[parser] disallow language mode directive in body of function with non-simple parameters

src/scopes.h

Index: src/scopes.h
diff --git a/src/scopes.h b/src/scopes.h
index 4990fab994574a9fb9fbb27814ba93faf3ad5c86..12b70668cf8b38d1f87241ddb091fc58053dbd19 100644
--- a/src/scopes.h
+++ b/src/scopes.h
@@ -390,10 +390,25 @@ class Scope: public ZoneObject {
   }
 
   bool has_simple_parameters() const {
-    DCHECK(is_function_scope());
     return has_simple_parameters_;
   }
 
+  // TODO(caitp): manage this state in a better way. PreParser must be able to
+  // communicate that the scope is non-simple, without allocating any parameters
+  // as the Parser does. This is necessary to ensure that TC39's proposed early
+  // error can be reported consistently regardless of whether lazily parsed or
+  // not.
+  void SetHasNonSimpleParameters() {
+    DCHECK(is_function_scope());
+    has_simple_parameters_ = false;
+  }
+
+  // Retrieve `IsSimpleParameterList` of current or outer function.
+  bool HasSimpleParameters() {
+    Scope* scope = ClosureScope();
+    return !scope->is_function_scope() || scope->has_simple_parameters();
+  }
+
   // The local variable 'arguments' if we need to allocate it; NULL otherwise.
   Variable* arguments() const {
     DCHECK(!is_arrow_scope() || arguments_ == nullptr);