Setting private properties causes NRE

[VelvetToroyashi]

Version used

Jint 3.1.5

Describe the bug

Setting a private property on a class in any capacity throws a NullReferenceException from native code.

To Reproduce

class ClassWithPrivateField {
    #nonexistent = 'evidently';
}

new ClassWithPrivateField().#nonexistent = 'explosion!';

Expected behavior

Jint throws a managed (JavaScript) exception as it does with attempting to use other invalid properties.

Additional context

This specifically occurs when attempting to set a private property outside of a class (e.g., in a module function). Interestingly, doing it in a class function throws a different (and equally as vague) exception (though, "not found" does seem more indicative of correct behavior here-):

Promise was rejected with value ReferenceError: TODO Not found!!
Stack trace: 
   at Bot (eventCallback, commandCallback) bootstrap:34:23
   at entrypoint () bootstrap:15:21
   at bootstrap:23:8

[lahma]

So iare there more code sample of specific cases? Ideally in c# utilizing the Engine.

[VelvetToroyashi]

@lahma Here's a minimal repro in .NET:
(Just realized I misread the message, oopsies,)

In normal code I don't foresee this really happening intentionally, but for arbitrary inputs to the engine this could happen intentionally or otherwise

using Jint;

new Engine().Evaluate
(
    """
    class A { }
    
    new A().#nonexistent = 1;
    """
);

And the produced exception:

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at Jint.Runtime.Interpreter.Expressions.JintPrivateIdentifierExpression.EvaluateInternal(EvaluationContext context)
   at Jint.Runtime.Interpreter.Expressions.JintExpression.GetValue(EvaluationContext context)
   at Jint.Runtime.Interpreter.Expressions.JintMemberExpression.EvaluateInternal(EvaluationContext context)
   at Jint.Runtime.Interpreter.Expressions.JintAssignmentExpression.SimpleAssignmentExpression.SetValue(EvaluationContext context)
   at Jint.Runtime.Interpreter.Expressions.JintAssignmentExpression.SimpleAssignmentExpression.EvaluateInternal(EvaluationContext context)
   at Jint.Runtime.Interpreter.Expressions.JintExpression.GetValue(EvaluationContext context)
   at Jint.Runtime.Interpreter.Statements.JintExpressionStatement.ExecuteInternal(EvaluationContext context)
   at Jint.Engine.ScriptEvaluation(ScriptRecord scriptRecord, ParserOptions parserOptions)
   at Jint.Engine.<>c__DisplayClass96_0.<Execute>b__0()
   at Jint.Engine.ExecuteWithConstraints[T](Boolean strict, Func`1 callback)
   at Jint.Engine.Execute(Prepared`1& preparedScript)
   at Jint.Engine.Evaluate(Prepared`1& preparedScript)

[lahma]

Thanks, what about the different error message in different call context?

[VelvetToroyashi]

class A { 
    constructor() { #nonexistent = 2; }
}
new A();

Produces the following error

Unhandled exception. Jint.Runtime.JavaScriptException: TODO Not found!!
 ---> Error: TODO Not found!!
   at A () <anonymous>:2:20
   at <anonymous>:5:5
   --- End of inner exception stack trace ---
   at Jint.Engine.ScriptEvaluation(ScriptRecord scriptRecord, ParserOptions parserOptions)
   at Jint.Engine.<>c__DisplayClass96_0.<Execute>b__0()
   at Jint.Engine.ExecuteWithConstraints[T](Boolean strict, Func`1 callback)
   at Jint.Engine.Execute(Prepared`1& preparedScript)
   at Jint.Engine.Execute(String code, String source)
   at Program.<Main>$(String[] args) in /media/velvet/NVMe/Projects/DiscordJSPluginsBot/DiscordJSPluginsBot/Program.cs:line 14

[lahma]

Thanks for the repros. Now far easier to investigate 👍🏻

[lahma]

This was a bit monkey-patched as in v4 the parser actually detects these errors better instead of allowing the code to get into Jint's runtime logic. But at least the error message should now be better.