refactor: Nonempty

quantinuum-hugr/Cargo.toml

@@ -52,6 +52,7 @@ delegate = "0.12.0"
 paste = "1.0"
 strum = "0.26.1"
 strum_macros = "0.26.1"
+nonempty = "0.10.0"
 
 [dev-dependencies]
 criterion = { version = "0.5.1", features = ["html_reports"] }

quantinuum-hugr/src/hugr/hugrmut.rs

@@ -4,6 +4,7 @@ use core::panic;
 use std::collections::HashMap;
 use std::ops::Range;
 
+use nonempty::NonEmpty;
 use portgraph::view::{NodeFilter, NodeFiltered};
 use portgraph::{LinkMut, NodeIndex, PortMut, PortView, SecondaryMap};
 
@@ -365,7 +366,7 @@ impl<T: RootTagged<RootHandle = Node> + AsMut<Hugr>> HugrMut for T {
         subgraph: &SiblingSubgraph,
     ) -> HashMap<Node, Node> {
         // Create a portgraph view with the explicit list of nodes defined by the subgraph.
-        let portgraph: NodeFiltered<_, NodeFilter<&[Node]>, &[Node]> =
+        let portgraph: NodeFiltered<_, NodeFilter<&NonEmpty<Node>>, &NonEmpty<Node>> =
             NodeFiltered::new_node_filtered(
                 other.portgraph(),
                 |node, ctx| ctx.contains(&node.into()),

quantinuum-hugr/src/hugr/rewrite/replace.rs

@@ -1,8 +1,8 @@
 //! Implementation of the `Replace` operation.
 
-use std::collections::{HashMap, HashSet, VecDeque};
-
 use itertools::Itertools;
+use nonempty::NonEmpty;
+use std::collections::{HashMap, HashSet, VecDeque};
 use thiserror::Error;
 
 use crate::hugr::hugrmut::InsertionResult;
@@ -59,7 +59,7 @@ pub struct Replacement {
     /// These must all have a common parent (i.e. be siblings).  Called "S" in the spec.
     /// Must be non-empty - otherwise there is no parent under which to place [Self::replacement],
     /// and there would be no possible [Self::mu_inp], [Self::mu_out] or [Self::adoptions].
-    pub removal: Vec<Node>,
+    pub removal: NonEmpty<Node>,
     /// A hugr (not necessarily valid, as it may be missing edges and/or nodes), whose root
     /// is the same type as the root of [Self::replacement].  "G" in the spec.
     pub replacement: Hugr,
@@ -440,6 +440,7 @@ mod test {
 
     use cool_asserts::assert_matches;
     use itertools::Itertools;
+    use nonempty::nonempty;
 
     use crate::algorithm::nest_cfgs::test::depth;
     use crate::builder::{
@@ -571,7 +572,7 @@ mod test {
         }
 
         h.apply_rewrite(Replacement {
-            removal: vec![entry.node(), bb2.node()],
+            removal: nonempty![entry.node(), bb2.node()],
             replacement,
             adoptions: HashMap::from([(r_df1.node(), entry.node()), (r_df2.node(), bb2.node())]),
             mu_inp: vec![],
@@ -700,7 +701,7 @@ mod test {
             },
         );
         let mut r = Replacement {
-            removal: vec![case1, case2],
+            removal: nonempty![case1, case2],
             replacement: rep1,
             adoptions: HashMap::from_iter([(r1, case1), (r2, baz_dfg.node())]),
             mu_inp: vec![],
@@ -724,14 +725,14 @@ mod test {
         // First, removed nodes...
         assert_eq!(
             verify_apply(Replacement {
-                removal: vec![h.root()],
+                removal: nonempty![h.root()],
                 ..r.clone()
             }),
             Err(ReplaceError::CantReplaceRoot)
         );
         assert_eq!(
             verify_apply(Replacement {
-                removal: vec![case1, baz_dfg.node()],
+                removal: nonempty![case1, baz_dfg.node()],
                 ..r.clone()
             }),
             Err(ReplaceError::MultipleParents(vec![cond.node(), case2]))

quantinuum-hugr/src/hugr/rewrite/simple_replace.rs

@@ -621,7 +621,7 @@ pub(in crate::hugr::rewrite) mod test {
         replacement.remove_node(in_);
         replacement.remove_node(out);
         Replacement {
-            removal: s.subgraph.nodes().to_vec(),
+            removal: s.subgraph.nodes().clone(),
             replacement,
             adoptions: HashMap::new(),
             mu_inp,

quantinuum-hugr/src/hugr/views/sibling_subgraph.rs

@@ -13,6 +13,7 @@ use std::collections::HashSet;
 use std::mem;
 
 use itertools::Itertools;
+use nonempty::NonEmpty;
 use portgraph::algorithms::ConvexChecker;
 use portgraph::{view::Subgraph, Direction, PortView};
 use thiserror::Error;
@@ -54,7 +55,7 @@ use crate::{Hugr, IncomingPort, Node, OutgoingPort, Port, SimpleReplacement};
 #[derive(Clone, Debug)]
 pub struct SiblingSubgraph {
     /// The nodes of the induced subgraph.
-    nodes: Vec<Node>,
+    nodes: NonEmpty<Node>,
     /// The input ports of the subgraph.
     ///
     /// Grouped by input parameter. Each port must be unique and belong to a
@@ -101,16 +102,12 @@ impl SiblingSubgraph {
         let (inputs, outputs) = get_input_output_ports(dfg_graph);
 
         validate_subgraph(dfg_graph, &nodes, &inputs, &outputs)?;
-
-        if nodes.is_empty() {
-            Err(InvalidSubgraph::EmptySubgraph)
-        } else {
-            Ok(Self {
-                nodes,
-                inputs,
-                outputs,
-            })
-        }
+        let nodes = NonEmpty::from_vec(nodes).ok_or(InvalidSubgraph::EmptySubgraph)?;
+        Ok(Self {
+            nodes,
+            inputs,
+            outputs,
+        })
     }
 
     /// Create a new convex sibling subgraph from input and output boundaries.
@@ -192,6 +189,8 @@ impl SiblingSubgraph {
             return Err(InvalidSubgraph::NotConvex);
         }
 
+        let nodes = NonEmpty::from_vec(nodes).ok_or(InvalidSubgraph::EmptySubgraph)?;
+
         Ok(Self {
             nodes,
             inputs,
@@ -269,7 +268,7 @@ impl SiblingSubgraph {
     }
 
     /// An iterator over the nodes in the subgraph.
-    pub fn nodes(&self) -> &[Node] {
+    pub fn nodes(&self) -> &NonEmpty<Node> {
         &self.nodes
     }
 
@@ -715,15 +714,12 @@ mod tests {
         fn from_sibling_graph(sibling_graph: &impl HugrView) -> Result<Self, InvalidSubgraph> {
             let root = sibling_graph.root();
             let nodes = sibling_graph.children(root).collect_vec();
-            if nodes.is_empty() {
-                Err(InvalidSubgraph::EmptySubgraph)
-            } else {
-                Ok(Self {
-                    nodes,
-                    inputs: Vec::new(),
-                    outputs: Vec::new(),
-                })
-            }
+            let nodes = NonEmpty::from_vec(nodes).ok_or(InvalidSubgraph::EmptySubgraph)?;
+            Ok(Self {
+                nodes,
+                inputs: Vec::new(),
+                outputs: Vec::new(),
+            })
         }
     }