[llvm-dev] [RFC] Error handling in LLVM libraries.
Lang Hames via llvm-dev
llvm-dev at lists.llvm.org
Wed Feb 10 08:47:59 PST 2016
ErrorOr still exists, and generally useful. This proposal introduces a
similar class, TypedErrorOr, that replaces the std::error_code with a
Any more detailed discussion of ErrorOr usage should probably happen on
another thread - this one is already getting long. :)
On Wed, Feb 10, 2016 at 8:44 AM, Paweł Bylica <llvm-dev at lists.llvm.org>
> Sorry for the question out of nowhere, but what happened to ErrorOr<>
> On Wed, Feb 10, 2016 at 5:41 PM Rafael Espíndola <llvm-dev at lists.llvm.org>
>> On 10 February 2016 at 11:10, David Blaikie <dblaikie at gmail.com> wrote:
>> > On Wed, Feb 10, 2016 at 6:47 AM, Rafael Espíndola <
>> llvm-dev at lists.llvm.org>
>> > wrote:
>> >> >> This highlights why I think it is important to keep diagnostics and
>> >> >> errors separate. In the solution you have there is a need to
>> >> >> a std::string, even if that is never used.
>> >> >
>> >> > Errors are only constructed on the error path. There is no
>> >> > 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.
>> > Removes diagnostic handlers in other parts of LLVM (& Clang) - the IR
>> > verifier's diagnostic handling is what you're referring to here ^?
>> > I don't think that would be an improvement - it seems like different
>> > situations call for different tools (as I was saying yesterday on this
>> > thread). In some places a diagnostic handler is the right tool, and in
>> > places error codes/results/etc are the right tool. We already live in
>> > world & it seems like a reasonable one (there doesn't seem to be a
>> > fundamental conflict between our bool+std::string or error_code returns
>> > existing diagnostic handlers - I think they can reasonably coexist in
>> > different parts of the codebase for different use cases)
>> In which case we do need a plain checked error_code. Right now we use
>> a diagnostic handler in the BitcodeReader, but it is really easy to
>> miss propagating an error out. We shouldn't be in a position where we
>> have to decide to use an diagnostic handler or have checked errors. It
>> should be possible to have both if it is not desired that the new
>> error handling replaces the use of diagnostic handling.
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