Suggestion : Assign 'this' to slot 0 only if the current context is a class, not the global scope

[nieuwmijnleven]

This pull request is a suggestion to improve compiler internal safety and clarity.

It addresses an issue where the compiler assigns the local variable "this" to slot 0 even when compiling non-method functions. This behavior causes this to behave like a valid local variable outside of class methods, which is unintended and can hide runtime errors.

What was wrong?

The compiler code did not check whether the current function was inside a class (currentClass != NULL) before assigning "this" to slot 0. As a result, even functions that are not methods received "this" as a local variable.

What is fixed?

• Added a check to ensure "this" is only assigned to slot 0 when compiling class methods.

• This prevents this from being a local variable outside of methods, allowing the runtime to properly catch errors when this is misused.

Additional notes

• This fix improves the safety and correctness of this handling in Lox.

• Existing tests pass; additional test cases for this usage outside of classes can be added if desired.

Closes #1203