2 files changed, 55 insertions, 0 deletions

diff --git a/crates/ra_syntax/src/lib.rs b/crates/ra_syntax/src/lib.rs
index bc311cbbc..97b196118 100644
--- a/crates/ra_syntax/src/lib.rs
+++ b/crates/ra_syntax/src/lib.rs
@@ -35,6 +35,7 @@ mod syntax_kinds;
 pub mod utils;
 mod validation;
 mod yellow;
+mod ptr;
 
 pub use rowan::{SmolStr, TextRange, TextUnit};
 pub use crate::{
@@ -42,6 +43,7 @@ pub use crate::{
     lexer::{tokenize, Token},
     syntax_kinds::SyntaxKind,
     yellow::{Direction, SyntaxError, SyntaxNode, WalkEvent, Location, TreeArc},
+    ptr::SyntaxNodePtr,
 };
 
 use ra_text_edit::AtomTextEdit;
diff --git a/crates/ra_syntax/src/ptr.rs b/crates/ra_syntax/src/ptr.rs
new file mode 100644
index 000000000..e8c40e5d3
--- /dev/null
+++ b/crates/ra_syntax/src/ptr.rs
@@ -0,0 +1,53 @@
+use crate::{
+    AstNode, SourceFile, SyntaxKind, SyntaxNode, TextRange,
+    algo::generate,
+};
+
+/// 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, Copy, PartialEq, Eq, Hash)]
+pub struct SyntaxNodePtr {
+    range: TextRange,
+    kind: SyntaxKind,
+}
+
+impl SyntaxNodePtr {
+    pub fn new(node: &SyntaxNode) -> SyntaxNodePtr {
+        SyntaxNodePtr {
+            range: node.range(),
+            kind: node.kind(),
+        }
+    }
+
+    pub fn to_node(self, source_file: &SourceFile) -> &SyntaxNode {
+        generate(Some(source_file.syntax()), |&node| {
+            node.children()
+                .find(|it| self.range.is_subrange(&it.range()))
+        })
+        .find(|it| it.range() == self.range && it.kind() == self.kind)
+        .unwrap_or_else(|| panic!("can't resolve local ptr to SyntaxNode: {:?}", self))
+    }
+
+    pub fn range(self) -> TextRange {
+        self.range
+    }
+
+    pub fn kind(self) -> SyntaxKind {
+        self.kind
+    }
+}
+
+#[test]
+fn test_local_syntax_ptr() {
+    use crate::{ast, AstNode};
+
+    let file = SourceFile::parse("struct Foo { f: u32, }");
+    let field = file
+        .syntax()
+        .descendants()
+        .find_map(ast::NamedFieldDef::cast)
+        .unwrap();
+    let ptr = SyntaxNodePtr::new(field.syntax());
+    let field_syntax = ptr.to_node(&file);
+    assert_eq!(field.syntax(), &*field_syntax);
+}