[easybuild] impact of collapsing 4.x branches into develop on open pull requests

[Kenneth Hoste]

Dear EasyBuilders,

Shortly after the release of EasyBuild v3.9.4 (which is planned for 
tomorrow Fri Aug 23rd), I will collapse the '4.x' branch into the 
'develop' branch in each of the 'easybuild*' GitHub repositories, to 
prepare to releasing EasyBuild v4.0.0 (sometime in the coming weeks, 
hopefully next week already).

This will have some impact on pull requests that were opened before this 
is done, since the tests run by Travis in the '4.x' branches are a bit 
more demanding; more specifically:

* the test suites will also be run using Python 3.5, 3.6 and 3.7 (next 
to Python 2.6 and 2.7), so code changes should be compatible with both 
Python 2.6, 2.7 & >=3.5 (more details on this later w.r.t. the changes 
that have been made in the EasyBuild framework to facilitate this);

* for easyconfig PRs, two additional requirements were added (next to 
being compatible with Python 3.x):

  - the recommended naming scheme for local variables in easyconfig 
files must be taken into account (see 
https://easybuild.readthedocs.io/en/4.x/Easyconfig-files-local-variables.html); 
this is done to avoid that easyconfig files included with a EasyBuild 
4.x release will produce warnings related to local variable names;

  - the new 'system' toolchain should be used rather than the 
(deprecated) 'dummy' toolchain (preferably via the 'SYSTEM' constant);


EasyBuild maintainers will re-trigger the tests in Travis (by closing & 
re-opening the PR) before merging pull requests, to try and avoid 
introducing changes into the 'develop' that break tests.



regards,

Kenneth