1 files changed, 20 insertions, 0 deletions
diff --git a/third_party/rust/wast/src/gensym.rs b/third_party/rust/wast/src/gensym.rs
new file mode 100644
index 0000000000..9f718f06d9
--- /dev/null
+++ b/third_party/rust/wast/src/gensym.rs
@@ -0,0 +1,20 @@
+use crate::token::{Id, Span};
+use std::cell::Cell;
+
+thread_local!(static NEXT: Cell<u32> = Cell::new(0));
+
+pub fn reset() {
+    NEXT.with(|c| c.set(0));
+}
+
+pub fn gen(span: Span) -> Id<'static> {
+    NEXT.with(|next| {
+        let gen = next.get() + 1;
+        next.set(gen);
+        Id::gensym(span, gen)
+    })
+}
+
+pub fn fill<'a>(span: Span, slot: &mut Option<Id<'a>>) -> Id<'a> {
+    *slot.get_or_insert_with(|| gen(span))
+}