From 6ff7425b839c7c19a69ed888e295616dd1f90964 Mon Sep 17 00:00:00 2001
From: Lucian Bargaoanu <lbargaoanu@hotmail.com>
Date: Wed, 9 Feb 2022 13:24:38 +0200
Subject: [PATCH] prefer derived interfaces

---
 .../Configuration/MapperConfiguration.cs      | 14 +++++-
 src/UnitTests/InterfaceMapping.cs             | 50 +++++++++++++++++++
 2 files changed, 62 insertions(+), 2 deletions(-)

diff --git a/src/AutoMapper/Configuration/MapperConfiguration.cs b/src/AutoMapper/Configuration/MapperConfiguration.cs
index f05acee714..d44b28f705 100644
--- a/src/AutoMapper/Configuration/MapperConfiguration.cs
+++ b/src/AutoMapper/Configuration/MapperConfiguration.cs
@@ -300,15 +300,25 @@ private TypeMap GetTypeMap(TypePair initialTypes)
         static List<Type> GetTypeInheritance(Type type)
         {
             var interfaces = type.GetInterfaces();
+            var lastIndex = interfaces.Length - 1;
             var types = new List<Type>(interfaces.Length + 2) { type };
             Type baseType = type;
             while ((baseType = baseType.BaseType) != null)
             {
                 types.Add(baseType);
+                foreach (var interfaceType in baseType.GetInterfaces())
+                {
+                    var interfaceIndex = Array.LastIndexOf(interfaces, interfaceType);
+                    if (interfaceIndex != lastIndex)
+                    {
+                        interfaces[interfaceIndex] = interfaces[lastIndex];
+                        interfaces[lastIndex] = interfaceType;
+                    }
+                }
             }
-            for(int index = interfaces.Length - 1; index >= 0; index--)
+            foreach (var interfaceType in interfaces)
             {
-                types.Add(interfaces[index]);
+                types.Add(interfaceType);
             }
             return types;
         }
diff --git a/src/UnitTests/InterfaceMapping.cs b/src/UnitTests/InterfaceMapping.cs
index b102a0b48b..c6360b0942 100644
--- a/src/UnitTests/InterfaceMapping.cs
+++ b/src/UnitTests/InterfaceMapping.cs
@@ -6,6 +6,56 @@
 using Xunit;
 namespace AutoMapper.UnitTests.InterfaceMapping
 {
+    public class InterfaceInheritance : AutoMapperSpecBase
+    {
+        protected override MapperConfiguration CreateConfiguration() => new(cfg =>
+        {
+            cfg.CreateMap<Source, IProperties>()
+                .IncludeBase<Source, IPropertyA>()
+                .IncludeBase<Source, IPropertyB>();
+            cfg.CreateMap<Source, IPropertyA>();
+            cfg.CreateMap<Source, IPropertyB>();
+        });
+        [Fact]
+        public void Should_choose_the_derived_interface()
+        {
+            var source = new Source
+            {
+                Name = "Name",
+                PropertyA = "PropertyA",
+                PropertyB = "PropertyB"
+            };
+            var destination = new Target();
+            Mapper.Map(source, destination);
+            destination.Name.ShouldBe(source.Name);
+            destination.PropertyA.ShouldBe(source.PropertyA);
+            destination.PropertyB.ShouldBe(source.PropertyB);
+        }
+        public class Source
+        {
+            public string PropertyA { get; set; }
+            public string PropertyB { get; set; }
+            public string Name { get; set; }
+        }
+        public class Target : IProperties
+        {
+            public string PropertyA { get; set; }
+            public string PropertyB { get; set; }
+            public string Name { get; set; }
+        }
+        public interface IProperties : IPropertyA, IPropertyB
+        {
+            string Name { get; set; }
+        }
+        public interface IPropertyA
+        {
+            string PropertyA { get; set; }
+        }
+        public interface IPropertyB
+        {
+            string PropertyB { get; set; }
+        }
+    }
     public class MapToInterface : NonValidatingSpecBase
     {
         protected override MapperConfiguration CreateConfiguration() => new(c=>c.CreateMap<object, IEnumerable<object>>());