Function import_toolchain 

pub fn import_toolchain(
    path: &Path,
    name: &str,
    hosts: Vec<String>,
    rustup: &str,
) -> Result<Config>

Import one project toolchain file. Hosts and bootstrap version remain explicit. Read a project toolchain file into one named, validated configuration.

Supports TOML and legacy rust-toolchain selectors. Caller-supplied name, hosts and manager version rustup remain explicit. The result is not written; use write_config. No upstream availability lookup occurs.

Errors

Refuses missing/oversized/malformed files, local custom paths, unsupported selectors or invalid profile/component/target/configuration constraints.