Test builds with minimal versions

[BurntSushi]

Steps to reproduce:

$ rustc --version
rustc 1.34.0-nightly (d8a0dd7ae 2019-01-28)
$ cargo --version
cargo 1.34.0-nightly (245818076 2019-01-27)
$ cargo generate-lockfile -Z minimal-versions
    Updating crates.io index
$ cargo build
  Downloaded autocfg v0.1.0
  Downloaded libc v0.2.0
   Compiling autocfg v0.1.0
   Compiling libc v0.2.0
   Compiling rand_os v0.1.2 (/home/andrew/clones/rand/rand_os)
error[E0425]: cannot find function `syscall` in module `libc`
   --> rand_os/src/linux_android.rs:127:15
    |
127 |         libc::syscall(NR_GETRANDOM, buf.as_mut_ptr(), buf.len(),
    |               ^^^^^^^ help: a function with a similar name exists: `sysctl`

warning: use of deprecated item 'std::sync::atomic::ATOMIC_BOOL_INIT': the `new` function is now preferred
  --> rand_os/src/linux_android.rs:21:37
   |
21 | use std::sync::atomic::{AtomicBool, ATOMIC_BOOL_INIT, Ordering};
   |                                     ^^^^^^^^^^^^^^^^
   |
   = note: #[warn(deprecated)] on by default

warning: use of deprecated item 'std::sync::atomic::ATOMIC_BOOL_INIT': the `new` function is now preferred
  --> rand_os/src/linux_android.rs:56:49
   |
56 |         static OS_RNG_INITIALIZED: AtomicBool = ATOMIC_BOOL_INIT;
   |                                                 ^^^^^^^^^^^^^^^^

warning: use of deprecated item 'std::sync::atomic::ATOMIC_BOOL_INIT': the `new` function is now preferred
   --> rand_os/src/linux_android.rs:163:36
    |
163 |     static AVAILABLE: AtomicBool = ATOMIC_BOOL_INIT;
    |                                    ^^^^^^^^^^^^^^^^

   Compiling rand_chacha v0.1.1 (/home/andrew/clones/rand/rand_chacha)
   Compiling rand_pcg v0.1.1 (/home/andrew/clones/rand/rand_pcg)
   Compiling rand v0.6.5 (/home/andrew/clones/rand)
error: aborting due to previous error

For more information about this error, try `rustc --explain E0425`.
error: Could not compile `rand_os`.
warning: build failed, waiting for other jobs to finish...
error: build failed

I think the issue here is that rand advertises that it works for all releases of libc that are 0.2 or newer, but this is actually not the case. So the dependency should be updated to require a newer version of libc.

There may be other issues lurking as well, see: crossbeam-rs/crossbeam#312

The regex crate does this check in its CI configuration to make sure its dependency specifications are always correct. See: https://github.com/rust-lang/regex/blob/60d087a23025e045ae754a345b04003c31d83d93/ci/script.sh#L53-L55 --- You might consider doing the same.

[dhardy]

On OSX we actually require a not-yet-released version of libc if using older versions of Rustc: rust-lang/libc#1232

Did you find which version of libc is required here?

[BurntSushi]

I'm on Linux. It looks like 0.2.22 is the minimal version for Linux. I think 0.2.3 added syscall (or thereabouts), but y'all also need pthread_atfork, which was added in 0.2.22.

But this is likely platform dependent. This test probably needs to be run for each supported target.

[dhardy]

Looks like we actually need libc 0.2.27 for the SYS_getrandom function.

I feel like testing the most recent lib version is more important than checking the minimal version; is it really worth having CI runs for each platform (we have several platform-specific deps) to check both?

Edit: I have enabled limited testing of min versions for the getrandom lib, which will become a dependency of this lib. Likely we will not do further min-version testing (though I wouldn't mind doing the same for Windows, if someone knows how to configure AppVeyor).

Edit 2: scratch that; -Z minimal-versions can't be used on stable and all our nightly runners already have jobs to do.

[BurntSushi]

Basically, if minimal versions doesn't work, then to me, there's a bug in the dependency specification because it's claiming support for something that doesn't actually work. The ecosystem is having trouble moving to minimal versions though, because it first needs to be adopted by core crates (like rand). Getting testing working on a common platform seems like a good place to start.

Edit 2: scratch that; -Z minimal-versions can't be used on stable and all our nightly runners already have jobs to do.

I imagine you might just add it to the end of an existing nightly runner?

[dhardy]

Sure it's a bug, but is it one that's worth fixing? The discussion seems to be here and hasn't reached a conclusion on this issue; additionally the mentioned --minimal-versions flag is not yet available on stable Cargo.

I will take some steps to address this (I already updated the minimal versions as I think are required in the getrandom crate, which will supersede the code in rand_os and thus replace its dependencies), and may add limited testing as suggested (but again probably only in the getrandom crate), however I'm also closing this issue since it does not appear there is any consensus on implementing this across the ecosystem due to low importance (i.e. we have more important bugs to fix).

[BurntSushi]

I think your link is broken? In any case, I'm a little confused here. What exactly is preventing the addition of this test to say, the rand crate itself? Is there some hidden burden that I'm missing? I've been using the minimal version check in CI for quite a while and it hasn't been any trouble at all.

[dhardy]

Sorry, fixed.

Pushing platform dependencies to getrandom helps keep CI load low. There are some extra deps in rand, but not many.

[BurntSushi]

Thanks!

[asomers]

Can we please reopen this? If rand doesn't build with its minimal dependencies, then nothing that depends on rand will. According to crates.io, that's 2462 crates.

Here's a start: you need to update the bincode dependency from 1.1.2 to 1.1.4 because bincode 1.1.3 and earlier incorrectly set its minimal autocfg dependency.