1 files changed, 150 insertions, 0 deletions

diff --git a/crates/ra_hir/src/source_id.rs b/crates/ra_hir/src/source_id.rs
new file mode 100644
index 000000000..0a8fb6d32
--- /dev/null
+++ b/crates/ra_hir/src/source_id.rs
@@ -0,0 +1,150 @@
+use std::{marker::PhantomData, sync::Arc, hash::{Hash, Hasher}};
+
+use ra_arena::{Arena, RawId, impl_arena_id};
+use ra_syntax::{SyntaxNodePtr, TreeArc, SyntaxNode, SourceFile, AstNode, ast};
+
+use crate::{HirFileId, DefDatabase};
+
+/// `AstId` points to an AST node in any file.
+///
+/// It is stable across reparses, and can be used as salsa key/value.
+#[derive(Debug)]
+pub(crate) struct AstId<N: AstNode> {
+    file_id: HirFileId,
+    file_ast_id: FileAstId<N>,
+}
+
+impl<N: AstNode> Clone for AstId<N> {
+    fn clone(&self) -> AstId<N> {
+        *self
+    }
+}
+impl<N: AstNode> Copy for AstId<N> {}
+
+impl<N: AstNode> PartialEq for AstId<N> {
+    fn eq(&self, other: &Self) -> bool {
+        (self.file_id, self.file_ast_id) == (other.file_id, other.file_ast_id)
+    }
+}
+impl<N: AstNode> Eq for AstId<N> {}
+impl<N: AstNode> Hash for AstId<N> {
+    fn hash<H: Hasher>(&self, hasher: &mut H) {
+        (self.file_id, self.file_ast_id).hash(hasher);
+    }
+}
+
+impl<N: AstNode> AstId<N> {
+    pub(crate) fn file_id(&self) -> HirFileId {
+        self.file_id
+    }
+
+    pub(crate) fn to_node(&self, db: &impl DefDatabase) -> TreeArc<N> {
+        let syntax_node = db.ast_id_to_node(self.file_id, self.file_ast_id.raw);
+        N::cast(&syntax_node).unwrap().to_owned()
+    }
+}
+
+/// `AstId` points to an AST node in a specific file.
+#[derive(Debug)]
+pub(crate) struct FileAstId<N: AstNode> {
+    raw: ErasedFileAstId,
+    _ty: PhantomData<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> FileAstId<N> {
+    pub(crate) fn with_file_id(self, file_id: HirFileId) -> AstId<N> {
+        AstId { file_id, file_ast_id: self }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct ErasedFileAstId(RawId);
+impl_arena_id!(ErasedFileAstId);
+
+/// Maps items' `SyntaxNode`s to `ErasedFileAstId`s and back.
+#[derive(Debug, PartialEq, Eq)]
+pub struct AstIdMap {
+    arena: Arena<ErasedFileAstId, SyntaxNodePtr>,
+}
+
+impl AstIdMap {
+    pub(crate) fn ast_id_map_query(db: &impl DefDatabase, file_id: HirFileId) -> Arc<AstIdMap> {
+        let source_file = db.hir_parse(file_id);
+        Arc::new(AstIdMap::from_source_file(&source_file))
+    }
+
+    pub(crate) fn file_item_query(
+        db: &impl DefDatabase,
+        file_id: HirFileId,
+        ast_id: ErasedFileAstId,
+    ) -> TreeArc<SyntaxNode> {
+        let source_file = db.hir_parse(file_id);
+        db.ast_id_map(file_id).arena[ast_id].to_node(&source_file).to_owned()
+    }
+
+    pub(crate) fn ast_id<N: AstNode>(&self, item: &N) -> FileAstId<N> {
+        let ptr = SyntaxNodePtr::new(item.syntax());
+        let raw = match self.arena.iter().find(|(_id, i)| **i == ptr) {
+            Some((it, _)) => it,
+            None => panic!(
+                "Can't find {:?} in AstIdMap:\n{:?}",
+                item.syntax(),
+                self.arena.iter().map(|(_id, i)| i).collect::<Vec<_>>(),
+            ),
+        };
+
+        FileAstId { raw, _ty: PhantomData }
+    }
+
+    fn from_source_file(source_file: &SourceFile) -> AstIdMap {
+        let mut res = AstIdMap { arena: Arena::default() };
+        // By walking the tree in bread-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.
+        bfs(source_file.syntax(), |it| {
+            if let Some(module_item) = ast::ModuleItem::cast(it) {
+                res.alloc(module_item.syntax());
+            } else if let Some(macro_call) = ast::MacroCall::cast(it) {
+                res.alloc(macro_call.syntax());
+            }
+        });
+        res
+    }
+
+    fn alloc(&mut self, item: &SyntaxNode) -> ErasedFileAstId {
+        self.arena.alloc(SyntaxNodePtr::new(item))
+    }
+}
+
+/// Walks the subtree in bfs order, calling `f` for each node.
+fn bfs(node: &SyntaxNode, mut f: impl FnMut(&SyntaxNode)) {
+    let mut curr_layer = vec![node];
+    let mut next_layer = vec![];
+    while !curr_layer.is_empty() {
+        curr_layer.drain(..).for_each(|node| {
+            next_layer.extend(node.children());
+            f(node);
+        });
+        std::mem::swap(&mut curr_layer, &mut next_layer);
+    }
+}