Coding standard for qdebug in libs

[Boudewijn Rempt]

There is one more thing about logging using qCDebug and friends:
the logging categories are supposed to be defined _per library_.

Which is actually pretty useless and not really how we've been
using categories in Calligra. Logging categories for file
handling, resource management or plugin handling that can be used
across libraries and applications make it possible to focus on
debugging a path through the application's execution.

I don't debug pigment, I debug color management, for instance, which
is present in pigment, the colorspace plugin and parts of Krita.

That's why for Krita, I made a generic debug interface in a little
global library that knows about all the categories and that can
be used from everywhere.


Boudewijn


Oe Sat, 5 Sep 2015, Jaroslaw Staniek wrote:

> Hi,
> This is a proposal for some consistency for naming of debug functions,
> debug headers and logging categories.
> I'll be trying to achieve in code I maintain. I can put some
> guidelines on the dev wiki.
>
> Details:
> After looking at recent commits such as Friedrich's 1dddbcdbceab0
> "kWarning -> warnPigment" I was wondering if we want to have standards
> for debug handling.
> I don't use one in Kexi, not yet, but use one in
> kdb/kreport/kproperty. With increasing modularity it's quite important
> for our debugging needs to have logging categories.
>
> A scheme could be like
> {libnamelowercase}{Debug|Warning|Critical}()
>
> e.g. I use kdbDebug() << ... ;
>
> Note, for clarity () is used here too like in qDebug().
> See kdb_debug.h https://quickgit.kde.org/?p=kdb.git&a=blob&f=src%2Fkdb_debug.h
>
> Furthermore, in kde_debug.cpp
> [https://quickgit.kde.org/?p=kdb.git&a=blob&f=src%2Fkdb_debug.cpp] I
> have:
> Q_LOGGING_CATEGORY(KDB_LOG, "org.kde.kdb.core")
>
> Note that you can pick your scheme for string, e.g.
> org.kde.calligra.{someapp} or org.calligra.{someapp}
> and for libs org.kde.{somelib}. It's important to have it unique and
> relatively short. Planning for future expansion is a good way too.
>
> For tests and example apps it may be enough to use default debug or
> for big code decide to add special category too.
>
> I also propose to use a libname prefix for the header name. This is
> what many bits in KF5 do. So we won't have to deal with dozens files
> prefixed with "Debug" soon (so libpigment's DebugPigment.h could
> become PigmentDebug.h or pigment_debug.h).
>
> PS: I am aware e.g. KF5 has various approaches there, use qDebug()
> with no categories, use qCDebug without defines.
> We have not fully migrated to logging categories in apps and internal
> libs so I thought it may be cool to think about consistency early
> enough.
>
> -- 
> regards, Jaroslaw Staniek
>
> KDE:
> : A world-wide network of software engineers, artists, writers, translators
> : and facilitators committed to Free Software development - http://kde.org
> Calligra Suite:
> : A graphic art and office suite - http://calligra.org
> Kexi:
> : A visual database apps builder - http://calligra.org/kexi
> Qt Certified Specialist:
> : http://www.linkedin.com/in/jstaniek
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