async_trait/
lifetime.rs

1use proc_macro2::{Span, TokenStream};
2use std::mem;
3use syn::visit_mut::{self, VisitMut};
4use syn::{
5    parse_quote_spanned, token, Expr, GenericArgument, Lifetime, Receiver, ReturnType, Token, Type,
6    TypeBareFn, TypeImplTrait, TypeParen, TypePtr, TypeReference,
7};
8
9pub struct CollectLifetimes {
10    pub elided: Vec<Lifetime>,
11    pub explicit: Vec<Lifetime>,
12}
13
14impl CollectLifetimes {
15    pub fn new() -> Self {
16        CollectLifetimes {
17            elided: Vec::new(),
18            explicit: Vec::new(),
19        }
20    }
21
22    fn visit_opt_lifetime(&mut self, reference: &Token![&], lifetime: &mut Option<Lifetime>) {
23        match lifetime {
24            None => *lifetime = Some(self.next_lifetime(reference.span)),
25            Some(lifetime) => self.visit_lifetime(lifetime),
26        }
27    }
28
29    fn visit_lifetime(&mut self, lifetime: &mut Lifetime) {
30        if lifetime.ident == "_" {
31            *lifetime = self.next_lifetime(lifetime.span());
32        } else {
33            self.explicit.push(lifetime.clone());
34        }
35    }
36
37    fn next_lifetime(&mut self, span: Span) -> Lifetime {
38        let name = format!("'life{}", self.elided.len());
39        let life = Lifetime::new(&name, span);
40        self.elided.push(life.clone());
41        life
42    }
43}
44
45impl VisitMut for CollectLifetimes {
46    fn visit_receiver_mut(&mut self, arg: &mut Receiver) {
47        if let Some((reference, lifetime)) = &mut arg.reference {
48            self.visit_opt_lifetime(reference, lifetime);
49        } else {
50            visit_mut::visit_type_mut(self, &mut arg.ty);
51        }
52    }
53
54    fn visit_type_reference_mut(&mut self, ty: &mut TypeReference) {
55        self.visit_opt_lifetime(&ty.and_token, &mut ty.lifetime);
56        visit_mut::visit_type_reference_mut(self, ty);
57    }
58
59    fn visit_generic_argument_mut(&mut self, gen: &mut GenericArgument) {
60        if let GenericArgument::Lifetime(lifetime) = gen {
61            self.visit_lifetime(lifetime);
62        }
63        visit_mut::visit_generic_argument_mut(self, gen);
64    }
65}
66
67pub struct AddLifetimeToImplTrait;
68
69impl VisitMut for AddLifetimeToImplTrait {
70    fn visit_type_impl_trait_mut(&mut self, ty: &mut TypeImplTrait) {
71        let span = ty.impl_token.span;
72        let lifetime = parse_quote_spanned!(span=> 'async_trait);
73        ty.bounds.insert(0, lifetime);
74        if let Some(punct) = ty.bounds.pairs_mut().next().unwrap().punct_mut() {
75            punct.span = span;
76        }
77        visit_mut::visit_type_impl_trait_mut(self, ty);
78    }
79
80    fn visit_type_reference_mut(&mut self, ty: &mut TypeReference) {
81        parenthesize_impl_trait(&mut ty.elem, ty.and_token.span);
82        visit_mut::visit_type_reference_mut(self, ty);
83    }
84
85    fn visit_type_ptr_mut(&mut self, ty: &mut TypePtr) {
86        parenthesize_impl_trait(&mut ty.elem, ty.star_token.span);
87        visit_mut::visit_type_ptr_mut(self, ty);
88    }
89
90    fn visit_type_bare_fn_mut(&mut self, ty: &mut TypeBareFn) {
91        if let ReturnType::Type(arrow, return_type) = &mut ty.output {
92            parenthesize_impl_trait(return_type, arrow.spans[0]);
93        }
94        visit_mut::visit_type_bare_fn_mut(self, ty);
95    }
96
97    fn visit_expr_mut(&mut self, _e: &mut Expr) {
98        // Do not recurse into impl Traits inside of an array length expression.
99        //
100        //    fn outer(arg: [u8; { fn inner(_: impl Trait) {}; 0 }]);
101    }
102}
103
104fn parenthesize_impl_trait(elem: &mut Type, paren_span: Span) {
105    if let Type::ImplTrait(_) = *elem {
106        let placeholder = Type::Verbatim(TokenStream::new());
107        *elem = Type::Paren(TypeParen {
108            paren_token: token::Paren(paren_span),
109            elem: Box::new(mem::replace(elem, placeholder)),
110        });
111    }
112}
async_trait/lifetime.rs

async_trait/
lifetime.rs
