Can't map to ImmutableArray

[drew-cooper]

Source/destination types

public class Foo
{
	public string Value { get; set; }
}

public class Bar
{
	public ImmutableArray<byte> Value { get; set; }
}

Mapping configuration

new MapperConfiguration(cfg => 
    cfg.CreateMap<Foo, Bar>()
        .ForMember(
            bar => bar.Value, 
            m => m.MapFrom((foo, bar) => Convert.FromBase64String(foo.Value).ToImmutableArray())));

Version: 10.1.1 and 11.0.0

Expected behavior

bar.Value should be assigned the ImmutableArray<byte> created by the MapFrom delegate.

Actual behavior

On v10.1.1 an exception was thrown while building the configuration:

The binary operator Equal is not defined for the types 'System.Collections.Immutable.ImmutableArray`1[System.Byte]' and 'System.Object'.
   at System.Linq.Expressions.Expression.GetEqualityComparisonOperator(ExpressionType binaryType, String opName, Expression left, Expression right, Boolean liftToNull)
   at System.Linq.Expressions.Expression.Equal(Expression left, Expression right, Boolean liftToNull, MethodInfo method)
   at System.Linq.Expressions.Expression.Equal(Expression left, Expression right)
   at AutoMapper.Internal.CollectionMapperExpressionFactory.<MapCollectionExpression>g__UseDestinationValue|1_0(<>c__DisplayClass1_0& )
   at AutoMapper.Internal.CollectionMapperExpressionFactory.MapCollectionExpression(IConfigurationProvider configurationProvider, ProfileMap profileMap, IMemberMap memberMap, Expression sourceExpression, Expression destExpression, Expression contextExpression, Type ifInterfaceType, MapItem mapItem)
   at AutoMapper.Mappers.CollectionMapper.MapExpression(IConfigurationProvider configurationProvider, ProfileMap profileMap, IMemberMap memberMap, Expression sourceExpression, Expression destExpression, Expression contextExpression)
   at AutoMapper.Execution.ExpressionBuilder.ObjectMapperExpression(IConfigurationProvider configurationProvider, ProfileMap profileMap, TypePair typePair, Expression sourceParameter, Expression contextParameter, IMemberMap propertyMap, Expression destinationParameter)
   at AutoMapper.Execution.ExpressionBuilder.MapExpression(IConfigurationProvider configurationProvider, ProfileMap profileMap, TypePair typePair, Expression sourceParameter, Expression contextParameter, IMemberMap propertyMap, Expression destinationParameter)
   at AutoMapper.Execution.TypeMapPlanBuilder.CreatePropertyMapFunc(IMemberMap memberMap, Expression destination, MemberInfo destinationMember)
   at AutoMapper.Execution.TypeMapPlanBuilder.CreateAssignmentFunc(Expression destinationFunc)
   at AutoMapper.Execution.TypeMapPlanBuilder.CreateMapperLambda(HashSet`1 typeMapsPath)
   at AutoMapper.TypeMap.CreateMapperLambda(IConfigurationProvider configurationProvider, HashSet`1 typeMapsPath)
   at AutoMapper.TypeMap.Seal(IConfigurationProvider configurationProvider)
   at AutoMapper.MapperConfiguration.Seal()
   at AutoMapper.MapperConfiguration..ctor(MapperConfigurationExpression configurationExpression)
   at AutoMapper.MapperConfiguration..ctor(Action`1 configure)
   at UserQuery.Main(), line 3

I tried v11.0.0 and it failed similarly, but with a different exception:

InvalidOperationException: Coalesce used with type that cannot be null
   at System.Linq.Expressions.Expression.ValidateCoalesceArgTypes(Type left, Type right)
   at System.Linq.Expressions.Expression.Coalesce(Expression left, Expression right, LambdaExpression conversion)
   at System.Linq.Expressions.Expression.Coalesce(Expression left, Expression right)
   at AutoMapper.Internal.Mappers.CollectionMapper.<MapExpression>g__UseDestinationValue|2_3(<>c__DisplayClass2_1& )
   at AutoMapper.Internal.Mappers.CollectionMapper.<MapExpression>g__MapCollectionCore|2_1(Expression destExpression, <>c__DisplayClass2_0& )
   at AutoMapper.Internal.Mappers.CollectionMapper.MapExpression(IGlobalConfiguration configurationProvider, ProfileMap profileMap, MemberMap memberMap, Expression sourceExpression, Expression destExpression)
   at AutoMapper.Execution.ExpressionBuilder.MapExpression(IGlobalConfiguration configurationProvider, ProfileMap profileMap, TypePair typePair, Expression sourceParameter, MemberMap propertyMap, Expression destinationParameter)
   at AutoMapper.Execution.TypeMapPlanBuilder.MapMember(MemberMap memberMap, Expression destinationMemberValue, ParameterExpression resolvedValue)
   at AutoMapper.Execution.TypeMapPlanBuilder.CreatePropertyMapFunc(MemberMap memberMap, Expression destination, MemberInfo destinationMember)
   at AutoMapper.Execution.TypeMapPlanBuilder.CreateAssignmentFunc(Expression createDestination)
   at AutoMapper.Execution.TypeMapPlanBuilder.CreateMapperLambda(HashSet`1 typeMapsPath)
   at AutoMapper.TypeMap.CreateMapperLambda(IGlobalConfiguration configurationProvider, HashSet`1 typeMapsPath)
   at AutoMapper.TypeMap.Seal(IGlobalConfiguration configurationProvider, HashSet`1 typeMapsPath)
   at AutoMapper.MapperConfiguration.Seal()
   at AutoMapper.MapperConfiguration..ctor(MapperConfigurationExpression configurationExpression)
   at AutoMapper.MapperConfiguration..ctor(Action`1 configure)
   at UserQuery.Main(), line 3

Steps to reproduce

Running the above code is all that is needed. Here is a minimal LinqPad query that repros the issue:

<Query Kind="Program">
  <NuGetReference Version="10.1.1">AutoMapper</NuGetReference>
  <Namespace>AutoMapper</Namespace>
  <Namespace>System.Collections.Immutable</Namespace>
  <Namespace>System.Threading.Tasks</Namespace>
</Query>

void Main()
{
	new MapperConfiguration(cfg => 
		cfg.CreateMap<Foo, Bar>()
			.ForMember(
				bar => bar.Value, 
				m => m.MapFrom((foo, bar) => Convert.FromBase64String(foo.Value).ToImmutableArray())));
}

// You can define other methods, fields, classes and namespaces here
public class Foo
{
	public string Value { get; set; }
}

public class Bar
{
	public ImmutableArray<byte> Value { get; set; }
}

Notes

• In my use-case I know that the source string value will not be null.
• I can work around this by ignoring the member in configuration and doing the mapping in the AfterMap action.

[lbargaoanu]

That's not built in. A PR is welcome.
Of course what you want here is a type converter, not a value resolver :)