Assuming types that override Equals to have value semantics (#740)

Replaced all mechanisms and options to control whether or not an object has value semantics by a single algorithm. Any object that overrides object.Equals and is not an anonymous type or tuple is treated as a value type, unless ComparingByMembers<T>() is used. Also removes the global AssertionOptions.IsValueType

Src/FluentAssertions.nuspec

@@ -29,15 +29,20 @@
       <frameworkAssembly assemblyName="System.Xml.Linq" targetFramework="net45" />
     </frameworkAssemblies>
     <dependencies>
+      <group targetFramework="net45">
+        <dependency id="System.ValueType" version="4.3.0" />
+      </group>
       <group targetFramework="netstandard1.4">
         <dependency id="NETStandard.Library" version="1.6.1" />
         <dependency id="System.Reflection.TypeExtensions" version="4.3.0" />
         <dependency id="System.Reflection.Emit.Lightweight" version="4.3.0" />
+        <dependency id="System.ValueType" version="4.3.0" />
       </group>
       <group targetFramework="netstandard1.6">
         <dependency id="NETStandard.Library" version="1.6.1" />
         <dependency id="System.Reflection.TypeExtensions" version="4.3.0" />
         <dependency id="System.Reflection.Emit.Lightweight" version="4.3.0" />
+          <dependency id="System.ValueType" version="4.3.0" />
       </group>
       <group targetFramework="netstandard2.0">
         <dependency id="System.Configuration.ConfigurationManager" version="4.4.0" />
@@ -47,7 +52,7 @@
     </dependencies>
   </metadata>
   <files>
-    <file src="..\Artifacts\Release\net45\*.*"  target="lib\net45" />
+    <file src="..\Artifacts\Release\net45\*.*"  target="lib\net45" exclude="**\System.*" />
     <file src="..\Artifacts\Release\netstandard1.4\FluentAssertions.*" exclude="**\*.json" target="lib\netstandard1.4" />
     <file src="..\Artifacts\Release\netstandard1.6\FluentAssertions*.*" exclude="**\*.json" target="lib\netstandard1.6" />
     <file src="..\Artifacts\Release\netstandard2.0\FluentAssertions*.*" exclude="**\*.json" target="lib\netstandard2.0" />

Src/FluentAssertions/AssertionOptions.cs

@@ -25,18 +25,6 @@ public static EquivalencyAssertionOptions<T> CloneDefaults<T>()
             return new EquivalencyAssertionOptions<T>(defaults);
         }
 
-        /// <summary>
-        /// Defines a predicate with which the <see cref="EquivalencyValidator"/> determines if it should process 
-        /// an object's properties or not. 
-        /// </summary>
-        /// <returns>
-        /// Returns <c>true</c> if the object should be treated as a value type and its <see cref="object.Equals(object)"/>
-        /// must be used during a structural equivalency check.
-        /// </returns>
-        public static Func<Type, bool> IsValueType { get; set; } = type =>
-              (type.Namespace == typeof(int).Namespace) &&
-              !type.IsSameOrInherits(typeof(Exception));
-
         /// <summary>
         /// Allows configuring the defaults used during a structural equivalency assertion.
         /// </summary>
@@ -50,7 +38,7 @@ public static EquivalencyAssertionOptions<T> CloneDefaults<T>()
         }
 
         /// <summary>
-        /// Represents a mutable collection of steps that are executed while asserting a (collection of) object(s) 
+        /// Represents a mutable collection of steps that are executed while asserting a (collection of) object(s)
         /// is structurally equivalent to another (collection of) object(s).
         /// </summary>
         public static EquivalencyStepCollection EquivalencySteps { get; private set; }

Src/FluentAssertions/Equivalency/CollectionMemberAssertionOptionsDecorator.cs

@@ -82,9 +82,9 @@ public bool IncludeFields
             get { return inner.IncludeFields; }
         }
 
-        public bool IsValueType(Type type)
+        public EqualityStrategy GetEqualityStrategy(Type type)
         {
-            return inner.IsValueType(type);
+            return inner.GetEqualityStrategy(type);
         }
 
         public ITraceWriter TraceWriter => inner.TraceWriter;

Src/FluentAssertions/Equivalency/CyclicReferenceDetector.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 
 using FluentAssertions.Execution;
@@ -23,7 +24,7 @@ public CyclicReferenceDetector(CyclicReferenceHandling handling)
         }
 
         /// <summary>
-        /// Determines whether the specified object reference is a cyclic reference to the same object earlier in the 
+        /// Determines whether the specified object reference is a cyclic reference to the same object earlier in the
         /// equivalency validation.
         /// </summary>
         /// <remarks>
@@ -57,7 +58,7 @@ public bool IsCyclicReference(ObjectReference reference)
         /// <summary>
         /// Creates a new object that is a copy of the current instance.
         /// </summary>
-        /// 
+        ///
         /// <returns>
         /// A new object that is a copy of this instance.
         /// </returns>
@@ -69,4 +70,4 @@ public object Clone()
             };
         }
     }
-}
+}

Src/FluentAssertions/Equivalency/IEquivalencyAssertionOptions.cs

@@ -76,8 +76,31 @@ public interface IEquivalencyAssertionOptions
         ITraceWriter TraceWriter { get; }
 
         /// <summary>
-        /// Gets a value indicating whether the <paramref name="type"/> should be treated as having value semantics.
+        /// Determines the right strategy for evaluating the equality of objects of this type.
         /// </summary>
-        bool IsValueType(Type type);
+        EqualityStrategy GetEqualityStrategy(Type type);
+    }
+
+    public enum EqualityStrategy
+    {
+        /// <summary>
+        /// The object overrides <see cref="object.Equals"/>, so use that.
+        /// </summary>
+        Equals,
+
+        /// <summary>
+        /// The object does not seem to override <see cref="object.Equals"/>, so compare by members
+        /// </summary>
+        Members,
+
+        /// <summary>
+        /// Compare using <see cref="object.Equals(object)"/>, whether or not the object overrides it.
+        /// </summary>
+        ForceEquals,
+
+        /// <summary>
+        /// Compare the members, regardless of an <see cref="object.Equals(object)"/> override exists or not.
+        /// </summary>
+        ForceMembers,
     }
 }

Src/FluentAssertions/Equivalency/ObjectReference.cs

@@ -43,7 +43,7 @@ private bool IsParentOf(ObjectReference other)
         }
 
         /// <summary>
-        /// Serves as a hash function for a particular type. 
+        /// Serves as a hash function for a particular type.
         /// </summary>
         /// <returns>
         /// A hash code for the current <see cref="T:System.Object"/>.
@@ -59,12 +59,9 @@ public override int GetHashCode()
 
         public override string ToString()
         {
-            return string.Format("{{\"{0}\", {1}}}", path, @object);
+            return $"{{\"{path}\", {@object}}}";
         }
 
-        public bool IsComplexType
-        {
-            get { return !ReferenceEquals(@object, null) && @object.GetType().IsComplexType(); }
-        }
+        public bool IsComplexType => !ReferenceEquals(@object, null) && !@object.GetType().OverridesEquals();
     }
-}
+}