[Bug 1509562] Re: no icons for menu, folders, directories, files

[Trogel]

My impression is that the affected KDE applications now rely on Qt5's
QIcon::fromTheme(...) to locate the icons. This is in line with the
documentation of KIconLoader::loadIconSet(...) (from source package
kiconthemes_5.15.0-0ubuntu1) that says: "@deprecated use
QIcon::fromTheme instead, which uses the iconloader internally".

But it seems that Qt5 only supports the very basic 'hicolor' icon theme
when not running in a KDE or Gnome session. The method
themeHint(ThemeHint hint) of the classes QKdeTheme and QGnomeTheme
support the hint QPlatformTheme::SystemIconThemeName, whereas the
implementation of this method for the class QGenericUnixTheme does not
support that hint (soruce package qtbase-opensource-src_5.4.2+dfsg-
2ubuntu9, file
src/platformsupport/themes/genericunix/qgenericunixthemes.cpp).
Therefore, I assume, the systems falls back to the fallback theme
'hicolor' using the hint QPlatformTheme::SystemIconFallbackThemeName. It
seems that 'hicolor' lacks of most icons needed by kate and the other
applications.

So it possibly requires a change in Qt5 rather than in specific KDE
applications or the KDE framework to get the icons back in these
applications when running in Xfce.

For a test (and as a rather dirty workaround) I have moved
/usr/share/icons/hicolor out of the way and replaced it with a symlink
to some other icon theme like 'oxygen' or 'elementary-xfce-darker'. For
example:

$ cd /usr/share/icons
$ sudo mv hicolor/ hicolor-bkp
$ sudo ln -s elementary-xfce-darker hicolor

Then I started kate, konsole, and dolphin manually from a terminal
window and they had most or even all of the missing icons back. When
started them from a launcher (from the panel in my case), the icons were
still missing. Now, after a fresh login to Xubuntu, the affected
applications have most or all of the missing icons, regardless of the
way I start them.

On the downside, now some other icons are missing. For instance, the
application icons of konqueror, kate, and other KDE applications are
missing in the launchers and in the Whisker Menu. But for the time being
I prefer to have a usable kate and happily accept some missing
application icons.

** Also affects: qtbase-opensource-src (Ubuntu)
   Importance: Undecided
       Status: New

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Title:
  no icons for menu, folders, directories, files

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