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 = "1.0"
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. It works on any Rust compiler 1.31+. The example derives
98//! a `HeapSize` trait which computes an estimate of the amount of heap memory
99//! owned by a value.
100//!
101//! [`heapsize`]: https://github.com/dtolnay/syn/tree/master/examples/heapsize
102//!
103//! ```
104//! pub trait HeapSize {
105//! /// Total number of bytes of heap memory owned by `self`.
106//! fn heap_size_of_children(&self) -> usize;
107//! }
108//! ```
109//!
110//! The derive macro allows users to write `#[derive(HeapSize)]` on data
111//! structures in their program.
112//!
113//! ```
114//! # const IGNORE_TOKENS: &str = stringify! {
115//! #[derive(HeapSize)]
116//! # };
117//! struct Demo<'a, T: ?Sized> {
118//! a: Box<T>,
119//! b: u8,
120//! c: &'a str,
121//! d: String,
122//! }
123//! ```
124//!
125//! <p><br></p>
126//!
127//! # Spans and error reporting
128//!
129//! The token-based procedural macro API provides great control over where the
130//! compiler's error messages are displayed in user code. Consider the error the
131//! user sees if one of their field types does not implement `HeapSize`.
132//!
133//! ```
134//! # const IGNORE_TOKENS: &str = stringify! {
135//! #[derive(HeapSize)]
136//! # };
137//! struct Broken {
138//! ok: String,
139//! bad: std::thread::Thread,
140//! }
141//! ```
142//!
143//! By tracking span information all the way through the expansion of a
144//! procedural macro as shown in the `heapsize` example, token-based macros in
145//! Syn are able to trigger errors that directly pinpoint the source of the
146//! problem.
147//!
148//! ```text
149//! error[E0277]: the trait bound `std::thread::Thread: HeapSize` is not satisfied
150//! --> src/main.rs:7:5
151//! |
152//! 7 | bad: std::thread::Thread,
153//! | ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `HeapSize` is not implemented for `Thread`
154//! ```
155//!
156//! <br>
157//!
158//! # Parsing a custom syntax
159//!
160//! The [`lazy-static`] example directory shows the implementation of a
161//! `functionlike!(...)` procedural macro in which the input tokens are parsed
162//! using Syn's parsing API.
163//!
164//! [`lazy-static`]: https://github.com/dtolnay/syn/tree/master/examples/lazy-static
165//!
166//! The example reimplements the popular `lazy_static` crate from crates.io as a
167//! procedural macro.
168//!
169//! ```
170//! # macro_rules! lazy_static {
171//! # ($($tt:tt)*) => {}
172//! # }
173//! #
174//! lazy_static! {
175//! static ref USERNAME: Regex = Regex::new("^[a-z0-9_-]{3,16}$").unwrap();
176//! }
177//! ```
178//!
179//! The implementation shows how to trigger custom warnings and error messages
180//! on the macro input.
181//!
182//! ```text
183//! warning: come on, pick a more creative name
184//! --> src/main.rs:10:16
185//! |
186//! 10 | static ref FOO: String = "lazy_static".to_owned();
187//! | ^^^
188//! ```
189//!
190//! <br>
191//!
192//! # Testing
193//!
194//! When testing macros, we often care not just that the macro can be used
195//! successfully but also that when the macro is provided with invalid input it
196//! produces maximally helpful error messages. Consider using the [`trybuild`]
197//! crate to write tests for errors that are emitted by your macro or errors
198//! detected by the Rust compiler in the expanded code following misuse of the
199//! macro. Such tests help avoid regressions from later refactors that
200//! mistakenly make an error no longer trigger or be less helpful than it used
201//! to be.
202//!
203//! [`trybuild`]: https://github.com/dtolnay/trybuild
204//!
205//! <br>
206//!
207//! # Debugging
208//!
209//! When developing a procedural macro it can be helpful to look at what the
210//! generated code looks like. Use `cargo rustc -- -Zunstable-options
211//! --pretty=expanded` or the [`cargo expand`] subcommand.
212//!
213//! [`cargo expand`]: https://github.com/dtolnay/cargo-expand
214//!
215//! To show the expanded code for some crate that uses your procedural macro,
216//! run `cargo expand` from that crate. To show the expanded code for one of
217//! your own test cases, run `cargo expand --test the_test_case` where the last
218//! argument is the name of the test file without the `.rs` extension.
219//!
220//! This write-up by Brandon W Maister discusses debugging in more detail:
221//! [Debugging Rust's new Custom Derive system][debugging].
222//!
223//! [debugging]: https://quodlibetor.github.io/posts/debugging-rusts-new-custom-derive-system/
224//!
225//! <br>
226//!
227//! # Optional features
228//!
229//! Syn puts a lot of functionality behind optional features in order to
230//! optimize compile time for the most common use cases. The following features
231//! are available.
232//!
233//! - **`derive`** *(enabled by default)* — Data structures for representing the
234//! possible input to a derive macro, including structs and enums and types.
235//! - **`full`** — Data structures for representing the syntax tree of all valid
236//! Rust source code, including items and expressions.
237//! - **`parsing`** *(enabled by default)* — Ability to parse input tokens into
238//! a syntax tree node of a chosen type.
239//! - **`printing`** *(enabled by default)* — Ability to print a syntax tree
240//! node as tokens of Rust source code.
241//! - **`visit`** — Trait for traversing a syntax tree.
242//! - **`visit-mut`** — Trait for traversing and mutating in place a syntax
243//! tree.
244//! - **`fold`** — Trait for transforming an owned syntax tree.
245//! - **`clone-impls`** *(enabled by default)* — Clone impls for all syntax tree
246//! types.
247//! - **`extra-traits`** — Debug, Eq, PartialEq, Hash impls for all syntax tree
248//! types.
249//! - **`proc-macro`** *(enabled by default)* — Runtime dependency on the
250//! dynamic library libproc_macro from rustc toolchain.
251
252// Syn types in rustdoc of other crates get linked to here.
253#![doc(html_root_url = "https://docs.rs/syn/1.0.109")]
254#![cfg_attr(doc_cfg, feature(doc_cfg))]
255#![allow(non_camel_case_types)]
256#![allow(
257 clippy::bool_to_int_with_if,
258 clippy::cast_lossless,
259 clippy::cast_possible_truncation,
260 clippy::cast_possible_wrap,
261 clippy::cast_ptr_alignment,
262 clippy::default_trait_access,
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::manual_assert,
271 clippy::match_on_vec_items,
272 clippy::match_same_arms,
273 clippy::match_wildcard_for_single_variants, // clippy bug: https://github.com/rust-lang/rust-clippy/issues/6984
274 clippy::missing_errors_doc,
275 clippy::missing_panics_doc,
276 clippy::module_name_repetitions,
277 clippy::must_use_candidate,
278 clippy::needless_doctest_main,
279 clippy::needless_pass_by_value,
280 clippy::never_loop,
281 clippy::redundant_else,
282 clippy::return_self_not_must_use,
283 clippy::similar_names,
284 clippy::single_match_else,
285 clippy::too_many_arguments,
286 clippy::too_many_lines,
287 clippy::trivially_copy_pass_by_ref,
288 clippy::unnecessary_unwrap,
289 clippy::used_underscore_binding,
290 clippy::wildcard_imports
291)]
292
293#[cfg(all(
294 not(all(target_arch = "wasm32", any(target_os = "unknown", target_os = "wasi"))),
295 feature = "proc-macro"
296))]
297extern crate proc_macro;
298extern crate proc_macro2;
299
300#[cfg(feature = "printing")]
301extern crate quote;
302
303#[macro_use]
304mod macros;
305
306#[cfg(feature = "parsing")]
307#[macro_use]
308mod group;
309
310#[macro_use]
311pub mod token;
312
313mod ident;
314pub use crate::ident::Ident;
315
316#[cfg(any(feature = "full", feature = "derive"))]
317mod attr;
318#[cfg(any(feature = "full", feature = "derive"))]
319pub use crate::attr::{
320 AttrStyle, Attribute, AttributeArgs, Meta, MetaList, MetaNameValue, NestedMeta,
321};
322
323mod bigint;
324
325#[cfg(any(feature = "full", feature = "derive"))]
326mod data;
327#[cfg(any(feature = "full", feature = "derive"))]
328pub use crate::data::{
329 Field, Fields, FieldsNamed, FieldsUnnamed, Variant, VisCrate, VisPublic, VisRestricted,
330 Visibility,
331};
332
333#[cfg(any(feature = "full", feature = "derive"))]
334mod expr;
335#[cfg(feature = "full")]
336pub use crate::expr::{
337 Arm, FieldValue, GenericMethodArgument, Label, MethodTurbofish, RangeLimits,
338};
339#[cfg(any(feature = "full", feature = "derive"))]
340pub use crate::expr::{
341 Expr, ExprArray, ExprAssign, ExprAssignOp, ExprAsync, ExprAwait, ExprBinary, ExprBlock,
342 ExprBox, ExprBreak, ExprCall, ExprCast, ExprClosure, ExprContinue, ExprField, ExprForLoop,
343 ExprGroup, ExprIf, ExprIndex, ExprLet, ExprLit, ExprLoop, ExprMacro, ExprMatch, ExprMethodCall,
344 ExprParen, ExprPath, ExprRange, ExprReference, ExprRepeat, ExprReturn, ExprStruct, ExprTry,
345 ExprTryBlock, ExprTuple, ExprType, ExprUnary, ExprUnsafe, ExprWhile, ExprYield, Index, Member,
346};
347
348#[cfg(any(feature = "full", feature = "derive"))]
349mod generics;
350#[cfg(any(feature = "full", feature = "derive"))]
351pub use crate::generics::{
352 BoundLifetimes, ConstParam, GenericParam, Generics, LifetimeDef, PredicateEq,
353 PredicateLifetime, PredicateType, TraitBound, TraitBoundModifier, TypeParam, TypeParamBound,
354 WhereClause, WherePredicate,
355};
356#[cfg(all(any(feature = "full", feature = "derive"), feature = "printing"))]
357pub use crate::generics::{ImplGenerics, Turbofish, TypeGenerics};
358
359#[cfg(feature = "full")]
360mod item;
361#[cfg(feature = "full")]
362pub use crate::item::{
363 FnArg, ForeignItem, ForeignItemFn, ForeignItemMacro, ForeignItemStatic, ForeignItemType,
364 ImplItem, ImplItemConst, ImplItemMacro, ImplItemMethod, ImplItemType, Item, ItemConst,
365 ItemEnum, ItemExternCrate, ItemFn, ItemForeignMod, ItemImpl, ItemMacro, ItemMacro2, ItemMod,
366 ItemStatic, ItemStruct, ItemTrait, ItemTraitAlias, ItemType, ItemUnion, ItemUse, Receiver,
367 Signature, TraitItem, TraitItemConst, TraitItemMacro, TraitItemMethod, TraitItemType, UseGlob,
368 UseGroup, UseName, UsePath, UseRename, UseTree,
369};
370
371#[cfg(feature = "full")]
372mod file;
373#[cfg(feature = "full")]
374pub use crate::file::File;
375
376mod lifetime;
377pub use crate::lifetime::Lifetime;
378
379mod lit;
380pub use crate::lit::{
381 Lit, LitBool, LitByte, LitByteStr, LitChar, LitFloat, LitInt, LitStr, StrStyle,
382};
383
384#[cfg(any(feature = "full", feature = "derive"))]
385mod mac;
386#[cfg(any(feature = "full", feature = "derive"))]
387pub use crate::mac::{Macro, MacroDelimiter};
388
389#[cfg(any(feature = "full", feature = "derive"))]
390mod derive;
391#[cfg(feature = "derive")]
392pub use crate::derive::{Data, DataEnum, DataStruct, DataUnion, DeriveInput};
393
394#[cfg(any(feature = "full", feature = "derive"))]
395mod op;
396#[cfg(any(feature = "full", feature = "derive"))]
397pub use crate::op::{BinOp, UnOp};
398
399#[cfg(feature = "full")]
400mod stmt;
401#[cfg(feature = "full")]
402pub use crate::stmt::{Block, Local, Stmt};
403
404#[cfg(any(feature = "full", feature = "derive"))]
405mod ty;
406#[cfg(any(feature = "full", feature = "derive"))]
407pub use crate::ty::{
408 Abi, BareFnArg, ReturnType, Type, TypeArray, TypeBareFn, TypeGroup, TypeImplTrait, TypeInfer,
409 TypeMacro, TypeNever, TypeParen, TypePath, TypePtr, TypeReference, TypeSlice, TypeTraitObject,
410 TypeTuple, Variadic,
411};
412
413#[cfg(feature = "full")]
414mod pat;
415#[cfg(feature = "full")]
416pub use crate::pat::{
417 FieldPat, Pat, PatBox, PatIdent, PatLit, PatMacro, PatOr, PatPath, PatRange, PatReference,
418 PatRest, PatSlice, PatStruct, PatTuple, PatTupleStruct, PatType, PatWild,
419};
420
421#[cfg(any(feature = "full", feature = "derive"))]
422mod path;
423#[cfg(any(feature = "full", feature = "derive"))]
424pub use crate::path::{
425 AngleBracketedGenericArguments, Binding, Constraint, GenericArgument,
426 ParenthesizedGenericArguments, Path, PathArguments, PathSegment, QSelf,
427};
428
429#[cfg(feature = "parsing")]
430#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
431pub mod buffer;
432mod drops;
433#[cfg(feature = "parsing")]
434#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
435pub mod ext;
436pub mod punctuated;
437#[cfg(all(any(feature = "full", feature = "derive"), feature = "extra-traits"))]
438mod tt;
439
440// Not public API except the `parse_quote!` macro.
441#[cfg(feature = "parsing")]
442#[doc(hidden)]
443pub mod parse_quote;
444
445// Not public API except the `parse_macro_input!` macro.
446#[cfg(all(
447 not(all(target_arch = "wasm32", any(target_os = "unknown", target_os = "wasi"))),
448 feature = "parsing",
449 feature = "proc-macro"
450))]
451#[doc(hidden)]
452pub mod parse_macro_input;
453
454#[cfg(all(feature = "parsing", feature = "printing"))]
455#[cfg_attr(doc_cfg, doc(cfg(all(feature = "parsing", feature = "printing"))))]
456pub mod spanned;
457
458#[cfg(all(feature = "parsing", feature = "full"))]
459mod whitespace;
460
461mod gen {
462 /// Syntax tree traversal to walk a shared borrow of a syntax tree.
463 ///
464 /// Each method of the [`Visit`] trait is a hook that can be overridden to
465 /// customize the behavior when visiting the corresponding type of node. By
466 /// default, every method recursively visits the substructure of the input
467 /// by invoking the right visitor method of each of its fields.
468 ///
469 /// [`Visit`]: visit::Visit
470 ///
471 /// ```
472 /// # use syn::{Attribute, BinOp, Expr, ExprBinary};
473 /// #
474 /// pub trait Visit<'ast> {
475 /// /* ... */
476 ///
477 /// fn visit_expr_binary(&mut self, node: &'ast ExprBinary) {
478 /// visit_expr_binary(self, node);
479 /// }
480 ///
481 /// /* ... */
482 /// # fn visit_attribute(&mut self, node: &'ast Attribute);
483 /// # fn visit_expr(&mut self, node: &'ast Expr);
484 /// # fn visit_bin_op(&mut self, node: &'ast BinOp);
485 /// }
486 ///
487 /// pub fn visit_expr_binary<'ast, V>(v: &mut V, node: &'ast ExprBinary)
488 /// where
489 /// V: Visit<'ast> + ?Sized,
490 /// {
491 /// for attr in &node.attrs {
492 /// v.visit_attribute(attr);
493 /// }
494 /// v.visit_expr(&*node.left);
495 /// v.visit_bin_op(&node.op);
496 /// v.visit_expr(&*node.right);
497 /// }
498 ///
499 /// /* ... */
500 /// ```
501 ///
502 /// *This module is available only if Syn is built with the `"visit"` feature.*
503 ///
504 /// <br>
505 ///
506 /// # Example
507 ///
508 /// This visitor will print the name of every freestanding function in the
509 /// syntax tree, including nested functions.
510 ///
511 /// ```
512 /// // [dependencies]
513 /// // quote = "1.0"
514 /// // syn = { version = "1.0", features = ["full", "visit"] }
515 ///
516 /// use quote::quote;
517 /// use syn::visit::{self, Visit};
518 /// use syn::{File, ItemFn};
519 ///
520 /// struct FnVisitor;
521 ///
522 /// impl<'ast> Visit<'ast> for FnVisitor {
523 /// fn visit_item_fn(&mut self, node: &'ast ItemFn) {
524 /// println!("Function with name={}", node.sig.ident);
525 ///
526 /// // Delegate to the default impl to visit any nested functions.
527 /// visit::visit_item_fn(self, node);
528 /// }
529 /// }
530 ///
531 /// fn main() {
532 /// let code = quote! {
533 /// pub fn f() {
534 /// fn g() {}
535 /// }
536 /// };
537 ///
538 /// let syntax_tree: File = syn::parse2(code).unwrap();
539 /// FnVisitor.visit_file(&syntax_tree);
540 /// }
541 /// ```
542 ///
543 /// The `'ast` lifetime on the input references means that the syntax tree
544 /// outlives the complete recursive visit call, so the visitor is allowed to
545 /// hold on to references into the syntax tree.
546 ///
547 /// ```
548 /// use quote::quote;
549 /// use syn::visit::{self, Visit};
550 /// use syn::{File, ItemFn};
551 ///
552 /// struct FnVisitor<'ast> {
553 /// functions: Vec<&'ast ItemFn>,
554 /// }
555 ///
556 /// impl<'ast> Visit<'ast> for FnVisitor<'ast> {
557 /// fn visit_item_fn(&mut self, node: &'ast ItemFn) {
558 /// self.functions.push(node);
559 /// visit::visit_item_fn(self, node);
560 /// }
561 /// }
562 ///
563 /// fn main() {
564 /// let code = quote! {
565 /// pub fn f() {
566 /// fn g() {}
567 /// }
568 /// };
569 ///
570 /// let syntax_tree: File = syn::parse2(code).unwrap();
571 /// let mut visitor = FnVisitor { functions: Vec::new() };
572 /// visitor.visit_file(&syntax_tree);
573 /// for f in visitor.functions {
574 /// println!("Function with name={}", f.sig.ident);
575 /// }
576 /// }
577 /// ```
578 #[cfg(feature = "visit")]
579 #[cfg_attr(doc_cfg, doc(cfg(feature = "visit")))]
580 #[rustfmt::skip]
581 pub mod visit;
582
583 /// Syntax tree traversal to mutate an exclusive borrow of a syntax tree in
584 /// place.
585 ///
586 /// Each method of the [`VisitMut`] trait is a hook that can be overridden
587 /// to customize the behavior when mutating the corresponding type of node.
588 /// By default, every method recursively visits the substructure of the
589 /// input by invoking the right visitor method of each of its fields.
590 ///
591 /// [`VisitMut`]: visit_mut::VisitMut
592 ///
593 /// ```
594 /// # use syn::{Attribute, BinOp, Expr, ExprBinary};
595 /// #
596 /// pub trait VisitMut {
597 /// /* ... */
598 ///
599 /// fn visit_expr_binary_mut(&mut self, node: &mut ExprBinary) {
600 /// visit_expr_binary_mut(self, node);
601 /// }
602 ///
603 /// /* ... */
604 /// # fn visit_attribute_mut(&mut self, node: &mut Attribute);
605 /// # fn visit_expr_mut(&mut self, node: &mut Expr);
606 /// # fn visit_bin_op_mut(&mut self, node: &mut BinOp);
607 /// }
608 ///
609 /// pub fn visit_expr_binary_mut<V>(v: &mut V, node: &mut ExprBinary)
610 /// where
611 /// V: VisitMut + ?Sized,
612 /// {
613 /// for attr in &mut node.attrs {
614 /// v.visit_attribute_mut(attr);
615 /// }
616 /// v.visit_expr_mut(&mut *node.left);
617 /// v.visit_bin_op_mut(&mut node.op);
618 /// v.visit_expr_mut(&mut *node.right);
619 /// }
620 ///
621 /// /* ... */
622 /// ```
623 ///
624 /// *This module is available only if Syn is built with the `"visit-mut"`
625 /// feature.*
626 ///
627 /// <br>
628 ///
629 /// # Example
630 ///
631 /// This mut visitor replace occurrences of u256 suffixed integer literals
632 /// like `999u256` with a macro invocation `bigint::u256!(999)`.
633 ///
634 /// ```
635 /// // [dependencies]
636 /// // quote = "1.0"
637 /// // syn = { version = "1.0", features = ["full", "visit-mut"] }
638 ///
639 /// use quote::quote;
640 /// use syn::visit_mut::{self, VisitMut};
641 /// use syn::{parse_quote, Expr, File, Lit, LitInt};
642 ///
643 /// struct BigintReplace;
644 ///
645 /// impl VisitMut for BigintReplace {
646 /// fn visit_expr_mut(&mut self, node: &mut Expr) {
647 /// if let Expr::Lit(expr) = &node {
648 /// if let Lit::Int(int) = &expr.lit {
649 /// if int.suffix() == "u256" {
650 /// let digits = int.base10_digits();
651 /// let unsuffixed: LitInt = syn::parse_str(digits).unwrap();
652 /// *node = parse_quote!(bigint::u256!(#unsuffixed));
653 /// return;
654 /// }
655 /// }
656 /// }
657 ///
658 /// // Delegate to the default impl to visit nested expressions.
659 /// visit_mut::visit_expr_mut(self, node);
660 /// }
661 /// }
662 ///
663 /// fn main() {
664 /// let code = quote! {
665 /// fn main() {
666 /// let _ = 999u256;
667 /// }
668 /// };
669 ///
670 /// let mut syntax_tree: File = syn::parse2(code).unwrap();
671 /// BigintReplace.visit_file_mut(&mut syntax_tree);
672 /// println!("{}", quote!(#syntax_tree));
673 /// }
674 /// ```
675 #[cfg(feature = "visit-mut")]
676 #[cfg_attr(doc_cfg, doc(cfg(feature = "visit-mut")))]
677 #[rustfmt::skip]
678 pub mod visit_mut;
679
680 /// Syntax tree traversal to transform the nodes of an owned syntax tree.
681 ///
682 /// Each method of the [`Fold`] trait is a hook that can be overridden to
683 /// customize the behavior when transforming the corresponding type of node.
684 /// By default, every method recursively visits the substructure of the
685 /// input by invoking the right visitor method of each of its fields.
686 ///
687 /// [`Fold`]: fold::Fold
688 ///
689 /// ```
690 /// # use syn::{Attribute, BinOp, Expr, ExprBinary};
691 /// #
692 /// pub trait Fold {
693 /// /* ... */
694 ///
695 /// fn fold_expr_binary(&mut self, node: ExprBinary) -> ExprBinary {
696 /// fold_expr_binary(self, node)
697 /// }
698 ///
699 /// /* ... */
700 /// # fn fold_attribute(&mut self, node: Attribute) -> Attribute;
701 /// # fn fold_expr(&mut self, node: Expr) -> Expr;
702 /// # fn fold_bin_op(&mut self, node: BinOp) -> BinOp;
703 /// }
704 ///
705 /// pub fn fold_expr_binary<V>(v: &mut V, node: ExprBinary) -> ExprBinary
706 /// where
707 /// V: Fold + ?Sized,
708 /// {
709 /// ExprBinary {
710 /// attrs: node
711 /// .attrs
712 /// .into_iter()
713 /// .map(|attr| v.fold_attribute(attr))
714 /// .collect(),
715 /// left: Box::new(v.fold_expr(*node.left)),
716 /// op: v.fold_bin_op(node.op),
717 /// right: Box::new(v.fold_expr(*node.right)),
718 /// }
719 /// }
720 ///
721 /// /* ... */
722 /// ```
723 ///
724 /// *This module is available only if Syn is built with the `"fold"` feature.*
725 ///
726 /// <br>
727 ///
728 /// # Example
729 ///
730 /// This fold inserts parentheses to fully parenthesizes any expression.
731 ///
732 /// ```
733 /// // [dependencies]
734 /// // quote = "1.0"
735 /// // syn = { version = "1.0", features = ["fold", "full"] }
736 ///
737 /// use quote::quote;
738 /// use syn::fold::{fold_expr, Fold};
739 /// use syn::{token, Expr, ExprParen};
740 ///
741 /// struct ParenthesizeEveryExpr;
742 ///
743 /// impl Fold for ParenthesizeEveryExpr {
744 /// fn fold_expr(&mut self, expr: Expr) -> Expr {
745 /// Expr::Paren(ExprParen {
746 /// attrs: Vec::new(),
747 /// expr: Box::new(fold_expr(self, expr)),
748 /// paren_token: token::Paren::default(),
749 /// })
750 /// }
751 /// }
752 ///
753 /// fn main() {
754 /// let code = quote! { a() + b(1) * c.d };
755 /// let expr: Expr = syn::parse2(code).unwrap();
756 /// let parenthesized = ParenthesizeEveryExpr.fold_expr(expr);
757 /// println!("{}", quote!(#parenthesized));
758 ///
759 /// // Output: (((a)()) + (((b)((1))) * ((c).d)))
760 /// }
761 /// ```
762 #[cfg(feature = "fold")]
763 #[cfg_attr(doc_cfg, doc(cfg(feature = "fold")))]
764 #[rustfmt::skip]
765 pub mod fold;
766
767 #[cfg(feature = "clone-impls")]
768 #[rustfmt::skip]
769 mod clone;
770
771 #[cfg(feature = "extra-traits")]
772 #[rustfmt::skip]
773 mod eq;
774
775 #[cfg(feature = "extra-traits")]
776 #[rustfmt::skip]
777 mod hash;
778
779 #[cfg(feature = "extra-traits")]
780 #[rustfmt::skip]
781 mod debug;
782
783 #[cfg(any(feature = "full", feature = "derive"))]
784 #[path = "../gen_helper.rs"]
785 mod helper;
786}
787pub use crate::gen::*;
788
789// Not public API.
790#[doc(hidden)]
791#[path = "export.rs"]
792pub mod __private;
793
794mod custom_keyword;
795mod custom_punctuation;
796mod sealed;
797mod span;
798mod thread;
799
800#[cfg(feature = "parsing")]
801mod lookahead;
802
803#[cfg(feature = "parsing")]
804#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
805pub mod parse;
806
807#[cfg(feature = "full")]
808mod reserved;
809
810#[cfg(all(any(feature = "full", feature = "derive"), feature = "parsing"))]
811mod verbatim;
812
813#[cfg(all(any(feature = "full", feature = "derive"), feature = "printing"))]
814mod print;
815
816////////////////////////////////////////////////////////////////////////////////
817
818mod error;
819pub use crate::error::{Error, Result};
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/// *This function is available only if Syn is built with both the `"parsing"` and
835/// `"proc-macro"` features.*
836///
837/// # Examples
838///
839/// ```
840/// # extern crate proc_macro;
841/// #
842/// use proc_macro::TokenStream;
843/// use quote::quote;
844/// use syn::DeriveInput;
845///
846/// # const IGNORE_TOKENS: &str = stringify! {
847/// #[proc_macro_derive(MyMacro)]
848/// # };
849/// pub fn my_macro(input: TokenStream) -> TokenStream {
850/// // Parse the tokens into a syntax tree
851/// let ast: DeriveInput = syn::parse(input).unwrap();
852///
853/// // Build the output, possibly using quasi-quotation
854/// let expanded = quote! {
855/// /* ... */
856/// };
857///
858/// // Convert into a token stream and return it
859/// expanded.into()
860/// }
861/// ```
862#[cfg(all(
863 not(all(target_arch = "wasm32", any(target_os = "unknown", target_os = "wasi"))),
864 feature = "parsing",
865 feature = "proc-macro"
866))]
867#[cfg_attr(doc_cfg, doc(cfg(all(feature = "parsing", feature = "proc-macro"))))]
868pub fn parse<T: parse::Parse>(tokens: proc_macro::TokenStream) -> Result<T> {
869 parse::Parser::parse(T::parse, tokens)
870}
871
872/// Parse a proc-macro2 token stream into the chosen syntax tree node.
873///
874/// This function will check that the input is fully parsed. If there are
875/// any unparsed tokens at the end of the stream, an error is returned.
876///
877/// This function parses a `proc_macro2::TokenStream` which is commonly useful
878/// when the input comes from a node of the Syn syntax tree, for example the
879/// body tokens of a [`Macro`] node. When in a procedural macro parsing the
880/// `proc_macro::TokenStream` provided by the compiler, use [`syn::parse`]
881/// instead.
882///
883/// [`syn::parse`]: parse()
884///
885/// *This function is available only if Syn is built with the `"parsing"` feature.*
886#[cfg(feature = "parsing")]
887#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
888pub fn parse2<T: parse::Parse>(tokens: proc_macro2::TokenStream) -> Result<T> {
889 parse::Parser::parse2(T::parse, tokens)
890}
891
892/// Parse a string of Rust code into the chosen syntax tree node.
893///
894/// *This function is available only if Syn is built with the `"parsing"` feature.*
895///
896/// # Hygiene
897///
898/// Every span in the resulting syntax tree will be set to resolve at the macro
899/// call site.
900///
901/// # Examples
902///
903/// ```
904/// use syn::{Expr, Result};
905///
906/// fn run() -> Result<()> {
907/// let code = "assert_eq!(u8::max_value(), 255)";
908/// let expr = syn::parse_str::<Expr>(code)?;
909/// println!("{:#?}", expr);
910/// Ok(())
911/// }
912/// #
913/// # run().unwrap();
914/// ```
915#[cfg(feature = "parsing")]
916#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
917pub fn parse_str<T: parse::Parse>(s: &str) -> Result<T> {
918 parse::Parser::parse_str(T::parse, s)
919}
920
921// FIXME the name parse_file makes it sound like you might pass in a path to a
922// file, rather than the content.
923/// Parse the content of a file of Rust code.
924///
925/// This is different from `syn::parse_str::<File>(content)` in two ways:
926///
927/// - It discards a leading byte order mark `\u{FEFF}` if the file has one.
928/// - It preserves the shebang line of the file, such as `#!/usr/bin/env rustx`.
929///
930/// If present, either of these would be an error using `from_str`.
931///
932/// *This function is available only if Syn is built with the `"parsing"` and
933/// `"full"` features.*
934///
935/// # Examples
936///
937/// ```no_run
938/// use std::error::Error;
939/// use std::fs::File;
940/// use std::io::Read;
941///
942/// fn run() -> Result<(), Box<Error>> {
943/// let mut file = File::open("path/to/code.rs")?;
944/// let mut content = String::new();
945/// file.read_to_string(&mut content)?;
946///
947/// let ast = syn::parse_file(&content)?;
948/// if let Some(shebang) = ast.shebang {
949/// println!("{}", shebang);
950/// }
951/// println!("{} items", ast.items.len());
952///
953/// Ok(())
954/// }
955/// #
956/// # run().unwrap();
957/// ```
958#[cfg(all(feature = "parsing", feature = "full"))]
959#[cfg_attr(doc_cfg, doc(cfg(all(feature = "parsing", feature = "full"))))]
960pub fn parse_file(mut content: &str) -> Result<File> {
961 // Strip the BOM if it is present
962 const BOM: &str = "\u{feff}";
963 if content.starts_with(BOM) {
964 content = &content[BOM.len()..];
965 }
966
967 let mut shebang = None;
968 if content.starts_with("#!") {
969 let rest = whitespace::skip(&content[2..]);
970 if !rest.starts_with('[') {
971 if let Some(idx) = content.find('\n') {
972 shebang = Some(content[..idx].to_string());
973 content = &content[idx..];
974 } else {
975 shebang = Some(content.to_string());
976 content = "";
977 }
978 }
979 }
980
981 let mut file: File = parse_str(content)?;
982 file.shebang = shebang;
983 Ok(file)
984}
985