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//! //! # Maybe-Async Procedure Macro //! //! **Why bother writing similar code twice for blocking and async code?** //! //! [![Build Status](https://github.com/fMeow/maybe-async-rs/workflows/CI%20%28Linux%29/badge.svg?branch=master)](https://github.com/fMeow/maybe-async-rs/actions) //! [![MIT licensed](https://img.shields.io/badge/license-MIT-blue.svg)](./LICENSE) //! [![Latest Version](https://img.shields.io/crates/v/maybe-async.svg)](https://crates.io/crates/maybe-async) //! [![maybe-async](https://docs.rs/maybe-async/badge.svg)](https://docs.rs/maybe-async) //! //! When implementing both sync and async versions of API in a crate, most API //! of the two version are almost the same except for some async/await keyword. //! //! `maybe-async` help unifying async and sync implementation. //! Write async code with normal `async`, `await`, and let `maybe_async` handles //! those `async` and `await` when you need a synchronized code. Switch between //! sync and async by toggling `is_sync` feature gate. A handy macro to //! unify unit test code is also provided. //! //! //! //! ## Key features //! //! `maybe-async` offers three attribute macros: `maybe_async`, `must_be_sync` //! and `must_be_async`. //! //! These macros can be applied to trait item, trait impl, function and struct //! impl. //! //! - `must_be_async` //! //! **Keep async**. Add `async_trait` attribute macro for trait declaration //! or implementation to bring async fn support in traits. //! //! To avoid having "Send" and "Sync" bounds placed on the async trait //! methods, invoke the maybe_async macro as #[must_be_async(?Send)]. //! //! - `must_be_sync` //! //! **Convert to sync code**. Convert the async code into sync code by //! removing all `async move`, `async` and `await` keyword //! //! - `maybe_async` //! //! Offers a unified feature gate to provide sync and async conversion on //! demand by feature gate `is_sync`, with **async first** policy. //! //! Want to keep async code? add `maybe_async` in dependencies with default //! features, which means `maybe_async` is the same as `must_be_async`: //! //! ```toml //! [dependencies] //! maybe_async = "0.1" //! ``` //! //! Wanna convert async code to sync? Add `maybe_async` to dependencies with //! an `is_sync` feature gate. In this way, `maybe_async` is the same as //! `must_be_sync`: //! //! ```toml //! [dependencies] //! maybe_async = { version = "0.1", features = ["is_sync"] } //! ``` //! //! Not all async traits need futures that are `dyn Future + Send`. //! To avoid having "Send" and "Sync" bounds placed on the async trait //! methods, invoke the maybe_async macro as #[maybe_async(?Send)] on both //! the trait and the impl blocks. //! //! //! - `sync_impl` //! //! Although most of the API are almost the same, there definitely come to a //! point when the async and sync version should differ greatly. For //! example, a MongoDB client may use the same API for async and sync //! verison, but the code to actually send reqeust are quite different. //! //! Here, we can use `sync_impl` to mark a synchronous implementation, and a //! sync implementation shoule disappear when we want async version. //! //! - `async_impl` //! //! An async implementation shoule simply disappear when we want sync //! version. //! //! To avoid having "Send" and "Sync" bounds placed on the async trait //! methods, invoke the maybe_async macro as #[async_impl(?Send)]. //! //! - `test` //! //! Handy macro to unify async and sync unit test code. //! //! You can specify the condition to compile to sync test code //! and also the conditions to compile to async test code with given test //! macro, e.x. `tokio::test`, `async_std::test` and etc. When only sync //! condition is specified,the test code only compiles when sync condition //! is met. //! //! ```rust //! # #[maybe_async::maybe_async] //! # async fn async_fn() -> bool { //! # true //! # } //! //! #[maybe_async::test( //! feature="is_sync", //! async(all(not(feature="is_sync"), feature="async_std"), async_std::test), //! async(all(not(feature="is_sync"), feature="tokio"), tokio::test) //! )] //! async fn test_async_fn() { //! let res = async_fn().await; //! assert_eq!(res, true); //! } //! ``` //! //! ## Motivation //! //! //! The async/await language feature alters the async world of rust. //! Comparing with the map/and_then style, now the async code really resembles //! sync version code. //! //! In many crates, the async and sync version of crates shares the same API, //! but the minor difference that all async code must be awaited prevent the //! unification of async and sync code. In other words, an async and sync //! implementation must be written repectively. //! //! ## Examples //! //! ### rust client for services //! //! When implementing rust client for any services, like awz3. The higher level //! API of async and sync version is almost the same, such as creating or //! deleting a bucket, retrieving an object and etc. //! //! Here is a proof of concept that `maybe_async` can actually free us from //! writing almost the same code for sync and async. //! //! ```rust //! type Response = String; //! type Url = &'static str; //! type Method = String; //! //! /// InnerClient are used to actually send request, //! /// which differ a lot between sync and async. //! #[maybe_async::maybe_async] //! trait InnerClient { //! async fn request(method: Method, url: Url, data: String) -> Response; //! #[inline] //! async fn post(url: Url, data: String) -> Response { //! Self::request(String::from("post"), url, data).await //! } //! #[inline] //! async fn delete(url: Url, data: String) -> Response { //! Self::request(String::from("delete"), url, data).await //! } //! } //! //! /// The higher level API for end user. //! pub struct ServiceClient; //! //! /// Code of upstream API are almost the same for sync and async, //! /// except for async/await keyword. //! impl ServiceClient { //! #[maybe_async::maybe_async] //! async fn create_bucket(name: String) -> Response { //! Self::post("http://correct_url4create", String::from("my_bucket")).await //! } //! #[maybe_async::maybe_async] //! async fn delete_bucket(name: String) -> Response { //! Self::delete("http://correct_url4delete", String::from("my_bucket")).await //! } //! // and another thousands of functions that interact with service side //! } //! //! /// Synchronous implementation, will be deleted when we want an async implementation. //! /// Else the compiler will complain that *request is defined multiple times* and blabla. //! #[maybe_async::sync_impl] //! impl InnerClient for ServiceClient { //! fn request(method: Method, url: Url, data: String) -> Response { //! // your implementation for sync, like use //! // `reqwest::blocking` to send request //! String::from("pretend we have a response") //! } //! } //! //! /// Asynchronous implementation, will be deleted when we want a sync implementation //! #[maybe_async::async_impl] //! impl InnerClient for ServiceClient { //! async fn request(method: Method, url: Url, data: String) -> Response { //! // your implementation for async, like use `reqwest::client` //! // or `async_std` to send request //! String::from("pretend we have a response") //! } //! } //! ``` //! //! With the code above, we can toggle between a sync AWZ3 client and async one //! by `is_sync` feature gate when we add `maybe-async` to dependency. //! //! ### Example for maybe_async conversion //! //! ```rust //! #[maybe_async::maybe_async(?Send)] //! trait A { //! async fn async_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! fn sync_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! } //! //! struct Foo; //! //! #[maybe_async::maybe_async(?Send)] //! impl A for Foo { //! async fn async_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! fn sync_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! } //! //! #[maybe_async::maybe_async] //! async fn maybe_async_fn() -> Result<(), ()> { //! let a = Foo::async_fn_name().await?; //! //! let b = Foo::sync_fn_name()?; //! Ok(()) //! } //! ``` //! //! When `maybe-async` feature gate `is_sync` is **NOT** set, the generated code //! is async code: //! //! ```rust //! # use async_trait::async_trait; //! #[async_trait(?Send)] //! trait A { //! async fn maybe_async_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! fn sync_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! } //! //! struct Foo; //! //! #[async_trait(?Send)] //! impl A for Foo { //! async fn maybe_async_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! fn sync_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! } //! //! async fn maybe_async_fn() -> Result<(), ()> { //! let a = Foo::maybe_async_fn_name().await?; //! let b = Foo::sync_fn_name()?; //! Ok(()) //! } //! ``` //! //! When `maybe-async` feature gate `is_sync` is set, all async keyword is //! ignored and yields a sync version code: //! //! ```rust //! trait A { //! fn maybe_async_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! fn sync_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! } //! //! struct Foo; //! //! impl A for Foo { //! fn maybe_async_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! fn sync_fn_name() -> Result<(), ()> { //! Ok(()) //! } //! } //! //! fn maybe_async_fn() -> Result<(), ()> { //! let a = Foo::maybe_async_fn_name()?; //! let b = Foo::sync_fn_name()?; //! Ok(()) //! } //! ``` //! //! # License //! MIT extern crate proc_macro; use proc_macro::TokenStream; use proc_macro2::{Span, TokenStream as TokenStream2}; use syn::{ parse_macro_input, spanned::Spanned, AttributeArgs, ImplItem, Lit, Meta, NestedMeta, TraitItem, }; use quote::quote; use crate::{parse::Item, visit::AsyncAwaitRemoval}; mod parse; mod visit; fn convert_async(input: &mut Item, send: bool) -> TokenStream2 { if send { match input { Item::Impl(item) => quote!(#[async_trait::async_trait]#item), Item::Trait(item) => quote!(#[async_trait::async_trait]#item), Item::Fn(item) => quote!(#item), } } else { match input { Item::Impl(item) => quote!(#[async_trait::async_trait(?Send)]#item), Item::Trait(item) => quote!(#[async_trait::async_trait(?Send)]#item), Item::Fn(item) => quote!(#item), } } .into() } fn convert_sync(input: &mut Item) -> TokenStream2 { match input { Item::Impl(item) => { for inner in &mut item.items { if let ImplItem::Method(ref mut method) = inner { if method.sig.asyncness.is_some() { method.sig.asyncness = None; } } } AsyncAwaitRemoval.remove_async_await(quote!(#item)) } Item::Trait(item) => { for inner in &mut item.items { if let TraitItem::Method(ref mut method) = inner { if method.sig.asyncness.is_some() { method.sig.asyncness = None; } } } AsyncAwaitRemoval.remove_async_await(quote!(#item)) } Item::Fn(item) => { if item.sig.asyncness.is_some() { item.sig.asyncness = None; } AsyncAwaitRemoval.remove_async_await(quote!(#item)) } } .into() } /// maybe_async attribute macro /// /// Can be applied to trait item, trait impl, functions and struct impls. #[proc_macro_attribute] pub fn maybe_async(args: TokenStream, input: TokenStream) -> TokenStream { let send = match args.to_string().replace(" ", "").as_str() { "" | "Send" => true, "?Send" => false, _ => { return syn::Error::new(Span::call_site(), "Only accepts `Send` or `?Send`") .to_compile_error() .into(); } }; let mut item = parse_macro_input!(input as Item); let token = if cfg!(feature = "is_sync") { convert_sync(&mut item) } else { convert_async(&mut item, send) }; token.into() } /// convert marked async code to async code with `async-trait` #[proc_macro_attribute] pub fn must_be_async(args: TokenStream, input: TokenStream) -> TokenStream { let send = match args.to_string().replace(" ", "").as_str() { "" | "Send" => true, "?Send" => false, _ => { return syn::Error::new(Span::call_site(), "Only accepts `Send` or `?Send`") .to_compile_error() .into(); } }; let mut item = parse_macro_input!(input as Item); convert_async(&mut item, send).into() } /// convert marked async code to sync code #[proc_macro_attribute] pub fn must_be_sync(_args: TokenStream, input: TokenStream) -> TokenStream { let mut item = parse_macro_input!(input as Item); convert_sync(&mut item).into() } /// mark sync implementation /// /// only compiled when `is_sync` feature gate is set. /// When `is_sync` is not set, marked code is removed. #[proc_macro_attribute] pub fn sync_impl(_args: TokenStream, input: TokenStream) -> TokenStream { let input = TokenStream2::from(input); let token = if cfg!(feature = "is_sync") { quote!(#input) } else { quote!() }; token.into() } /// mark async implementation /// /// only compiled when `is_sync` feature gate is not set. /// When `is_sync` is set, marked code is removed. #[proc_macro_attribute] pub fn async_impl(args: TokenStream, _input: TokenStream) -> TokenStream { let send = match args.to_string().replace(" ", "").as_str() { "" | "Send" => true, "?Send" => false, _ => { return syn::Error::new(Span::call_site(), "Only accepts `Send` or `?Send`") .to_compile_error() .into(); } }; let token = if cfg!(feature = "is_sync") { quote!() } else { let mut item = parse_macro_input!(_input as Item); convert_async(&mut item, send) }; token.into() } macro_rules! match_nested_meta_to_str_lit { ($t:expr) => { match $t { NestedMeta::Lit(lit) => { match lit { Lit::Str(s) => { s.value().parse::<TokenStream2>().unwrap() } _ => { return syn::Error::new(lit.span(), "expected meta or string literal").to_compile_error().into(); } } } NestedMeta::Meta(meta) => quote!(#meta) } }; } /// Handy macro to unify test code of sync and async code /// /// Since the API of both sync and async code are the same, /// with only difference that async functions must be awaited. /// So it's tedious to write unit sync and async respectively. /// /// This macro helps unify the sync and async unit test code. /// Pass the condition to treat test code as sync as the first /// argument. And specify the condition when to treat test code /// as async and the lib to run async test, e.x. `async-std::test`, /// `tokio::test`, or any valid attribute macro. /// /// **ATTENTION**: do not write await inside a assert macro /// /// - Examples /// /// ```rust /// #[maybe_async::maybe_async] /// async fn async_fn() -> bool { /// true /// } /// /// #[maybe_async::test( /// // when to treat the test code as sync version /// feature="is_sync", /// // when to run async test /// async(all(not(feature="is_sync"), feature="async_std"), async_std::test), /// // you can specify multiple conditions for different async runtime /// async(all(not(feature="is_sync"), feature="tokio"), tokio::test) /// )] /// async fn test_async_fn() { /// let res = async_fn().await; /// assert_eq!(res, true); /// } /// /// // Only run test in sync version /// #[maybe_async::test(feature = "is_sync")] /// async fn test_sync_fn() { /// let res = async_fn().await; /// assert_eq!(res, true); /// } /// ``` /// /// The above code is transcripted to the following code: /// /// ```rust /// # use maybe_async::{must_be_async, must_be_sync, sync_impl}; /// # #[maybe_async::maybe_async] /// # async fn async_fn() -> bool { true } /// /// // convert to sync version when sync condition is met, keep in async version when corresponding /// // condition is met /// #[cfg_attr(feature = "is_sync", must_be_sync, test)] /// #[cfg_attr( /// all(not(feature = "is_sync"), feature = "async_std"), /// must_be_async, /// async_std::test /// )] /// #[cfg_attr( /// all(not(feature = "is_sync"), feature = "tokio"), /// must_be_async, /// tokio::test /// )] /// async fn test_async_fn() { /// let res = async_fn().await; /// assert_eq!(res, true); /// } /// /// // force converted to sync function, and only compile on sync condition /// #[cfg(feature = "is_sync")] /// #[test] /// fn test_sync_fn() { /// let res = async_fn(); /// assert_eq!(res, true); /// } /// ``` #[proc_macro_attribute] pub fn test(args: TokenStream, input: TokenStream) -> TokenStream { let attr_args = parse_macro_input!(args as AttributeArgs); let input = TokenStream2::from(input); if attr_args.len() < 1 { return syn::Error::new( Span::call_site(), "Must not be empty, at least specify the condition for sync code", ) .to_compile_error() .into(); } // The first attributes indicates sync condition let sync_cond = match_nested_meta_to_str_lit!(attr_args.first().unwrap()); let mut ts = if attr_args.len() == 1 { quote!( #[cfg(#sync_cond)] #[cfg_attr(#sync_cond, maybe_async::must_be_sync, test)] ) } else { quote!(#[cfg_attr(#sync_cond, maybe_async::must_be_sync, test)]) }; // The rest attributes indicates async condition and async test macro // only accepts in the forms of `async(cond, test_macro)`, but `cond` and // `test_macro` can be either meta attributes or string literal let mut async_token = Vec::new(); for async_meta in attr_args.into_iter().skip(1) { match async_meta { NestedMeta::Meta(meta) => match meta { Meta::List(list) => { let name = list.path.segments[0].ident.to_string(); if name.ne("async") { return syn::Error::new( list.path.span(), format!("Unknown path: `{}`, must be `async`", name), ) .to_compile_error() .into(); } if list.nested.len() == 2 { let async_cond = match_nested_meta_to_str_lit!(list.nested.first().unwrap()); let async_test = match_nested_meta_to_str_lit!(list.nested.last().unwrap()); let attr = quote!( #[cfg_attr(#async_cond, maybe_async::must_be_async, #async_test)] ); async_token.push(attr); } else { let msg = format!( "Must pass two metas or string literals like `async(condition, \ async_test_macro)`, you passed {} metas.", list.nested.len() ); return syn::Error::new(list.span(), msg).to_compile_error().into(); } } _ => { return syn::Error::new( meta.span(), "Must be list of metas like: `async(condition, async_test_macro)`", ) .to_compile_error() .into(); } }, NestedMeta::Lit(lit) => { return syn::Error::new( lit.span(), "Must be list of metas like: `async(condition, async_test_macro)`", ) .to_compile_error() .into(); } }; } async_token.into_iter().for_each(|t| ts.extend(t)); ts.extend(quote!( #input )); ts.into() }