Tools to detect the minimum rustc version my project support

Is there any tool that can detect the minimum version of Rustc my crate support? I want to publish my crate. In practice, it'd be better to notice the user the minimum version of Rustc.

But there's no way I can test compilers one by one, So is there any tool to do this?

Not really. In Tokio we have a CI job to verify that it still works on our MSRV (minimum supported rust version), and we emit a compiler error saying "Tokio doesn't support that version" when the version is older than that. But we don't try to check if Tokio becomes able to compile on something older, and we don't check versions between the MSRV and the newest stable Rust version.

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You can have multiple Rust versions installed, and try them:

rustup toolchain add 1.55.0
cargo +1.55.0 check

I use this method to guess MSRV on lib.rs. To do this at scale I'm also parsing errors to see which feature flags are required, but for a single crate that's too much hassle.

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