SiblingSubgraph::try_from_nodes fails if there's a Const+LoadConst #2654
Description
Given the following hugr (fn build_hugr from sibling_subgraph::test)
graph LR
subgraph 0 ["(0) [**Module**]"]
direction LR
style 0 stroke:#832561,stroke-width:3px
subgraph 1 ["(1) FuncDefn: #quot;test#quot;"]
direction LR
2["(2) Input"]
3["(3) Output"]
4["(4) test.quantum.CX"]
5["(5) const:custom:f64(0.5)"]
6["(6) LoadConstant"]
7["(7) test.quantum.RzF64"]
2--"0:0<br>qubit"-->4
2--"1:1<br>qubit"-->4
2--"2:0<br>qubit"-->7
4--"0:0<br>qubit"-->3
4--"1:1<br>qubit"-->3
5--"0:0<br>float64"-->6
6--"0:1<br>float64"-->7
7--"0:2<br>qubit"-->3
end
end
Trying to create a subgraph containing the const definition and LoadConstant nodes fails with at NotConvex error.
Failing test:
#[test]
fn construct_load_const_subgraph() {
let (hugr, func_root) = build_hugr().unwrap(); // From sibling_subgraph.rs
let const_node = hugr
.children(func_root)
.find(|&n| hugr.get_optype(n).is_const())
.unwrap();
let load_const_node = hugr
.children(func_root)
.find(|&n| hugr.get_optype(n).is_load_constant())
.unwrap();
let nodes: BTreeSet<_> = BTreeSet::from_iter([const_node, load_const_node]);
let sub = SiblingSubgraph::try_from_nodes(vec![const_node, load_const_node], &hugr).unwrap();
let subgraph_nodes: BTreeSet<_> = sub.nodes().iter().copied().collect();
assert_eq!(subgraph_nodes, nodes);
}Error: NotConvex
test hugr::views::sibling_subgraph::tests::construct_load_const_subgraph ... FAILED