Not all mapping errors are surfaced when a map contains more than one sort of misconfiguration

[simonmckenzie]

When a map contains unmapped properties and properties with incompatible types, only the unmapped member error is thrown during validation. Once the unmapped member error is fixed, then the "unmappable member" error is thrown.

AssertConfigurationIsValid should surface all mapping errors upfront, to prevent the need for multiple passes when fixing configuration errors.

Example

class Foo
{
    public DateOnly IncompatibleProp { get; set; }
}

class FooDto
{
    public DateTime IncompatibleProp { get; set; }
    public string UnmappedProp { get; set; }
}

// ...

var configuration = new MapperConfiguration(cfg =>
{
    cfg.CreateMap<Foo, FooDto>();
});

configuration.AssertConfigurationIsValid();

This will throw this error:

Unmapped members were found. Review the types and members below
...
Unmapped properties:
UnmappedProp

When the unmapped member is mapped, the code will then start throwing this error:

The following member on AutomaticInterfaceExample.FooDto cannot be mapped: 
    IncompatibleProp 

I think it would be very helpful if the configuration exception showed both issues at once. I believe this could be done relatively easily by lifting the existing configExceptions collection higher in the AssertConfigurationIsValid method and having it collect type map errors together with dry run errors.

https://github.com/AutoMapper/AutoMapper/blob/b521096a3e05782df85fdb42356601a9bb3f35f8/src/AutoMapper/Configuration/ConfigurationValidator.cs#L28-L63

[lbargaoanu]

A PR is welcome.

[simonmckenzie]

Happy to. I'll have some time next week.

[lbargaoanu]

It could simply add the exception to the list instead of throwing.

[simonmckenzie]

Yep, that's what I was going to do :)

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