Use feature cfg outside macro

[dschatzberg]

cfg(feature="nightly") was being evaluated within the crate using the
lazy_static! macro. Instead we generate different macros depending on
the cfg.

[dschatzberg]

I unfortunately had to mark the second doctest as ignore, it fails without the const_fn feature flag but I have no way to access the "nightly" feature flag from within the doctest to make it conditional.

[durka]

I suppose this conflicts with #32. Is it bad for the cfg_attr to be evaluated in the invoking crate? They are going to have to declare the #![feature]s anyway to use the nightly version.

BTW: since rust-lang/rust#30372 was fixed, cfg_attr works fine in doctests.

[dschatzberg]

The problem is that the "nightly" config attribute is defined for the lazy-static crate, not the invoking crate. So checking the attribute inside the macro (which is evaluated inside the invoking crate) doesn't make sense. This change uses the attribute to generate a different macro altogether.

Thanks for the note on the doc test. It is now unignored

[durka]

Yes, you're right. i guess nobody noticed until now because everyone names their nightly feature "nightly" :)

[compressed]

I'm not sure defining the cfg feature outside the lazy_static! macro is a good idea. If I'm building a crate that needs to support both nightly and stable, I'd like to use the nightly features of the macro if the user of my crate is using nightly. I can do this currently by making a nightly feature in my crate. Users that opt into the nightly feature will gain the benefits of lazy_static's nightly features as well. Granted, there is some coupling with the feature name, but maybe this can just be better documented in lazy_static.

I don't believe we can specify conditional features based upon other features in Cargo.toml... Going with this PR's approach, we'd need something like this for a crate that wants to support both stable and nightly features using lazy_static:

[dependencies]
lazy_static = { version = "..", features = if nightly then ["nightly"] else [] }

[features]
nightly = []

[durka]

@compressed actually you can do that:

[dependencies]
lazy_static = "*"

[features]
nightly = ["lazy_static/nightly"]

Documented here but only in the code sample.

[compressed]

@durka oh awesome, that's perfect then. Yeah, I didn't spot that in the docs when I was going through, thanks!

👍

[Kimundi]

Hi, very very sorry for the long delay!

I incorporated the changes here into master. I didn't merge directly due to wanting to incoperate other PR's as well, and they all started to cause merge conflicts with each other. :P

Could you check if I missed something and then close this PR?

Note that current master is not yet a published cargo version since my computer literally broke while preparing the commits for this, and I'm still in the process of recovering.

[dschatzberg]

Looks good. Thank you! Hope you recover your machine.

[Kimundi]

Thanks! Seems to have all worked out so far. I'll publish the changes as v0.2 on crates.io now.