1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
use super::*;
use crate::punctuated::Punctuated;
use proc_macro2::TokenStream;
use std::iter;

#[cfg(feature = "parsing")]
use crate::parse::{Parse, ParseBuffer, ParseStream, Parser, Result};
#[cfg(feature = "parsing")]
use crate::punctuated::Pair;

ast_struct! {
    /// An attribute like `#[repr(transparent)]`.
    ///
    /// *This type is available only if Syn is built with the `"derive"` or `"full"`
    /// feature.*
    ///
    /// <br>
    ///
    /// # Syntax
    ///
    /// Rust has six types of attributes.
    ///
    /// - Outer attributes like `#[repr(transparent)]`. These appear outside or
    ///   in front of the item they describe.
    /// - Inner attributes like `#![feature(proc_macro)]`. These appear inside
    ///   of the item they describe, usually a module.
    /// - Outer doc comments like `/// # Example`.
    /// - Inner doc comments like `//! Please file an issue`.
    /// - Outer block comments `/** # Example */`.
    /// - Inner block comments `/*! Please file an issue */`.
    ///
    /// The `style` field of type `AttrStyle` distinguishes whether an attribute
    /// is outer or inner. Doc comments and block comments are promoted to
    /// attributes, as this is how they are processed by the compiler and by
    /// `macro_rules!` macros.
    ///
    /// The `path` field gives the possibly colon-delimited path against which
    /// the attribute is resolved. It is equal to `"doc"` for desugared doc
    /// comments. The `tokens` field contains the rest of the attribute body as
    /// tokens.
    ///
    /// ```text
    /// #[derive(Copy)]      #[crate::precondition x < 5]
    ///   ^^^^^^~~~~~~         ^^^^^^^^^^^^^^^^^^^ ~~~~~
    ///   path  tokens                 path        tokens
    /// ```
    ///
    /// <br>
    ///
    /// # Parsing from tokens to Attribute
    ///
    /// This type does not implement the [`Parse`] trait and thus cannot be
    /// parsed directly by [`ParseStream::parse`]. Instead use
    /// [`ParseStream::call`] with one of the two parser functions
    /// [`Attribute::parse_outer`] or [`Attribute::parse_inner`] depending on
    /// which you intend to parse.
    ///
    /// [`Parse`]: parse::Parse
    /// [`ParseStream::parse`]: parse::ParseBuffer::parse
    /// [`ParseStream::call`]: parse::ParseBuffer::call
    ///
    /// ```
    /// use syn::{Attribute, Ident, Result, Token};
    /// use syn::parse::{Parse, ParseStream};
    ///
    /// // Parses a unit struct with attributes.
    /// //
    /// //     #[path = "s.tmpl"]
    /// //     struct S;
    /// struct UnitStruct {
    ///     attrs: Vec<Attribute>,
    ///     struct_token: Token![struct],
    ///     name: Ident,
    ///     semi_token: Token![;],
    /// }
    ///
    /// impl Parse for UnitStruct {
    ///     fn parse(input: ParseStream) -> Result<Self> {
    ///         Ok(UnitStruct {
    ///             attrs: input.call(Attribute::parse_outer)?,
    ///             struct_token: input.parse()?,
    ///             name: input.parse()?,
    ///             semi_token: input.parse()?,
    ///         })
    ///     }
    /// }
    /// ```
    ///
    /// <p><br></p>
    ///
    /// # Parsing from Attribute to structured arguments
    ///
    /// The grammar of attributes in Rust is very flexible, which makes the
    /// syntax tree not that useful on its own. In particular, arguments of the
    /// attribute are held in an arbitrary `tokens: TokenStream`. Macros are
    /// expected to check the `path` of the attribute, decide whether they
    /// recognize it, and then parse the remaining tokens according to whatever
    /// grammar they wish to require for that kind of attribute.
    ///
    /// If the attribute you are parsing is expected to conform to the
    /// conventional structured form of attribute, use [`parse_meta()`] to
    /// obtain that structured representation. If the attribute follows some
    /// other grammar of its own, use [`parse_args()`] to parse that into the
    /// expected data structure.
    ///
    /// [`parse_meta()`]: Attribute::parse_meta
    /// [`parse_args()`]: Attribute::parse_args
    ///
    /// <p><br></p>
    ///
    /// # Doc comments
    ///
    /// The compiler transforms doc comments, such as `/// comment` and `/*!
    /// comment */`, into attributes before macros are expanded. Each comment is
    /// expanded into an attribute of the form `#[doc = r"comment"]`.
    ///
    /// As an example, the following `mod` items are expanded identically:
    ///
    /// ```
    /// # use syn::{ItemMod, parse_quote};
    /// let doc: ItemMod = parse_quote! {
    ///     /// Single line doc comments
    ///     /// We write so many!
    ///     /**
    ///      * Multi-line comments...
    ///      * May span many lines
    ///      */
    ///     mod example {
    ///         //! Of course, they can be inner too
    ///         /*! And fit in a single line */
    ///     }
    /// };
    /// let attr: ItemMod = parse_quote! {
    ///     #[doc = r" Single line doc comments"]
    ///     #[doc = r" We write so many!"]
    ///     #[doc = r"
    ///      * Multi-line comments...
    ///      * May span many lines
    ///      "]
    ///     mod example {
    ///         #![doc = r" Of course, they can be inner too"]
    ///         #![doc = r" And fit in a single line "]
    ///     }
    /// };
    /// assert_eq!(doc, attr);
    /// ```
    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
    pub struct Attribute {
        pub pound_token: Token![#],
        pub style: AttrStyle,
        pub bracket_token: token::Bracket,
        pub path: Path,
        pub tokens: TokenStream,
    }
}

impl Attribute {
    /// Parses the content of the attribute, consisting of the path and tokens,
    /// as a [`Meta`] if possible.
    ///
    /// *This function is available only if Syn is built with the `"parsing"`
    /// feature.*
    #[cfg(feature = "parsing")]
    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
    pub fn parse_meta(&self) -> Result<Meta> {
        fn clone_ident_segment(segment: &PathSegment) -> PathSegment {
            PathSegment {
                ident: segment.ident.clone(),
                arguments: PathArguments::None,
            }
        }

        let path = Path {
            leading_colon: self
                .path
                .leading_colon
                .as_ref()
                .map(|colon| Token![::](colon.spans)),
            segments: self
                .path
                .segments
                .pairs()
                .map(|pair| match pair {
                    Pair::Punctuated(seg, punct) => {
                        Pair::Punctuated(clone_ident_segment(seg), Token![::](punct.spans))
                    }
                    Pair::End(seg) => Pair::End(clone_ident_segment(seg)),
                })
                .collect(),
        };

        let parser = |input: ParseStream| parsing::parse_meta_after_path(path, input);
        parse::Parser::parse2(parser, self.tokens.clone())
    }

    /// Parse the arguments to the attribute as a syntax tree.
    ///
    /// This is similar to `syn::parse2::<T>(attr.tokens)` except that:
    ///
    /// - the surrounding delimiters are *not* included in the input to the
    ///   parser; and
    /// - the error message has a more useful span when `tokens` is empty.
    ///
    /// ```text
    /// #[my_attr(value < 5)]
    ///           ^^^^^^^^^ what gets parsed
    /// ```
    ///
    /// *This function is available only if Syn is built with the `"parsing"`
    /// feature.*
    #[cfg(feature = "parsing")]
    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
    pub fn parse_args<T: Parse>(&self) -> Result<T> {
        self.parse_args_with(T::parse)
    }

    /// Parse the arguments to the attribute using the given parser.
    ///
    /// *This function is available only if Syn is built with the `"parsing"`
    /// feature.*
    #[cfg(feature = "parsing")]
    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
    pub fn parse_args_with<F: Parser>(&self, parser: F) -> Result<F::Output> {
        let parser = |input: ParseStream| {
            let args = enter_args(self, input)?;
            parse::parse_stream(parser, &args)
        };
        parser.parse2(self.tokens.clone())
    }

    /// Parses zero or more outer attributes from the stream.
    ///
    /// *This function is available only if Syn is built with the `"parsing"`
    /// feature.*
    #[cfg(feature = "parsing")]
    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
    pub fn parse_outer(input: ParseStream) -> Result<Vec<Self>> {
        let mut attrs = Vec::new();
        while input.peek(Token![#]) {
            attrs.push(input.call(parsing::single_parse_outer)?);
        }
        Ok(attrs)
    }

    /// Parses zero or more inner attributes from the stream.
    ///
    /// *This function is available only if Syn is built with the `"parsing"`
    /// feature.*
    #[cfg(feature = "parsing")]
    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
    pub fn parse_inner(input: ParseStream) -> Result<Vec<Self>> {
        let mut attrs = Vec::new();
        parsing::parse_inner(input, &mut attrs)?;
        Ok(attrs)
    }
}

#[cfg(feature = "parsing")]
fn expected_parentheses(attr: &Attribute) -> String {
    let style = match attr.style {
        AttrStyle::Outer => "#",
        AttrStyle::Inner(_) => "#!",
    };

    let mut path = String::new();
    for segment in &attr.path.segments {
        if !path.is_empty() || attr.path.leading_colon.is_some() {
            path += "::";
        }
        path += &segment.ident.to_string();
    }

    format!("{}[{}(...)]", style, path)
}

#[cfg(feature = "parsing")]
fn enter_args<'a>(attr: &Attribute, input: ParseStream<'a>) -> Result<ParseBuffer<'a>> {
    if input.is_empty() {
        let expected = expected_parentheses(attr);
        let msg = format!("expected attribute arguments in parentheses: {}", expected);
        return Err(crate::error::new2(
            attr.pound_token.span,
            attr.bracket_token.span,
            msg,
        ));
    } else if input.peek(Token![=]) {
        let expected = expected_parentheses(attr);
        let msg = format!("expected parentheses: {}", expected);
        return Err(input.error(msg));
    };

    let content;
    if input.peek(token::Paren) {
        parenthesized!(content in input);
    } else if input.peek(token::Bracket) {
        bracketed!(content in input);
    } else if input.peek(token::Brace) {
        braced!(content in input);
    } else {
        return Err(input.error("unexpected token in attribute arguments"));
    }

    if input.is_empty() {
        Ok(content)
    } else {
        Err(input.error("unexpected token in attribute arguments"))
    }
}

ast_enum! {
    /// Distinguishes between attributes that decorate an item and attributes
    /// that are contained within an item.
    ///
    /// *This type is available only if Syn is built with the `"derive"` or `"full"`
    /// feature.*
    ///
    /// # Outer attributes
    ///
    /// - `#[repr(transparent)]`
    /// - `/// # Example`
    /// - `/** Please file an issue */`
    ///
    /// # Inner attributes
    ///
    /// - `#![feature(proc_macro)]`
    /// - `//! # Example`
    /// - `/*! Please file an issue */`
    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
    pub enum AttrStyle {
        Outer,
        Inner(Token![!]),
    }
}

ast_enum_of_structs! {
    /// Content of a compile-time structured attribute.
    ///
    /// *This type is available only if Syn is built with the `"derive"` or `"full"`
    /// feature.*
    ///
    /// ## Path
    ///
    /// A meta path is like the `test` in `#[test]`.
    ///
    /// ## List
    ///
    /// A meta list is like the `derive(Copy)` in `#[derive(Copy)]`.
    ///
    /// ## NameValue
    ///
    /// A name-value meta is like the `path = "..."` in `#[path =
    /// "sys/windows.rs"]`.
    ///
    /// # Syntax tree enum
    ///
    /// This type is a [syntax tree enum].
    ///
    /// [syntax tree enum]: Expr#syntax-tree-enums
    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
    pub enum Meta {
        Path(Path),

        /// A structured list within an attribute, like `derive(Copy, Clone)`.
        List(MetaList),

        /// A name-value pair within an attribute, like `feature = "nightly"`.
        NameValue(MetaNameValue),
    }
}

ast_struct! {
    /// A structured list within an attribute, like `derive(Copy, Clone)`.
    ///
    /// *This type is available only if Syn is built with the `"derive"` or
    /// `"full"` feature.*
    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
    pub struct MetaList {
        pub path: Path,
        pub paren_token: token::Paren,
        pub nested: Punctuated<NestedMeta, Token![,]>,
    }
}

ast_struct! {
    /// A name-value pair within an attribute, like `feature = "nightly"`.
    ///
    /// *This type is available only if Syn is built with the `"derive"` or
    /// `"full"` feature.*
    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
    pub struct MetaNameValue {
        pub path: Path,
        pub eq_token: Token![=],
        pub lit: Lit,
    }
}

impl Meta {
    /// Returns the identifier that begins this structured meta item.
    ///
    /// For example this would return the `test` in `#[test]`, the `derive` in
    /// `#[derive(Copy)]`, and the `path` in `#[path = "sys/windows.rs"]`.
    pub fn path(&self) -> &Path {
        match self {
            Meta::Path(path) => path,
            Meta::List(meta) => &meta.path,
            Meta::NameValue(meta) => &meta.path,
        }
    }
}

ast_enum_of_structs! {
    /// Element of a compile-time attribute list.
    ///
    /// *This type is available only if Syn is built with the `"derive"` or `"full"`
    /// feature.*
    #[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
    pub enum NestedMeta {
        /// A structured meta item, like the `Copy` in `#[derive(Copy)]` which
        /// would be a nested `Meta::Path`.
        Meta(Meta),

        /// A Rust literal, like the `"new_name"` in `#[rename("new_name")]`.
        Lit(Lit),
    }
}

/// Conventional argument type associated with an invocation of an attribute
/// macro.
///
/// For example if we are developing an attribute macro that is intended to be
/// invoked on function items as follows:
///
/// ```
/// # const IGNORE: &str = stringify! {
/// #[my_attribute(path = "/v1/refresh")]
/// # };
/// pub fn refresh() {
///     /* ... */
/// }
/// ```
///
/// The implementation of this macro would want to parse its attribute arguments
/// as type `AttributeArgs`.
///
/// ```
/// # extern crate proc_macro;
/// #
/// use proc_macro::TokenStream;
/// use syn::{parse_macro_input, AttributeArgs, ItemFn};
///
/// # const IGNORE: &str = stringify! {
/// #[proc_macro_attribute]
/// # };
/// pub fn my_attribute(args: TokenStream, input: TokenStream) -> TokenStream {
///     let args = parse_macro_input!(args as AttributeArgs);
///     let input = parse_macro_input!(input as ItemFn);
///
///     /* ... */
/// #   "".parse().unwrap()
/// }
/// ```
#[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
pub type AttributeArgs = Vec<NestedMeta>;

pub trait FilterAttrs<'a> {
    type Ret: Iterator<Item = &'a Attribute>;

    fn outer(self) -> Self::Ret;
    fn inner(self) -> Self::Ret;
}

impl<'a, T> FilterAttrs<'a> for T
where
    T: IntoIterator<Item = &'a Attribute>,
{
    type Ret = iter::Filter<T::IntoIter, fn(&&Attribute) -> bool>;

    fn outer(self) -> Self::Ret {
        fn is_outer(attr: &&Attribute) -> bool {
            match attr.style {
                AttrStyle::Outer => true,
                AttrStyle::Inner(_) => false,
            }
        }
        self.into_iter().filter(is_outer)
    }

    fn inner(self) -> Self::Ret {
        fn is_inner(attr: &&Attribute) -> bool {
            match attr.style {
                AttrStyle::Inner(_) => true,
                AttrStyle::Outer => false,
            }
        }
        self.into_iter().filter(is_inner)
    }
}

#[cfg(feature = "parsing")]
pub mod parsing {
    use super::*;
    use crate::ext::IdentExt;
    use crate::parse::{Parse, ParseStream, Result};

    pub fn parse_inner(input: ParseStream, attrs: &mut Vec<Attribute>) -> Result<()> {
        while input.peek(Token![#]) && input.peek2(Token![!]) {
            attrs.push(input.call(parsing::single_parse_inner)?);
        }
        Ok(())
    }

    pub fn single_parse_inner(input: ParseStream) -> Result<Attribute> {
        let content;
        Ok(Attribute {
            pound_token: input.parse()?,
            style: AttrStyle::Inner(input.parse()?),
            bracket_token: bracketed!(content in input),
            path: content.call(Path::parse_mod_style)?,
            tokens: content.parse()?,
        })
    }

    pub fn single_parse_outer(input: ParseStream) -> Result<Attribute> {
        let content;
        Ok(Attribute {
            pound_token: input.parse()?,
            style: AttrStyle::Outer,
            bracket_token: bracketed!(content in input),
            path: content.call(Path::parse_mod_style)?,
            tokens: content.parse()?,
        })
    }

    // Like Path::parse_mod_style but accepts keywords in the path.
    fn parse_meta_path(input: ParseStream) -> Result<Path> {
        Ok(Path {
            leading_colon: input.parse()?,
            segments: {
                let mut segments = Punctuated::new();
                while input.peek(Ident::peek_any) {
                    let ident = Ident::parse_any(input)?;
                    segments.push_value(PathSegment::from(ident));
                    if !input.peek(Token![::]) {
                        break;
                    }
                    let punct = input.parse()?;
                    segments.push_punct(punct);
                }
                if segments.is_empty() {
                    return Err(input.error("expected path"));
                } else if segments.trailing_punct() {
                    return Err(input.error("expected path segment"));
                }
                segments
            },
        })
    }

    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
    impl Parse for Meta {
        fn parse(input: ParseStream) -> Result<Self> {
            let path = input.call(parse_meta_path)?;
            parse_meta_after_path(path, input)
        }
    }

    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
    impl Parse for MetaList {
        fn parse(input: ParseStream) -> Result<Self> {
            let path = input.call(parse_meta_path)?;
            parse_meta_list_after_path(path, input)
        }
    }

    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
    impl Parse for MetaNameValue {
        fn parse(input: ParseStream) -> Result<Self> {
            let path = input.call(parse_meta_path)?;
            parse_meta_name_value_after_path(path, input)
        }
    }

    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
    impl Parse for NestedMeta {
        fn parse(input: ParseStream) -> Result<Self> {
            if input.peek(Lit) && !(input.peek(LitBool) && input.peek2(Token![=])) {
                input.parse().map(NestedMeta::Lit)
            } else if input.peek(Ident::peek_any)
                || input.peek(Token![::]) && input.peek3(Ident::peek_any)
            {
                input.parse().map(NestedMeta::Meta)
            } else {
                Err(input.error("expected identifier or literal"))
            }
        }
    }

    pub fn parse_meta_after_path(path: Path, input: ParseStream) -> Result<Meta> {
        if input.peek(token::Paren) {
            parse_meta_list_after_path(path, input).map(Meta::List)
        } else if input.peek(Token![=]) {
            parse_meta_name_value_after_path(path, input).map(Meta::NameValue)
        } else {
            Ok(Meta::Path(path))
        }
    }

    fn parse_meta_list_after_path(path: Path, input: ParseStream) -> Result<MetaList> {
        let content;
        Ok(MetaList {
            path,
            paren_token: parenthesized!(content in input),
            nested: content.parse_terminated(NestedMeta::parse)?,
        })
    }

    fn parse_meta_name_value_after_path(path: Path, input: ParseStream) -> Result<MetaNameValue> {
        Ok(MetaNameValue {
            path,
            eq_token: input.parse()?,
            lit: input.parse()?,
        })
    }
}

#[cfg(feature = "printing")]
mod printing {
    use super::*;
    use proc_macro2::TokenStream;
    use quote::ToTokens;

    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
    impl ToTokens for Attribute {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.pound_token.to_tokens(tokens);
            if let AttrStyle::Inner(b) = &self.style {
                b.to_tokens(tokens);
            }
            self.bracket_token.surround(tokens, |tokens| {
                self.path.to_tokens(tokens);
                self.tokens.to_tokens(tokens);
            });
        }
    }

    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
    impl ToTokens for MetaList {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.path.to_tokens(tokens);
            self.paren_token.surround(tokens, |tokens| {
                self.nested.to_tokens(tokens);
            })
        }
    }

    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
    impl ToTokens for MetaNameValue {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.path.to_tokens(tokens);
            self.eq_token.to_tokens(tokens);
            self.lit.to_tokens(tokens);
        }
    }
}