LibJS: Restore the environment if an exception is thrown in 'with' block

Author: https://github.com/davidot
Commit: https://github.com/SerenityOS/serenity/commit/db0a48d34c3
Pull-request: https://github.com/SerenityOS/serenity/pull/9895
Reviewed-by: https://github.com/linusg ✅

Userland/Libraries/LibJS/AST.cpp

@@ -379,12 +379,13 @@ Value WithStatement::execute(Interpreter& interpreter, GlobalObject& global_obje
 
     // 6. Let C be the result of evaluating Statement.
     auto result = interpreter.execute_statement(global_object, m_body).value_or(js_undefined());
-    if (interpreter.exception())
-        return {};
 
     // 7. Set the running execution context's LexicalEnvironment to oldEnv.
     interpreter.vm().running_execution_context().lexical_environment = old_environment;
 
+    if (interpreter.exception())
+        return {};
+
     // 8. Return Completion(UpdateEmpty(C, undefined)).
     return result;
 }

Userland/Libraries/LibJS/Tests/with-basic.js

@@ -15,6 +15,7 @@ test("basic with statement functionality", () => {
     }
 
     expect(object.bar).toBe(2);
+    expect(() => foo).toThrowWithMessage(ReferenceError, "'foo' is not defined");
 
     expect(bar).toBe(99);
 });
@@ -22,3 +23,23 @@ test("basic with statement functionality", () => {
 test("syntax error in strict mode", () => {
     expect("'use strict'; with (foo) {}").not.toEval();
 });
+
+test("restores lexical environment even when exception is thrown", () => {
+    var object = {
+        foo: 1,
+        get bar() {
+            throw Error();
+        },
+    };
+
+    try {
+        with (object) {
+            expect(foo).toBe(1);
+            bar;
+        }
+        expect().fail();
+    } catch (e) {
+        expect(() => foo).toThrowWithMessage(ReferenceError, "'foo' is not defined");
+    }
+    expect(() => foo).toThrowWithMessage(ReferenceError, "'foo' is not defined");
+});