feat: Implement petgraph traits on Hugr (#498)

This lets us treat HUGRs in the same way as views everywhere (e.g. use
them as Circuits) requiring `T: PetgraphHugr` where before we had `T:
HierarchyView`.

---------

Co-authored-by: Alan Lawrence <alan.lawrence@quantinuum.com>

src/hugr/validate.rs

@@ -101,7 +101,7 @@ impl<'a, 'b> ValidationContext<'a, 'b> {
  fn compute_dominator(&self, parent: Node) -> Dominators<Node> {
  let region: SiblingGraph = SiblingGraph::new(self.hugr, parent);
  let entry_node = self.hugr.children(parent).next().unwrap();
- dominators::simple_fast(&region, entry_node)
+ dominators::simple_fast(&region.as_petgraph(), entry_node)
  }
 
  /// Check the constraints on a single node.
@@ -365,8 +365,11 @@ impl<'a, 'b> ValidationContext<'a, 'b> {
  };
 
  let region: SiblingGraph = SiblingGraph::new(self.hugr, parent);
- let postorder = Topo::new(&region);
- let nodes_visited = postorder.iter(&region).filter(|n| *n != parent).count();
+ let postorder = Topo::new(&region.as_petgraph());
+ let nodes_visited = postorder
+ .iter(&region.as_petgraph())
+ .filter(|n| *n != parent)
+ .count();
  let node_count = self.hugr.children(parent).count();
  if nodes_visited != node_count {
  return Err(ValidationError::NotADag {

src/hugr/views.rs

@@ -1,13 +1,14 @@
 //! Read-only access into HUGR graphs and subgraphs.
 
 pub mod descendants;
-mod petgraph;
+pub mod petgraph;
 pub mod sibling;
 pub mod sibling_subgraph;
 
 #[cfg(test)]
 mod tests;
 
+pub use self::petgraph::PetgraphWrapper;
 pub use descendants::DescendantsGraph;
 pub use sibling::SiblingGraph;
 pub use sibling_subgraph::SiblingSubgraph;
@@ -22,7 +23,6 @@ use crate::ops::handle::NodeHandle;
 use crate::ops::{FuncDecl, FuncDefn, OpName, OpTag, OpType, DFG};
 use crate::types::{EdgeKind, FunctionType};
 use crate::{Direction, Node, Port};
-use ::petgraph::visit as pv;
 
 /// A trait for inspecting HUGRs.
 /// For end users we intend this to be superseded by region-specific APIs.
@@ -181,6 +181,15 @@ pub trait HugrView: sealed::HugrInternals {
  /// type. Otherwise return None.
  fn get_function_type(&self) -> Option<&FunctionType>;
 
+ /// Return a wrapper over the view that can be used in petgraph algorithms.
+ #[inline]
+ fn as_petgraph(&self) -> PetgraphWrapper<'_, Self>
+ where
+ Self: Sized,
+ {
+ PetgraphWrapper { hugr: self }
+ }
+
  /// Return dot string showing underlying graph and hierarchy side by side.
  fn dot_string(&self) -> String {
  let hugr = self.base_hugr();
@@ -232,19 +241,7 @@ pub trait HugrView: sealed::HugrInternals {
 }
 
 /// A common trait for views of a HUGR hierarchical subgraph.
-pub trait HierarchyView<'a>:
- HugrView
- + pv::GraphBase<NodeId = Node>
- + pv::GraphProp
- + pv::NodeCount
- + pv::NodeIndexable
- + pv::EdgeCount
- + pv::Visitable
- + pv::GetAdjacencyMatrix
- + pv::Visitable
-where
- for<'g> &'g Self: pv::IntoNeighborsDirected + pv::IntoNodeIdentifiers,
-{
+pub trait HierarchyView<'a>: HugrView {
  /// The base from which the subgraph is derived.
  type Base;
 

src/hugr/views/descendants.rs

@@ -21,8 +21,8 @@ type RegionGraph<'g> = portgraph::view::Region<'g, &'g MultiPortGraph>;
 /// its immediate children. Prefer using [`SiblingGraph`] when possible,
 /// as it is more efficient.
 ///
-/// Implements the [`HierarchyView`] trait, as well as [`HugrView`] and petgraph's
-/// _visit_ traits, so can be used interchangeably with [`SiblingGraph`].
+/// Implements the [`HierarchyView`] trait, as well as [`HugrView`], it can be
+/// used interchangeably with [`SiblingGraph`].
 ///
 /// [`SiblingGraph`]: super::SiblingGraph
 pub struct DescendantsGraph<'g, Root = Node, Base = Hugr>