zerofrom_derive/
visitor.rs

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1// This file is part of ICU4X. For terms of use, please see the file
2// called LICENSE at the top level of the ICU4X source tree
3// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
4
5//! Visitor for determining whether a type has type and non-static lifetime parameters
6//! (duplicated in yoke/derive/src/visitor.rs)
7
8use std::collections::HashMap;
9use syn::visit::{visit_lifetime, visit_type, visit_type_path, Visit};
10use syn::{Ident, Lifetime, Type, TypePath};
11
12struct TypeVisitor<'a> {
13    /// The type parameters in scope
14    typarams: &'a HashMap<Ident, Option<Ident>>,
15    /// Whether we found a type parameter
16    found_typarams: bool,
17    /// Whether we found a non-'static lifetime parameter
18    found_lifetimes: bool,
19}
20
21impl<'ast> Visit<'ast> for TypeVisitor<'_> {
22    fn visit_lifetime(&mut self, lt: &'ast Lifetime) {
23        if lt.ident != "static" {
24            self.found_lifetimes = true;
25        }
26        visit_lifetime(self, lt)
27    }
28    fn visit_type_path(&mut self, ty: &'ast TypePath) {
29        // We only need to check ty.path.get_ident() and not ty.qself or any
30        // generics in ty.path because the visitor will eventually visit those
31        // types on its own
32        if let Some(ident) = ty.path.get_ident() {
33            if let Some(maybe_borrowed) = self.typarams.get(ident) {
34                self.found_typarams = true;
35                if maybe_borrowed.is_some() {
36                    self.found_lifetimes = true;
37                }
38            }
39        }
40
41        visit_type_path(self, ty)
42    }
43}
44
45/// Checks if a type has type or lifetime parameters, given the local context of
46/// named type parameters. Returns (has_type_params, has_lifetime_params)
47pub fn check_type_for_parameters(
48    ty: &Type,
49    typarams: &HashMap<Ident, Option<Ident>>,
50) -> (bool, bool) {
51    let mut visit = TypeVisitor {
52        typarams,
53        found_typarams: false,
54        found_lifetimes: false,
55    };
56    visit_type(&mut visit, ty);
57
58    (visit.found_typarams, visit.found_lifetimes)
59}
60
61#[cfg(test)]
62mod tests {
63    use proc_macro2::Span;
64    use std::collections::HashMap;
65    use syn::{parse_quote, Ident};
66
67    use super::check_type_for_parameters;
68    fn make_typarams(params: &[&str]) -> HashMap<Ident, Option<Ident>> {
69        params
70            .iter()
71            .map(|x| (Ident::new(x, Span::call_site()), None))
72            .collect()
73    }
74
75    #[test]
76    fn test_simple_type() {
77        let environment = make_typarams(&["T", "U", "V"]);
78
79        let ty = parse_quote!(Foo<'a, T>);
80        let check = check_type_for_parameters(&ty, &environment);
81        assert_eq!(check, (true, true));
82
83        let ty = parse_quote!(Foo<T>);
84        let check = check_type_for_parameters(&ty, &environment);
85        assert_eq!(check, (true, false));
86
87        let ty = parse_quote!(Foo<'static, T>);
88        let check = check_type_for_parameters(&ty, &environment);
89        assert_eq!(check, (true, false));
90
91        let ty = parse_quote!(Foo<'a>);
92        let check = check_type_for_parameters(&ty, &environment);
93        assert_eq!(check, (false, true));
94
95        let ty = parse_quote!(Foo<'a, Bar<U>, Baz<(V, u8)>>);
96        let check = check_type_for_parameters(&ty, &environment);
97        assert_eq!(check, (true, true));
98
99        let ty = parse_quote!(Foo<'a, W>);
100        let check = check_type_for_parameters(&ty, &environment);
101        assert_eq!(check, (false, true));
102    }
103
104    #[test]
105    fn test_assoc_types() {
106        let environment = make_typarams(&["T"]);
107
108        let ty = parse_quote!(<Foo as SomeTrait<'a, T>>::Output);
109        let check = check_type_for_parameters(&ty, &environment);
110        assert_eq!(check, (true, true));
111
112        let ty = parse_quote!(<Foo as SomeTrait<'static, T>>::Output);
113        let check = check_type_for_parameters(&ty, &environment);
114        assert_eq!(check, (true, false));
115
116        let ty = parse_quote!(<T as SomeTrait<'static, Foo>>::Output);
117        let check = check_type_for_parameters(&ty, &environment);
118        assert_eq!(check, (true, false));
119    }
120}
zerofrom_derive/visitor.rs

zerofrom_derive/
visitor.rs
