1 files changed, 48 insertions, 0 deletions
diff --git a/src/libsyntax/node_id.rs b/src/libsyntax/node_id.rs
new file mode 100644
index 00000000000..58d2334a7b1
--- /dev/null
+++ b/src/libsyntax/node_id.rs
@@ -0,0 +1,48 @@
+use rustc_serialize::{Decoder, Encoder};
+use rustc_span::ExpnId;
+use std::fmt;
+
+rustc_index::newtype_index! {
+    pub struct NodeId {
+        ENCODABLE = custom
+        DEBUG_FORMAT = "NodeId({})"
+    }
+}
+
+rustc_data_structures::define_id_collections!(NodeMap, NodeSet, NodeId);
+
+/// `NodeId` used to represent the root of the crate.
+pub const CRATE_NODE_ID: NodeId = NodeId::from_u32_const(0);
+
+/// When parsing and doing expansions, we initially give all AST nodes this AST
+/// node value. Then later, in the renumber pass, we renumber them to have
+/// small, positive ids.
+pub const DUMMY_NODE_ID: NodeId = NodeId::MAX;
+
+impl NodeId {
+    pub fn placeholder_from_expn_id(expn_id: ExpnId) -> Self {
+        NodeId::from_u32(expn_id.as_u32())
+    }
+
+    pub fn placeholder_to_expn_id(self) -> ExpnId {
+        ExpnId::from_u32(self.as_u32())
+    }
+}
+
+impl fmt::Display for NodeId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.as_u32(), f)
+    }
+}
+
+impl rustc_serialize::UseSpecializedEncodable for NodeId {
+    fn default_encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_u32(self.as_u32())
+    }
+}
+
+impl rustc_serialize::UseSpecializedDecodable for NodeId {
+    fn default_decode<D: Decoder>(d: &mut D) -> Result<NodeId, D::Error> {
+        d.read_u32().map(NodeId::from_u32)
+    }
+}