LibJS: Add strict mode

Adds the ability for a scope (either a function or the entire program)
to be in strict mode. Scopes default to non-strict mode.

There are two ways to determine the strict-ness of the JS engine:

1. In the parser, this can be accessed with the parser_state variable
   m_is_strict_mode boolean. If true, the Parser is currently parsing in
   strict mode. This is done so that the Parser can generate syntax
   errors at parse time, which is required in some cases.

2. With Interpreter.is_strict_mode(). This allows strict mode checking
   at runtime as opposed to compile time.

Additionally, in order to test this, a global isStrictMode() function
has been added to the JS ReplObject under the test-mode flag.

1 files changed, 4 insertions, 0 deletions

diff --git a/Libraries/LibJS/AST.h b/Libraries/LibJS/AST.h
index 4dd15e5723..be605409c9 100644
--- a/Libraries/LibJS/AST.h
+++ b/Libraries/LibJS/AST.h
@@ -120,6 +120,9 @@ public:
     void add_variables(NonnullRefPtrVector<VariableDeclaration>);
     const NonnullRefPtrVector<VariableDeclaration>& variables() const { return m_variables; }
 
+    bool in_strict_mode() const { return m_strict_mode; }
+    void set_strict_mode() { m_strict_mode = true; }
+
 protected:
     ScopeNode() { }
 
@@ -127,6 +130,7 @@ private:
     virtual bool is_scope_node() const final { return true; }
     NonnullRefPtrVector<Statement> m_children;
     NonnullRefPtrVector<VariableDeclaration> m_variables;
+    bool m_strict_mode { false };
 };
 
 class Program : public ScopeNode {