Issuing a warning at compile time?

问题

I want to issue a warning at compile time, perhaps from a macro. It should not be silenceable by cap_lints. My current use case is feature deprecation, but there's other possible uses for this.

回答1:

This currently isn't possible in stable Rust. However, there is an unstable feature, procedural macro diagnostics, which provides this functionality for procedural macros, via the Diagnostic API.

To emit a compiler warning from inside a procedural macro, you would use it like this:

#![feature(proc_macro_diagnostic)]

use proc_macro::Diagnostic;

Diagnostic::new()
    .warning("This method is deprecated")
    .emit();

To associate the warning with a specific token span, you'd use spanned_warning instead. This makes the warning output show the relevant source tokens underlined along with the message.

来源：https://stackoverflow.com/questions/57025894/issuing-a-warning-at-compile-time