[QGIS-Developer] Understanding plugin management in QGIS - exposing QgsPluginRegistry to Python?

[Nyall Dawson]

On Sun, 15 Mar 2020 at 09:18, Matthias Kuhn <matthias at opengis.ch> wrote:
>
> Hi Sebastian, Borys,
>
> What about the opposite way: moving things to C++ and leaving only a
> very thing wrapper for interacting with the plugins in place?

That would be my preference too -- the overall movement in QGIS code
is to reduce the overall amount of Python code in master, not the
reverse.

> The rational is that plugin management is not performance-critical and could become much more easy to maintain,

Actually, over time we've found that the opposite is true -- the
Python code in QGIS master is the **most** work to maintain, and a
constant source of regressions. That's due to the nature of the Python
language itself, not a reflection of the quality of the code...

Nyall


>
> That should get rid of duplicated code and be compatible with everything.
>
> Best regards
>
> Matthias
>
> On 3/14/20 10:52 PM, Borys Jurgiel wrote:
> > Hi Sebastian,
> >
> > The reason the whole infrastructure is split between Plugin Manager and Python
> > Plugin Installer (and Python utils) is Python support is optional in QGIS.
> >
> > If QGIS is compiled without Python Support, the Plugin Manager still displays
> > all C++ plugins, it just lacks Python ones (and of course install/deinstall
> > funcions).
> >
> > I admit the the infrastructure became a bit complicated ;) However, porting
> > the Plugin Manager to Python would require making Python a hard dependency of
> > QGIS GUI (or we should drop C++ plugins by porting them all to core, what is
> > discussed from time to time and doesn't seem to may happen).
> >
> > Regards,
> >
> > Borys
> >
> >
> > Dnia sobota, 14 marca 2020 21:10:24 CET Sebastian M. Ernst pisze:
> >> Hi folks,
> >>
> >> out of curiosity I have started poking around in QGIS' code related to
> >> plugin management. It's an interesting mix of C++ and Python code. Even
> >> the plugin management GUI itself is partially C++ (the main window,
> >> QgsPluginManager[Interface], and part of its logic) and partially Python
> >> (all further dialogs and their logic). As an experiment for now, I am
> >> looking into how I could port at least the entire GUI to Python and
> >> disentangle some of the knots. The rational is that plugin management is
> >> not performance-critical and could become much more easy to maintain,
> >> among a lot of other interesting benefits that a potentially fully
> >> Python-based solution could offer. But that's a different story. For
> >> now, I think I have hit a roadblock and was wondering whether anyone
> >> could enlighten me. I'd greatly appreciate any help.
> >>
> >> I *believe* I have a fairly good understanding of what happens
> >> underneath `/python/pyplugin_installer/`. The class `QgsPluginInstaller`
> >> from `installer.py` appears to be a Python API that is called from the
> >> C++-interface (`QgsPluginManagerInterface`) through `QgsPythonRunner`.
> >> Most of the C++ appears to be located underneath
> >> `/src/app/pluginmanager/` (with a single ui-file elsewhere,
> >> `/src/ui/qgspluginmanagerbase.ui`). Having analyzed the C++ class
> >> `QgsPluginManager` I believe most of the interface can easily ported to
> >> Python.
> >>
> >> The tricky bit appears to be `/src/app/qgspluginregistry.cpp`. It offers
> >> a class named `QgsPluginRegistry` (which is being used by
> >> `QgsPluginManager`). I have not found a way to access this class (or
> >> an/the instance of it) from Python. I figure it is required to handle
> >> both Python *and* C++ plugins. `QgsPluginRegistry` makes heavy use of
> >> `mPythonUtils`, which appears to be a C++ wrapper around
> >> `/python/utils.py` (through `/src/python/qgspythonutilsimpl.cpp`). So
> >> this portion of `QgsPluginRegistry` (about 50%) can be rewritten in
> >> Python rather quickly. Methods such as `loadCppPlugin` or
> >> `unloadCppPlugin` are a lot more problematic. As far as I can tell,
> >> those would need to remain in C++ and they would need to be exposed to
> >> Python somehow (if they are not already).
> >>
> >> Have I found all relevant components of QGIS responsible for plugin
> >> management? Does my analysis contain any major flaws? Is there a way to
> >> manage C++ plugins (i.e. to call `loadCppPlugin` and `unloadCppPlugin`)
> >> from Python?
> >>
> >> Best regards,
> >> Sebastian
> >> _______________________________________________
> >> QGIS-Developer mailing list
> >> QGIS-Developer at lists.osgeo.org
> >> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> >> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> >
> >
> >
> > _______________________________________________
> > QGIS-Developer mailing list
> > QGIS-Developer at lists.osgeo.org
> > List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> >
> _______________________________________________
> QGIS-Developer mailing list
> QGIS-Developer at lists.osgeo.org
> List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-developer