From 600fcd2d467e3b2ebb5bf9e237c4255f53d7e329 Mon Sep 17 00:00:00 2001
From: Sergey Bugaev <bugaevc@serenityos.org>
Date: Mon, 1 Jun 2020 17:08:34 +0300
Subject: [PATCH] LibJS: Replace some parser assertions by syntax errors

When parsing JavaScript, we can get pretty much any sequnce of tokens,
and we shouldn't crash if it's not something that we normally expect.
Instead, emit syntax errors.
---
 Libraries/LibJS/Parser.cpp | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/Libraries/LibJS/Parser.cpp b/Libraries/LibJS/Parser.cpp
index f95a88c8f2..31807cad17 100644
--- a/Libraries/LibJS/Parser.cpp
+++ b/Libraries/LibJS/Parser.cpp
@@ -225,9 +225,12 @@ NonnullRefPtr<Program> Parser::parse_program()
             consume();
         }
     }
-    ASSERT(m_parser_state.m_var_scopes.size() == 1);
-    program->add_variables(m_parser_state.m_var_scopes.last());
-    program->add_variables(m_parser_state.m_let_scopes.last());
+    if (m_parser_state.m_var_scopes.size() == 1) {
+        program->add_variables(m_parser_state.m_var_scopes.last());
+        program->add_variables(m_parser_state.m_let_scopes.last());
+    } else {
+        syntax_error("Unclosed scope");
+    }
     return program;
 }
 
@@ -620,13 +623,19 @@ NonnullRefPtr<ObjectExpression> Parser::parse_object_expression()
 
             properties.append(create_ast_node<ObjectProperty>(*property_name, function, property_type));
         } else if (match(TokenType::Colon)) {
+            if (!property_name) {
+                syntax_error("Expected a property name");
+                skip_to_next_property();
+                continue;
+            }
             consume();
-            ASSERT(property_name);
             properties.append(create_ast_node<ObjectProperty>(*property_name, parse_expression(2), property_type));
-        } else {
-            ASSERT(property_name);
-            ASSERT(property_value);
+        } else if (property_name && property_value) {
             properties.append(create_ast_node<ObjectProperty>(*property_name, *property_value, property_type));
+        } else {
+            syntax_error("Expected a property");
+            skip_to_next_property();
+            continue;
         }
 
         if (!match(TokenType::Comma))
@@ -1342,7 +1351,7 @@ NonnullRefPtr<Statement> Parser::parse_for_statement()
             if (match_for_in_of())
                 return parse_for_in_of_statement(*init);
         } else {
-            ASSERT_NOT_REACHED();
+            syntax_error("Unexpected token in for loop");
         }
     }
     consume(TokenType::Semicolon);