Crate proc_macro2_diagnostics

Expand description

Diagnostic emulation on stable and nightly.

Usage

Depend on the library in your proc-macro.

[dependencies]
proc_macro2_diagnostics = "0.10"

Import SpanDiagnosticExt and use its methods on a proc_macro2::Span to create Diagnostics:

use syn::spanned::Spanned;
use proc_macro2::TokenStream;
use proc_macro2_diagnostics::{SpanDiagnosticExt, Diagnostic};

fn my_macro(input: TokenStream) -> Result<TokenStream, Diagnostic> {
    Err(input.span().error("there's a problem here..."))
}

If there’s an error, emit the diagnostic as tokens:

extern crate proc_macro;

#[proc_macro]
pub fn real_macro(tokens: proc_macro::TokenStream) -> proc_macro::TokenStream {
    match my_macro(tokens.into()) {
        Ok(tokens) => tokens.into(),
        Err(diag) => diag.emit_as_expr_tokens().into()
    }
}

This does the right thing on nightly or stable.

On stable, due to limitations, any top-level, non-error diagnostics are emitted as errors. This will abort compilation. To avoid this, you may want to cfg-gate emitting non-error diagnostics to nightly.

Colors

By default, error messages are colored on stable. To disable, disable default features:

[dependencies]
proc_macro2_diagnostics = { version = "0.10", default-features = false }

The compiler always colors diagnostics on nightly.

Structs

Diagnostic
A structure representing a diagnostic message and associated children messages.

Enums

Level
An enum representing a diagnostic level.

Traits