Macro fluent_messages

fluent_messages!() { /* proc-macro */ }

Implements the fluent_messages macro, which performs compile-time validation of the compiler’s Fluent resources (i.e. that the resources parse and don’t multiply define the same messages) and generates constants that make using those messages in diagnostics more ergonomic.

For example, given the following invocation of the macro..

fluent_messages! { "./typeck.ftl" }

..where typeck.ftl has the following contents..

typeck_field_multiply_specified_in_initializer =
    field `{$ident}` specified more than once
    .label = used more than once
    .label_previous_use = first use of `{$ident}`

…then the macro parse the Fluent resource, emitting a diagnostic if it fails to do so, and will generate the following code:

pub static DEFAULT_LOCALE_RESOURCE: &'static [&'static str] = include_str!("./typeck.ftl");

mod fluent_generated {
    mod typeck {
        pub const field_multiply_specified_in_initializer: DiagMessage =
            DiagMessage::fluent("typeck_field_multiply_specified_in_initializer");
        pub const field_multiply_specified_in_initializer_label_previous_use: DiagMessage =
            DiagMessage::fluent_attr(
                "typeck_field_multiply_specified_in_initializer",
                "previous_use_label"
            );
    }
}

When emitting a diagnostic, the generated constants can be used as follows:

let mut err = sess.struct_span_err(
    span,
    fluent::typeck::field_multiply_specified_in_initializer
);
err.span_default_label(span);
err.span_label(
    previous_use_span,
    fluent::typeck::field_multiply_specified_in_initializer_label_previous_use
);
err.emit();

Note: any crate using this macro must also have a dependency on rustc_errors, because the generated code refers to things from that crate.