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>>(
100 span: __S,
101 ) -> $ident {
102 $ident {
103 span: $crate::__private::IntoSpans::into_spans(span),
104 }
105 }
106
107 const _: () = {
108 impl $crate::__private::Default for $ident {
109 fn default() -> Self {
110 $ident {
111 span: $crate::__private::Span::call_site(),
112 }
113 }
114 }
115
116 $crate::impl_parse_for_custom_keyword!($ident);
117 $crate::impl_to_tokens_for_custom_keyword!($ident);
118 $crate::impl_clone_for_custom_keyword!($ident);
119 $crate::impl_extra_traits_for_custom_keyword!($ident);
120 };
121 };
122}
123
124// Not public API.
125#[cfg(feature = "parsing")]
126#[doc(hidden)]
127#[macro_export]
128macro_rules! impl_parse_for_custom_keyword {
129 ($ident:ident) => {
130 // For peek.
131 impl $crate::__private::CustomToken for $ident {
132 fn peek(cursor: $crate::buffer::Cursor) -> $crate::__private::bool {
133 if let $crate::__private::Some((ident, _rest)) = cursor.ident() {
134 ident == $crate::__private::stringify!($ident)
135 } else {
136 false
137 }
138 }
139
140 fn display() -> &'static $crate::__private::str {
141 $crate::__private::concat!("`", $crate::__private::stringify!($ident), "`")
142 }
143 }
144
145 impl $crate::parse::Parse for $ident {
146 fn parse(input: $crate::parse::ParseStream) -> $crate::parse::Result<$ident> {
147 input.step(|cursor| {
148 if let $crate::__private::Some((ident, rest)) = cursor.ident() {
149 if ident == $crate::__private::stringify!($ident) {
150 return $crate::__private::Ok(($ident { span: ident.span() }, rest));
151 }
152 }
153 $crate::__private::Err(cursor.error($crate::__private::concat!(
154 "expected `",
155 $crate::__private::stringify!($ident),
156 "`",
157 )))
158 })
159 }
160 }
161 };
162}
163
164// Not public API.
165#[cfg(not(feature = "parsing"))]
166#[doc(hidden)]
167#[macro_export]
168macro_rules! impl_parse_for_custom_keyword {
169 ($ident:ident) => {};
170}
171
172// Not public API.
173#[cfg(feature = "printing")]
174#[doc(hidden)]
175#[macro_export]
176macro_rules! impl_to_tokens_for_custom_keyword {
177 ($ident:ident) => {
178 impl $crate::__private::ToTokens for $ident {
179 fn to_tokens(&self, tokens: &mut $crate::__private::TokenStream2) {
180 let ident = $crate::Ident::new($crate::__private::stringify!($ident), self.span);
181 $crate::__private::TokenStreamExt::append(tokens, ident);
182 }
183 }
184 };
185}
186
187// Not public API.
188#[cfg(not(feature = "printing"))]
189#[doc(hidden)]
190#[macro_export]
191macro_rules! impl_to_tokens_for_custom_keyword {
192 ($ident:ident) => {};
193}
194
195// Not public API.
196#[cfg(feature = "clone-impls")]
197#[doc(hidden)]
198#[macro_export]
199macro_rules! impl_clone_for_custom_keyword {
200 ($ident:ident) => {
201 impl $crate::__private::Copy for $ident {}
202
203 #[allow(clippy::expl_impl_clone_on_copy)]
204 impl $crate::__private::Clone for $ident {
205 fn clone(&self) -> Self {
206 *self
207 }
208 }
209 };
210}
211
212// Not public API.
213#[cfg(not(feature = "clone-impls"))]
214#[doc(hidden)]
215#[macro_export]
216macro_rules! impl_clone_for_custom_keyword {
217 ($ident:ident) => {};
218}
219
220// Not public API.
221#[cfg(feature = "extra-traits")]
222#[doc(hidden)]
223#[macro_export]
224macro_rules! impl_extra_traits_for_custom_keyword {
225 ($ident:ident) => {
226 impl $crate::__private::Debug for $ident {
227 fn fmt(&self, f: &mut $crate::__private::Formatter) -> $crate::__private::FmtResult {
228 $crate::__private::Formatter::write_str(
229 f,
230 $crate::__private::concat!(
231 "Keyword [",
232 $crate::__private::stringify!($ident),
233 "]",
234 ),
235 )
236 }
237 }
238
239 impl $crate::__private::Eq for $ident {}
240
241 impl $crate::__private::PartialEq for $ident {
242 fn eq(&self, _other: &Self) -> $crate::__private::bool {
243 true
244 }
245 }
246
247 impl $crate::__private::Hash for $ident {
248 fn hash<__H: $crate::__private::Hasher>(&self, _state: &mut __H) {}
249 }
250 };
251}
252
253// Not public API.
254#[cfg(not(feature = "extra-traits"))]
255#[doc(hidden)]
256#[macro_export]
257macro_rules! impl_extra_traits_for_custom_keyword {
258 ($ident:ident) => {};
259}
260