Error code E0536

The not cfg-predicate was malformed.

Erroneous code example (using cargo doc):

#![feature(doc_cfg)]
#[doc(cfg(not()))]
pub fn main() {

}

The not predicate expects one cfg-pattern. Example:

#![feature(doc_cfg)]
#[doc(cfg(not(target_os = "linux")))] // ok!
pub fn main() {

}

For more information about the cfg macro, read the section on Conditional Compilation in the Reference.