From f4d0babd5dc5faffe57dc17584ea59552ea1bf52 Mon Sep 17 00:00:00 2001
From: Linus Groh <mail@linusgroh.de>
Date: Mon, 5 Oct 2020 00:00:10 +0100
Subject: [PATCH] LibJS: Make assignment to CallExpression a syntax error in
 strict mode

---
 Libraries/LibJS/Parser.cpp                         | 2 ++
 Libraries/LibJS/Tests/invalid-lhs-in-assignment.js | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/Libraries/LibJS/Parser.cpp b/Libraries/LibJS/Parser.cpp
index 273fef5ea2..deec9c0536 100644
--- a/Libraries/LibJS/Parser.cpp
+++ b/Libraries/LibJS/Parser.cpp
@@ -1129,6 +1129,8 @@ NonnullRefPtr<AssignmentExpression> Parser::parse_assignment_expression(Assignme
         auto name = static_cast<const Identifier&>(*lhs).string();
         if (name == "eval" || name == "arguments")
             syntax_error(String::formatted("'{}' cannot be assigned to in strict mode code", name));
+    } else if (m_parser_state.m_strict_mode && lhs->is_call_expression()) {
+        syntax_error("Cannot assign to function call");
     }
     return create_ast_node<AssignmentExpression>(assignment_op, move(lhs), parse_expression(min_precedence, associativity));
 }
diff --git a/Libraries/LibJS/Tests/invalid-lhs-in-assignment.js b/Libraries/LibJS/Tests/invalid-lhs-in-assignment.js
index 7018a94b78..ec5024f8ec 100644
--- a/Libraries/LibJS/Tests/invalid-lhs-in-assignment.js
+++ b/Libraries/LibJS/Tests/invalid-lhs-in-assignment.js
@@ -5,6 +5,10 @@ test("assignment to function call", () => {
     }).toThrowWithMessage(ReferenceError, "Invalid left-hand side in assignment");
 });
 
+test("assignment to function call in strict mode", () => {
+    expect("'use strict'; foo() = 'foo'").not.toEval();
+});
+
 test("assignment to inline function call", () => {
     expect(() => {
         (function () {})() = "foo";