From 6c9847f97f89de0abd3202142b86286ef3f330f0 Mon Sep 17 00:00:00 2001
From: Alec Edgington <54802828+cqc-alec@users.noreply.github.com>
Date: Fri, 17 Jan 2025 08:40:34 +0000
Subject: [PATCH] Ignore boxes when applying KAK decomposition to a circuit
 (#1740)

---
 pytket/conanfile.py                            | 2 +-
 pytket/docs/changelog.rst                      | 1 +
 pytket/tests/transform_test.py                 | 7 +++++++
 tket/conanfile.py                              | 2 +-
 tket/src/Transformations/BasicOptimisation.cpp | 4 +++-
 5 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/pytket/conanfile.py b/pytket/conanfile.py
index f2ff74f897..fc5a917d6d 100644
--- a/pytket/conanfile.py
+++ b/pytket/conanfile.py
@@ -38,7 +38,7 @@ def requirements(self):
         self.requires("pybind11_json/0.2.15")
         self.requires("symengine/0.13.0")
         self.requires("tkassert/0.3.4@tket/stable")
-        self.requires("tket/1.3.61@tket/stable")
+        self.requires("tket/1.3.62@tket/stable")
         self.requires("tklog/0.3.3@tket/stable")
         self.requires("tkrng/0.3.3@tket/stable")
         self.requires("tktokenswap/0.3.9@tket/stable")
diff --git a/pytket/docs/changelog.rst b/pytket/docs/changelog.rst
index 2e215cb5f1..223b0ff45c 100644
--- a/pytket/docs/changelog.rst
+++ b/pytket/docs/changelog.rst
@@ -11,6 +11,7 @@ Features:
 Fixes:
 
 * Fix issue with custom gates in qasm to circuit conversion.
+* Ignore boxes when applying `KAKDecomposition`.
 
 1.38.0 (January 2025)
 ---------------------
diff --git a/pytket/tests/transform_test.py b/pytket/tests/transform_test.py
index 4dfc15116a..0a824fa51c 100644
--- a/pytket/tests/transform_test.py
+++ b/pytket/tests/transform_test.py
@@ -1237,6 +1237,13 @@ def test_KAK_with_ClassicalExpBox() -> None:
     assert not kak.apply(circ)
 
 
+def test_KAK_with_CircBox() -> None:
+    # https://github.com/CQCL/tket/issues/1553
+    cbox = CircBox(Circuit(2))
+    c = Circuit(2).add_circbox(cbox, [0, 1]).add_circbox(cbox, [0, 1])
+    assert not Transform.KAKDecomposition().apply(c)
+
+
 def test_round_angles() -> None:
     circ0 = Circuit(3).H(0).CRz(0.001, 0, 1).TK2(0.5, 0.499, 0.501, 1, 2)
     circ1 = Circuit(3).H(0).TK2(0.5, 0.5, 0.5, 1, 2)
diff --git a/tket/conanfile.py b/tket/conanfile.py
index 2ff3a91a06..a2703a4cd4 100644
--- a/tket/conanfile.py
+++ b/tket/conanfile.py
@@ -23,7 +23,7 @@
 
 class TketConan(ConanFile):
     name = "tket"
-    version = "1.3.61"
+    version = "1.3.62"
     package_type = "library"
     license = "Apache 2"
     homepage = "https://github.com/CQCL/tket"
diff --git a/tket/src/Transformations/BasicOptimisation.cpp b/tket/src/Transformations/BasicOptimisation.cpp
index 9fa6fe86fd..850fc073b0 100644
--- a/tket/src/Transformations/BasicOptimisation.cpp
+++ b/tket/src/Transformations/BasicOptimisation.cpp
@@ -267,7 +267,9 @@ Transform two_qubit_squash(
                   circ.get_next_edge(*v, current_edge_on_qb[q]);
             }
           }
-        } else if (circ.n_in_edges_of_type(*v, EdgeType::Quantum) == 2) {
+        } else if (
+            is_gate_type(type) &&
+            circ.n_in_edges_of_type(*v, EdgeType::Quantum) == 2) {
           // Check for 2qb gate
           Qubit q0 = v_to_qb.at({*v, 0});
           Qubit q1 = v_to_qb.at({*v, 1});