LibJS: Allow 'yield' and 'await' as function expression names

The spec says so, and test262 checks for this too.

2 files changed, 8 insertions, 0 deletions

diff --git a/Userland/Libraries/LibJS/Parser.cpp b/Userland/Libraries/LibJS/Parser.cpp
index 93e110f83e..624846154c 100644
--- a/Userland/Libraries/LibJS/Parser.cpp
+++ b/Userland/Libraries/LibJS/Parser.cpp
@@ -1417,6 +1417,7 @@ NonnullRefPtr<FunctionNodeType> Parser::parse_function_node(u8 parse_options)
 
     ScopePusher scope(*this, ScopePusher::Var | ScopePusher::Function);
 
+    constexpr auto is_function_expression = IsSame<FunctionNodeType, FunctionExpression>;
     auto is_generator = (parse_options & FunctionNodeParseOptions::IsGeneratorFunction) != 0;
     String name;
     if (parse_options & FunctionNodeParseOptions::CheckForFunctionAndName) {
@@ -1431,6 +1432,8 @@ NonnullRefPtr<FunctionNodeType> Parser::parse_function_node(u8 parse_options)
 
         if (FunctionNodeType::must_have_name() || match(TokenType::Identifier))
             name = consume(TokenType::Identifier).value();
+        else if (is_function_expression && (match(TokenType::Yield) || match(TokenType::Await)))
+            name = consume().value();
     }
     consume(TokenType::ParenOpen);
     i32 function_length = -1;
diff --git a/Userland/Libraries/LibJS/Tests/syntax/generators.js b/Userland/Libraries/LibJS/Tests/syntax/generators.js
index ba521f9fed..99e0968c4b 100644
--- a/Userland/Libraries/LibJS/Tests/syntax/generators.js
+++ b/Userland/Libraries/LibJS/Tests/syntax/generators.js
@@ -49,3 +49,8 @@ describe("parsing classes with generator methods", () => {
         expect(`class Foo { *constructor() { yield 42; } }`).not.toEval();
     });
 });
+
+test("function expression names equal to 'yield'", () => {
+    expect(`function *foo() { (function yield() {}); }`).toEval();
+    expect(`function *foo() { function yield() {} }`).not.toEval();
+});