1//! [![github]](https://github.com/dtolnay/syn) [![crates-io]](https://crates.io/crates/syn) [![docs-rs]](crate)
2//!
3//! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
4//! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
5//! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs
6//!
7//! <br>
8//!
9//! Syn is a parsing library for parsing a stream of Rust tokens into a syntax
10//! tree of Rust source code.
11//!
12//! Currently this library is geared toward use in Rust procedural macros, but
13//! contains some APIs that may be useful more generally.
14//!
15//! - **Data structures** — Syn provides a complete syntax tree that can
16//! represent any valid Rust source code. The syntax tree is rooted at
17//! [`syn::File`] which represents a full source file, but there are other
18//! entry points that may be useful to procedural macros including
19//! [`syn::Item`], [`syn::Expr`] and [`syn::Type`].
20//!
21//! - **Derives** — Of particular interest to derive macros is
22//! [`syn::DeriveInput`] which is any of the three legal input items to a
23//! derive macro. An example below shows using this type in a library that can
24//! derive implementations of a user-defined trait.
25//!
26//! - **Parsing** — Parsing in Syn is built around [parser functions] with the
27//! signature `fn(ParseStream) -> Result<T>`. Every syntax tree node defined
28//! by Syn is individually parsable and may be used as a building block for
29//! custom syntaxes, or you may dream up your own brand new syntax without
30//! involving any of our syntax tree types.
31//!
32//! - **Location information** — Every token parsed by Syn is associated with a
33//! `Span` that tracks line and column information back to the source of that
34//! token. These spans allow a procedural macro to display detailed error
35//! messages pointing to all the right places in the user's code. There is an
36//! example of this below.
37//!
38//! - **Feature flags** — Functionality is aggressively feature gated so your
39//! procedural macros enable only what they need, and do not pay in compile
40//! time for all the rest.
41//!
42//! [`syn::File`]: File
43//! [`syn::Item`]: Item
44//! [`syn::Expr`]: Expr
45//! [`syn::Type`]: Type
46//! [`syn::DeriveInput`]: DeriveInput
47//! [parser functions]: mod@parse
48//!
49//! <br>
50//!
51//! # Example of a derive macro
52//!
53//! The canonical derive macro using Syn looks like this. We write an ordinary
54//! Rust function tagged with a `proc_macro_derive` attribute and the name of
55//! the trait we are deriving. Any time that derive appears in the user's code,
56//! the Rust compiler passes their data structure as tokens into our macro. We
57//! get to execute arbitrary Rust code to figure out what to do with those
58//! tokens, then hand some tokens back to the compiler to compile into the
59//! user's crate.
60//!
61//! [`TokenStream`]: proc_macro::TokenStream
62//!
63//! ```toml
64//! [dependencies]
65//! syn = "2.0"
66//! quote = "1.0"
67//!
68//! [lib]
69//! proc-macro = true
70//! ```
71//!
72//! ```
73//! # extern crate proc_macro;
74//! #
75//! use proc_macro::TokenStream;
76//! use quote::quote;
77//! use syn::{parse_macro_input, DeriveInput};
78//!
79//! # const IGNORE_TOKENS: &str = stringify! {
80//! #[proc_macro_derive(MyMacro)]
81//! # };
82//! pub fn my_macro(input: TokenStream) -> TokenStream {
83//! // Parse the input tokens into a syntax tree
84//! let input = parse_macro_input!(input as DeriveInput);
85//!
86//! // Build the output, possibly using quasi-quotation
87//! let expanded = quote! {
88//! // ...
89//! };
90//!
91//! // Hand the output tokens back to the compiler
92//! TokenStream::from(expanded)
93//! }
94//! ```
95//!
96//! The [`heapsize`] example directory shows a complete working implementation
97//! of a derive macro. The example derives a `HeapSize` trait which computes an
98//! estimate of the amount of heap memory owned by a value.
99//!
100//! [`heapsize`]: https://github.com/dtolnay/syn/tree/master/examples/heapsize
101//!
102//! ```
103//! pub trait HeapSize {
104//! /// Total number of bytes of heap memory owned by `self`.
105//! fn heap_size_of_children(&self) -> usize;
106//! }
107//! ```
108//!
109//! The derive macro allows users to write `#[derive(HeapSize)]` on data
110//! structures in their program.
111//!
112//! ```
113//! # const IGNORE_TOKENS: &str = stringify! {
114//! #[derive(HeapSize)]
115//! # };
116//! struct Demo<'a, T: ?Sized> {
117//! a: Box<T>,
118//! b: u8,
119//! c: &'a str,
120//! d: String,
121//! }
122//! ```
123//!
124//! <p><br></p>
125//!
126//! # Spans and error reporting
127//!
128//! The token-based procedural macro API provides great control over where the
129//! compiler's error messages are displayed in user code. Consider the error the
130//! user sees if one of their field types does not implement `HeapSize`.
131//!
132//! ```
133//! # const IGNORE_TOKENS: &str = stringify! {
134//! #[derive(HeapSize)]
135//! # };
136//! struct Broken {
137//! ok: String,
138//! bad: std::thread::Thread,
139//! }
140//! ```
141//!
142//! By tracking span information all the way through the expansion of a
143//! procedural macro as shown in the `heapsize` example, token-based macros in
144//! Syn are able to trigger errors that directly pinpoint the source of the
145//! problem.
146//!
147//! ```text
148//! error[E0277]: the trait bound `std::thread::Thread: HeapSize` is not satisfied
149//! --> src/main.rs:7:5
150//! |
151//! 7 | bad: std::thread::Thread,
152//! | ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `HeapSize` is not implemented for `Thread`
153//! ```
154//!
155//! <br>
156//!
157//! # Parsing a custom syntax
158//!
159//! The [`lazy-static`] example directory shows the implementation of a
160//! `functionlike!(...)` procedural macro in which the input tokens are parsed
161//! using Syn's parsing API.
162//!
163//! [`lazy-static`]: https://github.com/dtolnay/syn/tree/master/examples/lazy-static
164//!
165//! The example reimplements the popular `lazy_static` crate from crates.io as a
166//! procedural macro.
167//!
168//! ```
169//! # macro_rules! lazy_static {
170//! # ($($tt:tt)*) => {}
171//! # }
172//! #
173//! lazy_static! {
174//! static ref USERNAME: Regex = Regex::new("^[a-z0-9_-]{3,16}$").unwrap();
175//! }
176//! ```
177//!
178//! The implementation shows how to trigger custom warnings and error messages
179//! on the macro input.
180//!
181//! ```text
182//! warning: come on, pick a more creative name
183//! --> src/main.rs:10:16
184//! |
185//! 10 | static ref FOO: String = "lazy_static".to_owned();
186//! | ^^^
187//! ```
188//!
189//! <br>
190//!
191//! # Testing
192//!
193//! When testing macros, we often care not just that the macro can be used
194//! successfully but also that when the macro is provided with invalid input it
195//! produces maximally helpful error messages. Consider using the [`trybuild`]
196//! crate to write tests for errors that are emitted by your macro or errors
197//! detected by the Rust compiler in the expanded code following misuse of the
198//! macro. Such tests help avoid regressions from later refactors that
199//! mistakenly make an error no longer trigger or be less helpful than it used
200//! to be.
201//!
202//! [`trybuild`]: https://github.com/dtolnay/trybuild
203//!
204//! <br>
205//!
206//! # Debugging
207//!
208//! When developing a procedural macro it can be helpful to look at what the
209//! generated code looks like. Use `cargo rustc -- -Zunstable-options
210//! --pretty=expanded` or the [`cargo expand`] subcommand.
211//!
212//! [`cargo expand`]: https://github.com/dtolnay/cargo-expand
213//!
214//! To show the expanded code for some crate that uses your procedural macro,
215//! run `cargo expand` from that crate. To show the expanded code for one of
216//! your own test cases, run `cargo expand --test the_test_case` where the last
217//! argument is the name of the test file without the `.rs` extension.
218//!
219//! This write-up by Brandon W Maister discusses debugging in more detail:
220//! [Debugging Rust's new Custom Derive system][debugging].
221//!
222//! [debugging]: https://quodlibetor.github.io/posts/debugging-rusts-new-custom-derive-system/
223//!
224//! <br>
225//!
226//! # Optional features
227//!
228//! Syn puts a lot of functionality behind optional features in order to
229//! optimize compile time for the most common use cases. The following features
230//! are available.
231//!
232//! - **`derive`** *(enabled by default)* — Data structures for representing the
233//! possible input to a derive macro, including structs and enums and types.
234//! - **`full`** — Data structures for representing the syntax tree of all valid
235//! Rust source code, including items and expressions.
236//! - **`parsing`** *(enabled by default)* — Ability to parse input tokens into
237//! a syntax tree node of a chosen type.
238//! - **`printing`** *(enabled by default)* — Ability to print a syntax tree
239//! node as tokens of Rust source code.
240//! - **`visit`** — Trait for traversing a syntax tree.
241//! - **`visit-mut`** — Trait for traversing and mutating in place a syntax
242//! tree.
243//! - **`fold`** — Trait for transforming an owned syntax tree.
244//! - **`clone-impls`** *(enabled by default)* — Clone impls for all syntax tree
245//! types.
246//! - **`extra-traits`** — Debug, Eq, PartialEq, Hash impls for all syntax tree
247//! types.
248//! - **`proc-macro`** *(enabled by default)* — Runtime dependency on the
249//! dynamic library libproc_macro from rustc toolchain.
250
251// Syn types in rustdoc of other crates get linked to here.
252#![doc(html_root_url = "https://docs.rs/syn/2.0.32")]
253#![cfg_attr(doc_cfg, feature(doc_cfg))]
254#![allow(non_camel_case_types)]
255#![allow(
256 clippy::bool_to_int_with_if,
257 clippy::cast_lossless,
258 clippy::cast_possible_truncation,
259 clippy::cast_possible_wrap,
260 clippy::cast_ptr_alignment,
261 clippy::default_trait_access,
262 clippy::derivable_impls,
263 clippy::doc_markdown,
264 clippy::expl_impl_clone_on_copy,
265 clippy::explicit_auto_deref,
266 clippy::if_not_else,
267 clippy::inherent_to_string,
268 clippy::items_after_statements,
269 clippy::large_enum_variant,
270 clippy::let_underscore_untyped, // https://github.com/rust-lang/rust-clippy/issues/10410
271 clippy::manual_assert,
272 clippy::manual_let_else,
273 clippy::match_like_matches_macro,
274 clippy::match_on_vec_items,
275 clippy::match_same_arms,
276 clippy::match_wildcard_for_single_variants, // clippy bug: https://github.com/rust-lang/rust-clippy/issues/6984
277 clippy::missing_errors_doc,
278 clippy::missing_panics_doc,
279 clippy::module_name_repetitions,
280 clippy::must_use_candidate,
281 clippy::needless_doctest_main,
282 clippy::needless_pass_by_value,
283 clippy::never_loop,
284 clippy::range_plus_one,
285 clippy::redundant_else,
286 clippy::return_self_not_must_use,
287 clippy::similar_names,
288 clippy::single_match_else,
289 clippy::too_many_arguments,
290 clippy::too_many_lines,
291 clippy::trivially_copy_pass_by_ref,
292 clippy::uninlined_format_args,
293 clippy::unnecessary_box_returns,
294 clippy::unnecessary_unwrap,
295 clippy::used_underscore_binding,
296 clippy::wildcard_imports,
297)]
298
299#[cfg(feature = "proc-macro")]
300extern crate proc_macro;
301
302#[macro_use]
303mod macros;
304
305#[cfg(feature = "parsing")]
306#[macro_use]
307mod group;
308
309#[macro_use]
310pub mod token;
311
312#[cfg(any(feature = "full", feature = "derive"))]
313mod attr;
314#[cfg(any(feature = "full", feature = "derive"))]
315pub use crate::attr::{AttrStyle, Attribute, Meta, MetaList, MetaNameValue};
316
317mod bigint;
318
319#[cfg(feature = "parsing")]
320#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
321pub mod buffer;
322
323mod custom_keyword;
324
325mod custom_punctuation;
326
327#[cfg(any(feature = "full", feature = "derive"))]
328mod data;
329#[cfg(any(feature = "full", feature = "derive"))]
330pub use crate::data::{Field, Fields, FieldsNamed, FieldsUnnamed, Variant};
331
332#[cfg(any(feature = "full", feature = "derive"))]
333mod derive;
334#[cfg(feature = "derive")]
335pub use crate::derive::{Data, DataEnum, DataStruct, DataUnion, DeriveInput};
336
337mod drops;
338
339mod error;
340pub use crate::error::{Error, Result};
341
342#[cfg(any(feature = "full", feature = "derive"))]
343mod expr;
344#[cfg(feature = "full")]
345pub use crate::expr::{Arm, FieldValue, Label, RangeLimits};
346#[cfg(any(feature = "full", feature = "derive"))]
347pub use crate::expr::{
348 Expr, ExprArray, ExprAssign, ExprAsync, ExprAwait, ExprBinary, ExprBlock, ExprBreak, ExprCall,
349 ExprCast, ExprClosure, ExprConst, ExprContinue, ExprField, ExprForLoop, ExprGroup, ExprIf,
350 ExprIndex, ExprInfer, ExprLet, ExprLit, ExprLoop, ExprMacro, ExprMatch, ExprMethodCall,
351 ExprParen, ExprPath, ExprRange, ExprReference, ExprRepeat, ExprReturn, ExprStruct, ExprTry,
352 ExprTryBlock, ExprTuple, ExprUnary, ExprUnsafe, ExprWhile, ExprYield, Index, Member,
353};
354
355#[cfg(feature = "parsing")]
356#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
357pub mod ext;
358
359#[cfg(feature = "full")]
360mod file;
361#[cfg(feature = "full")]
362pub use crate::file::File;
363
364#[cfg(any(feature = "full", feature = "derive"))]
365mod generics;
366#[cfg(any(feature = "full", feature = "derive"))]
367pub use crate::generics::{
368 BoundLifetimes, ConstParam, GenericParam, Generics, LifetimeParam, PredicateLifetime,
369 PredicateType, TraitBound, TraitBoundModifier, TypeParam, TypeParamBound, WhereClause,
370 WherePredicate,
371};
372#[cfg(all(any(feature = "full", feature = "derive"), feature = "printing"))]
373pub use crate::generics::{ImplGenerics, Turbofish, TypeGenerics};
374
375mod ident;
376#[doc(inline)]
377pub use crate::ident::Ident;
378
379#[cfg(feature = "full")]
380mod item;
381#[cfg(feature = "full")]
382pub use crate::item::{
383 FnArg, ForeignItem, ForeignItemFn, ForeignItemMacro, ForeignItemStatic, ForeignItemType,
384 ImplItem, ImplItemConst, ImplItemFn, ImplItemMacro, ImplItemType, ImplRestriction, Item,
385 ItemConst, ItemEnum, ItemExternCrate, ItemFn, ItemForeignMod, ItemImpl, ItemMacro, ItemMod,
386 ItemStatic, ItemStruct, ItemTrait, ItemTraitAlias, ItemType, ItemUnion, ItemUse, Receiver,
387 Signature, StaticMutability, TraitItem, TraitItemConst, TraitItemFn, TraitItemMacro,
388 TraitItemType, UseGlob, UseGroup, UseName, UsePath, UseRename, UseTree, Variadic,
389};
390
391mod lifetime;
392#[doc(inline)]
393pub use crate::lifetime::Lifetime;
394
395mod lit;
396#[doc(inline)]
397pub use crate::lit::{
398 Lit, LitBool, LitByte, LitByteStr, LitChar, LitFloat, LitInt, LitStr, StrStyle,
399};
400
401#[cfg(feature = "parsing")]
402mod lookahead;
403
404#[cfg(any(feature = "full", feature = "derive"))]
405mod mac;
406#[cfg(any(feature = "full", feature = "derive"))]
407pub use crate::mac::{Macro, MacroDelimiter};
408
409#[cfg(all(feature = "parsing", any(feature = "full", feature = "derive")))]
410#[cfg_attr(
411 doc_cfg,
412 doc(cfg(all(feature = "parsing", any(feature = "full", feature = "derive"))))
413)]
414pub mod meta;
415
416#[cfg(any(feature = "full", feature = "derive"))]
417mod op;
418#[cfg(any(feature = "full", feature = "derive"))]
419pub use crate::op::{BinOp, UnOp};
420
421#[cfg(feature = "parsing")]
422#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
423pub mod parse;
424
425#[cfg(all(feature = "parsing", feature = "proc-macro"))]
426mod parse_macro_input;
427
428#[cfg(all(feature = "parsing", feature = "printing"))]
429mod parse_quote;
430
431#[cfg(feature = "full")]
432mod pat;
433#[cfg(feature = "full")]
434pub use crate::expr::{
435 ExprConst as PatConst, ExprLit as PatLit, ExprMacro as PatMacro, ExprPath as PatPath,
436 ExprRange as PatRange,
437};
438#[cfg(feature = "full")]
439pub use crate::pat::{
440 FieldPat, Pat, PatIdent, PatOr, PatParen, PatReference, PatRest, PatSlice, PatStruct, PatTuple,
441 PatTupleStruct, PatType, PatWild,
442};
443
444#[cfg(any(feature = "full", feature = "derive"))]
445mod path;
446#[cfg(any(feature = "full", feature = "derive"))]
447pub use crate::path::{
448 AngleBracketedGenericArguments, AssocConst, AssocType, Constraint, GenericArgument,
449 ParenthesizedGenericArguments, Path, PathArguments, PathSegment, QSelf,
450};
451
452#[cfg(all(any(feature = "full", feature = "derive"), feature = "printing"))]
453mod print;
454
455pub mod punctuated;
456
457#[cfg(any(feature = "full", feature = "derive"))]
458mod restriction;
459#[cfg(any(feature = "full", feature = "derive"))]
460pub use crate::restriction::{FieldMutability, VisRestricted, Visibility};
461
462mod sealed;
463
464mod span;
465
466#[cfg(all(feature = "parsing", feature = "printing"))]
467#[cfg_attr(doc_cfg, doc(cfg(all(feature = "parsing", feature = "printing"))))]
468pub mod spanned;
469
470#[cfg(feature = "full")]
471mod stmt;
472#[cfg(feature = "full")]
473pub use crate::stmt::{Block, Local, LocalInit, Stmt, StmtMacro};
474
475mod thread;
476
477#[cfg(all(any(feature = "full", feature = "derive"), feature = "extra-traits"))]
478mod tt;
479
480#[cfg(any(feature = "full", feature = "derive"))]
481mod ty;
482#[cfg(any(feature = "full", feature = "derive"))]
483pub use crate::ty::{
484 Abi, BareFnArg, BareVariadic, ReturnType, Type, TypeArray, TypeBareFn, TypeGroup,
485 TypeImplTrait, TypeInfer, TypeMacro, TypeNever, TypeParen, TypePath, TypePtr, TypeReference,
486 TypeSlice, TypeTraitObject, TypeTuple,
487};
488
489#[cfg(all(any(feature = "full", feature = "derive"), feature = "parsing"))]
490mod verbatim;
491
492#[cfg(all(feature = "parsing", feature = "full"))]
493mod whitespace;
494
495mod gen {
496 /// Syntax tree traversal to transform the nodes of an owned syntax tree.
497 ///
498 /// Each method of the [`Fold`] trait is a hook that can be overridden to
499 /// customize the behavior when transforming the corresponding type of node.
500 /// By default, every method recursively visits the substructure of the
501 /// input by invoking the right visitor method of each of its fields.
502 ///
503 /// [`Fold`]: fold::Fold
504 ///
505 /// ```
506 /// # use syn::{Attribute, BinOp, Expr, ExprBinary};
507 /// #
508 /// pub trait Fold {
509 /// /* ... */
510 ///
511 /// fn fold_expr_binary(&mut self, node: ExprBinary) -> ExprBinary {
512 /// fold_expr_binary(self, node)
513 /// }
514 ///
515 /// /* ... */
516 /// # fn fold_attribute(&mut self, node: Attribute) -> Attribute;
517 /// # fn fold_expr(&mut self, node: Expr) -> Expr;
518 /// # fn fold_bin_op(&mut self, node: BinOp) -> BinOp;
519 /// }
520 ///
521 /// pub fn fold_expr_binary<V>(v: &mut V, node: ExprBinary) -> ExprBinary
522 /// where
523 /// V: Fold + ?Sized,
524 /// {
525 /// ExprBinary {
526 /// attrs: node
527 /// .attrs
528 /// .into_iter()
529 /// .map(|attr| v.fold_attribute(attr))
530 /// .collect(),
531 /// left: Box::new(v.fold_expr(*node.left)),
532 /// op: v.fold_bin_op(node.op),
533 /// right: Box::new(v.fold_expr(*node.right)),
534 /// }
535 /// }
536 ///
537 /// /* ... */
538 /// ```
539 ///
540 /// <br>
541 ///
542 /// # Example
543 ///
544 /// This fold inserts parentheses to fully parenthesizes any expression.
545 ///
546 /// ```
547 /// // [dependencies]
548 /// // quote = "1.0"
549 /// // syn = { version = "2.0", features = ["fold", "full"] }
550 ///
551 /// use quote::quote;
552 /// use syn::fold::{fold_expr, Fold};
553 /// use syn::{token, Expr, ExprParen};
554 ///
555 /// struct ParenthesizeEveryExpr;
556 ///
557 /// impl Fold for ParenthesizeEveryExpr {
558 /// fn fold_expr(&mut self, expr: Expr) -> Expr {
559 /// Expr::Paren(ExprParen {
560 /// attrs: Vec::new(),
561 /// expr: Box::new(fold_expr(self, expr)),
562 /// paren_token: token::Paren::default(),
563 /// })
564 /// }
565 /// }
566 ///
567 /// fn main() {
568 /// let code = quote! { a() + b(1) * c.d };
569 /// let expr: Expr = syn::parse2(code).unwrap();
570 /// let parenthesized = ParenthesizeEveryExpr.fold_expr(expr);
571 /// println!("{}", quote!(#parenthesized));
572 ///
573 /// // Output: (((a)()) + (((b)((1))) * ((c).d)))
574 /// }
575 /// ```
576 #[cfg(feature = "fold")]
577 #[cfg_attr(doc_cfg, doc(cfg(feature = "fold")))]
578 #[rustfmt::skip]
579 pub mod fold;
580
581 /// Syntax tree traversal to walk a shared borrow of a syntax tree.
582 ///
583 /// Each method of the [`Visit`] trait is a hook that can be overridden to
584 /// customize the behavior when visiting the corresponding type of node. By
585 /// default, every method recursively visits the substructure of the input
586 /// by invoking the right visitor method of each of its fields.
587 ///
588 /// [`Visit`]: visit::Visit
589 ///
590 /// ```
591 /// # use syn::{Attribute, BinOp, Expr, ExprBinary};
592 /// #
593 /// pub trait Visit<'ast> {
594 /// /* ... */
595 ///
596 /// fn visit_expr_binary(&mut self, node: &'ast ExprBinary) {
597 /// visit_expr_binary(self, node);
598 /// }
599 ///
600 /// /* ... */
601 /// # fn visit_attribute(&mut self, node: &'ast Attribute);
602 /// # fn visit_expr(&mut self, node: &'ast Expr);
603 /// # fn visit_bin_op(&mut self, node: &'ast BinOp);
604 /// }
605 ///
606 /// pub fn visit_expr_binary<'ast, V>(v: &mut V, node: &'ast ExprBinary)
607 /// where
608 /// V: Visit<'ast> + ?Sized,
609 /// {
610 /// for attr in &node.attrs {
611 /// v.visit_attribute(attr);
612 /// }
613 /// v.visit_expr(&*node.left);
614 /// v.visit_bin_op(&node.op);
615 /// v.visit_expr(&*node.right);
616 /// }
617 ///
618 /// /* ... */
619 /// ```
620 ///
621 /// <br>
622 ///
623 /// # Example
624 ///
625 /// This visitor will print the name of every freestanding function in the
626 /// syntax tree, including nested functions.
627 ///
628 /// ```
629 /// // [dependencies]
630 /// // quote = "1.0"
631 /// // syn = { version = "2.0", features = ["full", "visit"] }
632 ///
633 /// use quote::quote;
634 /// use syn::visit::{self, Visit};
635 /// use syn::{File, ItemFn};
636 ///
637 /// struct FnVisitor;
638 ///
639 /// impl<'ast> Visit<'ast> for FnVisitor {
640 /// fn visit_item_fn(&mut self, node: &'ast ItemFn) {
641 /// println!("Function with name={}", node.sig.ident);
642 ///
643 /// // Delegate to the default impl to visit any nested functions.
644 /// visit::visit_item_fn(self, node);
645 /// }
646 /// }
647 ///
648 /// fn main() {
649 /// let code = quote! {
650 /// pub fn f() {
651 /// fn g() {}
652 /// }
653 /// };
654 ///
655 /// let syntax_tree: File = syn::parse2(code).unwrap();
656 /// FnVisitor.visit_file(&syntax_tree);
657 /// }
658 /// ```
659 ///
660 /// The `'ast` lifetime on the input references means that the syntax tree
661 /// outlives the complete recursive visit call, so the visitor is allowed to
662 /// hold on to references into the syntax tree.
663 ///
664 /// ```
665 /// use quote::quote;
666 /// use syn::visit::{self, Visit};
667 /// use syn::{File, ItemFn};
668 ///
669 /// struct FnVisitor<'ast> {
670 /// functions: Vec<&'ast ItemFn>,
671 /// }
672 ///
673 /// impl<'ast> Visit<'ast> for FnVisitor<'ast> {
674 /// fn visit_item_fn(&mut self, node: &'ast ItemFn) {
675 /// self.functions.push(node);
676 /// visit::visit_item_fn(self, node);
677 /// }
678 /// }
679 ///
680 /// fn main() {
681 /// let code = quote! {
682 /// pub fn f() {
683 /// fn g() {}
684 /// }
685 /// };
686 ///
687 /// let syntax_tree: File = syn::parse2(code).unwrap();
688 /// let mut visitor = FnVisitor { functions: Vec::new() };
689 /// visitor.visit_file(&syntax_tree);
690 /// for f in visitor.functions {
691 /// println!("Function with name={}", f.sig.ident);
692 /// }
693 /// }
694 /// ```
695 #[cfg(feature = "visit")]
696 #[cfg_attr(doc_cfg, doc(cfg(feature = "visit")))]
697 #[rustfmt::skip]
698 pub mod visit;
699
700 /// Syntax tree traversal to mutate an exclusive borrow of a syntax tree in
701 /// place.
702 ///
703 /// Each method of the [`VisitMut`] trait is a hook that can be overridden
704 /// to customize the behavior when mutating the corresponding type of node.
705 /// By default, every method recursively visits the substructure of the
706 /// input by invoking the right visitor method of each of its fields.
707 ///
708 /// [`VisitMut`]: visit_mut::VisitMut
709 ///
710 /// ```
711 /// # use syn::{Attribute, BinOp, Expr, ExprBinary};
712 /// #
713 /// pub trait VisitMut {
714 /// /* ... */
715 ///
716 /// fn visit_expr_binary_mut(&mut self, node: &mut ExprBinary) {
717 /// visit_expr_binary_mut(self, node);
718 /// }
719 ///
720 /// /* ... */
721 /// # fn visit_attribute_mut(&mut self, node: &mut Attribute);
722 /// # fn visit_expr_mut(&mut self, node: &mut Expr);
723 /// # fn visit_bin_op_mut(&mut self, node: &mut BinOp);
724 /// }
725 ///
726 /// pub fn visit_expr_binary_mut<V>(v: &mut V, node: &mut ExprBinary)
727 /// where
728 /// V: VisitMut + ?Sized,
729 /// {
730 /// for attr in &mut node.attrs {
731 /// v.visit_attribute_mut(attr);
732 /// }
733 /// v.visit_expr_mut(&mut *node.left);
734 /// v.visit_bin_op_mut(&mut node.op);
735 /// v.visit_expr_mut(&mut *node.right);
736 /// }
737 ///
738 /// /* ... */
739 /// ```
740 ///
741 /// <br>
742 ///
743 /// # Example
744 ///
745 /// This mut visitor replace occurrences of u256 suffixed integer literals
746 /// like `999u256` with a macro invocation `bigint::u256!(999)`.
747 ///
748 /// ```
749 /// // [dependencies]
750 /// // quote = "1.0"
751 /// // syn = { version = "2.0", features = ["full", "visit-mut"] }
752 ///
753 /// use quote::quote;
754 /// use syn::visit_mut::{self, VisitMut};
755 /// use syn::{parse_quote, Expr, File, Lit, LitInt};
756 ///
757 /// struct BigintReplace;
758 ///
759 /// impl VisitMut for BigintReplace {
760 /// fn visit_expr_mut(&mut self, node: &mut Expr) {
761 /// if let Expr::Lit(expr) = &node {
762 /// if let Lit::Int(int) = &expr.lit {
763 /// if int.suffix() == "u256" {
764 /// let digits = int.base10_digits();
765 /// let unsuffixed: LitInt = syn::parse_str(digits).unwrap();
766 /// *node = parse_quote!(bigint::u256!(#unsuffixed));
767 /// return;
768 /// }
769 /// }
770 /// }
771 ///
772 /// // Delegate to the default impl to visit nested expressions.
773 /// visit_mut::visit_expr_mut(self, node);
774 /// }
775 /// }
776 ///
777 /// fn main() {
778 /// let code = quote! {
779 /// fn main() {
780 /// let _ = 999u256;
781 /// }
782 /// };
783 ///
784 /// let mut syntax_tree: File = syn::parse2(code).unwrap();
785 /// BigintReplace.visit_file_mut(&mut syntax_tree);
786 /// println!("{}", quote!(#syntax_tree));
787 /// }
788 /// ```
789 #[cfg(feature = "visit-mut")]
790 #[cfg_attr(doc_cfg, doc(cfg(feature = "visit-mut")))]
791 #[rustfmt::skip]
792 pub mod visit_mut;
793
794 #[cfg(feature = "clone-impls")]
795 #[rustfmt::skip]
796 mod clone;
797
798 #[cfg(feature = "extra-traits")]
799 #[rustfmt::skip]
800 mod debug;
801
802 #[cfg(feature = "extra-traits")]
803 #[rustfmt::skip]
804 mod eq;
805
806 #[cfg(feature = "extra-traits")]
807 #[rustfmt::skip]
808 mod hash;
809
810 #[cfg(any(feature = "full", feature = "derive"))]
811 #[path = "../gen_helper.rs"]
812 mod helper;
813}
814pub use crate::gen::*;
815
816// Not public API.
817#[doc(hidden)]
818#[path = "export.rs"]
819pub mod __private;
820
821/// Parse tokens of source code into the chosen syntax tree node.
822///
823/// This is preferred over parsing a string because tokens are able to preserve
824/// information about where in the user's code they were originally written (the
825/// "span" of the token), possibly allowing the compiler to produce better error
826/// messages.
827///
828/// This function parses a `proc_macro::TokenStream` which is the type used for
829/// interop with the compiler in a procedural macro. To parse a
830/// `proc_macro2::TokenStream`, use [`syn::parse2`] instead.
831///
832/// [`syn::parse2`]: parse2
833///
834/// # Examples
835///
836/// ```
837/// # extern crate proc_macro;
838/// #
839/// use proc_macro::TokenStream;
840/// use quote::quote;
841/// use syn::DeriveInput;
842///
843/// # const IGNORE_TOKENS: &str = stringify! {
844/// #[proc_macro_derive(MyMacro)]
845/// # };
846/// pub fn my_macro(input: TokenStream) -> TokenStream {
847/// // Parse the tokens into a syntax tree
848/// let ast: DeriveInput = syn::parse(input).unwrap();
849///
850/// // Build the output, possibly using quasi-quotation
851/// let expanded = quote! {
852/// /* ... */
853/// };
854///
855/// // Convert into a token stream and return it
856/// expanded.into()
857/// }
858/// ```
859#[cfg(all(feature = "parsing", feature = "proc-macro"))]
860#[cfg_attr(doc_cfg, doc(cfg(all(feature = "parsing", feature = "proc-macro"))))]
861pub fn parse<T: parse::Parse>(tokens: proc_macro::TokenStream) -> Result<T> {
862 parse::Parser::parse(T::parse, tokens)
863}
864
865/// Parse a proc-macro2 token stream into the chosen syntax tree node.
866///
867/// This function will check that the input is fully parsed. If there are
868/// any unparsed tokens at the end of the stream, an error is returned.
869///
870/// This function parses a `proc_macro2::TokenStream` which is commonly useful
871/// when the input comes from a node of the Syn syntax tree, for example the
872/// body tokens of a [`Macro`] node. When in a procedural macro parsing the
873/// `proc_macro::TokenStream` provided by the compiler, use [`syn::parse`]
874/// instead.
875///
876/// [`syn::parse`]: parse()
877#[cfg(feature = "parsing")]
878#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
879pub fn parse2<T: parse::Parse>(tokens: proc_macro2::TokenStream) -> Result<T> {
880 parse::Parser::parse2(T::parse, tokens)
881}
882
883/// Parse a string of Rust code into the chosen syntax tree node.
884///
885/// # Hygiene
886///
887/// Every span in the resulting syntax tree will be set to resolve at the macro
888/// call site.
889///
890/// # Examples
891///
892/// ```
893/// use syn::{Expr, Result};
894///
895/// fn run() -> Result<()> {
896/// let code = "assert_eq!(u8::max_value(), 255)";
897/// let expr = syn::parse_str::<Expr>(code)?;
898/// println!("{:#?}", expr);
899/// Ok(())
900/// }
901/// #
902/// # run().unwrap();
903/// ```
904#[cfg(feature = "parsing")]
905#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
906pub fn parse_str<T: parse::Parse>(s: &str) -> Result<T> {
907 parse::Parser::parse_str(T::parse, s)
908}
909
910// FIXME the name parse_file makes it sound like you might pass in a path to a
911// file, rather than the content.
912/// Parse the content of a file of Rust code.
913///
914/// This is different from `syn::parse_str::<File>(content)` in two ways:
915///
916/// - It discards a leading byte order mark `\u{FEFF}` if the file has one.
917/// - It preserves the shebang line of the file, such as `#!/usr/bin/env rustx`.
918///
919/// If present, either of these would be an error using `from_str`.
920///
921/// # Examples
922///
923/// ```no_run
924/// use std::error::Error;
925/// use std::fs::File;
926/// use std::io::Read;
927///
928/// fn run() -> Result<(), Box<dyn Error>> {
929/// let mut file = File::open("path/to/code.rs")?;
930/// let mut content = String::new();
931/// file.read_to_string(&mut content)?;
932///
933/// let ast = syn::parse_file(&content)?;
934/// if let Some(shebang) = ast.shebang {
935/// println!("{}", shebang);
936/// }
937/// println!("{} items", ast.items.len());
938///
939/// Ok(())
940/// }
941/// #
942/// # run().unwrap();
943/// ```
944#[cfg(all(feature = "parsing", feature = "full"))]
945#[cfg_attr(doc_cfg, doc(cfg(all(feature = "parsing", feature = "full"))))]
946pub fn parse_file(mut content: &str) -> Result<File> {
947 // Strip the BOM if it is present
948 const BOM: &str = "\u{feff}";
949 if content.starts_with(BOM) {
950 content = &content[BOM.len()..];
951 }
952
953 let mut shebang = None;
954 if content.starts_with("#!") {
955 let rest = whitespace::skip(&content[2..]);
956 if !rest.starts_with('[') {
957 if let Some(idx) = content.find('\n') {
958 shebang = Some(content[..idx].to_string());
959 content = &content[idx..];
960 } else {
961 shebang = Some(content.to_string());
962 content = "";
963 }
964 }
965 }
966
967 let mut file: File = parse_str(content)?;
968 file.shebang = shebang;
969 Ok(file)
970}
971