LibJS: Parse "this" as ThisExpression

Author: https://github.com/sunverwerth
Commit: https://github.com/SerenityOS/serenity/commit/f8f65053bdb
Pull-request: https://github.com/SerenityOS/serenity/pull/1772

Libraries/LibJS/AST.cpp

@@ -662,6 +662,16 @@ void Identifier::dump(int indent) const
     printf("Identifier \"%s\"\n", m_string.characters());
 }
 
+Value ThisExpression::execute(Interpreter& interpreter) const
+{
+    return interpreter.this_value();
+}
+
+void ThisExpression::dump(int indent) const
+{
+    ASTNode::dump(indent);
+}
+
 Value AssignmentExpression::execute(Interpreter& interpreter) const
 {
     auto rhs_result = m_rhs->execute(interpreter);

Libraries/LibJS/AST.h

@@ -502,6 +502,15 @@ private:
     FlyString m_string;
 };
 
+class ThisExpression final : public Expression {
+public:
+    virtual Value execute(Interpreter&) const override;
+    virtual void dump(int indent) const override;
+
+private:
+    virtual const char* class_name() const override { return "ThisExpression"; }
+};
+
 class CallExpression : public Expression {
 public:
     CallExpression(NonnullRefPtr<Expression> callee, NonnullRefPtrVector<Expression> arguments = {})

Libraries/LibJS/Interpreter.cpp

@@ -158,10 +158,6 @@ void Interpreter::set_variable(const FlyString& name, Value value, bool first_as
 
 Optional<Value> Interpreter::get_variable(const FlyString& name)
 {
-    static FlyString this_name = "this";
-    if (name == this_name)
-        return this_value();
-
     for (ssize_t i = m_scope_stack.size() - 1; i >= 0; --i) {
         auto& scope = m_scope_stack.at(i);
         auto value = scope.variables.get(name);

Libraries/LibJS/Lexer.cpp

@@ -66,6 +66,7 @@ Lexer::Lexer(StringView source)
         s_keywords.set("null", TokenType::NullLiteral);
         s_keywords.set("return", TokenType::Return);
         s_keywords.set("switch", TokenType::Switch);
+        s_keywords.set("this", TokenType::This);
         s_keywords.set("throw", TokenType::Throw);
         s_keywords.set("true", TokenType::BoolLiteral);
         s_keywords.set("try", TokenType::Try);

Libraries/LibJS/Parser.cpp

@@ -317,6 +317,9 @@ NonnullRefPtr<Expression> Parser::parse_primary_expression()
         consume(TokenType::ParenClose);
         return expression;
     }
+    case TokenType::This:
+        consume();
+        return create_ast_node<ThisExpression>();
     case TokenType::Identifier: {
         auto arrow_function_result = try_parse_arrow_function_expression(false);
         if (!arrow_function_result.is_null()) {
@@ -400,14 +403,13 @@ NonnullRefPtr<ObjectExpression> Parser::parse_object_expression()
             m_parser_state.m_has_errors = true;
             auto& current_token = m_parser_state.m_current_token;
             fprintf(stderr, "Error: Unexpected token %s as member in object initialization. Expected a numeric literal, string literal or identifier (line: %zu, column: %zu))\n",
-                    current_token.name(),
-                    current_token.line_number(),
-                    current_token.line_column());
+                current_token.name(),
+                current_token.line_number(),
+                current_token.line_column());
             consume();
             continue;
         }
 
-
         if (match(TokenType::Colon)) {
             consume(TokenType::Colon);
             properties.set(property_name, parse_expression(0));
@@ -487,7 +489,7 @@ NonnullRefPtr<Expression> Parser::parse_secondary_expression(NonnullRefPtr<Expre
     case TokenType::Percent:
         consume();
         return create_ast_node<BinaryExpression>(BinaryOp::Modulo, move(lhs), parse_expression(min_precedence, associativity));
-   case TokenType::DoubleAsterisk:
+    case TokenType::DoubleAsterisk:
         consume();
         return create_ast_node<BinaryExpression>(BinaryOp::Exponentiation, move(lhs), parse_expression(min_precedence, associativity));
     case TokenType::GreaterThan:
@@ -905,6 +907,7 @@ bool Parser::match_expression() const
         || type == TokenType::BracketOpen
         || type == TokenType::ParenOpen
         || type == TokenType::Function
+        || type == TokenType::This
         || match_unary_prefixed_expression();
 }
 
@@ -997,10 +1000,10 @@ Token Parser::consume(TokenType type)
         m_parser_state.m_has_errors = true;
         auto& current_token = m_parser_state.m_current_token;
         fprintf(stderr, "Error: Unexpected token %s. Expected %s (line: %zu, column: %zu))\n",
-                current_token.name(),
-                Token::name(type),
-                current_token.line_number(),
-                current_token.line_column());
+            current_token.name(),
+            Token::name(type),
+            current_token.line_number(),
+            current_token.line_column());
     }
     return consume();
 }
@@ -1010,10 +1013,10 @@ void Parser::expected(const char* what)
     m_parser_state.m_has_errors = true;
     auto& current_token = m_parser_state.m_current_token;
     fprintf(stderr, "Error: Unexpected token %s. Expected %s (line: %zu, column: %zu)\n",
-            current_token.name(),
-            what,
-            current_token.line_number(),
-            current_token.line_column());
+        current_token.name(),
+        what,
+        current_token.line_number(),
+        current_token.line_column());
 }
 
 void Parser::save_state()

Libraries/LibJS/Token.h

@@ -111,6 +111,7 @@ namespace JS {
     __ENUMERATE_JS_TOKEN(SlashEquals)                 \
     __ENUMERATE_JS_TOKEN(StringLiteral)               \
     __ENUMERATE_JS_TOKEN(Switch)                      \
+    __ENUMERATE_JS_TOKEN(This)                        \
     __ENUMERATE_JS_TOKEN(Throw)                       \
     __ENUMERATE_JS_TOKEN(Tilde)                       \
     __ENUMERATE_JS_TOKEN(Try)                         \