[Development] Qt 6 buildsystem support requirements

[Jason Newton]

On Thu, Aug 2, 2018 at 11:21 PM Dominik Holland
<dominik.holland at pelagicore.com> wrote:
>
> Am 01.08.18 um 16:40 schrieb Ville Voutilainen:
>
> > On 1 August 2018 at 11:24, Jason Newton <nevion at gmail.com> wrote:
> >>> And... seriously, *Java*?! Talk about bloat-ware... As dependencies for
> >>> *a build tool* go, that's pretty insane. Especially if you're not
> >>> planning to use it to build Java code.
> >> As I said, ~300-400 megabytes for a JRE (~90MiB DL), in particular
> >> openjdk , prospectively in a development environment where you've got
> >> devel headers and packages installed.   The cost of the dependency is
> >> neither bloat nor unbounded, it really is just that size on a machine
> >> that's prepared to build software in 2018.  Please explain what issue
> >> this presents.
> > The prospect of having to install a JRE to build Qt or eventually Qt
> > applications
> > solicits a fairly loud "I think I'll pass" from me. I don't use java
> > for anything. Having
> > it around for a supposedly simple and easy-to-adopt build system is a cost
> > that I am not eager to pay. Do we expect to package a JRE with Qt? Do we
> > expect a JRE to be a package dependency of Qt for distro vendors?
> That would also have a big inpact on the yocto packages, as that would
> require building java itself to compile Qt (yocto usually doesn't use
> prepackaged binaries...),
> and also compile it again for the SDK architecture...
>
> For me JRE as a Qt build dependency is a no-go
>

Have a look at this:
http://zlika.github.io/presentations/compile-openjdk8/slides_en.html#/_generation_of_compact_profiles

If the java packager of the distribution puts in some time with the
openjdk packages they support, they can get it down to 13-25 MiB,
before compression, and 50% of those numbers with.  Bazel doesn't need
gui stuff.

>From OpenSUSE build service, here is the build time for the full
OpenJDK 8 build
https://build.opensuse.org/public/build/Java:Factory/openSUSE_Leap_15.0/x86_64/java-1_8_0-openjdk/_log
- 1976 seconds with what appears to be a single threaded build.  It
should be possible to considerably lean this down.

For control, here is qt5's build file
https://build.opensuse.org/public/build/KDE:Qt:5.11/openSUSE_Leap_15.0/x86_64/libqt5-qtbase/_log
clocking in 2455s

-Jason