[QGIS-Developer] Is the apps\qgis folder cleared before installing a new QGIS version in osgeo4w?

[Nyall Dawson]

Hi all, (but specifically Jürgen!)

I'm wondering if the existing content of the apps\qgis folder is
removed before a new QGIS version is install via osgeo4w?

My suspicion is that it is not -- at least on a desktop which
previously had 2.18 installed via the qgis package and which was just
upgraded to 3.0 I see some old content present. Specifically, the
fTools and GdalTools folder is left in apps\qgis\python\plugins.

This report leads me to believe I'm not seeing an isolated issue:
https://gis.stackexchange.com/questions/272679/gdaltools-core-plugin-missing-metadata-file/272682#272682

Does osgeo4w have support for preinstall scripts which we could use to
wipe the python/plugins folder prior to an install?

Nyall