This seems to work: https://play.rust-lang.org/?version=stable&mode=release&edition=2018&gist=8fcc8523bc24fffed6a110126afd59d7

You can also have currently-invalid cfgs in the conditional cfg. Are there any cfgs that are currently unstable?

cfg(rustdoc) is nightly-only.

@roblabla That compiles on release mode but not debug, so I think that path will work. In case the playground somehow breaks:

#[cfg_attr(debug_assertions, cfg(rustdoc))]
#[cfg(debug_assertions)]
fn func() {
    println!("{}", "hi");
}

...wait, all is short-circuiting, so that hack isn"t even necessary.

Assuming that Rust 1.xx.0 adds cfg(accessible), we should use cfg(all(rust_1_xx_0, accessible(core::error::WhateverError))). I don"t think this is actionable until cfg(accessible) is stabilized.

Let"s keep this open while waiting for cfg(accessible). Issues should only be closed once they"ve been completed (either as "won"t ever happen" or "this is implemented in master").