Bug 1339964 - Support export async function f() {}. r=till

js/src/frontend/Parser.cpp

@@ -5233,14 +5233,15 @@ Parser<ParseHandler>::exportVariableStatement(uint32_t begin)
 
 template <typename ParseHandler>
 typename ParseHandler::Node
-Parser<ParseHandler>::exportFunctionDeclaration(uint32_t begin)
+Parser<ParseHandler>::exportFunctionDeclaration(uint32_t begin,
+                                                FunctionAsyncKind asyncKind /* = SyncFunction */)
 {
     if (!abortIfSyntaxParser())
         return null();
 
     MOZ_ASSERT(tokenStream.isCurrentTokenType(TOK_FUNCTION));
 
-    Node kid = functionStmt(YieldIsKeyword, NameRequired);
+    Node kid = functionStmt(YieldIsKeyword, NameRequired, asyncKind);
     if (!kid)
         return null();
 
@@ -5463,6 +5464,20 @@ Parser<ParseHandler>::exportDeclaration()
       case TOK_FUNCTION:
         return exportFunctionDeclaration(begin);
 
+      case TOK_ASYNC: {
+        TokenKind nextSameLine = TOK_EOF;
+        if (!tokenStream.peekTokenSameLine(&nextSameLine))
+            return null();
+
+        if (nextSameLine == TOK_FUNCTION) {
+            tokenStream.consumeKnownToken(TOK_FUNCTION);
+            return exportFunctionDeclaration(begin, AsyncFunction);
+        }
+
+        error(JSMSG_DECLARATION_AFTER_EXPORT);
+        return null();
+      }
+
       case TOK_CLASS:
         return exportClassDeclaration(begin);
 

js/src/frontend/Parser.h

@@ -1203,7 +1203,8 @@ class Parser final : public ParserBase, private JS::AutoGCRooter
     Node exportBatch(uint32_t begin);
     bool checkLocalExportNames(Node node);
     Node exportClause(uint32_t begin);
-    Node exportFunctionDeclaration(uint32_t begin);
+    Node exportFunctionDeclaration(uint32_t begin,
+                                   FunctionAsyncKind asyncKind = SyncFunction);
     Node exportVariableStatement(uint32_t begin);
     Node exportClassDeclaration(uint32_t begin);
     Node exportLexicalDeclaration(uint32_t begin, DeclarationKind kind);

js/src/tests/ecma_2017/AsyncFunctions/syntax-modules.js

@@ -16,6 +16,12 @@ if (typeof parseModule === "function") {
     assertThrows(() => parseModule("async function f() { function g() { await 3; } }"), SyntaxError);
 
     if (typeof Reflect !== "undefined" && Reflect.parse) {
+        Reflect.parse("export async function f() {}", { target: "module" });
+        assertThrows(() => Reflect.parse("export async function() {}", { target: "module" }), SyntaxError);
+
+        Reflect.parse("export default async function() {}", { target: "module" });
+        Reflect.parse("export default async function f() {}", { target: "module" });
+
         assertThrows(() => Reflect.parse("export default async function() { yield; }", { target: "module" }), SyntaxError);
         assertThrows(() => Reflect.parse("export default async function() { yield = 1; }", { target: "module" }), SyntaxError);
     }