[QGIS-Developer] What to do about incorrect SAGA algorithms?

[Nyall Dawson]

On Mon, 4 Mar 2019 at 21:59, Pedro Venâncio <pedrongvenancio at gmail.com> wrote:
>
> Hi Nyall,
>
> I think this rises another problem, that is the use of a very old version of SAGA (2.3.2) in QGIS.
>
> I've just tested Difference algorithm with Lene dataset in native SAGA 2.3.2 and 7.2.0, and 2.3.2 gives the problem described, but 7.2.0 gives the correct result:
>
> https://cld.pt/dl/download/2dfb0db5-eb74-4396-ad18-7451fd1fe788/test_saga_232.jpg
>
> https://cld.pt/dl/download/92182907-d37a-4441-891c-3c85064b3100/test_saga_720.jpg

This is really frustrating -- I wonder if someone with links to the
SAGA project could approach them again and gently ask them to consider
a new LTR release? Unfortunately until they do make a new LTR, users
on our Windows installation and through the larger linux distros are
stuck with the 2.3 release. I don't believe either the windows nor
debian/ubuntu/fedora packaging team have any intention of moving to
non-ltr releases.

>
> So, we are faced again with the question of keep an old version of SAGA in QGIS core, or make it as an external plugin, with someone keeping an eye in the changes introduced by SAGA team between versions (as we saw in the past).
>
> Alexander Bruy had made an effort to keep a parallel SAGA plugin that support newer SAGA versions: https://plugins.bruy.me/processing-saga.html
> But it is not in the official repository. Maybe this is the time to discuss again the use of SAGA as an external plugin?

So -- my new proposal would be:

1. Leave the inbuilt support at LTR only. Deprecate all known broken
algorithms to avoid user error and frustration.
2. Copy the saga provider to a NEW "saga-next gen" plugin based
provider, which targets the current SAGA v7 .2 release ONLY. This
would be a community-maintained plugin (although, as a once off
goodwill gesture I'm willing to do the initial plugin setup and host
it on a North Road github repo). This plugin could be installed
alongside the inbuilt SAGA LTR provider without issue, but it would
NOT be included in a default QGIS install and users would have to
manually install it via the plugin installer.

I think this approach is the best solution when could get given the
constraints we are working around.

Nyall