1 files changed, 42 insertions, 0 deletions
diff --git a/third_party/rust/rustversion/src/iter.rs b/third_party/rust/rustversion/src/iter.rs
new file mode 100644
index 0000000000..722013c7d6
--- /dev/null
+++ b/third_party/rust/rustversion/src/iter.rs
@@ -0,0 +1,42 @@
+use proc_macro::{token_stream, Delimiter, TokenStream, TokenTree};
+
+pub type Iter<'a> = &'a mut IterImpl;
+
+pub struct IterImpl {
+    stack: Vec<token_stream::IntoIter>,
+    peeked: Option<TokenTree>,
+}
+
+pub fn new(tokens: TokenStream) -> IterImpl {
+    IterImpl {
+        stack: vec![tokens.into_iter()],
+        peeked: None,
+    }
+}
+
+impl IterImpl {
+    pub fn peek(&mut self) -> Option<&TokenTree> {
+        self.peeked = self.next();
+        self.peeked.as_ref()
+    }
+}
+
+impl Iterator for IterImpl {
+    type Item = TokenTree;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(tt) = self.peeked.take() {
+            return Some(tt);
+        }
+        loop {
+            let top = self.stack.last_mut()?;
+            match top.next() {
+                None => drop(self.stack.pop()),
+                Some(TokenTree::Group(ref group)) if group.delimiter() == Delimiter::None => {
+                    self.stack.push(group.stream().into_iter());
+                }
+                Some(tt) => return Some(tt),
+            }
+        }
+    }
+}