build: Use "stable" channel

[andygrove]

Which issue does this PR close?

• Closes error: toolchain '1.85.0-x86_64-unknown-linux-gnu' is not installed on CI / verification script #14982 (hopefully)

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[andygrove]

@alamb I am not 100% sure if this is the full fix, but seems to help

[alamb]

I think the reason we moved to putting a version in toolchain.toml is to avoid breakages when the next rust release gets released...

[andygrove]

I think the reason we moved to putting a version in toolchain.toml is to avoid breakages when the next rust release gets released...

We pin the Rust version in the rust-version attribute in the Cargo.toml though.

[andygrove]

Rust release notes: https://github.com/rust-lang/rustup/blob/master/CHANGELOG.md

rustup will no longer automatically install the active toolchain if it is not installed
- To ensure its installation, run rustup toolchain install with no arguments

[edmondop]

Thank you

[alamb]

So then I don't think this is the right fix -- instead we should be calling rustup install locally, right?

The idea of putting the toolchain file in the repo was so that we controlled the version of rust useed rather than automatically pick up whatever version of Rust happened to be latest stable

The rationale is described in more detail here:

• Buildable release builds #14479
• Specify rust toolchain explicitly, document how to change it #14655

Let me make an alternate proposal

[alamb]

Here is my alternate proposal

• Fix verification script and extended tests due to rustup changes #14990

(which is basically to call rustup toolchain install). I am testing it now some more