specifying ranges

[yoshuawuyts]

rust-lang/rfcs#3036 describes a family of predicates to target minimum versions of platform APIs. For example min_libc_version would return the version of libc. It was expected that max_* variants would be specified eventually as well ¹, allowing ranges of OS versions to be targeted.

Unfortunately the RFC hasn't seen any updates in a while, but the challenges it attempts to address still exist. I'm wondering whether efg could help prototype syntax to specify ranges within attributes. It'd be neat if we could target a specific version range Windows by writing something like this:

#[cfg(windows && os_version >= "6.0.6000" && os_version < "7.3.5000")]

Or possibly taking it further and allowing shorthands such as:

#[cfg(windows && "6.0.6000" <= os_version < "7.3.5000")]

I'm not sure what this feature should look like, but I think having the ability to specify ranges using shorthands would be neat as well. What do you think?

Footnotes

1. Being able to specify the maximum OS version is useful when you're writing polyfills for older versions. This would allow a developers to say something like: "This code runs on windows 10+ only", which can be leveraged to produce more optimized code. ↩

[dtolnay]

Thanks for the RFC link! I had not seen this. But I would prefer not to build this into this crate.

[yoshuawuyts]

Thanks for the RFC link! I had not seen this. But I would prefer not to build this into this crate.

Completely understandable! It makes sense to build out the min/max qualifiers as part of Rust's attribute expressions first, before attempting to add anything of the sort to efg.

What I do wonder though is how ranges could be expressed using the current syntax? It's probably not important to answer that straight away. But if efg ever graduates to an RFC, we would probably want to cover that, possibly under "Future Possibilities"?

Prior Art

For future reference, I found out today that CSS Media Queries level 4 introduces a change very similar to this proposal:

before

@media screen and (min-width: 500px) and (max-width: 1200px) {
  .bar {
    display: block;
  }
}

after

@media screen and (500px <= width <= 1200px) {
  .bar {
    display: block;
  }
}