luaur-rt 0.1.2

Safe, ergonomic, mlua-style API for luaur (pure-Rust Luau).
Documentation 
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//! Garbage-collector control. Mirrors `mlua::Lua`'s `gc_*` surface and the
//! `mlua::state::{GcMode, GcIncParams, GcGenParams}` types.
//!
//! Luau ships a single **incremental** GC (no generational mode). The control
//! ops map onto luaur's `lua_gc`:
//!
//! | mlua                | `lua_gc` op         |
//! |---------------------|---------------------|
//! | `gc_collect`        | `LUA_GCCOLLECT`     |
//! | `gc_stop`           | `LUA_GCSTOP`        |
//! | `gc_restart`        | `LUA_GCRESTART`     |
//! | `gc_is_running`     | `LUA_GCISRUNNING`   |
//! | `gc_count`          | `LUA_GCCOUNT`/`..B` |
//! | `gc_step`           | `LUA_GCSTEP`        |
//! | `gc_inc(goal,mul,sz)`| `LUA_GCSETGOAL/..` |
//!
//! **DEVIATION:** Luau has no generational GC, so `gc_gen` and
//! `GcMode::Generational` are not backed by the VM. `gc_set_mode` accepts the
//! incremental mode (applying its params) and *reports* the previous mode as
//! incremental; passing `Generational` is a no-op that returns the current
//! (incremental) mode, matching the only behavior Luau can honor.

use crate::error::Result;
use crate::state::Lua;
use crate::sys::*;

/// Parameters for Luau's incremental GC, mirroring `mlua::state::GcIncParams`.
///
/// On Luau the tunables are the **goal** (heap-growth target percentage),
/// the **step multiplier**, and the **step size** (KB). (Lua 5.x's `pause` is
/// replaced by `goal` here — see [`GcIncParams::goal`].)
#[derive(Debug, Clone, Copy, Default)]
pub struct GcIncParams {
    pub(crate) goal: Option<core::ffi::c_int>,
    pub(crate) step_multiplier: Option<core::ffi::c_int>,
    pub(crate) step_size: Option<core::ffi::c_int>,
}

impl GcIncParams {
    /// The heap-growth goal (percentage). Luau's analog of Lua's `pause`.
    /// Mirrors `mlua::state::GcIncParams::goal`.
    pub fn goal(mut self, goal: u32) -> Self {
        self.goal = Some(goal as core::ffi::c_int);
        self
    }

    /// The GC step multiplier (percentage of allocation to collect per step).
    /// Mirrors `mlua::state::GcIncParams::step_multiplier`.
    pub fn step_multiplier(mut self, mul: u32) -> Self {
        self.step_multiplier = Some(mul as core::ffi::c_int);
        self
    }

    /// The GC step size in KB. Mirrors `mlua::state::GcIncParams::step_size`.
    pub fn step_size(mut self, size: u32) -> Self {
        self.step_size = Some(size as core::ffi::c_int);
        self
    }
}

/// Parameters for a generational GC, mirroring `mlua::state::GcGenParams`.
///
/// **DEVIATION:** Luau has no generational GC; this exists only for signature
/// parity with mlua's Lua 5.4/5.5 surface and is never honored by the VM.
#[derive(Debug, Clone, Copy, Default)]
pub struct GcGenParams {
    pub minor_multiplier: u32,
    pub major_multiplier: u32,
}

/// The GC operating mode, mirroring `mlua::state::GcMode`.
///
/// Luau only supports [`GcMode::Incremental`]; [`GcMode::Generational`] is
/// provided for signature parity and is treated as a no-op by [`Lua::gc_set_mode`].
#[derive(Debug, Clone, Copy)]
pub enum GcMode {
    /// Incremental GC (the only mode Luau supports).
    Incremental(GcIncParams),
    /// Generational GC — **not supported by Luau** (see the module note).
    Generational(GcGenParams),
}

impl Lua {
    /// The number of bytes currently used by the VM. Mirrors
    /// `mlua::Lua::used_memory` (luaur's `totalbytes`).
    pub fn used_memory(&self) -> usize {
        unsafe {
            let g = (*self.state()).global;
            (*g).totalbytes
        }
    }

    /// Whether the GC is currently running. Mirrors `mlua::Lua::gc_is_running`.
    pub fn gc_is_running(&self) -> bool {
        lua_gc(self.state(), lua_GCOp::LUA_GCISRUNNING as c_int, 0) != 0
    }

    /// Stop the GC. Mirrors `mlua::Lua::gc_stop`.
    pub fn gc_stop(&self) {
        lua_gc(self.state(), lua_GCOp::LUA_GCSTOP as c_int, 0);
    }

    /// Restart the GC. Mirrors `mlua::Lua::gc_restart`.
    pub fn gc_restart(&self) {
        lua_gc(self.state(), lua_GCOp::LUA_GCRESTART as c_int, 0);
    }

    /// The total memory in use, in KB (the `LUA_GCCOUNT` op). Mirrors
    /// `mlua::Lua::gc_count`.
    pub fn gc_count(&self) -> usize {
        let kb = lua_gc(self.state(), lua_GCOp::LUA_GCCOUNT as c_int, 0).max(0) as usize;
        kb
    }

    /// Run one incremental GC step over `kbytes` of work. Returns whether a full
    /// collection cycle finished. Mirrors `mlua::Lua::gc_step_kbytes`/`gc_step`.
    pub fn gc_step_kbytes(&self, kbytes: c_int) -> Result<bool> {
        let finished = lua_gc(self.state(), lua_GCOp::LUA_GCSTEP as c_int, kbytes) != 0;
        Ok(finished)
    }

    /// Run a default-size incremental GC step. Mirrors `mlua::Lua::gc_step`.
    pub fn gc_step(&self) -> Result<bool> {
        self.gc_step_kbytes(0)
    }

    /// Apply incremental-GC parameters (goal / step multiplier / step size).
    /// Mirrors `mlua::Lua::gc_inc`; returns the previous [`GcMode`] (always
    /// incremental on Luau).
    pub fn gc_inc(&self, pause: c_int, step_multiplier: c_int, step_size: c_int) -> GcMode {
        let state = self.state();
        // mlua maps `pause` -> goal on the Luau backend.
        if pause > 0 {
            lua_gc(state, lua_GCOp::LUA_GCSETGOAL as c_int, pause);
        }
        if step_multiplier > 0 {
            lua_gc(state, lua_GCOp::LUA_GCSETSTEPMUL as c_int, step_multiplier);
        }
        if step_size > 0 {
            lua_gc(state, lua_GCOp::LUA_GCSETSTEPSIZE as c_int, step_size);
        }
        GcMode::Incremental(GcIncParams::default())
    }

    /// Set the GC mode, returning the previous mode. Mirrors
    /// `mlua::Lua::gc_set_mode`.
    ///
    /// **DEVIATION:** Luau is always incremental. Passing
    /// [`GcMode::Incremental`] applies its params and returns the prior
    /// (incremental) mode; passing [`GcMode::Generational`] is a no-op that
    /// returns the current incremental mode.
    pub fn gc_set_mode(&self, mode: GcMode) -> GcMode {
        let state = self.state();
        match mode {
            GcMode::Incremental(p) => {
                if let Some(goal) = p.goal {
                    lua_gc(state, lua_GCOp::LUA_GCSETGOAL as c_int, goal);
                }
                if let Some(mul) = p.step_multiplier {
                    lua_gc(state, lua_GCOp::LUA_GCSETSTEPMUL as c_int, mul);
                }
                if let Some(sz) = p.step_size {
                    lua_gc(state, lua_GCOp::LUA_GCSETSTEPSIZE as c_int, sz);
                }
            }
            GcMode::Generational(_) => {
                // Luau has no generational GC; nothing to apply.
            }
        }
        // Luau's only real mode is incremental.
        GcMode::Incremental(GcIncParams::default())
    }
}