Announcing Rust 1.95.0

Rust 1.95 introduces a cfg_select! macro that acts roughly similar to a compile-time match on cfgs. This fulfills the same purpose as the popular cfg-if crate, although with a different syntax. cfg_select! expands to the right-hand side of the first arm whose configuration predicate evaluates to true. Some examples:

cfg_select! {
    unix => {
        fn foo() { /* unix specific functionality */ }
    }
    target_pointer_width = "32" => {
        fn foo() { /* non-unix, 32-bit functionality */ }
    }
    _ => {
        fn foo() { /* fallback implementation */ }
    }
}

let is_windows_str = cfg_select! {
    windows => "windows",
    _ => "not windows",
};

Rust 1.88 stabilized let chains. Rust 1.95 brings that capability into match expressions, allowing for conditionals based on pattern matching.

match value {
    Some(x) if let Ok(y) = compute(x) => {
        // Both `x` and `y` are available here
        println!("{}, {}", x, y);
    }
    _ => {}
}

Note that the compiler will not currently consider the patterns matched in if let guards as part of the exhaustiveness evaluation of the overall match, just like if guards.

Rust 1.95 removes support on stable for passing a custom target specification to rustc. This should not affect any Rust users using a fully stable toolchain, as building the standard library (including just core) already required using nightly-only features.

We’re also gathering use cases for custom targets on the tracking issue as we consider whether some form of this feature should eventually be stabilized.