Better mixin error messages

[Bauss via Digitalmars-d]

Can there please be implemented something to retrieve the 
generated mixins that causes compiler errors; like perhaps a flag 
you pass that will print all mixins with compiler errors?

Sometimes when you create highly dynamic mixins it can be hard to 
identify errors in them, because you might not know exactly what 
code is generated.

I've had that issue multiple times with big mixins and it has 
been impossible to determine what the exact culprit of it is. I 
mean you get the line and stuff within the mixin, but sometimes 
that's not enough because you simply don't know the exact mixin 
string that's compiled.

Of course you can generate the mixin strings at runtime and print 
them out, but it can be a real hassle to translate compiletime 
data into runtime data to be able to generate the exact mixins. 
Sometimes it might not be an option either if your mixins rely on 
other mixins or simply because the data you rely on is too 
difficult to move.

I believe it would make compiler errors easier to handle for 
mixins if you could see the generated mixins, because you could 
pinpoint the issue to its exact location.

This might not be something that you face with small mixins, but 
I often deal with mixins of 100s - 1000s lines of code and it 
becomes really hard to deal with errors in them because I don't 
know what they exactly consists of.