breeze icons default and its inheritance

[Harald Sitter]

Aloha!

So, yesterday I switched the default kiconthemes theme from oxygen to
breeze [1] to get all builtin defaults of frameworks to be breeze
rather than oxygen.

Alas, as it turns out breeze icons do not inherit from oxygen for a
while now, which has the very unfortunate disadvantage of breaking if
an icon was in oxygen (by default, or installed by an application)
[2]. Ideally all icons in oxygen should be brought to breeze for
compat reasons, but in particular with icons installed by applications
themself that's a futile hope unless we break compat as it'd be hard
to catch everything and release updates within reasonable timeframe.

What to do?

As as I see it our options are:

# Temporarily revert kiconthemes commit until breeze-icons with a
suitable fix is released
a) make sure all icons that were in oxygen are in breeze and shame
apps that install to oxygen into fixing their code and use hicolor
b) make breeze inherit oxygen

# Postpone to kf6 where we then hard-break runtime compat WRT oxygen lookup
c) introduce a second hardcoded default (for oxygen) that is only used
internally so we continue having oxygen as a fallback
d) revert and leave kiconthemes to default to oxygen

Personally I would actually be rather content with option a) as it
means we get to remove one lookup tier and people really shouldn't
install to oxygen or breeze expecting that they will be always in the
lookup order (only hicolor should be expected to).
OTOH in a way this is breaking runtime compat.

[1] https://quickgit.kde.org/?p=kiconthemes.git&a=commit&h=b544c17decc22685207ac11fbd95536e0d798650
[2] http://markmail.org/message/eixuwfzsyulus5dm

HS