diff options
Diffstat (limited to 'syn/src/spanned.rs')
| -rw-r--r-- | syn/src/spanned.rs | 114 |
1 files changed, 0 insertions, 114 deletions
diff --git a/syn/src/spanned.rs b/syn/src/spanned.rs deleted file mode 100644 index 71ffe26..0000000 --- a/syn/src/spanned.rs +++ /dev/null @@ -1,114 +0,0 @@ -//! A trait that can provide the `Span` of the complete contents of a syntax -//! tree node. -//! -//! *This module is available if Syn is built with both the `"parsing"` and -//! `"printing"` features.* -//! -//! <br> -//! -//! # Example -//! -//! Suppose in a procedural macro we have a [`Type`] that we want to assert -//! implements the [`Sync`] trait. Maybe this is the type of one of the fields -//! of a struct for which we are deriving a trait implementation, and we need to -//! be able to pass a reference to one of those fields across threads. -//! -//! [`Type`]: ../enum.Type.html -//! [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html -//! -//! If the field type does *not* implement `Sync` as required, we want the -//! compiler to report an error pointing out exactly which type it was. -//! -//! The following macro code takes a variable `ty` of type `Type` and produces a -//! static assertion that `Sync` is implemented for that type. -//! -//! ``` -//! # extern crate proc_macro; -//! # -//! use proc_macro::TokenStream; -//! use proc_macro2::Span; -//! use quote::quote_spanned; -//! use syn::Type; -//! use syn::spanned::Spanned; -//! -//! # const IGNORE_TOKENS: &str = stringify! { -//! #[proc_macro_derive(MyMacro)] -//! # }; -//! pub fn my_macro(input: TokenStream) -> TokenStream { -//! # let ty = get_a_type(); -//! /* ... */ -//! -//! let assert_sync = quote_spanned! {ty.span()=> -//! struct _AssertSync where #ty: Sync; -//! }; -//! -//! /* ... */ -//! # input -//! } -//! # -//! # fn get_a_type() -> Type { -//! # unimplemented!() -//! # } -//! ``` -//! -//! By inserting this `assert_sync` fragment into the output code generated by -//! our macro, the user's code will fail to compile if `ty` does not implement -//! `Sync`. The errors they would see look like the following. -//! -//! ```text -//! error[E0277]: the trait bound `*const i32: std::marker::Sync` is not satisfied -//! --> src/main.rs:10:21 -//! | -//! 10 | bad_field: *const i32, -//! | ^^^^^^^^^^ `*const i32` cannot be shared between threads safely -//! ``` -//! -//! In this technique, using the `Type`'s span for the error message makes the -//! error appear in the correct place underlining the right type. -//! -//! <br> -//! -//! # Limitations -//! -//! The underlying [`proc_macro::Span::join`] method is nightly-only. When -//! called from within a procedural macro in a nightly compiler, `Spanned` will -//! use `join` to produce the intended span. When not using a nightly compiler, -//! only the span of the *first token* of the syntax tree node is returned. -//! -//! In the common case of wanting to use the joined span as the span of a -//! `syn::Error`, consider instead using [`syn::Error::new_spanned`] which is -//! able to span the error correctly under the complete syntax tree node without -//! needing the unstable `join`. -//! -//! [`syn::Error::new_spanned`]: crate::Error::new_spanned - -use proc_macro2::Span; -use quote::spanned::Spanned as ToTokens; - -/// A trait that can provide the `Span` of the complete contents of a syntax -/// tree node. -/// -/// This trait is automatically implemented for all types that implement -/// [`ToTokens`] from the `quote` crate, as well as for `Span` itself. -/// -/// [`ToTokens`]: quote::ToTokens -/// -/// See the [module documentation] for an example. -/// -/// [module documentation]: self -/// -/// *This trait is available if Syn is built with both the `"parsing"` and -/// `"printing"` features.* -pub trait Spanned { - /// Returns a `Span` covering the complete contents of this syntax tree - /// node, or [`Span::call_site()`] if this node is empty. - /// - /// [`Span::call_site()`]: proc_macro2::Span::call_site - fn span(&self) -> Span; -} - -impl<T: ?Sized + ToTokens> Spanned for T { - fn span(&self) -> Span { - self.__span() - } -} |