Does not build on default GitLab CI Docker image

[l0b0]

Describe the bug

I'm unable to build on the official ruby:2.5 Docker image using Cargo from the official repos.

To Reproduce
Steps to reproduce the behavior:

1. Run docker run --entrypoint=bash --interactive --tty ruby:2.5
2. Inside of the container, run apt-get update && apt-get install --assume-yes --no-install-recommends --reinstall cargo && cargo install nixpkgs-fmt

Expected behavior

The package should install without issues.

System information

• nixpkgs-fmt --version N/A

Additional context

Actual behavior (2nd try to make the output a bit less verbose):

root@7620dcea37cc:/# apt-get update && apt-get install --assume-yes --no-install-recommends --reinstall cargo && cargo install nixpkgs-fmt
Hit:1 http://security.debian.org/debian-security buster/updates InRelease
Hit:2 http://deb.debian.org/debian buster InRelease
Hit:3 http://deb.debian.org/debian buster-updates InRelease
Reading package lists... Done
Reading package lists... Done
Building dependency tree       
Reading state information... Done
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 3 not upgraded.
Need to get 3085 kB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://deb.debian.org/debian buster/main amd64 cargo amd64 0.43.1-3~deb10u1 [3085 kB]
Fetched 3085 kB in 1s (3917 kB/s)
debconf: delaying package configuration, since apt-utils is not installed
(Reading database ... 24109 files and directories currently installed.)
Preparing to unpack .../cargo_0.43.1-3~deb10u1_amd64.deb ...
Unpacking cargo (0.43.1-3~deb10u1) over (0.43.1-3~deb10u1) ...
Setting up cargo (0.43.1-3~deb10u1) ...
    Updating crates.io index
  Installing nixpkgs-fmt v1.2.0
   Compiling autocfg v1.0.1
   Compiling memchr v2.4.0
   Compiling serde v1.0.126
   Compiling lazy_static v1.4.0
   Compiling libc v0.2.98
   Compiling cfg-if v1.0.0
   Compiling log v0.4.14
   Compiling ryu v1.0.5
   Compiling bitflags v1.2.1
   Compiling regex-syntax v0.6.25
   Compiling crossbeam-utils v0.8.5
   Compiling fnv v1.0.7
   Compiling once_cell v1.8.0
   Compiling unicode-width v0.1.8
   Compiling rustc-hash v1.1.0
   Compiling countme v2.0.4
   Compiling hashbrown v0.9.1
   Compiling cfg-if v0.1.10
   Compiling serde_json v1.0.64
   Compiling same-file v1.0.6
   Compiling smol_str v0.1.18
error[E0658]: `while` is not allowed in a `const fn`
  --> /root/.cargo/registry/src/github.com-1ecc6299db9ec823/smol_str-0.1.18/src/lib.rs:58:9
   |
58 | /         while i < text.len() {
59 | |             buf[i] = text.as_bytes()[i];
60 | |             i += 1
61 | |         }
   | |_________^
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/52000

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.
error: could not compile `smol_str`.
warning: build failed, waiting for other jobs to finish...
error: failed to compile `nixpkgs-fmt v1.2.0`, intermediate artifacts can be found at `/tmp/cargo-installORwI5m`

Caused by:
  build failed

Example of this failing in build pipeline

[zimbatm]

Related issue: rust-analyzer/smol_str#25