From a3f58e4c739e545f432e7ce26931b31f02623b4f Mon Sep 17 00:00:00 2001
From: Raphael Koh <t-rkoh@microsoft.com>
Date: Mon, 17 Aug 2020 11:26:28 -0400
Subject: [PATCH] Fix stackoverflow error for QArray args

---
 src/Simulation/Core/TypeExtensions.cs         | 15 ++++++++-----
 .../Circuits/RuntimeMetadataTest.qs           |  4 ++++
 .../Simulators.Tests/RuntimeMetadataTests.cs  | 22 +++++++++++++++++++
 .../Simulators.Tests/TypeExtensionsTest.cs    |  3 +++
 4 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/src/Simulation/Core/TypeExtensions.cs b/src/Simulation/Core/TypeExtensions.cs
index 59cb0370b52..6b7722fc234 100644
--- a/src/Simulation/Core/TypeExtensions.cs
+++ b/src/Simulation/Core/TypeExtensions.cs
@@ -165,12 +165,6 @@ public static Type[] GetTupleFieldTypes(this Type arg)
                 return op.Name;
             }
 
-            // If object is an IApplyData, recursively extract arguments
-            if (o is IApplyData data)
-            {
-                return data.Value?.GetNonQubitArgumentsAsString();
-            }
-
             // If object is a string, enclose it in quotations
             if (o is string s)
             {
@@ -197,6 +191,15 @@ public static Type[] GetTupleFieldTypes(this Type arg)
                 return (items.Any()) ? $"({string.Join(", ", items)})" : null;
             }
 
+            // If object is an IApplyData, recursively extract arguments
+            if (o is IApplyData data)
+            {
+                if (data.Value != data)
+                {
+                    return data.Value?.GetNonQubitArgumentsAsString();
+                }
+            }
+
             // Otherwise, return argument as a string
             return (o != null) ? o.ToString() : null;
         }
diff --git a/src/Simulation/Simulators.Tests/Circuits/RuntimeMetadataTest.qs b/src/Simulation/Simulators.Tests/Circuits/RuntimeMetadataTest.qs
index 4e721723832..5836a3426f5 100644
--- a/src/Simulation/Simulators.Tests/Circuits/RuntimeMetadataTest.qs
+++ b/src/Simulation/Simulators.Tests/Circuits/RuntimeMetadataTest.qs
@@ -30,5 +30,9 @@ namespace Microsoft.Quantum.Simulation.Simulators.Tests.Circuits {
     operation TwoQubitOp (q1 : Qubit, q2 : Qubit) : Unit {
         // ...
     }
+
+    operation BoolArrayOp (bits : Bool[]) : Unit {
+        // ...
+    }
     
 }
diff --git a/src/Simulation/Simulators.Tests/RuntimeMetadataTests.cs b/src/Simulation/Simulators.Tests/RuntimeMetadataTests.cs
index e9f6e69e626..a84d4d76423 100644
--- a/src/Simulation/Simulators.Tests/RuntimeMetadataTests.cs
+++ b/src/Simulation/Simulators.Tests/RuntimeMetadataTests.cs
@@ -500,6 +500,28 @@ public void DuplicateQubitArgs()
 
             Assert.Equal(op.GetRuntimeMetadata(args), expected);
         }
+
+        [Fact]
+        public void QArrayArgs()
+        {
+            var op = new QuantumSimulator().Get<Circuits.BoolArrayOp>();
+            IQArray<Boolean> bits = new QArray<Boolean>(new bool[] { false, true });
+            var args = op.__dataIn(bits);
+            var expected = new RuntimeMetadata()
+            {
+                Label = "BoolArrayOp",
+                FormattedNonQubitArgs = "[False, True]",
+                IsAdjoint = false,
+                IsControlled = false,
+                IsMeasurement = false,
+                IsComposite = false,
+                Children = null,
+                Controls = new List<Qubit>() { },
+                Targets = new List<Qubit>() { },
+            };
+
+            Assert.Equal(op.GetRuntimeMetadata(args), expected);
+        }
     }
 
     public class UDTTests
diff --git a/src/Simulation/Simulators.Tests/TypeExtensionsTest.cs b/src/Simulation/Simulators.Tests/TypeExtensionsTest.cs
index a7942f7f110..2707ca2b150 100644
--- a/src/Simulation/Simulators.Tests/TypeExtensionsTest.cs
+++ b/src/Simulation/Simulators.Tests/TypeExtensionsTest.cs
@@ -94,6 +94,9 @@ public void ArrayTypes()
                 (new FreeQubit(1), "bar"),
             };
             Assert.Equal("[(\"foo\"), (\"bar\")]", qTupleArr.GetNonQubitArgumentsAsString());
+
+            var qArrayBool = new QArray<Boolean>(new[] { false, true });
+            Assert.Equal("[False, True]", qArrayBool.GetNonQubitArgumentsAsString());
         }
 
         [Fact]