Eliminate all nullable warnings and accept most analysis suggestions

src/Moq/Moq.DynamicProxy/DynamicMockFactory.cs

@@ -41,9 +41,9 @@ protected override object CreateProxy(Type baseType, Type[] implementedInterface
             return mocked;
         }
 
-        class MockInterceptor : IInterceptor
+        private class MockInterceptor : IInterceptor
         {
-            IMock? mock;
+            private IMock? mock;
 
             public void Intercept(IInvocation invocation)
             {

src/Moq/Moq.DynamicProxy/Mock.DynamicFactory.cs

@@ -1,6 +1,6 @@
 namespace Moq
 {
-    partial class Mock
+    internal partial class Mock
     {
         static Mock()
         {

src/Moq/Moq.Package/Mock.Overloads.cs

@@ -5,7 +5,7 @@ namespace Moq
     /// <summary>
     /// Instantiates stunts for the specified types.
     /// </summary>
-    partial class Mock
+    internal partial class Mock
     {
         /// <summary>
         /// Creates a mock that inherits or implements the type <typeparamref name="T"/>.

src/Moq/Moq.Package/Mock.StaticFactory.cs

@@ -1,6 +1,6 @@
 namespace Moq
 {
-    partial class Mock
+    internal partial class Mock
     {
         static Mock()
         {

src/Moq/Moq.Package/Mock.cs

@@ -11,7 +11,7 @@ namespace Moq
     /// </summary>
     [ExcludeFromCodeCoverage]
     [CompilerGenerated]
-    partial class Mock
+    internal partial class Mock
     {
         /// <summary>
         /// Gets the configuration and introspection for the given mocked instance.

src/Moq/Moq.Sdk.Tests/AnyMatcherTests.cs

@@ -106,9 +106,8 @@ public void MatchesDerivedType()
             Assert.True(x.Matches(new Derived()));
         }
 
+        private class Base { }
 
-
-        class Base { }
-        class Derived : Base { }
+        private class Derived : Base { }
     }
 }

src/Moq/Moq.Sdk.Tests/ConditionalMatcherTests.cs

@@ -56,7 +56,8 @@ public void EqualsByConditionFunctionAndName()
             Assert.False(matcher.Equals(new ConditionalMatcher<int>(_ => true, "foo")));
         }
 
-        class Base { }
-        class Derived : Base { }
+        private class Base { }
+
+        private class Derived : Base { }
     }
 }

src/Moq/Moq.Sdk.Tests/DefaultMockTests.cs

@@ -102,10 +102,10 @@ public void TracksTargetObject()
         public void InitializesState()
             => Assert.NotNull(new FakeStunt().Mock.State);
 
-        class FakeStunt : IStunt, IMocked
+        private class FakeStunt : IStunt, IMocked
         {
-            BehaviorPipeline pipeline = new BehaviorPipeline();
-            DefaultMock mock;
+            private readonly BehaviorPipeline pipeline = new BehaviorPipeline();
+            private DefaultMock mock;
 
             public IList<IStuntBehavior> Behaviors => pipeline.Behaviors;
 

src/Moq/Moq.Sdk.Tests/EqualityTests.cs

@@ -126,6 +126,6 @@ public void Matchers()
             Assert.False(hash.Add(value2));
         }
 
-        void AMethod(bool b, string s, PlatformID p) { }
+        private void AMethod(bool b, string s, PlatformID p) { }
     }
 }

src/Moq/Moq.Sdk.Tests/Fakes.cs

@@ -8,7 +8,7 @@ namespace Moq.Sdk.Tests
 {
     public class FakeMock : IStunt, IMocked
     {
-        DefaultMock mock;
+        private readonly DefaultMock mock;
 
         protected BehaviorPipeline Pipeline = new BehaviorPipeline();
 

src/Moq/Moq.Sdk.Tests/MockExtensionsTests.cs

@@ -42,8 +42,8 @@ public void CanAssertInvocations()
             Assert.Equal(0, target.Add(2, 3));
             Assert.Single(target.AsMock().InvocationsFor(c => c.Add(2, 3)));
         }
-        
-        class FakeCalls : FakeMock
+
+        private class FakeCalls : FakeMock
         {
             public void TurnOn() => Pipeline.Execute(new MethodInvocation(this, MethodBase.GetCurrentMethod()));
 

src/Moq/Moq.Sdk.Tests/MockTrackingBehaviorTests.cs

@@ -47,8 +47,7 @@ public void SkipInvocationRecordingIfSetupScopeActive()
             Assert.Empty(target.Mock.Invocations);
         }
 
-
-        class TrackingMock : FakeMock
+        private class TrackingMock : FakeMock
         {
             public void Do() => Pipeline.Execute(new MethodInvocation(this, MethodBase.GetCurrentMethod()));
         }

src/Moq/Moq.Sdk.Tests/Mocked.cs

@@ -7,8 +7,8 @@ namespace Moq.Sdk.Tests
 {
     public class Mocked : IMocked, IStunt
     {
-        IMock mock;
-        IList<IStuntBehavior> behaviors = new ObservableCollection<IStuntBehavior>();
+        private IMock mock;
+        private readonly IList<IStuntBehavior> behaviors = new ObservableCollection<IStuntBehavior>();
 
         public IMock Mock => LazyInitializer.EnsureInitialized(ref mock, () => new DefaultMock(this));
 

src/Moq/Moq.Sdk.Tests/NotMatcherTests.cs

@@ -48,7 +48,7 @@ public void MatcherEquals()
             Assert.Equal(expected.GetHashCode(), actual.GetHashCode());
         }
 
-        class Value
+        private class Value
         {
             public Value(Guid id) => Id = id;
 

src/Moq/Moq.Sdk/AnyMatcher.cs

@@ -12,9 +12,9 @@ namespace Moq.Sdk
     /// </summary>
     public class AnyMatcher : IArgumentMatcher, IEquatable<AnyMatcher>
     {
-        TypeInfo info;
-        bool isValueType;
-        bool isNullable;
+        private readonly TypeInfo info;
+        private readonly bool isValueType;
+        private readonly bool isNullable;
 
         /// <summary>
         /// Initializes the matcher with the given <paramref name="argumentType"/>.
@@ -38,7 +38,7 @@ public AnyMatcher(Type argumentType)
         /// <summary>
         /// Evaluates whether the given value matches this instance.
         /// </summary>
-        public bool Matches(object value)
+        public bool Matches(object? value)
         {
             // Non-nullable value types never match against a null value.
             if (isValueType && !isNullable && value == null)
@@ -61,10 +61,10 @@ public bool Matches(object value)
         #region Equality
 
         /// <inheritdoc />
-        public bool Equals(AnyMatcher other) => other != null && info.Equals(other.info);
+        public bool Equals(AnyMatcher other) => info.Equals(other.info);
 
         /// <inheritdoc />
-        public override bool Equals(object other) => Equals(other as AnyMatcher);
+        public override bool Equals(object other) => other is AnyMatcher matcher && Equals(matcher);
 
         /// <inheritdoc />
         public override int GetHashCode() => info.GetHashCode();

src/Moq/Moq.Sdk/AnyMatcher`1.cs

@@ -14,16 +14,16 @@ namespace Moq.Sdk
     public class AnyMatcher<T> : IArgumentMatcher, IEquatable<AnyMatcher<T>>
     {
         // Disable warning since we only use this member from this class
-        static bool IsValueType = typeof(T).GetTypeInfo().IsValueType;
-        static bool IsNullable = typeof(T).GetTypeInfo().IsGenericType &&
+        private static readonly bool IsValueType = typeof(T).GetTypeInfo().IsValueType;
+        private static readonly bool IsNullable = typeof(T).GetTypeInfo().IsGenericType &&
             typeof(T).GetGenericTypeDefinition() == typeof(Nullable<>);
 
         /// <summary>
         /// Gets the singleton instance of this matcher.
         /// </summary>
         public static IArgumentMatcher Default { get; } = new AnyMatcher<T>();
 
-        AnyMatcher() { }
+        private AnyMatcher() { }
 
         /// <summary>
         /// Gets the type of the argument this matcher supports.
@@ -33,7 +33,7 @@ public class AnyMatcher<T> : IArgumentMatcher, IEquatable<AnyMatcher<T>>
         /// <summary>
         /// Evaluates whether the given value matches this instance.
         /// </summary>
-        public bool Matches(object value)
+        public bool Matches(object? value)
         {
             // Non-nullable value types never match against a null value.
             if (IsValueType && !IsNullable && value == null)
@@ -71,7 +71,7 @@ public bool Matches(object value)
         /// </summary>
         /// <returns><see langword="true"/> if <paramref name="other"/> is not null and 
         /// it's an <see cref="AnyMatcher{T}"/> with the same <typeparamref name="T"/> .</returns>
-        public override bool Equals(object other) => Equals(other as AnyMatcher<T>);
+        public override bool Equals(object other) => other is AnyMatcher<T> matcher && Equals(matcher);
 
         /// <inheritdoc />
         public override int GetHashCode() => typeof(T).GetHashCode();

src/Moq/Moq.Sdk/CallContext.cs

@@ -10,44 +10,44 @@ namespace Moq.Sdk
     /// </summary>
     public static class CallContext<T>
     {
-        static readonly string defaultName = typeof(T).FullName;
-        static ConcurrentDictionary<string, AsyncLocal<T>> state = new ConcurrentDictionary<string, AsyncLocal<T>>();
+        private static readonly string defaultName = typeof(T).FullName;
+        private static readonly ConcurrentDictionary<string, AsyncLocal<T?>> state = new();
 
         /// <summary>
         /// Stores a given object.
         /// </summary>
         /// <param name="data">The object to store in the call context.</param>
-        public static void SetData(T data) => SetData(defaultName, data);
+        public static void SetData(T? data) => SetData(defaultName, data);
 
         /// <summary>
         /// Stores a given object and associates it with the specified name.
         /// </summary>
         /// <param name="name">The name with which to associate the new item in the call context.</param>
         /// <param name="data">The object to store in the call context.</param>
-        public static void SetData(string name, T data) => 
-            state.GetOrAdd(name, _ => new AsyncLocal<T>()).Value = data;
+        public static void SetData(string name, T? data) 
+            => state.GetOrAdd(name, _ => new AsyncLocal<T?>()).Value = data;
 
         /// <summary>
         /// Retrieves an object from the <see cref="CallContext"/>.
         /// </summary>
         /// <returns>The object in the call context associated with the specified name, or a default value for <typeparamref name="T"/> if none is found.</returns>
-        public static T GetData() => GetData(defaultName);
+        public static T? GetData() => GetData(defaultName);
 
         /// <summary>
         /// Retrieves an object with the specified name from the <see cref="CallContext"/>.
         /// </summary>
         /// <param name="name">The name of the item in the call context.</param>
         /// <returns>The object in the call context associated with the specified name, or a default value for <typeparamref name="T"/> if none is found.</returns>
-        public static T GetData(string name) =>
-            state.TryGetValue(name, out var data) ? data.Value : default;
+        public static T? GetData(string name) 
+            => state.TryGetValue(name, out var data) ? data.Value : default;
 
         /// <summary>
         /// Retrieves an object from the <see cref="CallContext"/>, and 
         /// sets an initial value if it was not found.
         /// </summary>
         /// <param name="setInitialValue">A function that will set the initial value of the given parameter, if it doesn't have a value already in the context.</param>
         /// <returns>The object in the call context associated with the specified name, or the initial value returned from <paramref name="setInitialValue"/>.</returns>
-        public static T GetData(Func<T> setInitialValue) => GetData(defaultName, setInitialValue);
+        public static T? GetData(Func<T?> setInitialValue) => GetData(defaultName, setInitialValue);
 
         /// <summary>
         /// Retrieves an object with the specified name from the <see cref="CallContext"/>, and 
@@ -56,10 +56,10 @@ public static T GetData(string name) =>
         /// <param name="name">The name of the item in the call context.</param>
         /// <param name="setInitialValue">A function that will set the initial value of the given parameter, if it doesn't have a value already in the context.</param>
         /// <returns>The object in the call context associated with the specified name, or the initial value returned from <paramref name="setInitialValue"/>.</returns>
-        public static T GetData(string name, Func<T> setInitialValue)
+        public static T? GetData(string name, Func<T?> setInitialValue)
         {
-            var local = state.GetOrAdd(name, _ => new AsyncLocal<T> { Value = setInitialValue() });
-            if (object.Equals(local.Value, default(T)))
+            var local = state.GetOrAdd(name, _ => new AsyncLocal<T?> { Value = setInitialValue() });
+            if (Equals(local.Value, default(T)))
                 local.Value = setInitialValue();
 
             return local.Value;
@@ -72,22 +72,30 @@ public static T GetData(string name, Func<T> setInitialValue)
     /// </summary>
     public static class CallContext
     {
-        static ConcurrentDictionary<string, AsyncLocal<object>> state = new ConcurrentDictionary<string, AsyncLocal<object>>();
+        private static readonly ConcurrentDictionary<string, AsyncLocal<object?>> state = new();
 
         /// <summary>
         /// Stores a given object and associates it with the specified name.
         /// </summary>
         /// <param name="name">The name with which to associate the new item in the call context.</param>
         /// <param name="data">The object to store in the call context.</param>
-        public static void SetData(string name, object data) =>
-            state.GetOrAdd(name, _ => new AsyncLocal<object>()).Value = data;
+        public static void SetData(string name, object? data) 
+            => state.GetOrAdd(name, _ => new AsyncLocal<object?>()).Value = data;
 
         /// <summary>
         /// Retrieves an object with the specified name from the <see cref="CallContext"/>.
         /// </summary>
         /// <param name="name">The name of the item in the call context.</param>
         /// <returns>The object in the call context associated with the specified name, or <see langword="null"/> if not found.</returns>
-        public static object GetData(string name) =>
-            state.TryGetValue(name, out var data) ? data.Value : null;
+        public static object? GetData(string name) 
+            => state.TryGetValue(name, out var data) ? data.Value : null;
+
+        /// <summary>
+        /// Throws <see cref="InvalidOperationException"/> with a message stating that an 
+        /// unexpected null value was found in the context.
+        /// </summary>
+        /// <typeparam name="T">Type of value that was unexpectedly null in the context. This is used as the key.</typeparam>
+        public static T ThrowUnexpectedNull<T>()
+            => throw new InvalidOperationException(ThisAssembly.Strings.UnexpectedNullContextState(typeof(T).FullName));
     }
 }

src/Moq/Moq.Sdk/ConditionalMatcher.cs

@@ -12,19 +12,19 @@ namespace Moq.Sdk
     /// <typeparam name="T">Type of argument being conditioned.</typeparam>
     public class ConditionalMatcher<T> : IArgumentMatcher, IEquatable<ConditionalMatcher<T>>
     {
-        static readonly bool IsValueType = typeof(T).GetTypeInfo().IsValueType;
-        static readonly bool IsNullable = typeof(T).GetTypeInfo().IsGenericType &&
+        private static readonly bool IsValueType = typeof(T).GetTypeInfo().IsValueType;
+        private static readonly bool IsNullable = typeof(T).GetTypeInfo().IsGenericType &&
             typeof(T).GetGenericTypeDefinition() == typeof(Nullable<>);
 
         [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-        readonly string name;
+        private readonly string name;
         [DebuggerBrowsable(DebuggerBrowsableState.Never)]
-        readonly Func<T, bool> condition;
+        private readonly Func<T?, bool> condition;
 
         /// <summary>
         /// Initializes the matcher with the condition and optional friendly name.
         /// </summary>
-        public ConditionalMatcher(Func<T, bool> condition, string name = "condition")
+        public ConditionalMatcher(Func<T?, bool> condition, string name = "condition")
         {
             this.condition = condition ?? throw new ArgumentNullException(nameof(condition));
             this.name = name ?? throw new ArgumentNullException(nameof(name));
@@ -38,7 +38,7 @@ public ConditionalMatcher(Func<T, bool> condition, string name = "condition")
         /// <summary>
         /// Evaluates whether the given value matches this instance.
         /// </summary>
-        public bool Matches(object value)
+        public bool Matches(object? value)
         {
             // Non-nullable value types never match against a null value.
             if (IsValueType && !IsNullable && value == null)
@@ -67,12 +67,12 @@ public bool Matches(object value)
         /// Checks whether <paramref name="other"/> has the same condition and friendly name.
         /// </summary>
         public bool Equals(ConditionalMatcher<T> other)
-            => other != null && ReferenceEquals(condition, other.condition) && name.Equals(other.name);
+            => ReferenceEquals(condition, other.condition) && name.Equals(other.name);
 
         /// <summary>
         /// Checks whether <paramref name="other"/> has the same condition and friendly name.
         /// </summary>
-        public override bool Equals(object other) => Equals(other as ConditionalMatcher<T>);
+        public override bool Equals(object other) => other is ConditionalMatcher<T> matcher && Equals(matcher);
 
         /// <inheritdoc />
         public override int GetHashCode() => HashCode.Combine(condition, name);

src/Moq/Moq.Sdk/DefaultMock.cs

@@ -76,7 +76,7 @@ public IMockBehaviorPipeline GetPipeline(IMockSetup setup)
                 return behavior;
             });
 
-        void OnBehaviorsChanged(object sender, NotifyCollectionChangedEventArgs e)
+        private void OnBehaviorsChanged(object sender, NotifyCollectionChangedEventArgs e)
         {
             switch (e.Action)
             {

src/Moq/Moq.Sdk/DelegateMockBehavior.cs

@@ -12,8 +12,8 @@ namespace Moq.Sdk
     [DebuggerDisplay("{DisplayName}")]
     public class DelegateMockBehavior : IMockBehavior
     {
-        readonly Lazy<string> displayName;
-        readonly ExecuteMockDelegate behavior;
+        private readonly Lazy<string> displayName;
+        private readonly ExecuteMockDelegate behavior;
 
         /// <summary>
         /// Creates an instance of the invokable behavior with the given