[p2-dev] patching a group?

["Haigermoser, Helmut" <Helmut.Haigermoser@xxxxxxxxxxxxx>]

Ciao Guys :)
After you @ll helped me understand the profile question I went on and
started work on a patch repository generator.
There is one issue I'd like you to clarify:
- Does p2 support updating single IUs?

An example: A profile containing these IUs:

Group "A" (1.0.0) -> IU "B" (1.0.0)
Group "A" (1.0.0) -> IU "C" (1.0.0)

Now, if I want to send out a patch for IU "C", let's say I want to move
it to "1.0.0.patch", do I need to patch "Group A" as well,
updating it to "1.0.0.1" and updating the requires statement to the IU B
but leaving IU C untouched? In theory, I could make the relation
"group->IU" loose enough so that an update of IU "C" to 1.0.0.patch
would still fulfil the requirement of the group but thinking about the
discussion we had last time, IUs that were explicitely installed and
ones that were only installed because of requirements, I'm not sure
that's gonna work out. Patch repositories would be really small if only
those IUs that really were modified were included but my gut tells me we
need some form of group to ship them...

Another reason for asking this is because I'm wondering if there is a
similar concept to pre-p2 "patch features" (or feature patches, can't
remember the exact name), where one would send out a completely new
feature that patched another feature with some content, mapping this
concept to p2 would look like this:

Group "A" (1.0.0) -> IU C (1.0.0)
Group "D" (1.0.0) patches Group "A" (1.0.0)
Group "D" (1.0.0) -> IU C (1.0.0.patch)

Is this supported? What version(s) of IU "C" would be living in my
profile in this scenario?
I've seen the concept of a PatchingIU in the code, but this looks very
feature-centric, so I'm guessing this is a legacy concept not applicable
to Groups etc..

Your answers will have a big impact on my patch generator so, whatever
input you can provide me with is highly appreciated! :)

TIA,
Ciao, hh