fix!: force_order failing on Const nodes, add arg to rank. (#1300)

BREAKING CHANGE: the `rank` argument of `force_order` takes an
additional argument.

hugr-passes/src/force_order.rs

@@ -1,15 +1,15 @@
 //! Provides [force_order], a tool for fixing the order of nodes in a Hugr.
-use std::{cmp::Reverse, collections::BinaryHeap};
+use std::{cmp::Reverse, collections::BinaryHeap, iter};
 
 use hugr_core::{
     hugr::{
         hugrmut::HugrMut,
         views::{DescendantsGraph, HierarchyView, SiblingGraph},
         HugrError,
     },
-    ops::{OpTag, OpTrait},
+    ops::{NamedOp, OpTag, OpTrait},
     types::EdgeKind,
-    Direction, HugrView as _, Node,
+    HugrView as _, Node,
 };
 use itertools::Itertools as _;
 use petgraph::{
@@ -36,45 +36,58 @@ use petgraph::{
 /// there is no path from `n2` to `n1` (otherwise this would invalidate `hugr`).
 /// Nodes of equal rank will be ordered arbitrarily, although that arbitrary
 /// order is deterministic.
-pub fn force_order(
-    hugr: &mut impl HugrMut,
+pub fn force_order<H: HugrMut>(
+    hugr: &mut H,
     root: Node,
-    rank: impl Fn(Node) -> i64,
+    rank: impl Fn(&H, Node) -> i64,
 ) -> Result<(), HugrError> {
     force_order_by_key(hugr, root, rank)
 }
 
 /// As [force_order], but allows a generic [Ord] choice for the result of the
 /// `rank` function.
-pub fn force_order_by_key<K: Ord>(
-    hugr: &mut impl HugrMut,
+pub fn force_order_by_key<H: HugrMut, K: Ord>(
+    hugr: &mut H,
     root: Node,
-    rank: impl Fn(Node) -> K,
+    rank: impl Fn(&H, Node) -> K,
 ) -> Result<(), HugrError> {
     let dataflow_parents = DescendantsGraph::<Node>::try_new(hugr, root)?
         .nodes()
         .filter(|n| hugr.get_optype(*n).tag() <= OpTag::DataflowParent)
         .collect_vec();
     for dp in dataflow_parents {
+        // we filter out the input and output nodes from the topological sort
+        let [i, o] = hugr.get_io(dp).unwrap();
+        let rank = |n| rank(hugr, n);
         let sg = SiblingGraph::<Node>::try_new(hugr, dp)?;
-        let petgraph = NodeFiltered::from_fn(sg.as_petgraph(), |x| x != dp);
+        let petgraph = NodeFiltered::from_fn(sg.as_petgraph(), |x| x != dp && x != i && x != o);
         let ordered_nodes = ForceOrder::new(&petgraph, &rank)
             .iter(&petgraph)
-            .filter(|&x| hugr.get_optype(x).tag() <= OpTag::DataflowChild)
+            .filter(|&x| {
+                let expected_edge = Some(EdgeKind::StateOrder);
+                let optype = hugr.get_optype(x);
+                if optype.other_input() == expected_edge || optype.other_output() == expected_edge {
+                    assert_eq!(
+                        optype.other_input(),
+                        optype.other_output(),
+                        "Optype does not have both input and output order edge: {}",
+                        optype.name()
+                    );
+                    true
+                } else {
+                    false
+                }
+            })
             .collect_vec();
 
-        for (&n1, &n2) in ordered_nodes.iter().tuple_windows() {
+        // we iterate over the topologically sorted nodes, prepending the input
+        // node and suffixing the output node.
+        for (&n1, &n2) in iter::once(&i)
+            .chain(ordered_nodes.iter())
+            .chain(iter::once(&o))
+            .tuple_windows()
+        {
             let (n1_ot, n2_ot) = (hugr.get_optype(n1), hugr.get_optype(n2));
-            assert_eq!(
-                Some(EdgeKind::StateOrder),
-                n1_ot.other_port_kind(Direction::Outgoing),
-                "Node {n1} does not support state order edges"
-            );
-            assert_eq!(
-                Some(EdgeKind::StateOrder),
-                n2_ot.other_port_kind(Direction::Incoming),
-                "Node {n2} does not support state order edges"
-            );
             if !hugr.output_neighbours(n1).contains(&n2) {
                 hugr.connect(
                     n1,
@@ -192,10 +205,13 @@ mod test {
 
     use super::*;
     use hugr_core::builder::{endo_ft, BuildHandle, Dataflow, DataflowHugr};
+    use hugr_core::extension::EMPTY_REG;
     use hugr_core::ops::handle::{DataflowOpID, NodeHandle};
 
+    use hugr_core::ops::Value;
     use hugr_core::std_extensions::arithmetic::int_ops::{self, IntOpDef};
     use hugr_core::std_extensions::arithmetic::int_types::INT_TYPES;
+    use hugr_core::types::{FunctionType, Type};
     use hugr_core::{builder::DFGBuilder, hugr::Hugr};
     use hugr_core::{HugrView, Wire};
 
@@ -257,7 +273,7 @@ mod test {
     type RankMap = HashMap<Node, i64>;
 
     fn force_order_test_impl(hugr: &mut Hugr, rank_map: RankMap) -> Vec<Node> {
-        force_order(hugr, hugr.root(), |n| *rank_map.get(&n).unwrap_or(&0)).unwrap();
+        force_order(hugr, hugr.root(), |_, n| *rank_map.get(&n).unwrap_or(&0)).unwrap();
 
         let topo_sorted = Topo::new(&hugr.as_petgraph())
             .iter(&hugr.as_petgraph())
@@ -303,4 +319,18 @@ mod test {
         let topo_sort = force_order_test_impl(&mut hugr, rank_map);
         assert_eq!(vec![v0, v1, v2, v3], topo_sort);
     }
+
+    #[test]
+    fn test_force_order_const() {
+        let mut hugr = {
+            let mut builder =
+                DFGBuilder::new(FunctionType::new(Type::EMPTY_TYPEROW, Type::UNIT)).unwrap();
+            let unit = builder.add_load_value(Value::unary_unit_sum());
+            builder
+                .finish_hugr_with_outputs([unit], &EMPTY_REG)
+                .unwrap()
+        };
+        let root = hugr.root();
+        force_order(&mut hugr, root, |_, _| 0).unwrap();
+    }
 }