1 files changed, 105 insertions, 0 deletions

diff --git a/crates/syntax/src/ptr.rs b/crates/syntax/src/ptr.rs
new file mode 100644
index 000000000..ca7957747
--- /dev/null
+++ b/crates/syntax/src/ptr.rs
@@ -0,0 +1,105 @@
+//! FIXME: write short doc here
+
+use std::{
+    hash::{Hash, Hasher},
+    iter::successors,
+    marker::PhantomData,
+};
+
+use crate::{AstNode, SyntaxKind, SyntaxNode, TextRange};
+
+/// A pointer to a syntax node inside a file. It can be used to remember a
+/// specific node across reparses of the same file.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct SyntaxNodePtr {
+    pub(crate) range: TextRange,
+    kind: SyntaxKind,
+}
+
+impl SyntaxNodePtr {
+    pub fn new(node: &SyntaxNode) -> SyntaxNodePtr {
+        SyntaxNodePtr { range: node.text_range(), kind: node.kind() }
+    }
+
+    pub fn to_node(&self, root: &SyntaxNode) -> SyntaxNode {
+        assert!(root.parent().is_none());
+        successors(Some(root.clone()), |node| {
+            node.children().find(|it| it.text_range().contains_range(self.range))
+        })
+        .find(|it| it.text_range() == self.range && it.kind() == self.kind)
+        .unwrap_or_else(|| panic!("can't resolve local ptr to SyntaxNode: {:?}", self))
+    }
+
+    pub fn cast<N: AstNode>(self) -> Option<AstPtr<N>> {
+        if !N::can_cast(self.kind) {
+            return None;
+        }
+        Some(AstPtr { raw: self, _ty: PhantomData })
+    }
+}
+
+/// Like `SyntaxNodePtr`, but remembers the type of node
+#[derive(Debug)]
+pub struct AstPtr<N: AstNode> {
+    raw: SyntaxNodePtr,
+    _ty: PhantomData<fn() -> N>,
+}
+
+impl<N: AstNode> Clone for AstPtr<N> {
+    fn clone(&self) -> AstPtr<N> {
+        AstPtr { raw: self.raw.clone(), _ty: PhantomData }
+    }
+}
+
+impl<N: AstNode> Eq for AstPtr<N> {}
+
+impl<N: AstNode> PartialEq for AstPtr<N> {
+    fn eq(&self, other: &AstPtr<N>) -> bool {
+        self.raw == other.raw
+    }
+}
+
+impl<N: AstNode> Hash for AstPtr<N> {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        self.raw.hash(state)
+    }
+}
+
+impl<N: AstNode> AstPtr<N> {
+    pub fn new(node: &N) -> AstPtr<N> {
+        AstPtr { raw: SyntaxNodePtr::new(node.syntax()), _ty: PhantomData }
+    }
+
+    pub fn to_node(&self, root: &SyntaxNode) -> N {
+        let syntax_node = self.raw.to_node(root);
+        N::cast(syntax_node).unwrap()
+    }
+
+    pub fn syntax_node_ptr(&self) -> SyntaxNodePtr {
+        self.raw.clone()
+    }
+
+    pub fn cast<U: AstNode>(self) -> Option<AstPtr<U>> {
+        if !U::can_cast(self.raw.kind) {
+            return None;
+        }
+        Some(AstPtr { raw: self.raw, _ty: PhantomData })
+    }
+}
+
+impl<N: AstNode> From<AstPtr<N>> for SyntaxNodePtr {
+    fn from(ptr: AstPtr<N>) -> SyntaxNodePtr {
+        ptr.raw
+    }
+}
+
+#[test]
+fn test_local_syntax_ptr() {
+    use crate::{ast, AstNode, SourceFile};
+
+    let file = SourceFile::parse("struct Foo { f: u32, }").ok().unwrap();
+    let field = file.syntax().descendants().find_map(ast::RecordField::cast).unwrap();
+    let ptr = SyntaxNodePtr::new(field.syntax());
+    let field_syntax = ptr.to_node(file.syntax());
+    assert_eq!(field.syntax(), &field_syntax);
+}