Use KDE 5 for the graphical installation DVD

[ttuegel]

Motivation for this change

Using KDE 4 for our graphical installation DVD does not present our best face to the world! The installation DVD is updated to use KDE 5. Combined with several of my multiple-outputs-related pull requests, there is no significant change in image size; it remains at 1.9 GB. I have also made several changes that make KDE 5 work more perfectly out of the box.

Things done

• Tested using sandboxing
  (nix.useSandbox on NixOS,
  or option build-use-sandbox in nix.conf
  on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • Linux
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

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[mention-bot]

@ttuegel, thanks for your PR! By analyzing the history of the files in this pull request, we identified @lethalman, @edolstra and @abbradar to be potential reviewers.

[edolstra]

@ttuegel I'm surprised there's no size increase. I just upgraded my 16.09 machine from KDE 4 to 5, and the system closure size went from 3.1 GB to 4.3 GB! (And that's despite the fact that I disabled some packages like kde4.ktorrent and kde4.kdemultimedia.)

[edolstra]

BTW, one reason for the size increase is the use of symlinks in the kde-env packages. For example, /nix/store/3bk7hcg6rrsjffniqfckj8c5krxsji7d-kde-env-gwenview-16.08.2 takes 68 MiB. That's because it consists of ~21K symlinks, each of which requires 4 KiB on my ext4 filesystem. In total the upgrade added ~108K symlinks == 432 MiB to the system closure.

[edolstra]

👍 on upgrading the installation DVD BTW, KDE 5 looks great!

[ttuegel]

I'm surprised there's no size increase. I just upgraded my 16.09 machine from KDE 4 to 5, and the system closure size went from 3.1 GB to 4.3 GB! (And that's despite the fact that I disabled some packages like kde4.ktorrent and kde4.kdemultimedia.)

That includes some multiple-outputs work I did on the installer, so there was some space saving there. There are no Qt 4 applications on the KDE 5 installer, so I added an option to omit support for Qt 4 applications. Between Qt 4 and kdelibs-4, that saves about 0.5 GB.

BTW, one reason for the size increase is the use of symlinks in the kde-env packages. For example, /nix/store/3bk7hcg6rrsjffniqfckj8c5krxsji7d-kde-env-gwenview-16.08.2 takes 68 MiB. That's because it consists of ~21K symlinks, each of which requires 4 KiB on my ext4 filesystem. In total the upgrade added ~108K symlinks == 432 MiB to the system closure.

That's disturbing. There may not be any good solution here: if I don't build the kdeEnv derivation, then we end up with very long lists in XDG_DATA_DIRS, QT_PLUGIN_PATH, etc. and the applications are slightly slower at runtime. That's probably not enough to justify the link farm. The link farms shouldn't hurt the installer image size much, though, since it uses squashfs! Still, I'll need to fix this before merging so we don't use too much RAM.

[edolstra]

Yeah, I was wondering about Qt 4. It looks like it's pulled in by Okular (which also pulls in kdelibs4) and breeze-qt4 and phonon-backend-gstreamer-qt4. Can the latter 2 be disabled somehow?

[ttuegel]

It looks like it's pulled in by Okular

Yeah, unfortunately, KDE plans to continue releasing Qt 4-based applications until December 2017.

and breeze-qt4 and phonon-backend-gstreamer-qt4. Can the latter 2 be disabled somehow?

Commit 8c3aa5a in this PR adds an option to disable them.

[ttuegel]

Finally, the image increases in size from 1918894080 bytes (after reducing the size with multiple outputs) to 2031091712 bytes, an increase of 112 MB or about 6%.