define 'system' toolchain, deprecate 'dummy' toolchain (WIP)

[boegel]

TODO:

• make sure all unit tests pass (at least one still fails, because of pulling in easyconfigs using dummy via --from-pr)
• add dedicated test to ensure that using dummy still works (and will keep working until v3.0)

[hpcugentbot]

Refer to this link for build results (access rights to CI server needed):
https://jenkins1.ugent.be/job/easybuild-framework-pr-builder/1524/
Test FAILed.

[wpoely86]

So, EB will not set $CC or $CXX right? The user can choose which system compiler to use?

[pforai]

Yes, and I'm not sure if we shouldn't add a SystemGCC TC to specifically pick GCC and populate $CC and friends and set them to the same values as for the GCC TC.
But I would tend to leave it as it here. This basically reflects what people have been using dummy for.

[boegel]

With this, EB will set $CC to SYSTEMCC, which mimics with dummy was doing. Maybe we shouldn't set it at all.

Introducing a separate SystemGCC may be interesting, but wouldn't buy us much I think (people have no trouble in using dummy even though EB sets $CC to DUMMYCC, so in practice setting $CC makes little difference, apparently).

[wpoely86]

I would expect that the system toolchain doesn't define $CC or $CXX at all. Any code build with it, should try to find it's own compiler using whatever build system it has. The end user should be able to choose what to do by setting $CC (choosing between clang and gcc for example) and EB will not touch that.

I'm not a fan of having a SystemGCC.

[pforai]

We could have the system TC expose a module that a site can customize to fit the needs to set $CC et al. ?

[hpcugentbot]

Refer to this link for build results (access rights to CI server needed):
https://jenkins1.ugent.be/job/easybuild-framework-pr-builder/1525/
Test FAILed.

[hpcugentbot]

Refer to this link for build results (access rights to CI server needed):
https://jenkins1.ugent.be/job/easybuild-framework-pr-builder/1526/
Test FAILed.

[damianam]

While you are at it, I'd argue too that the new system toolchain should load dependencies too (or have a mechanism to allow it). Example: Java packages that need to be compiled with javac and nothing else. Those depend on Java, but Java is not being loaded for dummy, which pushes the dependency up to GCCcore, which is not too bad, but not really necessary.

[boegel]

@damianam To get dependencies loaded when using the dummy toolchain, use an empty version rather than dummy as version, see also http://easybuild.readthedocs.io/en/latest/Concepts_and_Terminology.html#dummy-toolchain

[damianam]

That's very intuitive, I don't know how I missed that ;-P. Thanks!

[boegel]

replaced by #2877