//! This crate provides the [`quote!`] macro for turning Rust syntax tree data
//! structures into tokens of source code.
//!
//! [`quote!`]: macro.quote.html
//!
//! Procedural macros in Rust receive a stream of tokens as input, execute
//! arbitrary Rust code to determine how to manipulate those tokens, and produce
//! a stream of tokens to hand back to the compiler to compile into the caller's
//! crate. Quasi-quoting is a solution to one piece of that -- producing tokens
//! to return to the compiler.
//!
//! The idea of quasi-quoting is that we write *code* that we treat as *data*.
//! Within the `quote!` macro, we can write what looks like code to our text
//! editor or IDE. We get all the benefits of the editor's brace matching,
//! syntax highlighting, indentation, and maybe autocompletion. But rather than
//! compiling that as code into the current crate, we can treat it as data, pass
//! it around, mutate it, and eventually hand it back to the compiler as tokens
//! to compile into the macro caller's crate.
//!
//! This crate is motivated by the procedural macro use case, but is a
//! general-purpose Rust quasi-quoting library and is not specific to procedural
//! macros.
//!
//! *Version requirement: Quote supports any compiler version back to Rust's
//! very first support for procedural macros in Rust 1.15.0.*
//!
//! ```toml
//! [dependencies]
//! quote = "0.6"
//! ```
//!
//! ```
//! #[macro_use]
//! extern crate quote;
//! #
//! # fn main() {}
//! ```
//!
//! # Example
//!
//! The following quasi-quoted block of code is something you might find in [a]
//! procedural macro having to do with data structure serialization. The `#var`
//! syntax performs interpolation of runtime variables into the quoted tokens.
//! Check out the documentation of the [`quote!`] macro for more detail about
//! the syntax. See also the [`quote_spanned!`] macro which is important for
//! implementing hygienic procedural macros.
//!
//! [a]: https://serde.rs/
//! [`quote_spanned!`]: macro.quote_spanned.html
//!
//! ```
//! # #[macro_use]
//! # extern crate quote;
//! #
//! # fn main() {
//! # let generics = "";
//! # let where_clause = "";
//! # let field_ty = "";
//! # let item_ty = "";
//! # let path = "";
//! # let value = "";
//! #
//! let tokens = quote! {
//! struct SerializeWith #generics #where_clause {
//! value: &'a #field_ty,
//! phantom: ::std::marker::PhantomData<#item_ty>,
//! }
//!
//! impl #generics serde::Serialize for SerializeWith #generics #where_clause {
//! fn serialize<S>(&self, s: &mut S) -> Result<(), S::Error>
//! where
//! S: serde::Serializer,
//! {
//! #path(self.value, s)
//! }
//! }
//!
//! SerializeWith {
//! value: #value,
//! phantom: ::std::marker::PhantomData::<#item_ty>,
//! }
//! };
//! #
//! # }
//! ```
//!
//! ## Recursion limit
//!
//! The `quote!` macro relies on deep recursion so some large invocations may
//! fail with "recursion limit reached" when you compile. If it fails, bump up
//! the recursion limit by adding `#![recursion_limit = "128"]` to your crate.
//! An even higher limit may be necessary for especially large invocations.
// Quote types in rustdoc of other crates get linked to here.
extern crate proc_macro;
extern crate proc_macro2;
pub use TokenStreamExt;
pub use ToTokens;
// Not public API.
/// The whole point.
///
/// Performs variable interpolation against the input and produces it as
/// [`TokenStream`]. For returning tokens to the compiler in a procedural macro, use
/// `into()` to build a `TokenStream`.
///
/// [`TokenStream`]: https://docs.rs/proc-macro2/0.4/proc_macro2/struct.TokenStream.html
///
/// # Interpolation
///
/// Variable interpolation is done with `#var` (similar to `$var` in
/// `macro_rules!` macros). This grabs the `var` variable that is currently in
/// scope and inserts it in that location in the output tokens. Any type
/// implementing the [`ToTokens`] trait can be interpolated. This includes most
/// Rust primitive types as well as most of the syntax tree types from the [Syn]
/// crate.
///
/// [`ToTokens`]: trait.ToTokens.html
/// [Syn]: https://github.com/dtolnay/syn
///
/// Repetition is done using `#(...)*` or `#(...),*` again similar to
/// `macro_rules!`. This iterates through the elements of any variable
/// interpolated within the repetition and inserts a copy of the repetition body
/// for each one. The variables in an interpolation may be anything that
/// implements `IntoIterator`, including `Vec` or a pre-existing iterator.
///
/// - `#(#var)*` — no separators
/// - `#(#var),*` — the character before the asterisk is used as a separator
/// - `#( struct #var; )*` — the repetition can contain other tokens
/// - `#( #k => println!("{}", #v), )*` — even multiple interpolations
///
/// # Hygiene
///
/// Any interpolated tokens preserve the `Span` information provided by their
/// `ToTokens` implementation. Tokens that originate within the `quote!`
/// invocation are spanned with [`Span::call_site()`].
///
/// [`Span::call_site()`]: https://docs.rs/proc-macro2/0.4/proc_macro2/struct.Span.html#method.call_site
///
/// A different span can be provided through the [`quote_spanned!`] macro.
///
/// [`quote_spanned!`]: macro.quote_spanned.html
///
/// # Example
///
/// ```
/// # #[cfg(any())]
/// extern crate proc_macro;
/// # extern crate proc_macro2 as proc_macro;
///
/// #[macro_use]
/// extern crate quote;
///
/// use proc_macro::TokenStream;
///
/// # const IGNORE_TOKENS: &'static str = stringify! {
/// #[proc_macro_derive(HeapSize)]
/// # };
/// pub fn derive_heap_size(input: TokenStream) -> TokenStream {
/// // Parse the input and figure out what implementation to generate...
/// # const IGNORE_TOKENS: &'static str = stringify! {
/// let name = /* ... */;
/// let expr = /* ... */;
/// # };
/// #
/// # let name = 0;
/// # let expr = 0;
///
/// let expanded = quote! {
/// // The generated impl.
/// impl ::heapsize::HeapSize for #name {
/// fn heap_size_of_children(&self) -> usize {
/// #expr
/// }
/// }
/// };
///
/// // Hand the output tokens back to the compiler.
/// expanded.into()
/// }
/// #
/// # fn main() {}
/// ```
/// Same as `quote!`, but applies a given span to all tokens originating within
/// the macro invocation.
///
/// # Syntax
///
/// A span expression of type [`Span`], followed by `=>`, followed by the tokens
/// to quote. The span expression should be brief -- use a variable for anything
/// more than a few characters. There should be no space before the `=>` token.
///
/// [`Span`]: https://docs.rs/proc-macro2/0.4/proc_macro2/struct.Span.html
///
/// ```
/// # #[macro_use]
/// # extern crate quote;
/// # extern crate proc_macro2;
/// #
/// # use proc_macro2::Span;
/// #
/// # fn main() {
/// # const IGNORE_TOKENS: &'static str = stringify! {
/// let span = /* ... */;
/// # };
/// # let span = Span::call_site();
/// # let init = 0;
///
/// // On one line, use parentheses.
/// let tokens = quote_spanned!(span=> Box::into_raw(Box::new(#init)));
///
/// // On multiple lines, place the span at the top and use braces.
/// let tokens = quote_spanned! {span=>
/// Box::into_raw(Box::new(#init))
/// };
/// # }
/// ```
///
/// The lack of space before the `=>` should look jarring to Rust programmers
/// and this is intentional. The formatting is designed to be visibly
/// off-balance and draw the eye a particular way, due to the span expression
/// being evaluated in the context of the procedural macro and the remaining
/// tokens being evaluated in the generated code.
///
/// # Hygiene
///
/// Any interpolated tokens preserve the `Span` information provided by their
/// `ToTokens` implementation. Tokens that originate within the `quote_spanned!`
/// invocation are spanned with the given span argument.
///
/// # Example
///
/// The following procedural macro code uses `quote_spanned!` to assert that a
/// particular Rust type implements the [`Sync`] trait so that references can be
/// safely shared between threads.
///
/// [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html
///
/// ```
/// # #[macro_use]
/// # extern crate quote;
/// # extern crate proc_macro2;
/// #
/// # use quote::{TokenStreamExt, ToTokens};
/// # use proc_macro2::{Span, TokenStream};
/// #
/// # struct Type;
/// #
/// # impl Type {
/// # fn span(&self) -> Span {
/// # Span::call_site()
/// # }
/// # }
/// #
/// # impl ToTokens for Type {
/// # fn to_tokens(&self, _tokens: &mut TokenStream) {}
/// # }
/// #
/// # fn main() {
/// # let ty = Type;
/// # let call_site = Span::call_site();
/// #
/// let ty_span = ty.span();
/// let assert_sync = quote_spanned! {ty_span=>
/// struct _AssertSync where #ty: Sync;
/// };
/// # }
/// ```
///
/// If the assertion fails, the user will see an error like the following. The
/// input span of their type is hightlighted in the error.
///
/// ```text
/// error[E0277]: the trait bound `*const (): std::marker::Sync` is not satisfied
/// --> src/main.rs:10:21
/// |
/// 10 | static ref PTR: *const () = &();
/// | ^^^^^^^^^ `*const ()` cannot be shared between threads safely
/// ```
///
/// In this example it is important for the where-clause to be spanned with the
/// line/column information of the user's input type so that error messages are
/// placed appropriately by the compiler. But it is also incredibly important
/// that `Sync` resolves at the macro definition site and not the macro call
/// site. If we resolve `Sync` at the same span that the user's type is going to
/// be resolved, then they could bypass our check by defining their own trait
/// named `Sync` that is implemented for their type.
// Extract the names of all #metavariables and pass them to the $finish macro.
//
// in: pounded_var_names!(then () a #b c #( #d )* #e)
// out: then!(() b d e)
;
=> ;
=> ;
=> ;
=> ;
=> ;
=> ;
=> ;
=> ;
}
// in: nested_tuples_pat!(() a b c d e)
// out: ((((a b) c) d) e)
//
// in: nested_tuples_pat!(() a)
// out: a
;
=> ;
=> ;
=> ;
}
// in: multi_zip_expr!(() a b c d e)
// out: a.into_iter().zip(b).zip(c).zip(d).zip(e)
//
// in: multi_zip_iter!(() a)
// out: a
;
=> ;
=> ;
=> ;
=> ;
}
quote_each_token!;
};
=> ;
=> ;
=> ;
=> ;
=> ;
=> ;
=> ;
}