Make alabaster and sphinx_rtd_theme dependencies optional

[mitya57]

There is no need to pull these dependencies if i.e. the documentation is using the classic theme.

There will be no change in behavior for projects using alabaster or sphinx_rtd_theme.

Note: this PR does not remove these dependencies from setuptools requires list, as this can potentially break some reverse dependencies. If you think we should do this, please let me know and I will amend the PR. This change will be useful for us (Debian) anyway as we will be able to remove sphinx-rtd-theme from our our list of dependencies.

[keimlink]

Seems reasonable! 👍

[birkenfeld]

At least alabaster cannot be removed since it is the new default. The rtd theme was supposed to be merged, but the rtd guys wanted to have a little more time to do some changes, so we used the dependency solution to give them more flexibility.

Maybe it is time to revisit these choices for 1.4.

[mitya57]

@birkenfeld This PR does not change anything functionally, it just moves imports to where they are actually used.

As I said, I will be happy if at least sphinx-rtd-theme was removed from requirements (or merged), but this is not included in this pull request.

[mitya57]

Maybe it is time to revisit these choices for 1.4.

I am happy to retarget this PR to default branch, in case you do not want it in 1.3 (though, as I said, it doesn't break any existing setups).

[vitaut]

👍 but I think it's even more important to remove dependencies from requires in setup.py. I did this in #2087 but only for sphinx-rtd-theme. The same could be done for alabaster.

[mitya57]

@vitaut Your PR is what I would like to be done, but mine is absolutely safe (i.e. it doesn't break anything), while yours can potentially introduce incompatibilities.

[shimizukawa]

I've read this thread again, and +1 for this PR to merge into stable. If no objection, I'm going to merge into stable for sphinx-1.3.5.

[tk0miya]

@shimizukawa please tell me the plan of these dependencies before merging.
I hear the alabaster is default theme, and sphinx_rtd_theme will be removed at 1.4 (by #2087).
Is any reason to merge this? If you mean lazy loading of these themes, I agree.
Or not, I think we have to discuss more about the plan.

(I understand this is no breaking change, but I do not understand where we goes)

[shimizukawa]

@tk0miya

Is any reason to merge this? If you mean lazy loading of these themes, I agree.
Or not, I think we have to discuss more about the plan.

The former one.

[tk0miya]

@shimizukawa I understand. LGTM!

[mitya57]

FWIW I've rebased this pull request against the latest stable branch.

[shimizukawa]

Merged. Thanks!