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 #[allow(dead_code)]
95 pub span: $crate::__private::Span,
96 }
97
98 #[doc(hidden)]
99 #[allow(dead_code, non_snake_case)]
100 pub fn $ident<__S: $crate::__private::IntoSpans<$crate::__private::Span>>(
101 span: __S,
102 ) -> $ident {
103 $ident {
104 span: $crate::__private::IntoSpans::into_spans(span),
105 }
106 }
107
108 const _: () = {
109 impl $crate::__private::Default for $ident {
110 fn default() -> Self {
111 $ident {
112 span: $crate::__private::Span::call_site(),
113 }
114 }
115 }
116
117 $crate::impl_parse_for_custom_keyword!($ident);
118 $crate::impl_to_tokens_for_custom_keyword!($ident);
119 $crate::impl_clone_for_custom_keyword!($ident);
120 $crate::impl_extra_traits_for_custom_keyword!($ident);
121 };
122 };
123}
124
125// Not public API.
126#[cfg(feature = "parsing")]
127#[doc(hidden)]
128#[macro_export]
129macro_rules! impl_parse_for_custom_keyword {
130 ($ident:ident) => {
131 // For peek.
132 impl $crate::__private::CustomToken for $ident {
133 fn peek(cursor: $crate::buffer::Cursor) -> $crate::__private::bool {
134 if let $crate::__private::Some((ident, _rest)) = cursor.ident() {
135 ident == $crate::__private::stringify!($ident)
136 } else {
137 false
138 }
139 }
140
141 fn display() -> &'static $crate::__private::str {
142 $crate::__private::concat!("`", $crate::__private::stringify!($ident), "`")
143 }
144 }
145
146 impl $crate::parse::Parse for $ident {
147 fn parse(input: $crate::parse::ParseStream) -> $crate::parse::Result<$ident> {
148 input.step(|cursor| {
149 if let $crate::__private::Some((ident, rest)) = cursor.ident() {
150 if ident == $crate::__private::stringify!($ident) {
151 return $crate::__private::Ok(($ident { span: ident.span() }, rest));
152 }
153 }
154 $crate::__private::Err(cursor.error($crate::__private::concat!(
155 "expected `",
156 $crate::__private::stringify!($ident),
157 "`",
158 )))
159 })
160 }
161 }
162 };
163}
164
165// Not public API.
166#[cfg(not(feature = "parsing"))]
167#[doc(hidden)]
168#[macro_export]
169macro_rules! impl_parse_for_custom_keyword {
170 ($ident:ident) => {};
171}
172
173// Not public API.
174#[cfg(feature = "printing")]
175#[doc(hidden)]
176#[macro_export]
177macro_rules! impl_to_tokens_for_custom_keyword {
178 ($ident:ident) => {
179 impl $crate::__private::ToTokens for $ident {
180 fn to_tokens(&self, tokens: &mut $crate::__private::TokenStream2) {
181 let ident = $crate::Ident::new($crate::__private::stringify!($ident), self.span);
182 $crate::__private::TokenStreamExt::append(tokens, ident);
183 }
184 }
185 };
186}
187
188// Not public API.
189#[cfg(not(feature = "printing"))]
190#[doc(hidden)]
191#[macro_export]
192macro_rules! impl_to_tokens_for_custom_keyword {
193 ($ident:ident) => {};
194}
195
196// Not public API.
197#[cfg(feature = "clone-impls")]
198#[doc(hidden)]
199#[macro_export]
200macro_rules! impl_clone_for_custom_keyword {
201 ($ident:ident) => {
202 impl $crate::__private::Copy for $ident {}
203
204 #[allow(clippy::expl_impl_clone_on_copy)]
205 impl $crate::__private::Clone for $ident {
206 fn clone(&self) -> Self {
207 *self
208 }
209 }
210 };
211}
212
213// Not public API.
214#[cfg(not(feature = "clone-impls"))]
215#[doc(hidden)]
216#[macro_export]
217macro_rules! impl_clone_for_custom_keyword {
218 ($ident:ident) => {};
219}
220
221// Not public API.
222#[cfg(feature = "extra-traits")]
223#[doc(hidden)]
224#[macro_export]
225macro_rules! impl_extra_traits_for_custom_keyword {
226 ($ident:ident) => {
227 impl $crate::__private::Debug for $ident {
228 fn fmt(&self, f: &mut $crate::__private::Formatter) -> $crate::__private::FmtResult {
229 $crate::__private::Formatter::write_str(
230 f,
231 $crate::__private::concat!(
232 "Keyword [",
233 $crate::__private::stringify!($ident),
234 "]",
235 ),
236 )
237 }
238 }
239
240 impl $crate::__private::Eq for $ident {}
241
242 impl $crate::__private::PartialEq for $ident {
243 fn eq(&self, _other: &Self) -> $crate::__private::bool {
244 true
245 }
246 }
247
248 impl $crate::__private::Hash for $ident {
249 fn hash<__H: $crate::__private::Hasher>(&self, _state: &mut __H) {}
250 }
251 };
252}
253
254// Not public API.
255#[cfg(not(feature = "extra-traits"))]
256#[doc(hidden)]
257#[macro_export]
258macro_rules! impl_extra_traits_for_custom_keyword {
259 ($ident:ident) => {};
260}
261