[QGIS-Developer] using conda for development

[Ari Meyer]

Obrigado, Alexandre, for all the details. :-)  I guess I'm still baffled
by, "Conda-forge community always tries to use the most recent version of
all dependencies."  It just seems like a "recipe" for disaster -- just
built on assumptions.  Maybe you get lucky and everything just happens to
work.  Or maybe you get slightly less lucky and encounter breakages
immediately, forcing you to fiddle with the build until you find some
combination that seems to work, if you can't pin the versions.  Or maybe
you get unlucky and everything builds and *seems* to work based on the
extent of your testing, but your testing may have important gaps.

In my previous contract I was using PyViz, which was rebranded as HoloViz.
As that set of libraries was immature and constantly in flux, and we wanted
to take advantage of new features/fixes, our policy was to go with the
latest releases.  I wasn't comfortable with this, esp. after enduring many
problems, but we just dealt with bugs and regressions as they came up.
QGIS, though, is much more mature, after more than a decade since 1.0 was
released (2009 according to Wiki).  I assumed, therefore, that they
wouldn't trust such a hit-or-miss strategy with dependencies.  But maybe
I'm just being a worry wart. ;-)  In any case, I'm going to be hard-pressed
to sell conda to my team if the dependencies are out of sync with those of
the installers.

On Fri, Jul 31, 2020 at 8:49 AM Alexandre Neto <senhor.neto at gmail.com>
wrote:

> Hi,
>
> I will take this opportunity to give a brief explanation of how conda /
> conda-forge works. At least what I was able to understand so far.
>
> Full disclaimer: I know very little about building and maintaining
> packages and installers, including the QGIS ones, but I try to trigger the
> update of QGIS versions on Conda-forge.
>
> *Conda* - an open source package management system and environment
> management system developed mainly by anaconda. It provides tools to build,
> install and run packages, and setup environments. One interesting feature
> is that, in conda, the same building recipe can be used to build the
> packages for Windows, Mac and Linux. Normally, to build a package, you use
> prebuild packages of its dependencies which are available in conda online
> channels. This doesn't mean that the same versions of the dependencies are
> used for all platforms, as some dependency may not be available or doesn't
> work for a specific platform.
>
> *Conda-forge* - a community that maintains a big amount of conda recipes
> for many open source packages, which are stored in github repositories.
> Those are called feedstocks. Among them, there is a qgis-feedstock and also
> feedstocks for almost all of its dependencies. Collaboration to keep those
> recipes is normally very welcome.
>
> https://conda-forge.org/feedstocks/
>
> https://github.com/conda-forge/qgis-feedstock
>
> All conda-forge recipes (each feedstock github branch) are built
> automatically using Azure Pipelines and uploaded to the conda-forge channel
> in Anaconda cloud, making it easily deployed for installation. QGIS has a
> master (stable) and a LTR branch.
>
> *Anaconda cloud* is a repository of prebuilt packages, which is organized
> in channels.  Anyone can have a channel and upload their locally built
> packages so that others can use them. If you search for QGIS in Anaconda
> cloud you will find several channels with several versions available.
>
> Answering Ari question:
>
> On Fri, Jul 31, 2020 at 6:15 AM Ari Meyer <ari.meyer at gmail.com> wrote:
>
>> @Greg: I found that many of the exact dependencies were not even
>> available through the main channels.  So if the QGIS devs compile/build
>> against such versions, I'm not sure there's an easy way to even specify
>> such a conda recipe, unless all those dependencies are also made available
>> somehow.  I didn't expect that those versions would not even be there with
>> the others for the various libraries.  Could this imply that the library
>> developers don't want those versions to be used?  Not sure.
>>
>
> I can only speak for Conda Forge and mainly QGIS feedstock. I normally try
> to keep the recipes updated for every single new version of QGIS and QGIS
> LTR, but I may forget to do so. Then, sometimes the recipes don't work out
> of the box for a certain patch release of QGIS, the conda-forge folks try
> to fix them, but meanwhile, a new patch release is out, so we may just
> abandon that version recipe and move on. I expect the same may happen with
> other packages... There is no intention of excluding versions for any
> reason.
>
> Regarding the version of the dependencies. Conda-forge community always
> tries to use the most recent version of all dependencies. Sometimes that
> doesn't work, and one needs to pin the version of a dependency. Also, my
> idea was to keep the LTR main dependencies pinned during all its lifecycle,
> to avoid regressions.
>
> *Cool things about QGIS on conda (and conda-forge):*
> - One single transparent recipe to build QGIS in all three main platforms;
> - As users, to install one or several packages for a certain workflow, you
> normally create an environment to isolate the install, which allows having
> several versions of the same software in parallel in your machine.
> Nevertheless, the packages shared by different environments/QGIS versions
> are only downloaded once and don't take more space in the disk. Symbolic
> links are used.
> - Once set, you can share an environment with others, making it perfect
> for collaborative development.
> - Updating QGIS is like osfeo4w in all platforms, only the necessary
> packages are downloads and install.
> - Using Conda-forge infrastructure, you only need to update the recipe,
> the build and upload to anaconda cloud are done in azure pipelines
> "automagically".
> - It's a great way to use QGIS PyQGIS and the command line tools (the
> reason why I try to update QGIS versions in conda-forge)
>
> *Caveats of  conda-forge:*
> - As QGIS project, we have no direct control over dependencies used on the
> master version, as the community has the goal of using the most recent
> dependency versions that is possible. The same is not necessarily true for
> LTR, where I feel we would be allowed to control and pin the dependencies
> - Currently, there are some dependencies missing. For example, QtWebkit,
> which limits QGIS functionality, including some nice plugins like
> DataPlotly, and resource sharing plugin.
>
> It seems to me that, if the QGIS project wanted to use conda as their main
> building/packaging system, we would need to:
> - Keep a fork of conda-forge recipes, and upload the result to a dedicated
> channel, probably even outside anaconda cloud.
> - We could use dependencies available on conda-forge or other channels,
> but we would need to be ready to maintain abandoned packages that greatly
> impact QGIS, like QtWebkit;
> - Recreate the installers (at least Windows and Mac) to use conda tools
> for downloading, installing, and updating packages.
>
> Last bit, when I was working for Boundless, Larry Shaffer was trying to do
> all this mentioned above, but then the company was bought by Planet... Not
> sure what is the status of this work now.
>
> https://github.com/osgeo-forge
>
> Thanks, Sorry for the long post.
>
> Alexandre Neto
>
>
>
>
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