# proc-macro2-diagnostics   [![crates.io]][crate] [![docs.rs]][docs]

[crates.io]: https://img.shields.io/crates/v/proc-macro2-diagnostics.svg
[crate]: https://crates.io/crates/proc-macro2-diagnostics
[docs.rs]: https://docs.rs/proc-macro2-diagnostics/badge.svg
[docs]: https://docs.rs/proc-macro2-diagnostics

Diagnostics for stable and nightly proc-macros!

## Usage

1. Depend on the library in your proc-macro.

```toml
[dependencies]
proc_macro2_diagnostics = "0.10"
```

2. Import `SpanDiagnosticExt` and use its methods on a `proc_macro2::Span` to
   create `Diagnostic`s:

```rust
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..."))
}
```

3. If there's an error, emit the diagnostic as tokens:

```rust
extern crate 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:

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

The compiler always colors diagnostics on nightly.

## License

Licensed under either of the following, at your option:

  * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
  * MIT License ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)