1 files changed, 181 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/hir-expand/src/ast_id_map.rs b/src/tools/rust-analyzer/crates/hir-expand/src/ast_id_map.rs
new file mode 100644
index 000000000..c1ddef03b
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/hir-expand/src/ast_id_map.rs
@@ -0,0 +1,181 @@
+//! `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);
+    }
+}