fs: keep return type of options.filter in cpsync consistent with doc

Author: kylo5aby

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

@@ -46,7 +46,6 @@ const {
   parse,
   resolve,
 } = require('path');
-const { isPromise } = require('util/types');
 
 function cpSyncFn(src, dest, opts) {
   // Warn about using preserveTimestamps on 32-bit node
@@ -64,7 +63,7 @@ function cpSyncFn(src, dest, opts) {
 function checkPathsSync(src, dest, opts) {
   if (opts.filter) {
     const shouldCopy = opts.filter(src, dest);
-    if (isPromise(shouldCopy)) {
+    if (typeof shouldCopy !== 'boolean') {
       throw new ERR_INVALID_RETURN_VALUE('boolean', 'filter', shouldCopy);
     }
     if (!shouldCopy) return { __proto__: null, skipped: true };

test/parallel/test-fs-cp.mjs

@@ -826,6 +826,22 @@ if (!isWindows) {
   cpSync(src, dest, opts);
 }
 
+// It will throw error for invalid return value from filter
+{
+  const src = nextdir();
+  const dest = nextdir();
+
+  const opts = {
+    filter: (path) => {
+      // Undefined is not a valid return value.
+    },
+  };
+  assert.throws(
+    () => cpSync(src, dest, opts),
+    { code: 'ERR_INVALID_RETURN_VALUE' }
+  );
+}
+
 // Copy should not throw exception if dest is invalid but filtered out.
 {
   // Create dest as a file.