less: Move to new selector interpolation, supported from 1.3.1

[lukeapage]

less introduced a better selector interpolation format in 1,3,1. It will remove the old (undocumented) format in 1.4.0.

This pull request updates you to be compatible with future versions of less.

I am one of the core mantainers of less.

(had this on master then read the guidelines and moved to 2.3.0-wip - is that right?)

p.s. I can also remove those ugly

.spanX (0) {}

they are not needed in 1.3.3 but it depends what version of less you want to support.

[mdo]

Yup, pull requests should go towards *-wip branches for now (feature branches in the future, after v3).

We definitely want to support the latest, but we've burned folks before by implementing and running on the latest releases of dependencies with little to no heads up for them. As it stands now, does this break backward compatibility then for folks on 1.3.0?

Come v3, I'd be willing to drop support for older versions given the changes we're making there.

Thoughts? (And thanks for the pull request!)

[lukeapage]

yes, it breaks 1.3.0, and 1.3.1 came out only 4 months ago.. However 1.3.1 and 1.3.2 contains a very large number of bug fixes.. I wouldn't recommend anyone say they will work with 1.3.0. Our reason for removing the old selector interpolation in 1.4.0 is because we really don't like it and it was never a documented feature. I could put it back in, disabled by default, with a backwards compatible option, but I'd rather not.

I'd like it to get this merged because if I finish and release 1.4.0 and bootstrap doesn't compile then its going to annoy alot of people.

I see you use recess to build and recess only asks for less 1.3.0 so I guess you might have to bump the version required in recess and then bump the version required by bootstrap? It does sound pretty messy.

What are your thoughts? a) You would really like me to make less work with the old version with an option for a bit longer b) Your happy breaking 1.3.0 and requiring 1.3.1 when 1.4.0 comes out but you'd rather wait till the last possible moment (I'm hoping I can get 1.4.0 in the next month or so, as I'll be busy after that)?

I'm surprised if there aren't any features of 1.3.1 and 1.3.2 which bootstrap wouldn't find useful (https://github.com/cloudhead/less.js/blob/master/CHANGELOG.md) there is lots of good stuff ;)

In addition, there are some other breaking changes that I have added options for in 1.4.0 (so by default it will break at the moment, but you can switch on the option to stop it breaking) - strictUnits (disallowing 1% + 1px), but you don't do that anyway and strictMaths - we are going to require that maths operations are within parenthesis to fix a whole host of clashes with css and allow us to be better at being a superset of the language. I was planning on doing a pull request for that too - the fixes to your less will be backwards compatible with 1.3.0 (but its more of a pain to make the changes ;S)

[mdo]

I definitely want us to move forward with the new releases. I think we can get this in for 2.3.0-wip and not have any huge issues with folks and compatibility. We just have to update Recess first, but that shouldn't be a problem for @fat or I to handle before 2.3 is released.

When do you expect 1.4 to be released? I'd like those further breaking changes to happen with 3.0 since we're already fucking shit up in a real way there :D.

[lukeapage]

1.4 release - I am thinking the next month, depends how far we get.

When is v3 of bootstrap planned for?

When I say other breaking changes - they are breaking in that at the moment bootstrap 2.3 will only work with less 1.4 if you switch on an option. If we make the changes to bootstrap then it will continue to work with all versions of less.. you would still prefer just to do them on 1,3 ?

[mdo]

No real date on v3—hopefully end of March at the latest? Depends how far we get as well :D.

Let's push forward with this—fuck lagging behind. Whatever we have to do to get ready for the latest version of Less, and then 1.4, let's do that.

[fat]

Thanks man – super dope ❤️