Note: this error code is no longer emitted by the compiler

This is because it was too specific to the inline attribute. Similar diagnostics occur for other attributes too. The example here will now emit E0539

Erroneous code example:

#[inline(unknown)] // error: invalid argument
pub fn something() {}

fn main() {}

The inline attribute only supports two arguments:

• always
• never

All other arguments given to the inline attribute will return this error. Example:

#[inline(never)] // ok!
pub fn something() {}

fn main() {}

For more information see the inline Attribute section of the Reference.