Handle 0-qubit gates when computing resource data (#2068)

Author: cqc-alec

TKET_VERSION

@@ -1 +1 @@
-2.1.61
+2.1.62

pytket/docs/changelog.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+- Fix segfault from `Circuit::get_resources()` with 0-qubit gates.
+
 ## 2.10.3 (October 2025)
 
 - Add `tket_squash_phasedx_rz` to c api.

tket/src/Circuit/Circuit.cpp

@@ -406,10 +406,11 @@ ResourceData Circuit::get_resources() /*const*/ {
             op_type_count[pair.first].max += pair.second.max;
           }
         } else {
+          unsigned n_qubits = get_Op_ptr_from_Vertex(v)->n_qubits();
+          if (n_qubits == 0) continue;
           data.GateDepth = {1};
           data.OpTypeDepth[optype] = {1};
-          if (OpDesc(optype).is_gate() &&
-              get_Op_ptr_from_Vertex(v)->n_qubits() == 2) {
+          if (OpDesc(optype).is_gate() && n_qubits == 2) {
             data.TwoQubitGateDepth = {1};
           }
           op_type_count[optype].min += 1;

tket/test/src/Circuit/test_DummyBox.cpp

@@ -13,6 +13,7 @@
 // limitations under the License.
 
 #include <catch2/catch_test_macros.hpp>
+#include <tket/OpType/OpType.hpp>
 
 #include "tket/Circuit/Circuit.hpp"
 #include "tket/Circuit/DummyBox.hpp"
@@ -50,6 +51,15 @@ SCENARIO("DummyBox") {
         ResourceBounds<unsigned>(5, 9)};
     CHECK(data == expected);
   }
+
+  GIVEN("Phase op") {
+    // https://github.com/CQCL/tket/issues/2066
+    Circuit c(1);
+    c.add_op<unsigned>(OpType::Phase, 0.0, {});
+    ResourceData data = c.get_resources();
+    ResourceData expected{};
+    CHECK(data == expected);
+  }
 }
 
 }  // namespace tket