[−][src]Crate proc_macro2_diagnostics

Diagnostic emulation on stable and nightly.

Usage

  1. Depend on the library in your proc-macro.
[dependencies]
proc_macro2_diagnostics = "0.9"
  1. 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..."))
}
  1. 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.

Caveats

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 = "0.9", 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

SpanDiagnosticExt

Extension trait for proc_macro2::Span emulating the proc-macro diagnostic API on stable and nightly.