Address comments

src/portmatching.rs

@@ -65,13 +65,16 @@ impl PEdge {
         circ: &impl Circuit,
     ) -> Result<Self, InvalidEdgeProperty> {
         let src = port;
-        let (dst_node, dst) = circ.linked_ports(node, src).exactly_one().map_err(|e| {
-            if e.size_hint().0 > 0 {
-                InvalidEdgeProperty::AmbiguousEdge(src)
-            } else {
-                InvalidEdgeProperty::NoLinkedEdge(src)
-            }
-        })?;
+        let (dst_node, dst) = circ
+            .linked_ports(node, src)
+            .exactly_one()
+            .map_err(|mut e| {
+                if e.next().is_some() {
+                    InvalidEdgeProperty::AmbiguousEdge(src)
+                } else {
+                    InvalidEdgeProperty::NoLinkedEdge(src)
+                }
+            })?;
         if circ.get_optype(dst_node).tag() == OpTag::Input {
             return Ok(Self::InputEdge { src });
         }
@@ -120,6 +123,9 @@ impl portmatching::EdgeProperty for PEdge {
 ///
 /// A node is either a real node in the HUGR graph or a hidden copy node
 /// that is identified by its node and outgoing port.
+///
+/// A NodeID::CopyNode can only be found as a target of a PEdge::InputEdge
+/// property. Furthermore, a NodeID::CopyNode never has a node property.
 #[derive(
     Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, serde::Serialize, serde::Deserialize,
 )]

src/portmatching/matcher.rs

@@ -13,7 +13,7 @@ use hugr::{hugr::views::SiblingSubgraph, ops::OpType, Hugr, Node, Port};
 use itertools::Itertools;
 use portmatching::{
     automaton::{LineBuilder, ScopeAutomaton},
-    PatternID,
+    EdgeProperty, PatternID,
 };
 use thiserror::Error;
 
@@ -385,10 +385,7 @@ fn compatible_offsets(e1: &PEdge, e2: &PEdge) -> bool {
     let PEdge::InternalEdge { dst: dst1, .. } = e1 else {
         return false;
     };
-    let src2 = match *e2 {
-        PEdge::InternalEdge { src, .. } => src,
-        PEdge::InputEdge { src, .. } => src,
-    };
+    let src2 = e2.offset_id();
     dst1.direction() != src2.direction() && dst1.index() == src2.index()
 }
 

src/portmatching/pattern.rs

@@ -100,14 +100,12 @@ impl CircuitPattern {
             )
             .map(|m| {
                 m.into_iter()
-                    .filter_map(|(node_p, node_c)| {
-                        let NodeID::HugrNode(node_p) = node_p else {
-                            return None;
-                        };
-                        let NodeID::HugrNode(node_c) = node_c else {
-                            return None;
-                        };
-                        Some((node_p, node_c))
+                    .filter_map(|(node_p, node_c)| match (node_p, node_c) {
+                        (NodeID::HugrNode(node_p), NodeID::HugrNode(node_c)) => {
+                            Some((node_p, node_c))
+                        }
+                        (NodeID::CopyNode(..), NodeID::CopyNode(..)) => None,
+                        _ => panic!("Invalid match map"),
                     })
                     .collect()
             })