LibJS: Fix runaway let scope when parsing for-in/of statements

This requires variables that should be exported to the script host
or to other scripts to be declared as var (such as in test-common.js),
since lexically-scoped variables won't be visible.

2 files changed, 10 insertions, 9 deletions

diff --git a/Userland/Libraries/LibJS/Parser.cpp b/Userland/Libraries/LibJS/Parser.cpp
index d488df6147..bbfceebeec 100644
--- a/Userland/Libraries/LibJS/Parser.cpp
+++ b/Userland/Libraries/LibJS/Parser.cpp
@@ -2033,6 +2033,11 @@ NonnullRefPtr<Statement> Parser::parse_for_statement()
     consume(TokenType::ParenOpen);
 
     bool in_scope = false;
+    ScopeGuard guard([&]() {
+        if (in_scope)
+            m_state.let_scopes.take_last();
+    });
+
     RefPtr<ASTNode> init;
     if (!match(TokenType::Semicolon)) {
         if (match_expression()) {
@@ -2075,10 +2080,6 @@ NonnullRefPtr<Statement> Parser::parse_for_statement()
     TemporaryChange continue_change(m_state.in_continue_context, true);
     auto body = parse_statement();
 
-    if (in_scope) {
-        m_state.let_scopes.take_last();
-    }
-
     return create_ast_node<ForStatement>({ m_state.current_token.filename(), rule_start.position(), position() }, move(init), move(test), move(update), move(body));
 }
 
diff --git a/Userland/Libraries/LibJS/Tests/test-common.js b/Userland/Libraries/LibJS/Tests/test-common.js
index 94cbbfbb4a..b192a5d9a8 100644
--- a/Userland/Libraries/LibJS/Tests/test-common.js
+++ b/Userland/Libraries/LibJS/Tests/test-common.js
@@ -1,10 +1,10 @@
-let describe;
-let test;
-let expect;
+var describe;
+var test;
+var expect;
 
 // Stores the results of each test and suite. Has a terrible
 // name to avoid name collision.
-let __TestResults__ = {};
+var __TestResults__ = {};
 
 // So test names like "toString" don't automatically produce an error
 Object.setPrototypeOf(__TestResults__, null);
@@ -12,7 +12,7 @@ Object.setPrototypeOf(__TestResults__, null);
 // This array is used to communicate with the C++ program. It treats
 // each message in this array as a separate message. Has a terrible
 // name to avoid name collision.
-let __UserOutput__ = [];
+var __UserOutput__ = [];
 
 // We also rebind console.log here to use the array above
 console.log = (...args) => {