Reject async generators during semantic validation

Summary:
Hermes does not currently support async generators. As such, reject those early in compilation
(i.e., during ```SemanticValidation```).

Reviewed By: werew

Differential Revision: D45155647

fbshipit-source-id: a7b83c5a9956e21889f43708483441228309082b

lib/AST/SemanticValidator.cpp

@@ -779,6 +779,10 @@ void SemanticValidator::visitFunction(
       haveActiveContext() ? curFunction()->sourceVisibility
                           : SourceVisibility::Default};
 
+  if (compile_ && ESTree::isAsync(node) && ESTree::isGenerator(node)) {
+    sm_.error(node->getSourceRange(), "async generators are unsupported");
+  }
+
   // It is a Syntax Error if UniqueFormalParameters Contains YieldExpression
   // is true.
   // NOTE: isFormalParams_ is reset to false on encountering a new function,

lib/IRGen/ESTreeIRGen-func.cpp

@@ -86,12 +86,6 @@ EnterBlockScope::~EnterBlockScope() {
 
 void ESTreeIRGen::genFunctionDeclaration(
     ESTree::FunctionDeclarationNode *func) {
-  if (func->_async && func->_generator) {
-    Builder.getModule()->getContext().getSourceErrorManager().error(
-        func->getSourceRange(), Twine("async generators are unsupported"));
-    return;
-  }
-
   // Find the name of the function.
   Identifier functionName = getNameFieldFromID(func->_id);
   LLVM_DEBUG(llvh::dbgs() << "IRGen function \"" << functionName << "\".\n");
@@ -142,12 +136,6 @@ void ESTreeIRGen::hoistCreateFunctions(ESTree::Node *containingNode) {
 Value *ESTreeIRGen::genFunctionExpression(
     ESTree::FunctionExpressionNode *FE,
     Identifier nameHint) {
-  if (FE->_async && FE->_generator) {
-    Builder.getModule()->getContext().getSourceErrorManager().error(
-        FE->getSourceRange(), Twine("async generators are unsupported"));
-    return Builder.getLiteralUndefined();
-  }
-
   LLVM_DEBUG(
       llvh::dbgs()
       << "Creating anonymous closure. "

test/IRGen/es6/async-generators.js

@@ -0,0 +1,11 @@
+/**
+ * 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.
+ */
+
+// RUN: (! %hermesc %s --dump-bytecode 2>&1) | %FileCheck %s
+
+async function* f() {};
+// CHECK: async generators are unsupported