fix: #954 fix mapping optional ValueType params

src/Mapster.Tests/WhenCtorNullableParamMapping.cs

@@ -1,5 +1,6 @@
 using Microsoft.VisualStudio.TestTools.UnitTesting;
 using Shouldly;
+using System;
 using System.Collections.Generic;
 
 namespace Mapster.Tests
@@ -82,6 +83,27 @@ public void NullableCtorPropagationCurrentWorkWithDestinationTransform()
             foo.Strings.ShouldNotBeNull();
         }
 
+
+        /// <summary>
+        /// https://github.com/MapsterMapper/Mapster/issues/954
+        /// </summary>
+        [TestMethod]
+        public void MappingValueTypeParametrUsingDefaultValueCorrect()
+        {
+            // Arrange
+            var src = new DateTimeFoo954(DateTime.Today);
+
+            // Assert
+            Should.NotThrow(() =>
+            {
+                var foo = src.Adapt<DateTimeFooDto954>();
+
+                foo.Timestamp.ShouldBe(src.Timestamp);
+            });
+        }
+
+
+
         #region Immutable classes with private setters, map via ctors
         private abstract class AbstractDomainTestClass
         {
@@ -119,6 +141,18 @@ public DomainTestClass(
 
         #region DTO classes
 
+        public class DateTimeFooDto954
+        {
+            public DateTime Timestamp { get; set; }
+
+            public DateTimeFooDto954(DateTime timestamp = default(DateTime))
+            {
+                this.Timestamp = timestamp;
+            }
+        }
+
+        record DateTimeFoo954(DateTime Timestamp);
+
         class FooDto943
         {
             public string[] Strings { get; set; }

src/Mapster/Adapters/BaseClassAdapter.cs

@@ -15,7 +15,7 @@
 
         #region Build the Adapter Model
 
         protected ClassMapping CreateClassConverter(Expression source, ClassModel classModel, CompileArgument arg, Expression? destination = null, bool ctorMapping = false, ClassModel recordRestorMemberModel = null)
         {
             var destinationMembers = classModel.Members;
             var unmappedDestinationMembers = new List<string>();
@@ -213,7 +213,7 @@
                    && ignore.Condition == null;
         }
 
         protected Expression CreateInstantiationExpression(Expression source, ClassMapping classConverter, CompileArgument arg, Expression? destination, ClassModel recordRestorParamModel = null)
         {
             var members = classConverter.Members;
 
@@ -222,11 +222,27 @@
             {
                 arg.Context.NullChecks.UnionWith(members.Where(x=>x.Getter != null).Select(x=>(x.Getter,arg)));
                 var parameterInfo = (ParameterInfo)member.DestinationMember.Info!;
-                var defaultConst = parameterInfo.IsOptional
+                Expression defaultConst;
+                Expression getter;
+
+#if NETSTANDARD2_0
+                try
+                {
+                    defaultConst = parameterInfo.IsOptional && parameterInfo.DefaultValue != null
                     ? Expression.Constant(parameterInfo.DefaultValue, member.DestinationMember.Type)
                     : parameterInfo.ParameterType.CreateDefault();
+                }
+                catch (FormatException)
+                {
+                    defaultConst = parameterInfo.ParameterType.CreateDefault();
+                }
 
-                Expression getter;
+#else
+                defaultConst = parameterInfo.IsOptional && parameterInfo.DefaultValue != null
+                    ? Expression.Constant(parameterInfo.DefaultValue, member.DestinationMember.Type)
+                    : parameterInfo.ParameterType.CreateDefault();
+#endif
+
                 if (member.Getter == null)
                 {
                     getter = defaultConst;
@@ -352,6 +368,6 @@
                 new[] { member.Destination, memberAsObject });
         }
 
-        #endregion
+#endregion
     }
 }