rustdoc with `doc(cfg(false))` prints an extra "on"

[Urgau]

I tried this code:

#![feature(doc_cfg)]

#[doc(cfg(false))]
pub fn foo() {}

I expected to see this happen: Avalaible nowhere (without the on)

Instead, this happened:

Meta

rustdoc --version --verbose:

rustdoc 1.87.0-nightly (e16a049ad 2025-03-03)
binary: rustdoc
commit-hash: e16a049adbf94d610787430b6efdf31d896dc5b6
commit-date: 2025-03-03
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0