1/// Define a type that supports parsing and printing a given identifier as if it
2/// were a keyword.
3///
4/// # Usage
5///
6/// As a convention, it is recommended that this macro be invoked within a
7/// module called `kw` or `keyword` and that the resulting parser be invoked
8/// with a `kw::` or `keyword::` prefix.
9///
10/// ```
11/// mod kw {
12/// syn::custom_keyword!(whatever);
13/// }
14/// ```
15///
16/// The generated syntax tree node supports the following operations just like
17/// any built-in keyword token.
18///
19/// - [Peeking] — `input.peek(kw::whatever)`
20///
21/// - [Parsing] — `input.parse::<kw::whatever>()?`
22///
23/// - [Printing] — `quote!( ... #whatever_token ... )`
24///
25/// - Construction from a [`Span`] — `let whatever_token = kw::whatever(sp)`
26///
27/// - Field access to its span — `let sp = whatever_token.span`
28///
29/// [Peeking]: crate::parse::ParseBuffer::peek
30/// [Parsing]: crate::parse::ParseBuffer::parse
31/// [Printing]: quote::ToTokens
32/// [`Span`]: proc_macro2::Span
33///
34/// # Example
35///
36/// This example parses input that looks like `bool = true` or `str = "value"`.
37/// The key must be either the identifier `bool` or the identifier `str`. If
38/// `bool`, the value may be either `true` or `false`. If `str`, the value may
39/// be any string literal.
40///
41/// The symbols `bool` and `str` are not reserved keywords in Rust so these are
42/// not considered keywords in the `syn::token` module. Like any other
43/// identifier that is not a keyword, these can be declared as custom keywords
44/// by crates that need to use them as such.
45///
46/// ```
47/// use syn::{LitBool, LitStr, Result, Token};
48/// use syn::parse::{Parse, ParseStream};
49///
50/// mod kw {
51/// syn::custom_keyword!(bool);
52/// syn::custom_keyword!(str);
53/// }
54///
55/// enum Argument {
56/// Bool {
57/// bool_token: kw::bool,
58/// eq_token: Token![=],
59/// value: LitBool,
60/// },
61/// Str {
62/// str_token: kw::str,
63/// eq_token: Token![=],
64/// value: LitStr,
65/// },
66/// }
67///
68/// impl Parse for Argument {
69/// fn parse(input: ParseStream) -> Result<Self> {
70/// let lookahead = input.lookahead1();
71/// if lookahead.peek(kw::bool) {
72/// Ok(Argument::Bool {
73/// bool_token: input.parse::<kw::bool>()?,
74/// eq_token: input.parse()?,
75/// value: input.parse()?,
76/// })
77/// } else if lookahead.peek(kw::str) {
78/// Ok(Argument::Str {
79/// str_token: input.parse::<kw::str>()?,
80/// eq_token: input.parse()?,
81/// value: input.parse()?,
82/// })
83/// } else {
84/// Err(lookahead.error())
85/// }
86/// }
87/// }
88/// ```
89#[macro_export]
90macro_rules! custom_keyword {
91 ($ident:ident) => {
92 #[allow(non_camel_case_types)]
93 pub struct $ident {
94 pub span: $crate::__private::Span,
95 }
96
97 #[doc(hidden)]
98 #[allow(dead_code, non_snake_case)]
99 pub fn $ident<__S: $crate::__private::IntoSpans<[$crate::__private::Span; 1]>>(
100 span: __S,
101 ) -> $ident {
102 $ident {
103 span: $crate::__private::IntoSpans::into_spans(span)[0],
104 }
105 }
106
107 impl $crate::__private::Default for $ident {
108 fn default() -> Self {
109 $ident {
110 span: $crate::__private::Span::call_site(),
111 }
112 }
113 }
114
115 $crate::impl_parse_for_custom_keyword!($ident);
116 $crate::impl_to_tokens_for_custom_keyword!($ident);
117 $crate::impl_clone_for_custom_keyword!($ident);
118 $crate::impl_extra_traits_for_custom_keyword!($ident);
119 };
120}
121
122// Not public API.
123#[cfg(feature = "parsing")]
124#[doc(hidden)]
125#[macro_export]
126macro_rules! impl_parse_for_custom_keyword {
127 ($ident:ident) => {
128 // For peek.
129 impl $crate::token::CustomToken for $ident {
130 fn peek(cursor: $crate::buffer::Cursor) -> $crate::__private::bool {
131 if let $crate::__private::Some((ident, _rest)) = cursor.ident() {
132 ident == stringify!($ident)
133 } else {
134 false
135 }
136 }
137
138 fn display() -> &'static $crate::__private::str {
139 concat!("`", stringify!($ident), "`")
140 }
141 }
142
143 impl $crate::parse::Parse for $ident {
144 fn parse(input: $crate::parse::ParseStream) -> $crate::parse::Result<$ident> {
145 input.step(|cursor| {
146 if let $crate::__private::Some((ident, rest)) = cursor.ident() {
147 if ident == stringify!($ident) {
148 return $crate::__private::Ok(($ident { span: ident.span() }, rest));
149 }
150 }
151 $crate::__private::Err(cursor.error(concat!(
152 "expected `",
153 stringify!($ident),
154 "`"
155 )))
156 })
157 }
158 }
159 };
160}
161
162// Not public API.
163#[cfg(not(feature = "parsing"))]
164#[doc(hidden)]
165#[macro_export]
166macro_rules! impl_parse_for_custom_keyword {
167 ($ident:ident) => {};
168}
169
170// Not public API.
171#[cfg(feature = "printing")]
172#[doc(hidden)]
173#[macro_export]
174macro_rules! impl_to_tokens_for_custom_keyword {
175 ($ident:ident) => {
176 impl $crate::__private::ToTokens for $ident {
177 fn to_tokens(&self, tokens: &mut $crate::__private::TokenStream2) {
178 let ident = $crate::Ident::new(stringify!($ident), self.span);
179 $crate::__private::TokenStreamExt::append(tokens, ident);
180 }
181 }
182 };
183}
184
185// Not public API.
186#[cfg(not(feature = "printing"))]
187#[doc(hidden)]
188#[macro_export]
189macro_rules! impl_to_tokens_for_custom_keyword {
190 ($ident:ident) => {};
191}
192
193// Not public API.
194#[cfg(feature = "clone-impls")]
195#[doc(hidden)]
196#[macro_export]
197macro_rules! impl_clone_for_custom_keyword {
198 ($ident:ident) => {
199 impl $crate::__private::Copy for $ident {}
200
201 #[allow(clippy::expl_impl_clone_on_copy)]
202 impl $crate::__private::Clone for $ident {
203 fn clone(&self) -> Self {
204 *self
205 }
206 }
207 };
208}
209
210// Not public API.
211#[cfg(not(feature = "clone-impls"))]
212#[doc(hidden)]
213#[macro_export]
214macro_rules! impl_clone_for_custom_keyword {
215 ($ident:ident) => {};
216}
217
218// Not public API.
219#[cfg(feature = "extra-traits")]
220#[doc(hidden)]
221#[macro_export]
222macro_rules! impl_extra_traits_for_custom_keyword {
223 ($ident:ident) => {
224 impl $crate::__private::Debug for $ident {
225 fn fmt(&self, f: &mut $crate::__private::Formatter) -> $crate::__private::fmt::Result {
226 $crate::__private::Formatter::write_str(
227 f,
228 concat!("Keyword [", stringify!($ident), "]"),
229 )
230 }
231 }
232
233 impl $crate::__private::Eq for $ident {}
234
235 impl $crate::__private::PartialEq for $ident {
236 fn eq(&self, _other: &Self) -> $crate::__private::bool {
237 true
238 }
239 }
240
241 impl $crate::__private::Hash for $ident {
242 fn hash<__H: $crate::__private::Hasher>(&self, _state: &mut __H) {}
243 }
244 };
245}
246
247// Not public API.
248#[cfg(not(feature = "extra-traits"))]
249#[doc(hidden)]
250#[macro_export]
251macro_rules! impl_extra_traits_for_custom_keyword {
252 ($ident:ident) => {};
253}
254