use borrow<> for AST selectors

fixes #1128

.changeset/two-drinks-check.md

@@ -0,0 +1,5 @@
+---
+"@nomicfoundation/slang": patch
+---
+
+fix a bug where CST nodes are invalidated after using AST types

crates/codegen/runtime/cargo/wasm/src/runtime/interface/ast.wit.jinja2

@@ -2,9 +2,9 @@ interface ast {
     use cst.{node, nonterminal-node};
 
     resource selectors {
-        sequence: static func(node: nonterminal-node) -> result<list<option<node>>, string>;
-        choice: static func(node: nonterminal-node) -> result<node, string>;
-        repeated: static func(node: nonterminal-node) -> result<list<node>, string>;
-        separated: static func(node: nonterminal-node) -> result<list<list<node>>, string>;
+        sequence: static func(node: borrow<nonterminal-node>) -> result<list<option<node>>, string>;
+        choice: static func(node: borrow<nonterminal-node>) -> result<node, string>;
+        repeated: static func(node: borrow<nonterminal-node>) -> result<list<node>, string>;
+        separated: static func(node: borrow<nonterminal-node>) -> result<list<list<node>>, string>;
     }
 }

crates/codegen/runtime/cargo/wasm/src/runtime/wrappers/ast/mod.rs

@@ -8,7 +8,7 @@ mod ffi {
         Guest, GuestSelectors,
     };
     pub use crate::wasm_crate::bindings::exports::nomic_foundation::slang::cst::{
-        Node, NonterminalNode,
+        Node, NonterminalNodeBorrow,
     };
 }
 
@@ -27,25 +27,25 @@ impl ffi::Guest for crate::wasm_crate::World {
 pub struct SelectorsWrapper;
 
 impl ffi::GuestSelectors for SelectorsWrapper {
-    fn sequence(node: ffi::NonterminalNode) -> Result<Vec<Option<ffi::Node>>, String> {
+    fn sequence(node: ffi::NonterminalNodeBorrow<'_>) -> Result<Vec<Option<ffi::Node>>, String> {
         Ok(selectors::select_sequence(node._borrow_ffi())?
             .into_iter()
             .map(|opt| opt.map(|node| node._into_ffi()))
             .collect())
     }
 
-    fn choice(node: ffi::NonterminalNode) -> Result<ffi::Node, String> {
+    fn choice(node: ffi::NonterminalNodeBorrow<'_>) -> Result<ffi::Node, String> {
         Ok(selectors::select_choice(node._borrow_ffi())?._into_ffi())
     }
 
-    fn repeated(node: ffi::NonterminalNode) -> Result<Vec<ffi::Node>, String> {
+    fn repeated(node: ffi::NonterminalNodeBorrow<'_>) -> Result<Vec<ffi::Node>, String> {
         Ok(selectors::select_repeated(node._borrow_ffi())?
             .into_iter()
             .map(|node| node._into_ffi())
             .collect())
     }
 
-    fn separated(node: ffi::NonterminalNode) -> Result<Vec<Vec<ffi::Node>>, String> {
+    fn separated(node: ffi::NonterminalNodeBorrow<'_>) -> Result<Vec<Vec<ffi::Node>>, String> {
         Ok(selectors::select_separated(node._borrow_ffi())?
             .into_iter()
             .map(|vec| vec.into_iter().map(|node| node._into_ffi()).collect())

crates/testlang/outputs/npm/tests/src/tests/ast/ast.mts

@@ -201,3 +201,22 @@ test("create and use binary expressions", () => {
   assertIsTerminalNode(operator, TerminalKind.Plus, "+");
   assertIsTerminalNode(rightOperand.variant, TerminalKind.Identifier, "bar");
 });
+
+it("can reuse the same CST nodes after selectors", () => {
+  // Bug: https://github.com/NomicFoundation/slang/issues/1128
+
+  const source = `foo + bar`;
+
+  const parser = Parser.create("1.0.0");
+  const parseOutput = parser.parse(NonterminalKind.SourceUnit, source);
+  parseOutput.isValid(); // true
+
+  const cst = parseOutput.tree.asNonterminalNode()!;
+  const ast = new SourceUnit(cst);
+
+  expect(ast.cst.kind).toBe(NonterminalKind.SourceUnit);
+
+  expect(ast.members.cst.kind).toBe(NonterminalKind.SourceUnitMembers);
+
+  expect(ast.cst.kind).toBe(NonterminalKind.SourceUnit);
+});