rust/crates/hir_expand/src/ast_id_map.rs
2021-12-29 23:48:53 -08:00

182 lines
5.8 KiB
Rust

//! `AstIdMap` allows to create stable IDs for "large" syntax nodes like items
//! and macro calls.
//!
//! Specifically, it enumerates all items in a file and uses position of a an
//! item as an ID. That way, id's don't change unless the set of items itself
//! changes.
use std::{
any::type_name,
fmt,
hash::{BuildHasher, BuildHasherDefault, Hash, Hasher},
marker::PhantomData,
};
use la_arena::{Arena, Idx};
use profile::Count;
use rustc_hash::FxHasher;
use syntax::{ast, match_ast, AstNode, AstPtr, SyntaxNode, SyntaxNodePtr};
/// `AstId` points to an AST node in a specific file.
pub struct FileAstId<N: AstNode> {
raw: ErasedFileAstId,
_ty: PhantomData<fn() -> N>,
}
impl<N: AstNode> Clone for FileAstId<N> {
fn clone(&self) -> FileAstId<N> {
*self
}
}
impl<N: AstNode> Copy for FileAstId<N> {}
impl<N: AstNode> PartialEq for FileAstId<N> {
fn eq(&self, other: &Self) -> bool {
self.raw == other.raw
}
}
impl<N: AstNode> Eq for FileAstId<N> {}
impl<N: AstNode> Hash for FileAstId<N> {
fn hash<H: Hasher>(&self, hasher: &mut H) {
self.raw.hash(hasher);
}
}
impl<N: AstNode> fmt::Debug for FileAstId<N> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "FileAstId::<{}>({})", type_name::<N>(), self.raw.into_raw())
}
}
impl<N: AstNode> FileAstId<N> {
// Can't make this a From implementation because of coherence
pub fn upcast<M: AstNode>(self) -> FileAstId<M>
where
N: Into<M>,
{
FileAstId { raw: self.raw, _ty: PhantomData }
}
}
type ErasedFileAstId = Idx<SyntaxNodePtr>;
/// Maps items' `SyntaxNode`s to `ErasedFileAstId`s and back.
#[derive(Default)]
pub struct AstIdMap {
/// Maps stable id to unstable ptr.
arena: Arena<SyntaxNodePtr>,
/// Reverse: map ptr to id.
map: hashbrown::HashMap<Idx<SyntaxNodePtr>, (), ()>,
_c: Count<Self>,
}
impl fmt::Debug for AstIdMap {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("AstIdMap").field("arena", &self.arena).finish()
}
}
impl PartialEq for AstIdMap {
fn eq(&self, other: &Self) -> bool {
self.arena == other.arena
}
}
impl Eq for AstIdMap {}
impl AstIdMap {
pub(crate) fn from_source(node: &SyntaxNode) -> AstIdMap {
assert!(node.parent().is_none());
let mut res = AstIdMap::default();
// By walking the tree in breadth-first order we make sure that parents
// get lower ids then children. That is, adding a new child does not
// change parent's id. This means that, say, adding a new function to a
// trait does not change ids of top-level items, which helps caching.
bdfs(node, |it| {
match_ast! {
match it {
ast::Item(module_item) => {
res.alloc(module_item.syntax());
true
},
ast::BlockExpr(block) => {
res.alloc(block.syntax());
true
},
_ => false,
}
}
});
res.map = hashbrown::HashMap::with_capacity_and_hasher(res.arena.len(), ());
for (idx, ptr) in res.arena.iter() {
let hash = hash_ptr(ptr);
match res.map.raw_entry_mut().from_hash(hash, |idx2| *idx2 == idx) {
hashbrown::hash_map::RawEntryMut::Occupied(_) => unreachable!(),
hashbrown::hash_map::RawEntryMut::Vacant(entry) => {
entry.insert_with_hasher(hash, idx, (), |&idx| hash_ptr(&res.arena[idx]));
}
}
}
res
}
pub fn ast_id<N: AstNode>(&self, item: &N) -> FileAstId<N> {
let raw = self.erased_ast_id(item.syntax());
FileAstId { raw, _ty: PhantomData }
}
fn erased_ast_id(&self, item: &SyntaxNode) -> ErasedFileAstId {
let ptr = SyntaxNodePtr::new(item);
let hash = hash_ptr(&ptr);
match self.map.raw_entry().from_hash(hash, |&idx| self.arena[idx] == ptr) {
Some((&idx, &())) => idx,
None => panic!(
"Can't find {:?} in AstIdMap:\n{:?}",
item,
self.arena.iter().map(|(_id, i)| i).collect::<Vec<_>>(),
),
}
}
pub fn get<N: AstNode>(&self, id: FileAstId<N>) -> AstPtr<N> {
AstPtr::try_from_raw(self.arena[id.raw].clone()).unwrap()
}
fn alloc(&mut self, item: &SyntaxNode) -> ErasedFileAstId {
self.arena.alloc(SyntaxNodePtr::new(item))
}
}
fn hash_ptr(ptr: &SyntaxNodePtr) -> u64 {
let mut hasher = BuildHasherDefault::<FxHasher>::default().build_hasher();
ptr.hash(&mut hasher);
hasher.finish()
}
/// Walks the subtree in bdfs order, calling `f` for each node. What is bdfs
/// order? It is a mix of breadth-first and depth first orders. Nodes for which
/// `f` returns true are visited breadth-first, all the other nodes are explored
/// depth-first.
///
/// In other words, the size of the bfs queue is bound by the number of "true"
/// nodes.
fn bdfs(node: &SyntaxNode, mut f: impl FnMut(SyntaxNode) -> bool) {
let mut curr_layer = vec![node.clone()];
let mut next_layer = vec![];
while !curr_layer.is_empty() {
curr_layer.drain(..).for_each(|node| {
let mut preorder = node.preorder();
while let Some(event) = preorder.next() {
match event {
syntax::WalkEvent::Enter(node) => {
if f(node.clone()) {
next_layer.extend(node.children());
preorder.skip_subtree();
}
}
syntax::WalkEvent::Leave(_) => {}
}
}
});
std::mem::swap(&mut curr_layer, &mut next_layer);
}
}