this `impl` can be derived

Summary

It looks like clippy is confused by presence of cfg in enum type and still offers to implement Default using derive macro which is unlikely to work.

Lint Name

derivable_impls

Reproducer

I tried this code:

#[derive(Debug, Clone, Eq, PartialEq)]
pub enum WireguardMultihopMode {
    /// Multihop using two tun devices to nest tunnels.
    #[cfg(not(any(target_os = "android", target_os = "ios")))]
    TunTun,

    /// Netstack based multihop.
    Netstack,
}

impl Default for WireguardMultihopMode {
    fn default() -> Self {
        #[cfg(any(target_os = "ios", target_os = "android"))]
        {
            Self::Netstack
        }

        #[cfg(not(any(target_os = "android", target_os = "ios")))]
        {
            Self::TunTun
        }
    }
}

I saw this happen:

warning: this `impl` can be derived
   --> crates\nym-vpn-lib\src\tunnel_state_machine\mod.rs:211:1
    |
211 | / impl Default for WireguardMultihopMode {
212 | |     fn default() -> Self {
213 | |         #[cfg(any(target_os = "ios", target_os = "android"))]
...   |
223 | | }
    | |_^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#derivable_impls
    = note: `#[warn(clippy::derivable_impls)]` on by default
help: replace the manual implementation with a derive attribute and mark the default variant
    |
202 + #[derive(Default)]
203 | pub enum WireguardMultihopMode {
204 |     /// Multihop using two tun devices to nest tunnels.
205 |     #[cfg(not(any(target_os = "android", target_os = "ios")))]
206 ~     #[default]
207 ~     TunTun,
    |

warning: `nym-vpn-lib` (lib) generated 1 warning (run `cargo clippy --fix --lib -p nym-vpn-lib` to apply 1 suggestion)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 47.82s

I expected to see this happen:

Nothing.

Version

rustc 1.93.0-nightly (f37aa9955 2025-10-26)

Additional Labels

No response

Start at the derivable_impls lint and reproduce the supplied enum with its cfg-gated variants on the affected targets. Check the lint's existing tests, if present, and add coverage for this case; done means Clippy emits neither the warning nor the derive suggestion when the suggested default variant is unavailable.