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#![deny(rustdoc, missing_docs, warnings, clippy::pedantic)] #![allow(missing_doc_code_examples)] #![doc(test(attr(deny(warnings))))] //! An attribute macro to apply function-like macros. //! It can improve the readability of your code. //! //! This crate has *no* dependency so you don't need to worry about compile time. //! //! # Examples //! ``` //! use apply_macro::apply; //! //! macro_rules! common_derive { //! ($input:item) => { //! #[derive(Debug, PartialEq)] //! $input //! }; //! } //! //! #[apply(common_derive)] //! struct Num(i32); //! //! assert_eq!(Num(-1), Num(-1)); //! assert_ne!(Num(1), Num(-1)); //! //! #[apply(common_derive,)] //! struct TrailingCommaIsAllowed; //! //! assert_eq!(TrailingCommaIsAllowed, TrailingCommaIsAllowed); //! ``` //! //! The `#[apply(common_derive)]` on `Num` expands to: //! ``` //! # macro_rules! common_derive { //! # ($dummy:item) => {}; //! # } //! common_derive! { //! struct Num(i32); //! } //! ``` //! //! Multiple arguments are allowed and seperated by commas: //! ``` //! use apply_macro::apply; //! //! macro_rules! derive_debug { //! { //! #[$attr:meta] // will receive `#[apply(derive_partial_eq)]` //! $input:item //! } => { //! #[$attr] // avoid "error: macro attributes must be placed before `#[derive]`" //! #[derive(Debug)] //! $input //! }; //! } //! //! macro_rules! derive_partial_eq { //! ($input:item) => { //! #[derive(PartialEq)] //! $input //! }; //! } //! //! #[apply(derive_debug, derive_partial_eq)] //! struct Num(i32); //! //! assert_eq!(Num(-1), Num(-1)); //! assert_ne!(Num(1), Num(-1)); //! //! #[apply(derive_debug, derive_partial_eq,)] //! struct TrailingCommaIsAllowed; //! //! assert_eq!(TrailingCommaIsAllowed, TrailingCommaIsAllowed); //! ``` //! //! Empty argument is also allowed (consistent with `#[derive()]`): //! ``` //! use apply_macro::apply; //! //! #[apply()] //! #[derive()] // consistent //! # #[allow(unused_attributes, dead_code)] //! struct EmptyArg; //! ``` //! Although, as a procedural macro, `#[apply]` can't be banned: //! ``` //! use apply_macro::apply; //! //! #[apply] //! # #[allow(dead_code)] //! struct Oops; //! ``` #![no_std] use core::iter::once; use proc_macro::{Delimiter, Group, Ident, Punct, Spacing, Span, TokenStream, TokenTree}; fn into_tt(tt: impl Into<TokenTree>) -> impl Iterator<Item = TokenTree> { once(tt.into()) } macro_rules! p { [$punct1:literal $($punct:literal)*] => { into_tt(Punct::new($punct1, Spacing::Joint)) $(.chain(into_tt(Punct::new($punct, Spacing::Joint))))* }; } /// The main attribute macro of this crate. /// /// This accepts paths to the function-like macros you want to call as argument. /// See also [examples in the crate-level documentation](crate#example). /// /// ## Limitation /// **Note that this may be fixed in the future without a major version bump. /// Do not rely on it.** /// /// This macro does not check for invalid arguments: /// ``` /// use apply_macro::apply; /// /// macro_rules! derive_debug { /// ($input:item) => { /// #[derive(Debug)] /// $input /// }; /// } /// /// #[apply(#[derive(Debug)] struct AnotherStruct; derive_debug)] /// struct ImplsDebug; /// /// dbg!(AnotherStruct, ImplsDebug); /// ``` #[proc_macro_attribute] pub fn apply(args: TokenStream, input: TokenStream) -> TokenStream { if args.is_empty() { input } else { let mut args = args.into_iter(); let mut result = TokenStream::new(); for tt in &mut args { if let TokenTree::Punct(ref punct) = tt { // TODO: https://github.com/rust-lang/rust/pull/78636 if punct.as_char() == ',' { let args: TokenStream = args.collect(); if args.is_empty() { break; } result.extend( p!['!'].chain(into_tt(Group::new( Delimiter::Brace, p!['#'] .chain(into_tt(Group::new( Delimiter::Bracket, p![':' ':'] .chain(into_tt(Ident::new( "apply_macro", Span::call_site(), ))) .chain(p![':' ':']) .chain(into_tt(Ident::new("apply", Span::call_site()))) .chain(into_tt(Group::new(Delimiter::Parenthesis, args))) .collect(), ))) .chain(input) .collect(), ))), ); return result; } } result.extend(once(tt)); } result.extend(p!['!'].chain(into_tt(Group::new(Delimiter::Brace, input)))); result } }