LibJS: Tweak generated source in 'new Function()' to match ES 2015 spec

ES 5(.1) described parsing of the function body string as:

https://www.ecma-international.org/ecma-262/5.1/#sec-15.3.2.1

7. If P is not parsable as a FormalParameterList[opt] then throw a SyntaxError exception.
8. If body is not parsable as FunctionBody then throw a SyntaxError exception.

We implemented it as building the source string of a complete function
and feeding that to the parser, with the same outcome. ES 2015+ does
exactly that, but with newlines at certain positions:

https://tc39.es/ecma262/#sec-createdynamicfunction

16. Let bodyString be the string-concatenation of 0x000A (LINE FEED), ? ToString(bodyArg), and 0x000A (LINE FEED).
17. Let prefix be the prefix associated with kind in Table 49.
18. Let sourceString be the string-concatenation of prefix, " anonymous(", P, 0x000A (LINE FEED), ") {", bodyString, and "}".

This patch updates the generated source string to match these
requirements. This will make certain edge cases work, e.g.
'new Function("-->")', where the user supplied input must be placed on
its own line to be valid syntax.

1 files changed, 1 insertions, 1 deletions

diff --git a/Libraries/LibJS/Runtime/FunctionConstructor.cpp b/Libraries/LibJS/Runtime/FunctionConstructor.cpp
index 7b269269c0..b8664907f2 100644
--- a/Libraries/LibJS/Runtime/FunctionConstructor.cpp
+++ b/Libraries/LibJS/Runtime/FunctionConstructor.cpp
@@ -81,7 +81,7 @@ Value FunctionConstructor::construct(Function&)
         if (vm.exception())
             return {};
     }
-    auto source = String::formatted("function anonymous({}) {{ {} }}", parameters_source, body_source);
+    auto source = String::formatted("function anonymous({}\n) {{\n{}\n}}", parameters_source, body_source);
     auto parser = Parser(Lexer(source));
     auto function_expression = parser.parse_function_node<FunctionExpression>();
     if (parser.has_errors()) {