordials;
 
 const { Buffer } = require('buffer');
+const { isPromise } = require('util/types');
 const { posix: pathPosix } = require('path');
 const { VirtualProvider } = require('internal/vfs/provider');
 const { MemoryFileHandle } = require('internal/vfs/file_handle');
@@ -88,7 +89,7 @@ class MemoryEntry {
   getContentSync() {
     if (this.contentProvider !== null) {
       const result = this.contentProvider();
-      if (typeof result?.then === 'function') {
+      if (isPromise(result)) {
         // It's a Promise - can't use sync API
         throw new ERR_INVALID_STATE('cannot use sync API with async content provider');
       }

lib/vfs.js

@@ -1,5 +1,9 @@
 'use strict';
 
+const {
+  FunctionPrototypeSymbolHasInstance,
+} = primordials;
+
 const { VirtualFileSystem } = require('internal/vfs/file_system');
 const { VirtualProvider } = require('internal/vfs/provider');
 const { MemoryProvider } = require('internal/vfs/providers/memory');
@@ -16,7 +20,7 @@ const { RealFSProvider } = require('internal/vfs/providers/real');
 function create(provider, options) {
   // Handle case where first arg is options (no provider)
   if (provider != null &&
-      !(provider instanceof VirtualProvider) &&
+      !FunctionPrototypeSymbolHasInstance(VirtualProvider, provider) &&
       typeof provider === 'object') {
     options = provider;
     provider = undefined;