neyuki 0.5.0

A small Lua-like scripting language implemented in Rust
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//! Metatables and raw access: setmetatable, getmetatable, rawget, rawset,
//! rawequal, rawlen.

use std::rc::Rc;

use crate::vm::machine::VM;
use crate::vm::value::Value;

pub fn builtin_setmetatable(vm: &mut VM, args: &[Value]) -> Result<Vec<Value>, String> {
    let tbl_val = args
        .first()
        .ok_or_else(|| "setmetatable expects table as first argument".to_string())?;
    let mt_val = args
        .get(1)
        .ok_or_else(|| "setmetatable expects 2 arguments".to_string())?;
    match tbl_val {
        Value::Table(t) => {
            if let Some(existing_mt) = &t.borrow().metatable
                && let Some(metaname) = existing_mt.borrow().fields.get("__metatable")
                && !matches!(metaname, Value::Nil)
            {
                return Err("cannot change a protected metatable".to_string());
            }
            // Pin tables carrying a finalizer so refcounting alone can
            // never destroy them before a sweep runs their `__gc`; unpin
            // as soon as the metatable stops providing one.
            let pinned_now = matches!(
                mt_val,
                Value::Table(mt)
                    if matches!(
                        mt.borrow().fields.get("__gc"),
                        Some(Value::Closure(_) | Value::Native(_))
                    )
            );
            match mt_val {
                Value::Nil => {
                    t.borrow_mut().metatable = None;
                    vm.gc.unpin_table(t);
                    Ok(vec![tbl_val.clone()])
                }
                Value::Table(mt) => {
                    t.borrow_mut().metatable = Some(mt.clone());
                    if pinned_now {
                        vm.gc.pin_table(t);
                    } else {
                        vm.gc.unpin_table(t);
                    }
                    if crate::vm::gc::table_weak_values(t) {
                        vm.gc.has_weak_tables = true;
                    }
                    Ok(vec![tbl_val.clone()])
                }
                _ => Err("metatable must be a table or nil".to_string()),
            }
        }
        _ => Err("setmetatable expects a table as first argument".to_string()),
    }
}

pub fn builtin_getmetatable(_vm: &mut VM, args: &[Value]) -> Result<Vec<Value>, String> {
    let tbl_val = args
        .first()
        .ok_or_else(|| "getmetatable expects 1 argument".to_string())?;
    match tbl_val {
        Value::Table(t) => {
            if let Some(mt) = &t.borrow().metatable {
                if let Some(metaname) = mt.borrow().fields.get("__metatable")
                    && !matches!(metaname, Value::Nil)
                {
                    return Ok(vec![metaname.clone()]);
                }
                Ok(vec![Value::Table(mt.clone())])
            } else {
                Ok(vec![Value::Nil])
            }
        }
        _ => Ok(vec![Value::Nil]),
    }
}

pub fn builtin_rawget(_vm: &mut VM, args: &[Value]) -> Result<Vec<Value>, String> {
    let Some(Value::Table(t)) = args.first() else {
        return Err("rawget expects a table".to_string());
    };
    let key = args.get(1).unwrap_or(&Value::Nil);
    Ok(vec![t.borrow().raw_get(key)])
}

pub fn builtin_rawset(vm: &mut VM, args: &[Value]) -> Result<Vec<Value>, String> {
    let table = args.first().unwrap_or(&Value::Nil);
    let Value::Table(t) = table else {
        return Err("rawset expects a table".to_string());
    };
    let key = args.get(1).cloned().unwrap_or(Value::Nil);
    let val = args.get(2).cloned().unwrap_or(Value::Nil);
    if t.borrow().frozen {
        return Err("attempted to mutate a frozen table".to_string());
    }
    if let Value::BigInt(_) = key {
        return Err("table index too large".to_string());
    }
    vm.gc.write_barrier(table, &val);
    t.borrow_mut().raw_set(key, val)?;
    Ok(vec![table.clone()])
}

pub fn builtin_rawequal(_vm: &mut VM, args: &[Value]) -> Result<Vec<Value>, String> {
    let a = args.first().unwrap_or(&Value::Nil);
    let b = args.get(1).unwrap_or(&Value::Nil);
    match (a, b) {
        (Value::Nil, Value::Nil) => Ok(vec![Value::Bool(true)]),
        (Value::Bool(x), Value::Bool(y)) => Ok(vec![Value::Bool(x == y)]),
        (Value::Int(x), Value::Int(y)) => Ok(vec![Value::Bool(x == y)]),
        (Value::Float(x), Value::Float(y)) => Ok(vec![Value::Bool(x == y)]),
        (Value::String(x), Value::String(y)) => Ok(vec![Value::Bool(x == y)]),
        (Value::Table(x), Value::Table(y)) => Ok(vec![Value::Bool(Rc::ptr_eq(x, y))]),
        (Value::Buffer(x), Value::Buffer(y)) => Ok(vec![Value::Bool(Rc::ptr_eq(x, y))]),
        (Value::Closure(x), Value::Closure(y)) => Ok(vec![Value::Bool(Rc::ptr_eq(x, y))]),
        (Value::Native(na), Value::Native(nb)) => Ok(vec![Value::Bool(na.name == nb.name)]),
        _ => Ok(vec![Value::Bool(false)]),
    }
}

pub fn builtin_rawlen(_vm: &mut VM, args: &[Value]) -> Result<Vec<Value>, String> {
    let val = args
        .first()
        .ok_or_else(|| "rawlen expects 1 argument".to_string())?;
    match val {
        Value::Table(t) => Ok(vec![Value::from_usize(t.borrow().array.len())]),
        Value::String(s) => Ok(vec![Value::from_usize(s.len())]),
        Value::Buffer(b) => Ok(vec![Value::from_usize(b.borrow().len())]),
        _ => Err("rawlen expects table, string, or buffer".to_string()),
    }
}