From 26305f321fc79f5432134bf8314fa2de4c972386 Mon Sep 17 00:00:00 2001
From: Erik Davis <ejdavis@hrl.com>
Date: Tue, 19 Oct 2021 15:05:27 -0700
Subject: [PATCH] bugfix: use layout when placing tikz operations for nq gates

---
 src/tools/circuit-diagram.lisp         | 27 +++++++++++++++++---------
 tests/tools/circuit-diagram-tests.lisp | 27 ++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 9 deletions(-)

diff --git a/src/tools/circuit-diagram.lisp b/src/tools/circuit-diagram.lisp
index a0eaa5917..6b3045d18 100644
--- a/src/tools/circuit-diagram.lisp
+++ b/src/tools/circuit-diagram.lisp
@@ -297,15 +297,24 @@ The convention is that the source operation takes two arguments: the qubit index
                     :for offset := (- (first target-qubits) q)
                     :do (append-to-diagram diagram q (tikz-control q offset)))
               ;; per quantikz: we put the gate on first target line, with correct size
-              (append-to-diagram diagram
-                                 (first target-qubits)
-                                 (tikz-gate name
-                                            :size (length target-qubits)
-                                            :params (quil:application-parameters instr)
-                                            :dagger dagger))
-              ;; and then NOP on the rest
-              (loop :for q :in (rest target-qubits)
-                    :do (append-to-diagram diagram q (tikz-nop))))))))))
+              (let ((actual-target
+                      (resolve-gate-target target-qubits (diagram-layout diagram))))
+                (append-to-diagram diagram
+                                   actual-target
+                                   (tikz-gate name
+                                              :size (length target-qubits)
+                                              :params (quil:application-parameters instr)
+                                              :dagger dagger))
+                ;; and then NOP on the rest
+                (loop :for q :in target-qubits
+                      :unless (= q actual-target)
+                        :do (append-to-diagram diagram q (tikz-nop)))))))))))
+
+
+(defun resolve-gate-target (qubits layout)
+  (flet ((qubit-line (q)
+           (gethash q layout)))
+    (a:extremum qubits #'< :key #'qubit-line)))
 
 
 (defun qubits-in-applications-or-measurements (instrs)
diff --git a/tests/tools/circuit-diagram-tests.lisp b/tests/tools/circuit-diagram-tests.lisp
index 16f9afd46..f7f168d8a 100644
--- a/tests/tools/circuit-diagram-tests.lisp
+++ b/tests/tools/circuit-diagram-tests.lisp
@@ -48,3 +48,30 @@
                  (cl-quil.tools:plot-circuit pp
                                              :backend :latex
                                              :right-align-measurements t)))))
+
+(deftest test-plot-circuit-nq-gate-layout ()
+  (let ((pp (quil:parse-quil "
+DEFGATE FOO p q r AS PAULI-SUM:
+    X(pi) p
+    Y(pi) q
+    Z(pi) r
+
+FOO 3 2 1"))
+        (expected
+          "\\documentclass[convert={density=300,outext=.png}]{standalone}
+\\usepackage[margin=1in]{geometry}
+\\usepackage{tikz}
+\\usepackage{quantikz}
+
+\\begin{document}
+\\begin{tikzcd}
+ \\lstick{\\ket{q_1}} &  \\gate[wires=3]{FOO} &  \\qw \\\\
+ \\lstick{\\ket{q_2}} &  \\qw &  \\qw \\\\
+ \\lstick{\\ket{q_3}} &  \\qw &  \\qw \\\\
+\\end{tikzcd}
+\\end{document}
+"))
+    (is (string= expected
+                 (cl-quil.tools:plot-circuit pp
+                                             :backend :latex
+                                             :layout-strategy ':increasing)))))