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From "Barber, Christopher" <Christopher.Bar...@analog.com>
Subject Re: Proposal for treating warnings as errors in Linux & Clang builds (-Werror)
Date Tue, 16 Jan 2018 15:11:51 GMT
Personally, I don’t like treating warnings as errors because it prevents compilation from
completing and causes you to lose any ability to test the code and get any other information.
Killing the build because of a failed warning for something that might not matter means that
you may not find out about other important test failures until much later. Better to add a
test that grovels the build logs for warning messages and treat it as a test failure.

I also prefer to only enable exactly those warnings that truly matter.

On 1/16/18, 8:23 AM, "Marco de Abreu" <marco.g.abreu@googlemail.com> wrote:

    I'd vote for having warnings as errors only for CI but not in general
    builds which are getting executed by users on their local machine. Just in
    case CI misses a warning due to a different version, this could block a
    developer from compiling MXNet locally even though it might just be a
    warning which is not critical enough (otherwise it would be an error) to
    justify blocking the compilation. In my opinion, it would be good if we can
    filter most warnings during PR-stage and risk that some are getting into
    the master branch due to a different compiler version. A reduction of (for
    example) 95% without risking to break the master branch on different
    compilers is way better in my opinion than having a 100% coverage which
    could block compilation - especially because we would only notice if a user
    tells us afterwards.
    
    -Marco
    
    On Tue, Jan 16, 2018 at 1:32 PM, Pedro Larroy <pedro.larroy.lists@gmail.com>
    wrote:
    
    > Hi Chris
    >
    > I get the rationale of the point you raise, but In my opinion, and
    > considering the complexity of C++ and the potential for difficult and
    > expensive to track bugs, I think this should be enabled by default for
    > both release and debug. A developer is free to disable warnings in his
    > own private branch, but I don't see what would be the benefit of this.
    >
    > Regarding your second point, I think this is a minor issue which is
    > outweighed by the benefits. In the case you propose, the author of a
    > PR can easily fix a bunch of warnings when CI fails as usual. For
    > example in case he gets one or two warnings that his version of the
    > compiler didn't catch, or if she has an additional warning of some
    > type with a different version of GCC / Clang.
    >
    > This has the objective to prevent warning inflation. In practice, a
    > different version of GCC might produce just a couple of new warning
    > types that will be easily fixable once we upgrade the compiler in CI.
    > We also get the benefit of preventing warnings on the gcc versions
    > that the author is using, in the case he has a different one. Another
    > option is to enable warnings as errors only on CI. I would prefer to
    > have it enabled by default, for correctness. As first time users are
    > not likely to compile MXNet by themselves, and also considering the
    > significant complexity of compiling MXNet from scratch for newcomers.
    >
    > In general, the compilers that we have running on CI should be our
    > reference compilers. And for practical purposes, having no warnings in
    > those versions of Clang and GCC would be a positive step towards more
    > code quality, clean compilation and a more mantainable code base.
    > Once we have CI stable we can build a matrix of supported compilers in
    > the docs, as for example there are versions of GCC which are not
    > supported by the nvidia tools.
    >
    > Pedro.
    >
    >
    >
    >
    > On Mon, Jan 15, 2018 at 7:27 PM, Chris Olivier <cjolivier01@gmail.com>
    > wrote:
    > > If enabled, it should only cause errors in Release builds, since having
    > > warnings in WIP code is not unusual.
    > >
    > > In addition, different developers use different gcc/clang versions. Some
    > > gcc versions, for instance, generate warnings where others do not.  It
    > > would not be fair to render unbuildable a developer who is using a newer
    > > (or older) gcc version is different from CI.  Can this argument be tied
    > to
    > > a particular compiler/platform/version?
    > >
    > > On Mon, Jan 15, 2018 at 9:43 AM, Marco de Abreu <
    > > marco.g.abreu@googlemail.com> wrote:
    > >
    > >> +1
    > >>
    > >> On Mon, Jan 15, 2018 at 6:27 PM, Pedro Larroy <
    > >> pedro.larroy.lists@gmail.com>
    > >> wrote:
    > >>
    > >> > Hi
    > >> >
    > >> > I would like to propose to compile in CI with warnings as errors for
    > >> > increased code quality. This has a dual purpose:
    > >> >
    > >> > 1. Enforce a clean compilation output. Warnings often indicate
    > >> > deficiencies in the code and hide new warnings which can be an
    > >> > indicator of problems.
    > >> >
    > >> > 2. Warnings can surface bugs as has happened before.
    > >> >
    > >> > While this might be impractical in all architectures, I would propose
    > >> > having the Linux and Clang build run without warnings in CI.
    > >> >
    > >> > I think we are very close to this as I personally have been fixing
    > >> > warnings in Linux and OSX / Clang.
    > >> >
    > >> > References:
    > >> >
    > >> > https://github.com/apache/incubator-mxnet/pull/9398
    > >> >
    > >> > http://jenkins.mxnet-ci.amazon-ml.com/blue/organizations/jenkins/
    > >> > incubator-mxnet/detail/PR-9398/1/pipeline
    > >> >
    > >> > Pedro.
    > >> >
    > >>
    >
    

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