From 91bc14c3ffd96f3f024d5be7b850c3e85ec8dd3a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?C=C3=A9dric=20Luthi?= <cedric.luthi@gmail.com>
Date: Wed, 7 Aug 2019 12:16:12 +0200
Subject: [PATCH 1/2] Fix NullReferenceException when creating a default
 immutable instance

---
 src/CommandLine/Infrastructure/ReflectionHelper.cs        | 5 +++++
 tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs | 8 ++++++++
 2 files changed, 13 insertions(+)

diff --git a/src/CommandLine/Infrastructure/ReflectionHelper.cs b/src/CommandLine/Infrastructure/ReflectionHelper.cs
index a7926cb7..1373b2b3 100644
--- a/src/CommandLine/Infrastructure/ReflectionHelper.cs
+++ b/src/CommandLine/Infrastructure/ReflectionHelper.cs
@@ -91,6 +91,11 @@ public static T CreateDefaultImmutableInstance<T>(Type[] constructorTypes)
         public static object CreateDefaultImmutableInstance(Type type, Type[] constructorTypes)
         {
             var ctor = type.GetTypeInfo().GetConstructor(constructorTypes);
+            if (ctor == null)
+            {
+                throw new InvalidOperationException($"Type appears to be immutable, but no constructor found for type {type.FullName} to accept values.");
+            }
+
             var values = (from prms in ctor.GetParameters()
                           select prms.ParameterType.CreateDefaultForImmutable()).ToArray();
             return ctor.Invoke(values);
diff --git a/tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs b/tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs
index c6234089..59fcf9cc 100644
--- a/tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs
+++ b/tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs
@@ -1158,6 +1158,14 @@ public void OptionClass_IsImmutable_HasNoCtor()
             act.Should().Throw<InvalidOperationException>();
         }
 
+        [Fact]
+        public void OptionClass_IsImmutable_HasNoCtor_HelpRequested()
+        {
+            Action act = () => InvokeBuild<ValueWithNoSetterOptions>(new string[] { "--help" });
+
+            act.Should().Throw<InvalidOperationException>();
+        }
+
         private class ValueWithNoSetterOptions
         {
             [Value(0, MetaName = "Test", Default = 0)]

From d6333553baeda33cb20cf719955416e113d7e0b4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?C=C3=A9dric=20Luthi?= <cedric.luthi@gmail.com>
Date: Wed, 7 Aug 2019 12:22:45 +0200
Subject: [PATCH 2/2] Improve exception message when immutable type can't be
 created

---
 src/CommandLine/Core/InstanceBuilder.cs                   | 2 +-
 src/CommandLine/Infrastructure/ReflectionHelper.cs        | 2 +-
 tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs | 6 ++++--
 3 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/CommandLine/Core/InstanceBuilder.cs b/src/CommandLine/Core/InstanceBuilder.cs
index a1fdd9f2..5ea056d8 100644
--- a/src/CommandLine/Core/InstanceBuilder.cs
+++ b/src/CommandLine/Core/InstanceBuilder.cs
@@ -167,7 +167,7 @@ private static T BuildImmutable<T>(Type typeInfo, Maybe<Func<T>> factory, IEnume
 
             if(ctor == null)
             {
-                throw new InvalidOperationException($"Type appears to be immutable, but no constructor found for type {typeInfo.FullName} to accept values.");
+                throw new InvalidOperationException($"Type {typeInfo.FullName} appears to be immutable, but no constructor found to accept values.");
             }
 
             var values =
diff --git a/src/CommandLine/Infrastructure/ReflectionHelper.cs b/src/CommandLine/Infrastructure/ReflectionHelper.cs
index 1373b2b3..47fe70ea 100644
--- a/src/CommandLine/Infrastructure/ReflectionHelper.cs
+++ b/src/CommandLine/Infrastructure/ReflectionHelper.cs
@@ -93,7 +93,7 @@ public static object CreateDefaultImmutableInstance(Type type, Type[] constructo
             var ctor = type.GetTypeInfo().GetConstructor(constructorTypes);
             if (ctor == null)
             {
-                throw new InvalidOperationException($"Type appears to be immutable, but no constructor found for type {type.FullName} to accept values.");
+                throw new InvalidOperationException($"Type {type.FullName} appears to be immutable, but no constructor found to accept values.");
             }
 
             var values = (from prms in ctor.GetParameters()
diff --git a/tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs b/tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs
index 59fcf9cc..bb88595e 100644
--- a/tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs
+++ b/tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs
@@ -1155,7 +1155,8 @@ public void OptionClass_IsImmutable_HasNoCtor()
         {
             Action act = () => InvokeBuild<ValueWithNoSetterOptions>(new string[] { "Test" }, false, false);
 
-            act.Should().Throw<InvalidOperationException>();
+            act.Should().Throw<InvalidOperationException>()
+                .Which.Message.Should().Be("Type CommandLine.Tests.Unit.Core.InstanceBuilderTests+ValueWithNoSetterOptions appears to be immutable, but no constructor found to accept values.");
         }
 
         [Fact]
@@ -1163,7 +1164,8 @@ public void OptionClass_IsImmutable_HasNoCtor_HelpRequested()
         {
             Action act = () => InvokeBuild<ValueWithNoSetterOptions>(new string[] { "--help" });
 
-            act.Should().Throw<InvalidOperationException>();
+            act.Should().Throw<InvalidOperationException>()
+                .Which.Message.Should().Be("Type CommandLine.Tests.Unit.Core.InstanceBuilderTests+ValueWithNoSetterOptions appears to be immutable, but no constructor found to accept values.");
         }
 
         private class ValueWithNoSetterOptions