Fix Issue #4502 - Confusing exception when trying top map types with in parameters in ctor

Author: Biotronic

src/AutoMapper/ConstructorMap.cs

@@ -70,6 +70,7 @@ public class ConstructorParameterMap : MemberMap
     public ConstructorParameterMap(TypeMap typeMap, ParameterInfo parameter, MemberInfo[] sourceMembers) : base(typeMap)
     {
         Parameter = parameter;
+        DestinationType = parameter.ParameterType.IsByRef ? parameter.ParameterType.GetElementType() : parameter.ParameterType;
         if (sourceMembers.Length > 0)
         {
             MapByConvention(sourceMembers);
@@ -80,7 +81,7 @@ public ConstructorParameterMap(TypeMap typeMap, ParameterInfo parameter, MemberI
         }
     }
     public ParameterInfo Parameter { get; }
-    public override Type DestinationType => Parameter.ParameterType;
+    public override Type DestinationType { get; protected set; }
     public override IncludedMember IncludedMember { get; protected set; }
     public override MemberInfo[] SourceMembers { get; set; }
     public override string DestinationName => Parameter.Name;

src/AutoMapper/Internal/TypePair.cs

@@ -7,10 +7,19 @@ public MapRequest(TypePair types) : this(types, types, MemberMap.Instance) { }
     public override int GetHashCode() => HashCode.Combine(RequestedTypes, RuntimeTypes);
 }
 [DebuggerDisplay("{SourceType.Name}, {DestinationType.Name}")]
-public readonly record struct TypePair(Type SourceType, Type DestinationType)
+public readonly record struct TypePair
 {
+    public TypePair(Type sourceType, Type destinationType)
+    {
+        SourceType = sourceType;
+        DestinationType = destinationType.IsByRef ? destinationType.GetElementType() : destinationType;
+    }
+
     public bool IsConstructedGenericType => SourceType.IsConstructedGenericType || DestinationType.IsConstructedGenericType;
     public bool ContainsGenericParameters => SourceType.ContainsGenericParameters || DestinationType.ContainsGenericParameters;
+    public Type DestinationType { get; init; }
+    public Type SourceType { get; init; }
+
     public TypePair CloseGenericTypes(TypePair closedTypes)
     {
         var sourceArguments = closedTypes.SourceType.GenericTypeArguments;

src/UnitTests/Bug/ByrefConstructorParameter.cs

@@ -0,0 +1,41 @@
+namespace AutoMapper.UnitTests.Bug;
+
+public class ByrefConstructorParameter : AutoMapperSpecBase
+{
+    private Destination _destination;
+
+    class Source
+    {
+        public TimeSpan X { get; set; }
+    }
+
+    class Destination
+    {
+        public Destination(in TimeSpan x)
+        {
+            Y = x;
+        }
+
+        public TimeSpan Y { get; }
+    }
+
+    protected override MapperConfiguration CreateConfiguration() => new(cfg =>
+    {
+        cfg.CreateMap<Source, Destination>();
+    });
+
+    protected override void Because_of()
+    {
+        var source = new Source
+        {
+            X = TimeSpan.FromSeconds(17)
+        };
+        _destination = Mapper.Map<Destination>(source);
+    }
+
+    [Fact]
+    public void should_just_work()
+    {
+        _destination.Y.ShouldBe(TimeSpan.FromSeconds(17));
+    }
+}