Dependency on Crate "bs58" sets Minimum Rust Version to > 1.46

[bodo-hugo-barwich]

Issue summary

I'm trying to compile the project on Debian Buster with Default Rust Compiler 1.41.1

$ uname -a
Linux <hostname> 4.19.0-8-amd64 #1 SMP Debian 4.19.98-1+deb10u1 (2020-04-27) x86_64 GNU/Linux
$ rustc --version
rustc 1.41.1

This fails at the Crate bs58 with Error E0658:

$ cargo build
[...]
   Compiling bs58 v0.4.0
error[E0658]: `while` is not allowed in a `const fn`
   --> /path/to/home/.cargo/registry/src/github.com-1ecc6299db9ec823/bs58-0.4.0/src/alphabet.rs:107:9
    |
107 | /         while i < encode.len() {
108 | |             if base[i] >= 128 {
109 | |                 return Err(Error::NonAsciiCharacter { index: i });
110 | |             }
...   |
120 | |             i += 1;
121 | |         }
    | |_________^
    |
    = note: for more information, see https://github.com/rust-lang/rust/issues/52000

The GitHub Reference takes me to the Pull Request
Milestone 1.46 Pull Request

So, I understand this Error as the Crate bs58 requires at least rustc 1.46 to compile which only was released in August 2020.

The Project Documentation states that it only requires rustc 1.40 to compile. So, it should compile with the Default Debian Rust Compiler.

(I found most Ubuntu Distributions ship already Rust 1.47 but Debian Buster still ships the older version.)

Other information and links

$ rustc --explain E0658|more
An unstable feature was used.

Erroneous code example:

"
#[repr(u128)] // error: use of unstable library feature 'repr128'
enum Foo {
    Bar(u64),
}
"

If you're using a stable or a beta version of rustc, you won't be able to use
any unstable features. In order to do so, please switch to a nightly version of
rustc (by using rustup).

If you're using a nightly version of rustc, just add the corresponding feature
to be able to use it:

"
#![feature(repr128)]

#[repr(u128)] // ok!
enum Foo {
    Bar(u64),
}
"

The GitHub Reference takes me to the Pull Request
Milestone 1.46 Pull Request

Debian Buster Default Rust Compiler
Debian Buster Rust Package

[bodo-hugo-barwich]

This issue is reproducable with the GitHub Workflow Container Facilities
GitHub Workflow Debian Container

Operating System:
PRETTY_NAME="Debian GNU/Linux 10 (buster)"
NAME="Debian GNU/Linux"
VERSION_ID="10"
VERSION="10 (buster)"
VERSION_CODENAME=buster
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/"
Rust Compiler Version:
rustc 1.41.1

[austinabell]

Ah yes, thanks for pointing this out. The minimum version hasn't been updated in a while. This should be made sure to not happen with adding a msrv check in the CI. I'll try to find some time to do that soon (or now).

Unfortunately for that dependency, we don't have a way of avoiding it because it is one of rust-libp2p, but I can absolutely pinpoint what the msrv is to make it easier to work around

[austinabell]

Going to close for now because we do not have control over this msrv requirement and I've updated the README.md to reflect the requirement and made the change to the CI to make sure this doesn't happen again.

Feel free to open if you feel there is something else we can do. Thanks!

[bodo-hugo-barwich]

I was studying if newer Debian Bullseye rustc compiler library packages are installable on Debian Buster. This would produce a nice predictable and reproducible Build Environment.

Unfortunately the tight dependency of the Rust Standard Library on the systems libc library version makes them uninstallable.
As seen in this test:
rustc from Debian Bullseye

libstd-rust-1.48:amd64 depends on libc6 (>= 2.29); however:
  Version of libc6:amd64 on system is 2.28-10.

Actually this a known limitation that precompiled Rust binaries are not backwards compatible and thus not portable.