error: override toolchain 'stable' is not installed

[abitrolly]

Trying to build 3rd party project with rust:1.20-stretch gives this error:

error: override toolchain 'stable' is not installed

info: caused by: the toolchain file at '/build/rust-toolchain' specifies an uninstalled toolchain

Is it possible to ship the stable toolchain with those images?

[sfackler]

The images use the toolchain for the specific release - 1.20.0 in the case of rust:1.20-stretch.

[abitrolly]

@sfackler official blog says that 1.20.0 is stable, so why the error?

[sfackler]

Rustup has multiple toolchains it can use. "stable" means the newest stable release. We can't use "stable" in the docker images because it isn't reproducible. If we did and you reran the build for the 1.19.0 image now, it'd have 1.20.0 on it. We instead use the toolchains that pin to the specific stable release.

[abitrolly]

So, the solution is to patch rust-toolchain file with specific version tag.

But 1.20.0 is the newest stable release, so why it still fails?

[abitrolly]

echo 1.20.0 > rust-toolchain

Fixes the issue.