1 files changed, 41 insertions, 0 deletions
diff --git a/compiler/rustc_ast_pretty/src/pprust/state/delimited.rs b/compiler/rustc_ast_pretty/src/pprust/state/delimited.rs
new file mode 100644
index 000000000..fe0640baa
--- /dev/null
+++ b/compiler/rustc_ast_pretty/src/pprust/state/delimited.rs
@@ -0,0 +1,41 @@
+use std::iter::Peekable;
+use std::mem;
+use std::ops::Deref;
+
+pub struct Delimited<I: Iterator> {
+    is_first: bool,
+    iter: Peekable<I>,
+}
+
+pub trait IterDelimited: Iterator + Sized {
+    fn delimited(self) -> Delimited<Self> {
+        Delimited { is_first: true, iter: self.peekable() }
+    }
+}
+
+impl<I: Iterator> IterDelimited for I {}
+
+pub struct IteratorItem<T> {
+    value: T,
+    pub is_first: bool,
+    pub is_last: bool,
+}
+
+impl<I: Iterator> Iterator for Delimited<I> {
+    type Item = IteratorItem<I::Item>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let value = self.iter.next()?;
+        let is_first = mem::replace(&mut self.is_first, false);
+        let is_last = self.iter.peek().is_none();
+        Some(IteratorItem { value, is_first, is_last })
+    }
+}
+
+impl<T> Deref for IteratorItem<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.value
+    }
+}