From 72d2bd56ce558764424918dee274903b7e044184 Mon Sep 17 00:00:00 2001
From: Linus Groh <mail@linusgroh.de>
Date: Mon, 4 May 2020 23:07:05 +0100
Subject: [PATCH] LibJS: Implement modulo assignment operator (%=)

---
 Libraries/LibJS/AST.cpp                       | 9 +++++++++
 Libraries/LibJS/AST.h                         | 1 +
 Libraries/LibJS/Parser.cpp                    | 4 ++++
 Libraries/LibJS/Tests/assignment-operators.js | 4 ++++
 4 files changed, 18 insertions(+)

diff --git a/Libraries/LibJS/AST.cpp b/Libraries/LibJS/AST.cpp
index 5579e3cd68..70a181d7fe 100644
--- a/Libraries/LibJS/AST.cpp
+++ b/Libraries/LibJS/AST.cpp
@@ -850,6 +850,12 @@ Value AssignmentExpression::execute(Interpreter& interpreter) const
             return {};
         rhs_result = div(interpreter, lhs_result, rhs_result);
         break;
+    case AssignmentOp::ModuloAssignment:
+        lhs_result = m_lhs->execute(interpreter);
+        if (interpreter.exception())
+            return {};
+        rhs_result = mod(interpreter, lhs_result, rhs_result);
+        break;
     case AssignmentOp::ExponentiationAssignment:
         lhs_result = m_lhs->execute(interpreter);
         if (interpreter.exception())
@@ -960,6 +966,9 @@ void AssignmentExpression::dump(int indent) const
     case AssignmentOp::DivisionAssignment:
         op_string = "/=";
         break;
+    case AssignmentOp::ModuloAssignment:
+        op_string = "%=";
+        break;
     case AssignmentOp::ExponentiationAssignment:
         op_string = "**=";
         break;
diff --git a/Libraries/LibJS/AST.h b/Libraries/LibJS/AST.h
index ab02e02572..245fa7ac4d 100644
--- a/Libraries/LibJS/AST.h
+++ b/Libraries/LibJS/AST.h
@@ -604,6 +604,7 @@ enum class AssignmentOp {
     SubtractionAssignment,
     MultiplicationAssignment,
     DivisionAssignment,
+    ModuloAssignment,
     ExponentiationAssignment,
     BitwiseAndAssignment,
     BitwiseOrAssignment,
diff --git a/Libraries/LibJS/Parser.cpp b/Libraries/LibJS/Parser.cpp
index c98a827056..a999b4b325 100644
--- a/Libraries/LibJS/Parser.cpp
+++ b/Libraries/LibJS/Parser.cpp
@@ -634,6 +634,9 @@ 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::PercentEquals:
+        consume();
+        return create_ast_node<AssignmentExpression>(AssignmentOp::ModuloAssignment, move(lhs), parse_expression(min_precedence, associativity));
     case TokenType::DoubleAsterisk:
         consume();
         return create_ast_node<BinaryExpression>(BinaryOp::Exponentiation, move(lhs), parse_expression(min_precedence, associativity));
@@ -1194,6 +1197,7 @@ bool Parser::match_secondary_expression() const
         || type == TokenType::Slash
         || type == TokenType::SlashEquals
         || type == TokenType::Percent
+        || type == TokenType::PercentEquals
         || type == TokenType::DoubleAsterisk
         || type == TokenType::DoubleAsteriskEquals
         || type == TokenType::Equals
diff --git a/Libraries/LibJS/Tests/assignment-operators.js b/Libraries/LibJS/Tests/assignment-operators.js
index ec2a693988..fd1d82ca74 100644
--- a/Libraries/LibJS/Tests/assignment-operators.js
+++ b/Libraries/LibJS/Tests/assignment-operators.js
@@ -23,6 +23,10 @@ try {
     assert((x /= 2) === 3);
     assert(x === 3);
 
+    x = 6;
+    assert((x %= 4) === 2);
+    assert(x === 2);
+
     x = 2;
     assert((x **= 3) === 8);
     assert(x === 8);