FlowLib: Add typed Set wrapper

Summary:
Add a generic `Set<T>` to FlowLib that wraps the native Set
with typed add/has/delete/clear/forEach methods, allowing
typed code to use Set methods directly.

Differential Revision: D96520014

Author: avp

lib/FlowLib/04-set.js

@@ -0,0 +1,49 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+class Set<T> {
+  /// Native implementation of this Set.
+  #impl: any;
+
+  constructor() {
+    "inline";
+    this.#impl = new globalThis.Set();
+  }
+
+  @Hermes.final
+  add(v: T): Set<T> {
+    "inline";
+    this.#impl.add(v);
+    return this;
+  }
+
+  @Hermes.final
+  has(v: T): bool {
+    "inline";
+    return this.#impl.has(v) as bool;
+  }
+
+  @Hermes.final
+  delete(v: T): bool {
+    "inline";
+    return this.#impl.delete(v) as bool;
+  }
+
+  @Hermes.final
+  clear(): void {
+    "inline";
+    this.#impl.clear();
+  }
+
+  @Hermes.final
+  forEach(cb: (v: T, k?: T, s?: Set<T>) => any): void {
+    "inline";
+    this.#impl.forEach((v, k, s) => {
+      return cb(v, k, this);
+    });
+  }
+}

lib/FlowLib/CMakeLists.txt

@@ -16,6 +16,7 @@ set(flowlib_sources
   "01-array.js"
   "02-string.js"
   "03-map.js"
+  "04-set.js"
 )
 list(SORT flowlib_sources)
 

test/hermes/flow/set.js

@@ -0,0 +1,58 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+// RUN: %hermes -O0 -typed %s | %FileCheck --match-full-lines %s
+// RUN: %hermes -typed %s | %FileCheck --match-full-lines %s
+// RUN: %shermes -typed -exec %s | %FileCheck --match-full-lines %s
+
+// Basic add/has.
+let s = new Set<string>();
+s.add('a');
+s.add('b');
+print(s.has('a'));
+// CHECK: true
+print(s.has('b'));
+// CHECK-NEXT: true
+print(s.has('c'));
+// CHECK-NEXT: false
+
+// Chained add.
+let s2 = new Set<number>();
+s2.add(1).add(2).add(3);
+print(s2.has(1));
+// CHECK-NEXT: true
+print(s2.has(3));
+// CHECK-NEXT: true
+
+// delete().
+print(s.delete('a'));
+// CHECK-NEXT: true
+print(s.has('a'));
+// CHECK-NEXT: false
+print(s.delete('a'));
+// CHECK-NEXT: false
+
+// clear().
+s.add('x');
+s.add('y');
+print(s.has('x'));
+// CHECK-NEXT: true
+s.clear();
+print(s.has('x'));
+// CHECK-NEXT: false
+print(s.has('b'));
+// CHECK-NEXT: false
+
+// forEach().
+let s3 = new Set<number>();
+s3.add(10).add(20).add(30);
+s3.forEach(v => { print(v); });
+// CHECK-NEXT: 10
+// CHECK-NEXT: 20
+// CHECK-NEXT: 30