1use std::iter;
2
3use proc_macro2::TokenStream;
4use quote::{quote, quote_spanned, ToTokens};
5use syn::visit_mut::VisitMut;
6use syn::{
7 punctuated::Punctuated, spanned::Spanned, Block, Expr, ExprAsync, ExprCall, FieldPat, FnArg,
8 Ident, Item, ItemFn, Pat, PatIdent, PatReference, PatStruct, PatTuple, PatTupleStruct, PatType,
9 Path, ReturnType, Signature, Stmt, Token, Type, TypePath,
10};
11
12use crate::{
13 attr::{Field, Fields, FormatMode, InstrumentArgs, Level},
14 MaybeItemFn, MaybeItemFnRef,
15};
16
17/// Given an existing function, generate an instrumented version of that function
18pub(crate) fn gen_function<'a, B: ToTokens + 'a>(
19 input: MaybeItemFnRef<'a, B>,
20 args: InstrumentArgs,
21 instrumented_function_name: &str,
22 self_type: Option<&TypePath>,
23) -> proc_macro2::TokenStream {
24 // these are needed ahead of time, as ItemFn contains the function body _and_
25 // isn't representable inside a quote!/quote_spanned! macro
26 // (Syn's ToTokens isn't implemented for ItemFn)
27 let MaybeItemFnRef {
28 outer_attrs,
29 inner_attrs,
30 vis,
31 sig,
32 block,
33 } = input;
34
35 let Signature {
36 output,
37 inputs: params,
38 unsafety,
39 asyncness,
40 constness,
41 abi,
42 ident,
43 generics:
44 syn::Generics {
45 params: gen_params,
46 where_clause,
47 ..
48 },
49 ..
50 } = sig;
51
52 let warnings = args.warnings();
53
54 let (return_type, return_span) = if let ReturnType::Type(_, return_type) = &output {
55 (erase_impl_trait(return_type), return_type.span())
56 } else {
57 // Point at function name if we don't have an explicit return type
58 (syn::parse_quote! { () }, ident.span())
59 };
60 // Install a fake return statement as the first thing in the function
61 // body, so that we eagerly infer that the return type is what we
62 // declared in the async fn signature.
63 // The `#[allow(..)]` is given because the return statement is
64 // unreachable, but does affect inference, so it needs to be written
65 // exactly that way for it to do its magic.
66 let fake_return_edge = quote_spanned! {return_span=>
67 #[allow(
68 unknown_lints, unreachable_code, clippy::diverging_sub_expression,
69 clippy::let_unit_value, clippy::unreachable, clippy::let_with_type_underscore,
70 clippy::empty_loop
71 )]
72 if false {
73 let __tracing_attr_fake_return: #return_type = loop {};
74 return __tracing_attr_fake_return;
75 }
76 };
77 let block = quote! {
78 {
79 #fake_return_edge
80 #block
81 }
82 };
83
84 let body = gen_block(
85 &block,
86 params,
87 asyncness.is_some(),
88 args,
89 instrumented_function_name,
90 self_type,
91 );
92
93 quote!(
94 #(#outer_attrs) *
95 #vis #constness #unsafety #asyncness #abi fn #ident<#gen_params>(#params) #output
96 #where_clause
97 {
98 #(#inner_attrs) *
99 #warnings
100 #body
101 }
102 )
103}
104
105/// Instrument a block
106fn gen_block<B: ToTokens>(
107 block: &B,
108 params: &Punctuated<FnArg, Token![,]>,
109 async_context: bool,
110 mut args: InstrumentArgs,
111 instrumented_function_name: &str,
112 self_type: Option<&TypePath>,
113) -> proc_macro2::TokenStream {
114 // generate the span's name
115 let span_name = args
116 // did the user override the span's name?
117 .name
118 .as_ref()
119 .map(|name| quote!(#name))
120 .unwrap_or_else(|| quote!(#instrumented_function_name));
121
122 let args_level = args.level();
123 let level = args_level.clone();
124
125 let follows_from = args.follows_from.iter();
126 let follows_from = quote! {
127 #(for cause in #follows_from {
128 __tracing_attr_span.follows_from(cause);
129 })*
130 };
131
132 // generate this inside a closure, so we can return early on errors.
133 let span = (|| {
134 // Pull out the arguments-to-be-skipped first, so we can filter results
135 // below.
136 let param_names: Vec<(Ident, (Ident, RecordType))> = params
137 .clone()
138 .into_iter()
139 .flat_map(|param| match param {
140 FnArg::Typed(PatType { pat, ty, .. }) => {
141 param_names(*pat, RecordType::parse_from_ty(&ty))
142 }
143 FnArg::Receiver(_) => Box::new(iter::once((
144 Ident::new("self", param.span()),
145 RecordType::Debug,
146 ))),
147 })
148 // Little dance with new (user-exposed) names and old (internal)
149 // names of identifiers. That way, we could do the following
150 // even though async_trait (<=0.1.43) rewrites "self" as "_self":
151 // ```
152 // #[async_trait]
153 // impl Foo for FooImpl {
154 // #[instrument(skip(self))]
155 // async fn foo(&self, v: usize) {}
156 // }
157 // ```
158 .map(|(x, record_type)| {
159 // if we are inside a function generated by async-trait <=0.1.43, we need to
160 // take care to rewrite "_self" as "self" for 'user convenience'
161 if self_type.is_some() && x == "_self" {
162 (Ident::new("self", x.span()), (x, record_type))
163 } else {
164 (x.clone(), (x, record_type))
165 }
166 })
167 .collect();
168
169 for skip in &args.skips {
170 if !param_names.iter().map(|(user, _)| user).any(|y| y == skip) {
171 return quote_spanned! {skip.span()=>
172 compile_error!("attempting to skip non-existent parameter")
173 };
174 }
175 }
176
177 let target = args.target();
178
179 let parent = args.parent.iter();
180
181 // filter out skipped fields
182 let quoted_fields: Vec<_> = param_names
183 .iter()
184 .filter(|(param, _)| {
185 if args.skip_all || args.skips.contains(param) {
186 return false;
187 }
188
189 // If any parameters have the same name as a custom field, skip
190 // and allow them to be formatted by the custom field.
191 if let Some(ref fields) = args.fields {
192 fields.0.iter().all(|Field { ref name, .. }| {
193 let first = name.first();
194 first != name.last() || !first.iter().any(|name| name == &param)
195 })
196 } else {
197 true
198 }
199 })
200 .map(|(user_name, (real_name, record_type))| match record_type {
201 RecordType::Value => quote!(#user_name = #real_name),
202 RecordType::Debug => quote!(#user_name = tracing::field::debug(&#real_name)),
203 })
204 .collect();
205
206 // replace every use of a variable with its original name
207 if let Some(Fields(ref mut fields)) = args.fields {
208 let mut replacer = IdentAndTypesRenamer {
209 idents: param_names.into_iter().map(|(a, (b, _))| (a, b)).collect(),
210 types: Vec::new(),
211 };
212
213 // when async-trait <=0.1.43 is in use, replace instances
214 // of the "Self" type inside the fields values
215 if let Some(self_type) = self_type {
216 replacer.types.push(("Self", self_type.clone()));
217 }
218
219 for e in fields.iter_mut().filter_map(|f| f.value.as_mut()) {
220 syn::visit_mut::visit_expr_mut(&mut replacer, e);
221 }
222 }
223
224 let custom_fields = &args.fields;
225
226 quote!(tracing::span!(
227 target: #target,
228 #(parent: #parent,)*
229 #level,
230 #span_name,
231 #(#quoted_fields,)*
232 #custom_fields
233
234 ))
235 })();
236
237 let target = args.target();
238
239 let err_event = match args.err_args {
240 Some(event_args) => {
241 let level_tokens = event_args.level(Level::Error);
242 match event_args.mode {
243 FormatMode::Default | FormatMode::Display => Some(quote!(
244 tracing::event!(target: #target, #level_tokens, error = %e)
245 )),
246 FormatMode::Debug => Some(quote!(
247 tracing::event!(target: #target, #level_tokens, error = ?e)
248 )),
249 }
250 }
251 _ => None,
252 };
253
254 let ret_event = match args.ret_args {
255 Some(event_args) => {
256 let level_tokens = event_args.level(args_level);
257 match event_args.mode {
258 FormatMode::Display => Some(quote!(
259 tracing::event!(target: #target, #level_tokens, return = %x)
260 )),
261 FormatMode::Default | FormatMode::Debug => Some(quote!(
262 tracing::event!(target: #target, #level_tokens, return = ?x)
263 )),
264 }
265 }
266 _ => None,
267 };
268
269 // Generate the instrumented function body.
270 // If the function is an `async fn`, this will wrap it in an async block,
271 // which is `instrument`ed using `tracing-futures`. Otherwise, this will
272 // enter the span and then perform the rest of the body.
273 // If `err` is in args, instrument any resulting `Err`s.
274 // If `ret` is in args, instrument any resulting `Ok`s when the function
275 // returns `Result`s, otherwise instrument any resulting values.
276 if async_context {
277 let mk_fut = match (err_event, ret_event) {
278 (Some(err_event), Some(ret_event)) => quote_spanned!(block.span()=>
279 async move {
280 match async move #block.await {
281 #[allow(clippy::unit_arg)]
282 Ok(x) => {
283 #ret_event;
284 Ok(x)
285 },
286 Err(e) => {
287 #err_event;
288 Err(e)
289 }
290 }
291 }
292 ),
293 (Some(err_event), None) => quote_spanned!(block.span()=>
294 async move {
295 match async move #block.await {
296 #[allow(clippy::unit_arg)]
297 Ok(x) => Ok(x),
298 Err(e) => {
299 #err_event;
300 Err(e)
301 }
302 }
303 }
304 ),
305 (None, Some(ret_event)) => quote_spanned!(block.span()=>
306 async move {
307 let x = async move #block.await;
308 #ret_event;
309 x
310 }
311 ),
312 (None, None) => quote_spanned!(block.span()=>
313 async move #block
314 ),
315 };
316
317 return quote!(
318 let __tracing_attr_span = #span;
319 let __tracing_instrument_future = #mk_fut;
320 if !__tracing_attr_span.is_disabled() {
321 #follows_from
322 tracing::Instrument::instrument(
323 __tracing_instrument_future,
324 __tracing_attr_span
325 )
326 .await
327 } else {
328 __tracing_instrument_future.await
329 }
330 );
331 }
332
333 let span = quote!(
334 // These variables are left uninitialized and initialized only
335 // if the tracing level is statically enabled at this point.
336 // While the tracing level is also checked at span creation
337 // time, that will still create a dummy span, and a dummy guard
338 // and drop the dummy guard later. By lazily initializing these
339 // variables, Rust will generate a drop flag for them and thus
340 // only drop the guard if it was created. This creates code that
341 // is very straightforward for LLVM to optimize out if the tracing
342 // level is statically disabled, while not causing any performance
343 // regression in case the level is enabled.
344 let __tracing_attr_span;
345 let __tracing_attr_guard;
346 if tracing::level_enabled!(#level) || tracing::if_log_enabled!(#level, {true} else {false}) {
347 __tracing_attr_span = #span;
348 #follows_from
349 __tracing_attr_guard = __tracing_attr_span.enter();
350 }
351 );
352
353 match (err_event, ret_event) {
354 (Some(err_event), Some(ret_event)) => quote_spanned! {block.span()=>
355 #span
356 #[allow(clippy::redundant_closure_call)]
357 match (move || #block)() {
358 #[allow(clippy::unit_arg)]
359 Ok(x) => {
360 #ret_event;
361 Ok(x)
362 },
363 Err(e) => {
364 #err_event;
365 Err(e)
366 }
367 }
368 },
369 (Some(err_event), None) => quote_spanned!(block.span()=>
370 #span
371 #[allow(clippy::redundant_closure_call)]
372 match (move || #block)() {
373 #[allow(clippy::unit_arg)]
374 Ok(x) => Ok(x),
375 Err(e) => {
376 #err_event;
377 Err(e)
378 }
379 }
380 ),
381 (None, Some(ret_event)) => quote_spanned!(block.span()=>
382 #span
383 #[allow(clippy::redundant_closure_call)]
384 let x = (move || #block)();
385 #ret_event;
386 x
387 ),
388 (None, None) => quote_spanned!(block.span() =>
389 // Because `quote` produces a stream of tokens _without_ whitespace, the
390 // `if` and the block will appear directly next to each other. This
391 // generates a clippy lint about suspicious `if/else` formatting.
392 // Therefore, suppress the lint inside the generated code...
393 #[allow(clippy::suspicious_else_formatting)]
394 {
395 #span
396 // ...but turn the lint back on inside the function body.
397 #[warn(clippy::suspicious_else_formatting)]
398 #block
399 }
400 ),
401 }
402}
403
404/// Indicates whether a field should be recorded as `Value` or `Debug`.
405enum RecordType {
406 /// The field should be recorded using its `Value` implementation.
407 Value,
408 /// The field should be recorded using `tracing::field::debug()`.
409 Debug,
410}
411
412impl RecordType {
413 /// Array of primitive types which should be recorded as [RecordType::Value].
414 const TYPES_FOR_VALUE: &'static [&'static str] = &[
415 "bool",
416 "str",
417 "u8",
418 "i8",
419 "u16",
420 "i16",
421 "u32",
422 "i32",
423 "u64",
424 "i64",
425 "f32",
426 "f64",
427 "usize",
428 "isize",
429 "NonZeroU8",
430 "NonZeroI8",
431 "NonZeroU16",
432 "NonZeroI16",
433 "NonZeroU32",
434 "NonZeroI32",
435 "NonZeroU64",
436 "NonZeroI64",
437 "NonZeroUsize",
438 "NonZeroIsize",
439 "Wrapping",
440 ];
441
442 /// Parse `RecordType` from [Type] by looking up
443 /// the [RecordType::TYPES_FOR_VALUE] array.
444 fn parse_from_ty(ty: &Type) -> Self {
445 match ty {
446 Type::Path(TypePath { path, .. })
447 if path
448 .segments
449 .iter()
450 .last()
451 .map(|path_segment| {
452 let ident = path_segment.ident.to_string();
453 Self::TYPES_FOR_VALUE.iter().any(|&t| t == ident)
454 })
455 .unwrap_or(false) =>
456 {
457 RecordType::Value
458 }
459 Type::Reference(syn::TypeReference { elem, .. }) => RecordType::parse_from_ty(elem),
460 _ => RecordType::Debug,
461 }
462 }
463}
464
465fn param_names(pat: Pat, record_type: RecordType) -> Box<dyn Iterator<Item = (Ident, RecordType)>> {
466 match pat {
467 Pat::Ident(PatIdent { ident, .. }) => Box::new(iter::once((ident, record_type))),
468 Pat::Reference(PatReference { pat, .. }) => param_names(*pat, record_type),
469 // We can't get the concrete type of fields in the struct/tuple
470 // patterns by using `syn`. e.g. `fn foo(Foo { x, y }: Foo) {}`.
471 // Therefore, the struct/tuple patterns in the arguments will just
472 // always be recorded as `RecordType::Debug`.
473 Pat::Struct(PatStruct { fields, .. }) => Box::new(
474 fields
475 .into_iter()
476 .flat_map(|FieldPat { pat, .. }| param_names(*pat, RecordType::Debug)),
477 ),
478 Pat::Tuple(PatTuple { elems, .. }) => Box::new(
479 elems
480 .into_iter()
481 .flat_map(|p| param_names(p, RecordType::Debug)),
482 ),
483 Pat::TupleStruct(PatTupleStruct { elems, .. }) => Box::new(
484 elems
485 .into_iter()
486 .flat_map(|p| param_names(p, RecordType::Debug)),
487 ),
488
489 // The above *should* cover all cases of irrefutable patterns,
490 // but we purposefully don't do any funny business here
491 // (such as panicking) because that would obscure rustc's
492 // much more informative error message.
493 _ => Box::new(iter::empty()),
494 }
495}
496
497/// The specific async code pattern that was detected
498enum AsyncKind<'a> {
499 /// Immediately-invoked async fn, as generated by `async-trait <= 0.1.43`:
500 /// `async fn foo<...>(...) {...}; Box::pin(foo<...>(...))`
501 Function(&'a ItemFn),
502 /// A function returning an async (move) block, optionally `Box::pin`-ed,
503 /// as generated by `async-trait >= 0.1.44`:
504 /// `Box::pin(async move { ... })`
505 Async {
506 async_expr: &'a ExprAsync,
507 pinned_box: bool,
508 },
509}
510
511pub(crate) struct AsyncInfo<'block> {
512 // statement that must be patched
513 source_stmt: &'block Stmt,
514 kind: AsyncKind<'block>,
515 self_type: Option<TypePath>,
516 input: &'block ItemFn,
517}
518
519impl<'block> AsyncInfo<'block> {
520 /// Get the AST of the inner function we need to hook, if it looks like a
521 /// manual future implementation.
522 ///
523 /// When we are given a function that returns a (pinned) future containing the
524 /// user logic, it is that (pinned) future that needs to be instrumented.
525 /// Were we to instrument its parent, we would only collect information
526 /// regarding the allocation of that future, and not its own span of execution.
527 ///
528 /// We inspect the block of the function to find if it matches any of the
529 /// following patterns:
530 ///
531 /// - Immediately-invoked async fn, as generated by `async-trait <= 0.1.43`:
532 /// `async fn foo<...>(...) {...}; Box::pin(foo<...>(...))`
533 ///
534 /// - A function returning an async (move) block, optionally `Box::pin`-ed,
535 /// as generated by `async-trait >= 0.1.44`:
536 /// `Box::pin(async move { ... })`
537 ///
538 /// We the return the statement that must be instrumented, along with some
539 /// other information.
540 /// 'gen_body' will then be able to use that information to instrument the
541 /// proper function/future.
542 ///
543 /// (this follows the approach suggested in
544 /// https://github.com/dtolnay/async-trait/issues/45#issuecomment-571245673)
545 pub(crate) fn from_fn(input: &'block ItemFn) -> Option<Self> {
546 // are we in an async context? If yes, this isn't a manual async-like pattern
547 if input.sig.asyncness.is_some() {
548 return None;
549 }
550
551 let block = &input.block;
552
553 // list of async functions declared inside the block
554 let inside_funs = block.stmts.iter().filter_map(|stmt| {
555 if let Stmt::Item(Item::Fn(fun)) = &stmt {
556 // If the function is async, this is a candidate
557 if fun.sig.asyncness.is_some() {
558 return Some((stmt, fun));
559 }
560 }
561 None
562 });
563
564 // last expression of the block: it determines the return value of the
565 // block, this is quite likely a `Box::pin` statement or an async block
566 let (last_expr_stmt, last_expr) = block.stmts.iter().rev().find_map(|stmt| {
567 if let Stmt::Expr(expr, _semi) = stmt {
568 Some((stmt, expr))
569 } else {
570 None
571 }
572 })?;
573
574 // is the last expression an async block?
575 if let Expr::Async(async_expr) = last_expr {
576 return Some(AsyncInfo {
577 source_stmt: last_expr_stmt,
578 kind: AsyncKind::Async {
579 async_expr,
580 pinned_box: false,
581 },
582 self_type: None,
583 input,
584 });
585 }
586
587 // is the last expression a function call?
588 let (outside_func, outside_args) = match last_expr {
589 Expr::Call(ExprCall { func, args, .. }) => (func, args),
590 _ => return None,
591 };
592
593 // is it a call to `Box::pin()`?
594 let path = match outside_func.as_ref() {
595 Expr::Path(path) => &path.path,
596 _ => return None,
597 };
598 if !path_to_string(path).ends_with("Box::pin") {
599 return None;
600 }
601
602 // Does the call take an argument? If it doesn't,
603 // it's not gonna compile anyway, but that's no reason
604 // to (try to) perform an out of bounds access
605 if outside_args.is_empty() {
606 return None;
607 }
608
609 // Is the argument to Box::pin an async block that
610 // captures its arguments?
611 if let Expr::Async(async_expr) = &outside_args[0] {
612 return Some(AsyncInfo {
613 source_stmt: last_expr_stmt,
614 kind: AsyncKind::Async {
615 async_expr,
616 pinned_box: true,
617 },
618 self_type: None,
619 input,
620 });
621 }
622
623 // Is the argument to Box::pin a function call itself?
624 let func = match &outside_args[0] {
625 Expr::Call(ExprCall { func, .. }) => func,
626 _ => return None,
627 };
628
629 // "stringify" the path of the function called
630 let func_name = match **func {
631 Expr::Path(ref func_path) => path_to_string(&func_path.path),
632 _ => return None,
633 };
634
635 // Was that function defined inside of the current block?
636 // If so, retrieve the statement where it was declared and the function itself
637 let (stmt_func_declaration, func) = inside_funs
638 .into_iter()
639 .find(|(_, fun)| fun.sig.ident == func_name)?;
640
641 // If "_self" is present as an argument, we store its type to be able to rewrite "Self" (the
642 // parameter type) with the type of "_self"
643 let mut self_type = None;
644 for arg in &func.sig.inputs {
645 if let FnArg::Typed(ty) = arg {
646 if let Pat::Ident(PatIdent { ref ident, .. }) = *ty.pat {
647 if ident == "_self" {
648 let mut ty = *ty.ty.clone();
649 // extract the inner type if the argument is "&self" or "&mut self"
650 if let Type::Reference(syn::TypeReference { elem, .. }) = ty {
651 ty = *elem;
652 }
653
654 if let Type::Path(tp) = ty {
655 self_type = Some(tp);
656 break;
657 }
658 }
659 }
660 }
661 }
662
663 Some(AsyncInfo {
664 source_stmt: stmt_func_declaration,
665 kind: AsyncKind::Function(func),
666 self_type,
667 input,
668 })
669 }
670
671 pub(crate) fn gen_async(
672 self,
673 args: InstrumentArgs,
674 instrumented_function_name: &str,
675 ) -> Result<proc_macro::TokenStream, syn::Error> {
676 // let's rewrite some statements!
677 let mut out_stmts: Vec<TokenStream> = self
678 .input
679 .block
680 .stmts
681 .iter()
682 .map(|stmt| stmt.to_token_stream())
683 .collect();
684
685 if let Some((iter, _stmt)) = self
686 .input
687 .block
688 .stmts
689 .iter()
690 .enumerate()
691 .find(|(_iter, stmt)| *stmt == self.source_stmt)
692 {
693 // instrument the future by rewriting the corresponding statement
694 out_stmts[iter] = match self.kind {
695 // `Box::pin(immediately_invoked_async_fn())`
696 AsyncKind::Function(fun) => {
697 let fun = MaybeItemFn::from(fun.clone());
698 gen_function(
699 fun.as_ref(),
700 args,
701 instrumented_function_name,
702 self.self_type.as_ref(),
703 )
704 }
705 // `async move { ... }`, optionally pinned
706 AsyncKind::Async {
707 async_expr,
708 pinned_box,
709 } => {
710 let instrumented_block = gen_block(
711 &async_expr.block,
712 &self.input.sig.inputs,
713 true,
714 args,
715 instrumented_function_name,
716 None,
717 );
718 let async_attrs = &async_expr.attrs;
719 if pinned_box {
720 quote! {
721 Box::pin(#(#async_attrs) * async move { #instrumented_block })
722 }
723 } else {
724 quote! {
725 #(#async_attrs) * async move { #instrumented_block }
726 }
727 }
728 }
729 };
730 }
731
732 let vis = &self.input.vis;
733 let sig = &self.input.sig;
734 let attrs = &self.input.attrs;
735 Ok(quote!(
736 #(#attrs) *
737 #vis #sig {
738 #(#out_stmts) *
739 }
740 )
741 .into())
742 }
743}
744
745// Return a path as a String
746fn path_to_string(path: &Path) -> String {
747 use std::fmt::Write;
748 // some heuristic to prevent too many allocations
749 let mut res = String::with_capacity(path.segments.len() * 5);
750 for i in 0..path.segments.len() {
751 write!(&mut res, "{}", path.segments[i].ident)
752 .expect("writing to a String should never fail");
753 if i < path.segments.len() - 1 {
754 res.push_str("::");
755 }
756 }
757 res
758}
759
760/// A visitor struct to replace idents and types in some piece
761/// of code (e.g. the "self" and "Self" tokens in user-supplied
762/// fields expressions when the function is generated by an old
763/// version of async-trait).
764struct IdentAndTypesRenamer<'a> {
765 types: Vec<(&'a str, TypePath)>,
766 idents: Vec<(Ident, Ident)>,
767}
768
769impl<'a> VisitMut for IdentAndTypesRenamer<'a> {
770 // we deliberately compare strings because we want to ignore the spans
771 // If we apply clippy's lint, the behavior changes
772 #[allow(clippy::cmp_owned)]
773 fn visit_ident_mut(&mut self, id: &mut Ident) {
774 for (old_ident, new_ident) in &self.idents {
775 if id.to_string() == old_ident.to_string() {
776 *id = new_ident.clone();
777 }
778 }
779 }
780
781 fn visit_type_mut(&mut self, ty: &mut Type) {
782 for (type_name, new_type) in &self.types {
783 if let Type::Path(TypePath { path, .. }) = ty {
784 if path_to_string(path) == *type_name {
785 *ty = Type::Path(new_type.clone());
786 }
787 }
788 }
789 }
790}
791
792// A visitor struct that replace an async block by its patched version
793struct AsyncTraitBlockReplacer<'a> {
794 block: &'a Block,
795 patched_block: Block,
796}
797
798impl<'a> VisitMut for AsyncTraitBlockReplacer<'a> {
799 fn visit_block_mut(&mut self, i: &mut Block) {
800 if i == self.block {
801 *i = self.patched_block.clone();
802 }
803 }
804}
805
806// Replaces any `impl Trait` with `_` so it can be used as the type in
807// a `let` statement's LHS.
808struct ImplTraitEraser;
809
810impl VisitMut for ImplTraitEraser {
811 fn visit_type_mut(&mut self, t: &mut Type) {
812 if let Type::ImplTrait(..) = t {
813 *t = syn::TypeInfer {
814 underscore_token: Token![_](t.span()),
815 }
816 .into();
817 } else {
818 syn::visit_mut::visit_type_mut(self, t);
819 }
820 }
821}
822
823fn erase_impl_trait(ty: &Type) -> Type {
824 let mut ty = ty.clone();
825 ImplTraitEraser.visit_type_mut(&mut ty);
826 ty
827}
828