feat: Replace Circuit::num_gates with num_operations (#384)

Closes #105. Closes #108.

`num_gates` used to count every node in the top-level region, giving
unexpected results on results with constants, control flow, or anything
other than simple gates.

`num_operations` now only counts `CustomOp`s, traversing containers as
needed.

I also improved the circuit unit tests, to include circuits in modules
and circuits in `FuncDefn`s (instead of `DFG`s).

Some notes:
- Part of the tests testing parametric operations is commented out until
we solve CQCL/hugr#1166.
- Although the test circuits have function names, `Circuit::name`
returns `None`. I'll address that in another PR.

tket2/src/circuit.rs

@@ -147,14 +147,31 @@ impl<T: HugrView> Circuit<T> {
             .expect("Circuit has no I/O nodes")
     }
 
-    /// The number of quantum gates in the circuit.
+    /// The number of operations in the circuit.
+    ///
+    /// This includes [`Tk2Op`]s, pytket ops, and any other custom operations.
+    ///
+    /// Nested circuits are traversed to count their operations.
+    ///
+    ///   [`Tk2Op`]: crate::Tk2Op
     #[inline]
-    pub fn num_gates(&self) -> usize
+    pub fn num_operations(&self) -> usize
     where
         Self: Sized,
     {
-        // TODO: Discern quantum gates in the commands iterator.
-        self.hugr().children(self.parent).count() - 2
+        let mut count = 0;
+        let mut roots = vec![self.parent];
+        while let Some(node) = roots.pop() {
+            for child in self.hugr().children(node) {
+                let optype = self.hugr().get_optype(child);
+                if optype.is_custom_op() {
+                    count += 1;
+                } else if OpTag::DataflowParent.is_superset(optype.tag()) {
+                    roots.push(child);
+                }
+            }
+        }
+        count
     }
 
     /// Count the number of qubits in the circuit.
@@ -471,6 +488,7 @@ fn update_signature(
 #[cfg(test)]
 mod tests {
     use cool_asserts::assert_matches;
+    use rstest::{fixture, rstest};
 
     use hugr::types::FunctionType;
     use hugr::{
@@ -479,38 +497,83 @@ mod tests {
     };
 
     use super::*;
+    use crate::utils::build_module_with_circuit;
     use crate::{json::load_tk1_json_str, utils::build_simple_circuit, Tk2Op};
 
-    fn test_circuit() -> Circuit {
+    #[fixture]
+    fn tk1_circuit() -> Circuit {
         load_tk1_json_str(
             r#"{ "phase": "0",
             "bits": [["c", [0]]],
             "qubits": [["q", [0]], ["q", [1]]],
             "commands": [
                 {"args": [["q", [0]]], "op": {"type": "H"}},
                 {"args": [["q", [0]], ["q", [1]]], "op": {"type": "CX"}},
-                {"args": [["q", [1]]], "op": {"type": "X"}}
+                {"args": [["q", [1]]], "op": {"params": ["0.25"], "type": "Rz"}}
             ],
             "implicit_permutation": [[["q", [0]], ["q", [0]]], [["q", [1]], ["q", [1]]]]
         }"#,
         )
         .unwrap()
     }
 
-    #[test]
-    fn test_circuit_properties() {
-        let circ = test_circuit();
+    /// 2-qubit circuit with a Hadamard, a CNOT, and a X gate.
+    #[fixture]
+    fn simple_circuit() -> Circuit {
+        build_simple_circuit(2, |circ| {
+            circ.append(Tk2Op::H, [0])?;
+            circ.append(Tk2Op::CX, [0, 1])?;
+            circ.append(Tk2Op::X, [1])?;
 
-        assert_eq!(circ.name(), None);
-        assert_eq!(circ.circuit_signature().body().input_count(), 3);
-        assert_eq!(circ.circuit_signature().body().output_count(), 3);
-        assert_eq!(circ.qubit_count(), 2);
-        assert_eq!(circ.num_gates(), 3);
+            // TODO: Replace the `X` with the following once Hugr adds `CircuitBuilder::add_constant`.
+            // See https://github.com/CQCL/hugr/pull/1168
+
+            //let angle = circ.add_constant(ConstF64::new(0.5));
+            //circ.append_and_consume(
+            //    Tk2Op::RzF64,
+            //    [CircuitUnit::Linear(1), CircuitUnit::Wire(angle)],
+            //)?;
+            Ok(())
+        })
+        .unwrap()
+    }
+
+    /// 2-qubit circuit with a Hadamard, a CNOT, and a X gate,
+    /// defined inside a module.
+    #[fixture]
+    fn simple_module() -> Circuit {
+        build_module_with_circuit(2, |circ| {
+            circ.append(Tk2Op::H, [0])?;
+            circ.append(Tk2Op::CX, [0, 1])?;
+            circ.append(Tk2Op::X, [1])?;
+            Ok(())
+        })
+        .unwrap()
+    }
+
+    #[rstest]
+    #[case::simple(simple_circuit(), 2, 0, None)]
+    #[case::module(simple_module(), 2, 0, None)]
+    #[case::tk1(tk1_circuit(), 2, 1, None)]
+    fn test_circuit_properties(
+        #[case] circ: Circuit,
+        #[case] qubits: usize,
+        #[case] bits: usize,
+        #[case] name: Option<&str>,
+    ) {
+        assert_eq!(circ.name(), name);
+        assert_eq!(circ.circuit_signature().body().input_count(), qubits + bits);
+        assert_eq!(
+            circ.circuit_signature().body().output_count(),
+            qubits + bits
+        );
+        assert_eq!(circ.qubit_count(), qubits);
+        assert_eq!(circ.num_operations(), 3);
 
-        assert_eq!(circ.units().count(), 3);
+        assert_eq!(circ.units().count(), qubits + bits);
         assert_eq!(circ.nonlinear_units().count(), 0);
-        assert_eq!(circ.linear_units().count(), 3);
-        assert_eq!(circ.qubits().count(), 2);
+        assert_eq!(circ.linear_units().count(), qubits + bits);
+        assert_eq!(circ.qubits().count(), qubits);
     }
 
     #[test]

tket2/src/lib.rs

@@ -27,7 +27,7 @@
 //! let mut circ: Circuit = tket2::json::load_tk1_json_file("../test_files/barenco_tof_5.json").unwrap();
 //!
 //! assert_eq!(circ.qubit_count(), 9);
-//! assert_eq!(circ.num_gates(), 170);
+//! assert_eq!(circ.num_operations(), 170);
 //!
 //! // Traverse the circuit and print the gates.
 //! for command in circ.commands() {

tket2/src/optimiser/badger/eq_circ_class.rs

@@ -74,7 +74,10 @@ impl EqCircClass {
         };
 
         // Find the index for the smallest circuit
-        let min_index = circs.iter().position_min_by_key(|c| c.num_gates()).unwrap();
+        let min_index = circs
+            .iter()
+            .position_min_by_key(|c| c.num_operations())
+            .unwrap();
         let representative = circs.swap_remove(min_index);
         Ok(Self::new(representative, circs))
     }

tket2/src/portmatching/pattern.rs

@@ -32,7 +32,7 @@ impl CircuitPattern {
     /// Construct a pattern from a circuit.
     pub fn try_from_circuit(circuit: &Circuit) -> Result<Self, InvalidPattern> {
         let hugr = circuit.hugr();
-        if circuit.num_gates() == 0 {
+        if circuit.num_operations() == 0 {
             return Err(InvalidPattern::EmptyCircuit);
         }
         let mut pattern = Pattern::new();

tket2/src/rewrite.rs

@@ -84,7 +84,7 @@ impl CircuitRewrite {
     /// The difference between the new number of nodes minus the old. A positive
     /// number is an increase in node count, a negative number is a decrease.
     pub fn node_count_delta(&self) -> isize {
-        let new_count = self.replacement().num_gates() as isize;
+        let new_count = self.replacement().num_operations() as isize;
         let old_count = self.subcircuit().node_count() as isize;
         new_count - old_count
     }

tket2/src/rewrite/strategy.rs

@@ -144,7 +144,7 @@ impl RewriteStrategy for GreedyRewriteStrategy {
     }
 
     fn circuit_cost(&self, circ: &Circuit<impl HugrView>) -> Self::Cost {
-        circ.num_gates()
+        circ.num_operations()
     }
 
     fn op_cost(&self, _op: &OpType) -> Self::Cost {
@@ -488,7 +488,7 @@ mod tests {
         let strategy = GreedyRewriteStrategy;
         let rewritten = strategy.apply_rewrites(rws, &circ).collect_vec();
         assert_eq!(rewritten.len(), 1);
-        assert_eq!(rewritten[0].circ.num_gates(), 5);
+        assert_eq!(rewritten[0].circ.num_operations(), 5);
 
         if REWRITE_TRACING_ENABLED {
             assert_eq!(rewritten[0].circ.rewrite_trace().unwrap().len(), 3);
@@ -511,7 +511,7 @@ mod tests {
         let strategy = LexicographicCostFunction::default_cx();
         let rewritten = strategy.apply_rewrites(rws, &circ).collect_vec();
         let exp_circ_lens = HashSet::from_iter([3, 7, 9]);
-        let circ_lens: HashSet<_> = rewritten.iter().map(|r| r.circ.num_gates()).collect();
+        let circ_lens: HashSet<_> = rewritten.iter().map(|r| r.circ.num_operations()).collect();
         assert_eq!(circ_lens, exp_circ_lens);
 
         if REWRITE_TRACING_ENABLED {
@@ -547,7 +547,7 @@ mod tests {
         let strategy = GammaStrategyCost::exhaustive_cx_with_gamma(10.);
         let rewritten = strategy.apply_rewrites(rws, &circ);
         let exp_circ_lens = HashSet::from_iter([8, 17, 6, 9]);
-        let circ_lens: HashSet<_> = rewritten.map(|r| r.circ.num_gates()).collect();
+        let circ_lens: HashSet<_> = rewritten.map(|r| r.circ.num_operations()).collect();
         assert_eq!(circ_lens, exp_circ_lens);
     }