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//! A procedural macro attribute for instrumenting functions with [`tracing`]. //! //! [`tracing`] is a framework for instrumenting Rust programs to collect //! structured, event-based diagnostic information. This crate provides the //! [`#[instrument]`][instrument] procedural macro attribute. //! //! Note that this macro is also re-exported by the main `tracing` crate. //! //! ## Usage //! //! First, add this to your `Cargo.toml`: //! //! ```toml //! [dependencies] //! tracing-attributes = "0.1.10" //! ``` //! //! *Compiler support: requires rustc 1.39+* //! //! The [`#[instrument]`][instrument] attribute can now be added to a function //! to automatically create and enter `tracing` [span] when that function is //! called. For example: //! //! ``` //! use tracing_attributes::instrument; //! //! #[instrument] //! pub fn my_function(my_arg: usize) { //! // ... //! } //! //! # fn main() {} //! ``` //! //! [`tracing`]: https://crates.io/crates/tracing //! [span]: https://docs.rs/tracing/latest/tracing/span/index.html //! [instrument]: attr.instrument.html #![doc(html_root_url = "https://docs.rs/tracing-attributes/0.1.10")] #![doc( html_logo_url = "https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo.svg", issue_tracker_base_url = "https://github.com/tokio-rs/tracing/issues/" )] #![warn( missing_debug_implementations, missing_docs, rust_2018_idioms, unreachable_pub, bad_style, const_err, dead_code, improper_ctypes, non_shorthand_field_patterns, no_mangle_generic_items, overflowing_literals, path_statements, patterns_in_fns_without_body, private_in_public, unconditional_recursion, unused, unused_allocation, unused_comparisons, unused_parens, while_true )] // TODO: once `tracing` bumps its MSRV to 1.42, remove this allow. #![allow(unused)] extern crate proc_macro; use std::collections::{HashMap, HashSet}; use std::iter; use proc_macro2::TokenStream; use quote::{quote, quote_spanned, ToTokens, TokenStreamExt as _}; use syn::ext::IdentExt as _; use syn::parse::{Parse, ParseStream}; use syn::{ punctuated::Punctuated, spanned::Spanned, AttributeArgs, Block, Expr, ExprCall, FieldPat, FnArg, Ident, Item, ItemFn, Lit, LitInt, LitStr, Meta, MetaList, MetaNameValue, NestedMeta, Pat, PatIdent, PatReference, PatStruct, PatTuple, PatTupleStruct, PatType, Path, Signature, Stmt, Token, }; /// Instruments a function to create and enter a `tracing` [span] every time /// the function is called. /// /// The generated span's name will be the name of the function. Any arguments /// to that function will be recorded as fields using [`fmt::Debug`]. To skip /// recording a function's or method's argument, pass the argument's name /// to the `skip` argument on the `#[instrument]` macro. For example, /// `skip` can be used when an argument to an instrumented function does /// not implement [`fmt::Debug`], or to exclude an argument with a verbose /// or costly Debug implementation. Note that: /// - multiple argument names can be passed to `skip`. /// - arguments passed to `skip` do _not_ need to implement `fmt::Debug`. /// /// You can also pass additional fields (key-value pairs with arbitrary data) /// to the generated span. This is achieved using the `fields` argument on the /// `#[instrument]` macro. You can use a string, integer or boolean literal as /// a value for each field. The name of the field must be a single valid Rust /// identifier, nested (dotted) field names are not supported. /// /// Note that overlap between the names of fields and (non-skipped) arguments /// will result in a compile error. /// /// # Examples /// Instrumenting a function: /// ``` /// # use tracing_attributes::instrument; /// #[instrument] /// pub fn my_function(my_arg: usize) { /// // This event will be recorded inside a span named `my_function` with the /// // field `my_arg`. /// tracing::info!("inside my_function!"); /// // ... /// } /// ``` /// Setting the level for the generated span: /// ``` /// # use tracing_attributes::instrument; /// #[instrument(level = "debug")] /// pub fn my_function() { /// // ... /// } /// ``` /// Overriding the generated span's name: /// ``` /// # use tracing_attributes::instrument; /// #[instrument(name = "my_name")] /// pub fn my_function() { /// // ... /// } /// ``` /// Overriding the generated span's target: /// ``` /// # use tracing_attributes::instrument; /// #[instrument(target = "my_target")] /// pub fn my_function() { /// // ... /// } /// ``` /// /// To skip recording an argument, pass the argument's name to the `skip`: /// /// ``` /// # use tracing_attributes::instrument; /// struct NonDebug; /// /// #[instrument(skip(non_debug))] /// fn my_function(arg: usize, non_debug: NonDebug) { /// // ... /// } /// ``` /// /// To add an additional context to the span, you can pass key-value pairs to `fields`: /// /// ``` /// # use tracing_attributes::instrument; /// #[instrument(fields(foo="bar", id=1, show=true))] /// fn my_function(arg: usize) { /// // ... /// } /// ``` /// /// If the function returns a `Result<T, E>` and `E` implements `std::fmt::Display`, you can add /// `err` to emit error events when the function returns `Err`: /// /// ``` /// # use tracing_attributes::instrument; /// #[instrument(err)] /// fn my_function(arg: usize) -> Result<(), std::io::Error> { /// Ok(()) /// } /// ``` /// /// If `tracing_futures` is specified as a dependency in `Cargo.toml`, /// `async fn`s may also be instrumented: /// /// ``` /// # use tracing_attributes::instrument; /// #[instrument] /// pub async fn my_function() -> Result<(), ()> { /// // ... /// # Ok(()) /// } /// ``` /// /// It also works with [async-trait](https://crates.io/crates/async-trait) /// (a crate that allows defining async functions in traits, /// something not currently possible in Rust), /// and hopefully most libraries that exhibit similar behaviors: /// /// ``` /// # use tracing::instrument; /// use async_trait::async_trait; /// /// #[async_trait] /// pub trait Foo { /// async fn foo(&self, arg: usize); /// } /// /// #[derive(Debug)] /// struct FooImpl(usize); /// /// #[async_trait] /// impl Foo for FooImpl { /// #[instrument(fields(value = self.0, tmp = std::any::type_name::<Self>()))] /// async fn foo(&self, arg: usize) {} /// } /// ``` /// /// An interesting note on this subject is that references to the `Self` /// type inside the `fields` argument are only allowed when the instrumented /// function is a method aka. the function receives `self` as an argument. /// For example, this *will not work* because it doesn't receive `self`: /// ```compile_fail /// # use tracing::instrument; /// use async_trait::async_trait; /// /// #[async_trait] /// pub trait Bar { /// async fn bar(); /// } /// /// #[derive(Debug)] /// struct BarImpl(usize); /// /// #[async_trait] /// impl Bar for BarImpl { /// #[instrument(fields(tmp = std::any::type_name::<Self>()))] /// async fn bar() {} /// } /// ``` /// Instead, you should manually rewrite any `Self` types as the type for /// which you implement the trait: `#[instrument(fields(tmp = std::any::type_name::<Bar>()))]`. /// /// [span]: https://docs.rs/tracing/latest/tracing/span/index.html /// [`tracing`]: https://github.com/tokio-rs/tracing /// [`fmt::Debug`]: https://doc.rust-lang.org/std/fmt/trait.Debug.html #[proc_macro_attribute] pub fn instrument( args: proc_macro::TokenStream, item: proc_macro::TokenStream, ) -> proc_macro::TokenStream { let input: ItemFn = syn::parse_macro_input!(item as ItemFn); let args = syn::parse_macro_input!(args as InstrumentArgs); let instrumented_function_name = input.sig.ident.to_string(); // check for async_trait-like patterns in the block and wrap the // internal function with Instrument instead of wrapping the // async_trait generated wrapper if let Some(internal_fun) = get_async_trait_info(&input.block, input.sig.asyncness.is_some()) { // let's rewrite some statements! let mut stmts: Vec<Stmt> = input.block.stmts.to_vec(); for stmt in &mut stmts { if let Stmt::Item(Item::Fn(fun)) = stmt { // instrument the function if we considered it as the one we truly want to trace if fun.sig.ident == internal_fun.name { *stmt = syn::parse2(gen_body( fun, args, instrumented_function_name, Some(internal_fun), )) .unwrap(); break; } } } let sig = &input.sig; let attrs = &input.attrs; quote!( #(#attrs) * #sig { #(#stmts) * } ) .into() } else { gen_body(&input, args, instrumented_function_name, None).into() } } fn gen_body( input: &ItemFn, mut args: InstrumentArgs, instrumented_function_name: String, async_trait_fun: Option<AsyncTraitInfo>, ) -> proc_macro2::TokenStream { // these are needed ahead of time, as ItemFn contains the function body _and_ // isn't representable inside a quote!/quote_spanned! macro // (Syn's ToTokens isn't implemented for ItemFn) let ItemFn { attrs, vis, block, sig, .. } = input; let Signature { output: return_type, inputs: params, unsafety, asyncness, constness, abi, ident, generics: syn::Generics { params: gen_params, where_clause, .. }, .. } = sig; let err = args.err; let warnings = args.warnings(); // generate the span's name let span_name = args // did the user override the span's name? .name .as_ref() .map(|name| quote!(#name)) .unwrap_or_else(|| quote!(#instrumented_function_name)); // generate this inside a closure, so we can return early on errors. let span = (|| { // Pull out the arguments-to-be-skipped first, so we can filter results // below. let param_names: Vec<(Ident, Ident)> = params .clone() .into_iter() .flat_map(|param| match param { FnArg::Typed(PatType { pat, .. }) => param_names(*pat), FnArg::Receiver(_) => Box::new(iter::once(Ident::new("self", param.span()))), }) // Little dance with new (user-exposed) names and old (internal) // names of identifiers. That way, you can do the following // even though async_trait rewrite "self" as "_self": // ``` // #[async_trait] // impl Foo for FooImpl { // #[instrument(skip(self))] // async fn foo(&self, v: usize) {} // } // ``` .map(|x| { // if we are inside a function generated by async-trait, we // should take care to rewrite "_self" as "self" for // 'user convenience' if async_trait_fun.is_some() && x == "_self" { (Ident::new("self", x.span()), x) } else { (x.clone(), x) } }) .collect(); for skip in &args.skips { if !param_names.iter().map(|(user, _)| user).any(|y| y == skip) { return quote_spanned! {skip.span()=> compile_error!("attempting to skip non-existent parameter") }; } } let level = args.level(); let target = args.target(); // filter out skipped fields let mut quoted_fields: Vec<_> = param_names .into_iter() .filter(|(param, _)| { if args.skips.contains(param) { return false; } // If any parameters have the same name as a custom field, skip // and allow them to be formatted by the custom field. if let Some(ref fields) = args.fields { fields.0.iter().all(|Field { ref name, .. }| { let first = name.first(); first != name.last() || !first.iter().any(|name| name == ¶m) }) } else { true } }) .map(|(user_name, real_name)| quote!(#user_name = tracing::field::debug(&#real_name))) .collect(); // when async-trait is in use, replace instances of "self" with "_self" inside the fields values if let (Some(ref async_trait_fun), Some(Fields(ref mut fields))) = (async_trait_fun, &mut args.fields) { let mut replacer = SelfReplacer { ty: async_trait_fun.self_type.clone(), }; for e in fields.iter_mut().filter_map(|f| f.value.as_mut()) { syn::visit_mut::visit_expr_mut(&mut replacer, e); } } let custom_fields = &args.fields; quote!(tracing::span!( target: #target, #level, #span_name, #(#quoted_fields,)* #custom_fields )) })(); // Generate the instrumented function body. // If the function is an `async fn`, this will wrap it in an async block, // which is `instrument`ed using `tracing-futures`. Otherwise, this will // enter the span and then perform the rest of the body. // If `err` is in args, instrument any resulting `Err`s. let body = if asyncness.is_some() { if err { quote_spanned! {block.span()=> let __tracing_attr_span = #span; tracing_futures::Instrument::instrument(async move { match async move { #block }.await { Ok(x) => Ok(x), Err(e) => { tracing::error!(error = %e); Err(e) } } }, __tracing_attr_span).await } } else { quote_spanned!(block.span()=> let __tracing_attr_span = #span; tracing_futures::Instrument::instrument( async move { #block }, __tracing_attr_span ) .await ) } } else if err { quote_spanned!(block.span()=> let __tracing_attr_span = #span; let __tracing_attr_guard = __tracing_attr_span.enter(); match { #block } { Ok(x) => Ok(x), Err(e) => { tracing::error!(error = %e); Err(e) } } ) } else { quote_spanned!(block.span()=> let __tracing_attr_span = #span; let __tracing_attr_guard = __tracing_attr_span.enter(); #block ) }; quote!( #(#attrs) * #vis #constness #unsafety #asyncness #abi fn #ident<#gen_params>(#params) #return_type #where_clause { #warnings #body } ) } #[derive(Default, Debug)] struct InstrumentArgs { level: Option<Level>, name: Option<LitStr>, target: Option<LitStr>, skips: HashSet<Ident>, fields: Option<Fields>, err: bool, /// Errors describing any unrecognized parse inputs that we skipped. parse_warnings: Vec<syn::Error>, } impl InstrumentArgs { fn level(&self) -> impl ToTokens { fn is_level(lit: &LitInt, expected: u64) -> bool { match lit.base10_parse::<u64>() { Ok(value) => value == expected, Err(_) => false, } } match &self.level { Some(Level::Str(ref lit)) if lit.value().eq_ignore_ascii_case("trace") => { quote!(tracing::Level::TRACE) } Some(Level::Str(ref lit)) if lit.value().eq_ignore_ascii_case("debug") => { quote!(tracing::Level::DEBUG) } Some(Level::Str(ref lit)) if lit.value().eq_ignore_ascii_case("info") => { quote!(tracing::Level::INFO) } Some(Level::Str(ref lit)) if lit.value().eq_ignore_ascii_case("warn") => { quote!(tracing::Level::WARN) } Some(Level::Str(ref lit)) if lit.value().eq_ignore_ascii_case("error") => { quote!(tracing::Level::ERROR) } Some(Level::Int(ref lit)) if is_level(lit, 1) => quote!(tracing::Level::TRACE), Some(Level::Int(ref lit)) if is_level(lit, 2) => quote!(tracing::Level::DEBUG), Some(Level::Int(ref lit)) if is_level(lit, 3) => quote!(tracing::Level::INFO), Some(Level::Int(ref lit)) if is_level(lit, 4) => quote!(tracing::Level::WARN), Some(Level::Int(ref lit)) if is_level(lit, 5) => quote!(tracing::Level::ERROR), Some(Level::Path(ref pat)) => quote!(#pat), Some(lit) => quote! { compile_error!( "unknown verbosity level, expected one of \"trace\", \ \"debug\", \"info\", \"warn\", or \"error\", or a number 1-5" ) }, None => quote!(tracing::Level::INFO), } } fn target(&self) -> impl ToTokens { if let Some(ref target) = self.target { quote!(#target) } else { quote!(module_path!()) } } /// Generate "deprecation" warnings for any unrecognized attribute inputs /// that we skipped. /// /// For backwards compatibility, we need to emit compiler warnings rather /// than errors for unrecognized inputs. Generating a fake deprecation is /// the only way to do this on stable Rust right now. fn warnings(&self) -> impl ToTokens { let warnings = self.parse_warnings.iter().map(|err| { let msg = format!("found unrecognized input, {}", err); let msg = LitStr::new(&msg, err.span()); // TODO(eliza): This is a bit of a hack, but it's just about the // only way to emit warnings from a proc macro on stable Rust. // Eventually, when the `proc_macro::Diagnostic` API stabilizes, we // should definitely use that instead. quote_spanned! {err.span()=> #[warn(deprecated)] { #[deprecated(since = "not actually deprecated", note = #msg)] const TRACING_INSTRUMENT_WARNING: () = (); let _ = TRACING_INSTRUMENT_WARNING; } } }); quote! { { #(#warnings)* } } } } impl Parse for InstrumentArgs { fn parse(input: ParseStream<'_>) -> syn::Result<Self> { let mut args = Self::default(); while !input.is_empty() { let lookahead = input.lookahead1(); if lookahead.peek(kw::name) { if args.name.is_some() { return Err(input.error("expected only a single `name` argument")); } let name = input.parse::<StrArg<kw::name>>()?.value; args.name = Some(name); } else if lookahead.peek(LitStr) { // XXX: apparently we support names as either named args with an // sign, _or_ as unnamed string literals. That's weird, but // changing it is apparently breaking. if args.name.is_some() { return Err(input.error("expected only a single `name` argument")); } args.name = Some(input.parse()?); } else if lookahead.peek(kw::target) { if args.target.is_some() { return Err(input.error("expected only a single `target` argument")); } let target = input.parse::<StrArg<kw::target>>()?.value; args.target = Some(target); } else if lookahead.peek(kw::level) { if args.level.is_some() { return Err(input.error("expected only a single `level` argument")); } args.level = Some(input.parse()?); } else if lookahead.peek(kw::skip) { if !args.skips.is_empty() { return Err(input.error("expected only a single `skip` argument")); } let Skips(skips) = input.parse()?; args.skips = skips; } else if lookahead.peek(kw::fields) { if args.fields.is_some() { return Err(input.error("expected only a single `fields` argument")); } args.fields = Some(input.parse()?); } else if lookahead.peek(kw::err) { let _ = input.parse::<kw::err>()?; args.err = true; } else if lookahead.peek(Token![,]) { let _ = input.parse::<Token![,]>()?; } else { // We found a token that we didn't expect! // We want to emit warnings for these, rather than errors, so // we'll add it to the list of unrecognized inputs we've seen so // far and keep going. args.parse_warnings.push(lookahead.error()); // Parse the unrecognized token tree to advance the parse // stream, and throw it away so we can keep parsing. let _ = input.parse::<proc_macro2::TokenTree>(); } } Ok(args) } } struct StrArg<T> { value: LitStr, _p: std::marker::PhantomData<T>, } impl<T: Parse> Parse for StrArg<T> { fn parse(input: ParseStream<'_>) -> syn::Result<Self> { let _ = input.parse::<T>()?; let _ = input.parse::<Token![=]>()?; let value = input.parse()?; Ok(Self { value, _p: std::marker::PhantomData, }) } } struct Skips(HashSet<Ident>); impl Parse for Skips { fn parse(input: ParseStream<'_>) -> syn::Result<Self> { let _ = input.parse::<kw::skip>(); let content; let _ = syn::parenthesized!(content in input); let names: Punctuated<Ident, Token![,]> = content.parse_terminated(Ident::parse_any)?; let mut skips = HashSet::new(); for name in names { if skips.contains(&name) { return Err(syn::Error::new( name.span(), "tried to skip the same field twice", )); } else { skips.insert(name); } } Ok(Self(skips)) } } #[derive(Debug)] struct Fields(Punctuated<Field, Token![,]>); #[derive(Debug)] struct Field { name: Punctuated<Ident, Token![.]>, value: Option<Expr>, kind: FieldKind, } #[derive(Debug, Eq, PartialEq)] enum FieldKind { Debug, Display, Value, } impl Parse for Fields { fn parse(input: ParseStream<'_>) -> syn::Result<Self> { let _ = input.parse::<kw::fields>(); let content; let _ = syn::parenthesized!(content in input); let fields: Punctuated<_, Token![,]> = content.parse_terminated(Field::parse)?; Ok(Self(fields)) } } impl ToTokens for Fields { fn to_tokens(&self, tokens: &mut TokenStream) { self.0.to_tokens(tokens) } } impl Parse for Field { fn parse(input: ParseStream<'_>) -> syn::Result<Self> { let mut kind = FieldKind::Value; if input.peek(Token![%]) { input.parse::<Token![%]>()?; kind = FieldKind::Display; } else if input.peek(Token![?]) { input.parse::<Token![?]>()?; kind = FieldKind::Debug; }; let name = Punctuated::parse_separated_nonempty_with(input, Ident::parse_any)?; let value = if input.peek(Token![=]) { input.parse::<Token![=]>()?; if input.peek(Token![%]) { input.parse::<Token![%]>()?; kind = FieldKind::Display; } else if input.peek(Token![?]) { input.parse::<Token![?]>()?; kind = FieldKind::Debug; }; Some(input.parse()?) } else { None }; Ok(Self { name, kind, value }) } } impl ToTokens for Field { fn to_tokens(&self, tokens: &mut TokenStream) { if let Some(ref value) = self.value { let name = &self.name; let kind = &self.kind; tokens.extend(quote! { #name = #kind#value }) } else if self.kind == FieldKind::Value { // XXX(eliza): I don't like that fields without values produce // empty fields rather than local variable shorthand...but, // we've released a version where field names without values in // `instrument` produce empty field values, so changing it now // is a breaking change. agh. let name = &self.name; tokens.extend(quote!(#name = tracing::field::Empty)) } else { self.kind.to_tokens(tokens); self.name.to_tokens(tokens); } } } impl ToTokens for FieldKind { fn to_tokens(&self, tokens: &mut TokenStream) { match self { FieldKind::Debug => tokens.extend(quote! { ? }), FieldKind::Display => tokens.extend(quote! { % }), _ => {} } } } #[derive(Debug)] enum Level { Str(LitStr), Int(LitInt), Path(Path), } impl Parse for Level { fn parse(input: ParseStream<'_>) -> syn::Result<Self> { let _ = input.parse::<kw::level>()?; let _ = input.parse::<Token![=]>()?; let lookahead = input.lookahead1(); if lookahead.peek(LitStr) { Ok(Self::Str(input.parse()?)) } else if lookahead.peek(LitInt) { Ok(Self::Int(input.parse()?)) } else if lookahead.peek(Ident) { Ok(Self::Path(input.parse()?)) } else { Err(lookahead.error()) } } } fn param_names(pat: Pat) -> Box<dyn Iterator<Item = Ident>> { match pat { Pat::Ident(PatIdent { ident, .. }) => Box::new(iter::once(ident)), Pat::Reference(PatReference { pat, .. }) => param_names(*pat), Pat::Struct(PatStruct { fields, .. }) => Box::new( fields .into_iter() .flat_map(|FieldPat { pat, .. }| param_names(*pat)), ), Pat::Tuple(PatTuple { elems, .. }) => Box::new(elems.into_iter().flat_map(param_names)), Pat::TupleStruct(PatTupleStruct { pat: PatTuple { elems, .. }, .. }) => Box::new(elems.into_iter().flat_map(param_names)), // The above *should* cover all cases of irrefutable patterns, // but we purposefully don't do any funny business here // (such as panicking) because that would obscure rustc's // much more informative error message. _ => Box::new(iter::empty()), } } mod kw { syn::custom_keyword!(fields); syn::custom_keyword!(skip); syn::custom_keyword!(level); syn::custom_keyword!(target); syn::custom_keyword!(name); syn::custom_keyword!(err); } // Get the AST of the inner function we need to hook, if it was generated // by async-trait. // When we are given a function annotated by async-trait, that function // is only a placeholder that returns a pinned future containing the // user logic, and it is that pinned future that needs to be instrumented. // Were we to instrument its parent, we would only collect information // regarding the allocation of that future, and not its own span of execution. // So we inspect the block of the function to find if it matches the pattern // `async fn foo<...>(...) {...}; Box::pin(foo<...>(...))` and we return // the name `foo` if that is the case. 'gen_body' will then be able // to use that information to instrument the proper function. // (this follows the approach suggested in // https://github.com/dtolnay/async-trait/issues/45#issuecomment-571245673) fn get_async_trait_function(block: &Block, block_is_async: bool) -> Option<&ItemFn> { // are we in an async context? If yes, this isn't a async_trait-like pattern if block_is_async { return None; } // list of async functions declared inside the block let mut inside_funs = Vec::new(); // last expression declared in the block (it determines the return // value of the block, so that if we are working on a function // whose `trait` or `impl` declaration is annotated by async_trait, // this is quite likely the point where the future is pinned) let mut last_expr = None; // obtain the list of direct internal functions and the last // expression of the block for stmt in &block.stmts { if let Stmt::Item(Item::Fn(fun)) = &stmt { // is the function declared as async? If so, this is a good // candidate, let's keep it in hand if fun.sig.asyncness.is_some() { inside_funs.push(fun); } } else if let Stmt::Expr(e) = &stmt { last_expr = Some(e); } } // let's play with (too much) pattern matching // is the last expression a function call? if let Some(Expr::Call(ExprCall { func: outside_func, args: outside_args, .. })) = last_expr { if let Expr::Path(path) = outside_func.as_ref() { // is it a call to `Box::pin()`? if "Box::pin" == path_to_string(&path.path) { // does it takes at least an argument? (if it doesn't, // it's not gonna compile anyway, but that's no reason // to (try to) perform an out of bounds access) if outside_args.is_empty() { return None; } // is the argument to Box::pin a function call itself? if let Expr::Call(ExprCall { func, args, .. }) = &outside_args[0] { if let Expr::Path(inside_path) = func.as_ref() { // "stringify" the path of the function called let func_name = path_to_string(&inside_path.path); // is this function directly defined insided the current block? for fun in inside_funs { if fun.sig.ident == func_name { // we must hook this function now return Some(fun); } } } } } } } None } struct AsyncTraitInfo { name: String, self_type: Option<syn::TypePath>, } // Return the informations necessary to process a function annotated with async-trait. fn get_async_trait_info(block: &Block, block_is_async: bool) -> Option<AsyncTraitInfo> { let fun = get_async_trait_function(block, block_is_async)?; // if "_self" is present as an argument, we store its type to be able to rewrite "Self" (the // parameter type) with the type of "_self" let self_type = fun .sig .inputs .iter() .map(|arg| { if let FnArg::Typed(ty) = arg { if let Pat::Ident(PatIdent { ident, .. }) = &*ty.pat { if ident == "_self" { let mut ty = &*ty.ty; // extract the inner type if the argument is "&self" or "&mut self" if let syn::Type::Reference(syn::TypeReference { elem, .. }) = ty { ty = &*elem; } if let syn::Type::Path(tp) = ty { return Some(tp.clone()); } } } } None }) .next() .flatten(); Some(AsyncTraitInfo { name: fun.sig.ident.to_string(), self_type, }) } // Return a path as a String fn path_to_string(path: &Path) -> String { use std::fmt::Write; // some heuristic to prevent too many allocations let mut res = String::with_capacity(path.segments.len() * 5); for i in 0..path.segments.len() { write!(&mut res, "{}", path.segments[i].ident) .expect("writing to a String should never fail"); if i < path.segments.len() - 1 { res.push_str("::"); } } res } // A visitor struct replacing the "self" and "Self" tokens in user-supplied fields expressions when // the function is generated by async-trait. struct SelfReplacer { ty: Option<syn::TypePath>, } impl syn::visit_mut::VisitMut for SelfReplacer { fn visit_ident_mut(&mut self, id: &mut Ident) { if id == "self" { *id = Ident::new("_self", id.span()) } } fn visit_type_mut(&mut self, ty: &mut syn::Type) { if let syn::Type::Path(syn::TypePath { ref mut path, .. }) = ty { if path_to_string(path) == "Self" { if let Some(ref true_type) = self.ty { *path = true_type.path.clone(); } } } } }