Require minimum rust version in Cargo.toml instead of rust-toolchain file

[silwol]

Description

Review

• Add a short description of the change to the CHANGELOG.md file

[syrusakbary]

I'm not sure if we want this. We need to double check that people using wasmer (as a lib) will not be enforced to use a specific Rust version

[silwol]

The question is, what is the reason for having a rust-toolchain in the first place? This is what interfered with my rust setup which is actually pretty mainline, so I expect this to cause issues for others as well if they want to start developing. My thought was that adding a MSRV is close enough to what the rust-toolchain file does right now. If there is no hard requirement on a MSRV, we can of course leave that out or think about other options.

[syrusakbary]

The question is, what is the reason for having a rust-toolchain in the first place?

Basically, when people clone the project and contribute to it they must know what is the minimum version expected to work to compile Wasmer and run it's tests with.

When people use the library, they should not enforced to use a specific version of Rust.

[epilys]

From Cargo docs:

Setting the rust-version key in [package] will affect all targets/crates in the package, including test suites, benchmarks, binaries, examples, etc.

As for the libraries that use wasmer as a dependency, apparently Cargo does not use rust-version for dependencies.

It does not provide any value to wasmer to require a specific version because we're not (I think) using features that don't exist on earlier versions. To have this documented for ourselves we can build it for all versions after let's say 1.56 and see if there's something unexpected.

[jcaesar]

Basically, when people clone the project and contribute to it they must know what is the minimum version expected to work to compile Wasmer and run it's tests with.

You do want this.

• The rust-toolchain file will be ignored if you're not using rustup
• The rust-toolchain file doesn't set a minimum, but the default version which will be auto-installed even if you have a newer rust
• Cargo-toml's rust-version sets a minimum and gives nice error message:

error: package `bar v0.1.0 (/src/bar)` cannot be built because it requires rustc 1.59 or newer, while the currently active rustc version is 1.56.1

Caveat here is that rust before 1.56 will ignore rust-version:

warning: `rust-version` is not supported on this version of Cargo and will be ignored

This could be fixed by also bumping the edition to 2021.

Anyway: wasmer-vm depends on corosensei, which already sets rust-version = "1.59" and edition = "2021". So this PR doesn't really change the situation much, but makes it a bit clearer. ¯\_(つ)_/¯

As for the libraries that use wasmer as a dependency, apparently Cargo does not use rust-version for dependencies

You're misinterpreting this. The rust-version isn't used as a constraint for dependency resolution. The rust-version on dependencies is definitely checked.