//! Trace is a pretty niche data structure which is used when lowering a CST //! into HIR. //! //! Lowering process calculates two bits of information: //! * the lowered syntax itself //! * a mapping between lowered syntax and original syntax //! //! Due to the way salsa works, the mapping is usually hot lava, as it contains //! absolute offsets. The `Trace` structure (inspired, at least in name, by //! Kotlin's `BindingTrace`) allows use the same code to compute both //! projections. use la_arena::{Arena, ArenaMap, Idx, RawIdx}; pub(crate) struct Trace { arena: Option>, map: Option, V>>, len: u32, } impl Trace { #[allow(dead_code)] pub(crate) fn new_for_map() -> Trace { Trace { arena: None, map: Some(ArenaMap::default()), len: 0 } } pub(crate) fn alloc(&mut self, value: impl FnOnce() -> V, data: impl FnOnce() -> T) -> Idx { let id = if let Some(arena) = &mut self.arena { arena.alloc(data()) } else { let id = Idx::::from_raw(RawIdx::from(self.len)); self.len += 1; id }; if let Some(map) = &mut self.map { map.insert(id, value()); } id } #[allow(dead_code)] pub(crate) fn into_arena(mut self) -> Arena { self.arena.take().unwrap() } pub(crate) fn into_map(mut self) -> ArenaMap, V> { self.map.take().unwrap() } }