Merge pull request AutoMapper#2136 from AutoMapper/DuplicateCreateMapCalls

Disallow duplicate create map calls

Author: jbogard

src/AutoMapper/AdvancedConfiguration.cs

@@ -22,6 +22,8 @@ public class AdvancedConfiguration
         /// <param name="validator">the validation callback</param>
         public void Validator(Validator validator) => _validators.Add(validator);
 
+        public bool AllowAdditiveTypeMapCreation { get; set; }
+
         internal Validator[] GetValidators() => _validators.ToArray();
     }
 }

src/AutoMapper/Configuration/MappingExpression.cs

@@ -2,7 +2,6 @@
 using System.Collections.Generic;
 using System.Linq;
 using AutoMapper.Configuration;
-using AutoMapper.Mappers;
 
 namespace AutoMapper
 {

src/AutoMapper/ConfigurationValidator.cs

@@ -0,0 +1,40 @@
+using System;
+using System.Text;
+
+namespace AutoMapper
+{
+    public class DuplicateTypeMapConfigurationException : Exception
+    {
+        public TypeMapConfigErrors[] Errors { get; }
+
+        public DuplicateTypeMapConfigurationException(TypeMapConfigErrors[] errors)
+        {
+            Errors = errors;
+            var builder = new StringBuilder();
+            builder.AppendLine("The following type maps were found in multiple profiles:");
+            foreach (var error in Errors)
+            {
+                builder.AppendLine($"{error.Types.SourceType.FullName} to {error.Types.DestinationType.FullName} defined in profiles:");
+                builder.AppendLine(string.Join(Environment.NewLine, error.ProfileNames));
+            }
+            builder.AppendLine("This can cause configuration collisions and inconsistent mapping.");
+            builder.AppendLine("Consolidate the CreateMap calls into one profile, or set the root Advanced.AllowAdditiveTypeMapCreation configuration value to 'true'.");
+
+            Message = builder.ToString();
+        }
+
+        public class TypeMapConfigErrors
+        {
+            public string[] ProfileNames { get; }
+            public TypePair Types { get; }
+
+            public TypeMapConfigErrors(TypePair types, string[] profileNames)
+            {
+                Types = types;
+                ProfileNames = profileNames;
+            }
+        }
+
+        public override string Message { get; }
+    }
+}