Duplicate Mappings of generics throwing an exception

[tiasmt]

Mapping configuration

protected override MapperConfiguration CreateConfiguration() => new(cfg =>
    {
        cfg.CreateMap(typeof (Source<>), typeof (Dest<>));
        cfg.CreateMap(typeof (Source<>), typeof (Dest<>));
    });

Version: 12.0.1

Expected behavior

Maps are created and when calling mapperConfiguration.AssertConfigurationIsValid(); an error is thrown. (Same as when adding duplicate mappings of non open generics)

Actual behavior

Maps are not created and a duplicate key exception is thrown.

Steps to reproduce

Run the GenericsTests changing the Create Configuration as per above snippet

[lbargaoanu]

I don't know. It seems easier to debug things when the error is thrown where the problem is. What's the point of throwing later, how is that better? You'd have to go back and find the mapping in question.
Not calling AssertConfigurationIsValid is a mistake :) But I guess we'll take a PR to improve the error message if you feel that's useful.

[tiasmt]

Thanks much appreciated - it was just an example no particular reason.
Shall I open a PR for it?

[lbargaoanu]

What exactly would be the fix? Other than a better exception message, I'm not sure I see a trivial fix here, one that isn't worse than the problem itself :)
Maybe we could have CreateMap always throw on duplicated maps. But that would mean using dictionaries or hashsets for each profile. For many profiles the cost could matter, in terms of memory and CPU, a list is smaller and faster for enumeration.

[tiasmt]

I tried the below and it the end result was that an error was only thrown when calling AssertConfigurationIsValid

#4307

[lbargaoanu]

There is little value in that. As I've said above, I'd rather have CreateMap throw, but I'm not sure it's worth the trouble.

[tiasmt]

OK - in that case feel free to close this issue / discussion

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