add check port is output

src/hugr/rewrite/insert_identity.rs

@@ -3,7 +3,7 @@
 use crate::hugr::{HugrMut, Node};
 use crate::ops::LeafOp;
 use crate::types::EdgeKind;
-use crate::{Hugr, HugrView, Port};
+use crate::{Direction, Hugr, HugrView, Port};
 
 use super::Rewrite;
 
@@ -38,6 +38,10 @@ pub enum IdentityInsertionError {
  /// Invalid port kind.
  #[error("post_port has invalid kind {0:?}. Must be Value.")]
  InvalidPortKind(Option<EdgeKind>),
+
+ /// Must be input port.
+ #[error("post_port is an output port, must be input.")]
+ PortIsOutput,
 }
 
 impl Rewrite for IdentityInsertion {
@@ -53,11 +57,15 @@ impl Rewrite for IdentityInsertion {
  Conditions:
  1. post_port is Value kind.
  2. post_port is connected to a sibling of post_node.
+ 3. post_port is input.
  */
 
  unimplemented!()
  }
  fn apply(self, h: &mut Hugr) -> Result<Self::ApplyResult, IdentityInsertionError> {
+ if self.post_port.direction() != Direction::Incoming {
+ return Err(IdentityInsertionError::PortIsOutput);
+ }
  let (pre_node, pre_port) = h
  .linked_ports(self.post_node, self.post_port)
  .exactly_one()
@@ -73,7 +81,6 @@ impl Rewrite for IdentityInsertion {
  h.connect(pre_node, pre_port.index(), new_node, 0)
  .expect("Should only fail if ports don't exist.");
 
- // TODO Check type, insert Noop...
  h.connect(new_node, 0, self.post_node, self.post_port.index())
  .expect("Should only fail if ports don't exist.");
  Ok(new_node)
@@ -121,9 +128,14 @@ mod tests {
 
  let final_node = tail.node();
 
- let final_node_port = h.node_inputs(final_node).next().unwrap();
+ let final_node_output = h.node_outputs(final_node).next().unwrap();
+ let rw = IdentityInsertion::new(final_node, final_node_output);
+ let apply_result = h.apply_rewrite(rw);
+ assert_eq!(apply_result, Err(IdentityInsertionError::PortIsOutput));
 
- let rw = IdentityInsertion::new(final_node, final_node_port);
+ let final_node_input = h.node_inputs(final_node).next().unwrap();
+
+ let rw = IdentityInsertion::new(final_node, final_node_input);
 
  let apply_result = h.apply_rewrite(rw);
  assert_eq!(