[llvm-dev] [RFC] Error handling in LLVM libraries.

[Rafael Espíndola via llvm-dev]

>> This highlights why I think it is important to keep diagnostics and
>> errors separate. In the solution you have there is a need to allocate
>> a std::string, even if that is never used.
>
> Errors are only constructed on the error path. There is no construction on
> the success path.

But they are always created, even if it as error the caller wants to
ignore. For example, you will always create a "file foo.o in bar.a is
not a bitcode" message (or copy sufficient information for that to be
created). With a dignostic handler no copying is needed, since the
call happens in the context where the error is found. It is easy to
see us in a position where a lot of context is copied because some
client somewhere might want it.

So I am worried we are coding for the hypothetical and adding
complexity. In particular, if we are going this way I think it is
critical that your patch *removes* the existing diagnostic handlers
(while making sure test/Bitcode/invalid.ll still passes) so that we
don't end up with two overlapping solutions. We were still not even
done converting away from bool+std::string :-(

Cheers,
Rafael