Don’t suggest 'help: add #![feature(…)]' when it’s forbidden

[SimonSapin]

Steps to reproduce:

mkdir foo
cd foo
multirust override beta  # Or obtain Rust beta in some other way
echo 'extern crate core; fn main(){}' > a.rs
echo '#![feature(core)] extern crate core; fn main(){}' > b.rs

The output of rustc a.rs is:

a.rs:1:1: 1:19 error: use of unstable library feature 'core'
a.rs:1 extern crate core; fn main(){}
       ^~~~~~~~~~~~~~~~~~
a.rs:1:19: 1:19 help: add #![feature(core)] to the crate attributes to enable

b.rs does as suggested by the help message, but that fails too (as expected):

b.rs:1:1: 1:18 error: unstable feature
b.rs:1 #![feature(core)] extern crate core; fn main(){}
       ^~~~~~~~~~~~~~~~~
note: this feature may not be used in the beta release channel
error: aborting due to previous error

Proposed fix: in the beta and stable channels (i.e. whenever #![feature(…)] is forbidden), the help message that suggests adding #![feature(…)] should not be shown.

(Clean up the test case with multirust remove-override; cd ..; rm -r foo.)

CC @brson

[steveklabnik]

Gonna milestone this real quick, as it seems quite important.

[pnkfelix]

I might be able to whip up a quick fix, though I'm not 100% sure about testing it properly ... (I've never actually tried building something for a non-dev release channel before...)

[steveklabnik]

after chatting with @pnkfelix it seems like I have a patch, building it now

[steveklabnik]

gonna leave @pnkfelix to it

[conradkleinespel]

Hello good Rust folks 😄

Before the beta, I used std::slice::bytes:MutableByteVector which is in core. Is there any way to use this trait during the beta ? I'm not sure how I can get the code to compile.

Thanks for any tip / hints you can offer 👍

[SimonSapin]

Hi @conradkleinespel. Commenting on random unrelated issues is usually not the right thing to do. You should rather open a new issue, or ask on http://users.rust-lang.org/ . But to answer your question anyway, that trait only has one method:

    /// A trait for operations on mutable `[u8]`s.
    pub trait MutableByteVector {
        /// Sets all bytes of the receiver to the given value.
        fn set_memory(&mut self, value: u8);
    }

    impl MutableByteVector for [u8] {
        #[inline]
        fn set_memory(&mut self, value: u8) {
            unsafe { ptr::write_bytes(self.as_mut_ptr(), value, self.len()) };
        }
    }

… and std::ptr::write_bytes is stable and can be used on beta. So I’d recommend you copy/paste the trait into your code, or make a function.

[conradkleinespel]

@SimonSapin Thanks for taking the time to answer. I appreciate it.

I don't see how this is unrelated. This is related, since the code I'm talking about used to compile with #![feature(core)] and the compiler suggests to do that, during the beta period.

Thanks for your tip on copying the function 👍 I guess I'll just do that if nothing better is available and change this again when the trait is stable.

[SimonSapin]

This specific issue is about fixing one of the compiler’s error message, not about fixing code that triggers that error. It really helps everyone to keep discussions on topic.

[conradkleinespel]

Alright. I understand. I'll make sure to open a new issue or go on StackOverflow next time if appropriate. Thanks again 👍

[jonalmeida]

This doesn't seem to be properly fixed in the beta channel. I'm still being recommended to add #![feature(libc)] in the errors, and then told it's not available in the beta channel.

[/tmp] rustc snappy.rs
snappy.rs:1:1: 1:19 error: use of unstable library feature 'libc'
snappy.rs:1 extern crate libc;
            ^~~~~~~~~~~~~~~~~~
snappy.rs:1:19: 1:19 help: add #![feature(libc)] to the crate attributes to enable
snappy.rs:2:5: 2:17 error: use of unstable library feature 'libc'
snappy.rs:2 use libc::size_t;
                ^~~~~~~~~~~~
snappy.rs:2:17: 2:17 help: add #![feature(libc)] to the crate attributes to enable
snappy.rs:6:56: 6:62 error: use of unstable library feature 'libc'
snappy.rs:6         fn snappy_max_compressed_length(source_length: size_t) -> size_t;
                                                                   ^~~~~~
snappy.rs:6:62: 6:62 help: add #![feature(libc)] to the crate attributes to enable
snappy.rs:6:67: 6:73 error: use of unstable library feature 'libc'
snappy.rs:6         fn snappy_max_compressed_length(source_length: size_t) -> size_t;
                                                                              ^~~~~~
snappy.rs:6:73: 6:73 help: add #![feature(libc)] to the crate attributes to enable
error: aborting due to 4 previous errors
[/tmp] rustc snappy.rs
snappy.rs:1:1: 1:18 error: unstable feature
snappy.rs:1 #![feature(libc)]
            ^~~~~~~~~~~~~~~~~
note: this feature may not be used in the beta release channel
error: aborting due to previous error

Rust version:

[/tmp] rustc --version
rustc 1.0.0-beta (9854143cb 2015-04-02) (built 2015-04-02)

The code I used (snappy example in the docs with the extra addition on the first line:

#![feature(libc)]
extern crate libc;
use libc::size_t;

#[link(name = "snappy")]
extern {
        fn snappy_max_compressed_length(source_length: size_t) -> size_t;
}

fn main() {
        let x = unsafe { snappy_max_compressed_length(100) };
            println!("max compressed length of a 100 byte buffer: {}", x); 
}

[bombless]

This happened after Beta release.
We'll see the effect of this patch in 1.0 and afterwards Beta, etc.

[jonalmeida]

Whoops, I thought this made it in before beta. Thanks!

[SimonSapin]

@brson, are there plans to release updates to the beta channel within a given 6 weeks cycle? Either this one or in the future.

[pnkfelix]

I'm certain there will be updates; see discussion from last night here: https://github.com/rust-lang/meeting-minutes/blob/master/weekly-meetings/2015-04-07.md#policy-for-prs-targeting-beta-vs-master

[ghost]

So how does one fix this error? I'm a new user of the rust library and I can't seem to use the collections library during the beta due to this problem. Given this git issue is a top google result, it would be nice if there were a solution here.

Edit: Looks like the solution is to switch to the rust nightly. Is the entire collections library off-limits in the beta?

[pnkfelix]

@Russell91 by design, you have access to the parts of libcollections that are re-exported from libstd (and are stable).

http://doc.rust-lang.org/1.0.0-beta/std/collections/