compile_msg

A syntax extension for emitting messages at compile time, via the compiler, similar to #warning and #error in the C preprocessor. Four macros are provided (in order of increasing severity):

• compile_note: tell the user a tidbit of information without implying it is a problem,
• compile_warning: tell the user that something could go wrong,
• compile_error: tell the user about some error, compilation will not stop immediately, but will halt before any compiler passes after macro expansion.
• compile_fatal: tell the user about a catastrophic error and immediately halt compilation. compile_error is strongly preferred as it allows further errors and warnings to be picked up in a single pass.

The macros can be placed as an item (expanding to nothing), and as an expression (expanding to a literal unit, i.e. ()). They are best used in conditionally compiled items, e.g. if a certain operating system is entirely unsupported, one can use compile_error! with an appropriate #[cfg] attribute.

Usage

Ensure your Cargo.toml contains:

[dependencies]
compile_msg = "0"

and then load the syntax in the normal manner:

#![feature(plugin)]

#[plugin] extern crate compile_msg;

#[cfg(target_os = "hal")]
compile_error!("I'm sorry, Dave, I'm afraid I can't do that.");


fn main() {
    compile_note!("please be careful"); // note: please be careful


    compile_warning!("take more care"); // warning: take more care


    compile_error!("things are breaking"); // error: things are breaking


    compile_fatal!("catastrophic failure!"); // error: catastrophic failure
    // (compilation stops here)


    compile_warning!("not emitted");
}

(If that compiled, it would be equivalent to fn main() {} at runtime.)