Initial vendor packages

Signed-off-by: Valentin Popov <valentin@popov.link>

1 files changed, 1010 insertions, 0 deletions

diff --git a/vendor/syn/src/lib.rs b/vendor/syn/src/lib.rs
new file mode 100644
index 0000000..cb8daf6
--- /dev/null
+++ b/vendor/syn/src/lib.rs
@@ -0,0 +1,1010 @@
+//! [![github]](https://github.com/dtolnay/syn) [![crates-io]](https://crates.io/crates/syn) [![docs-rs]](crate)
+//!
+//! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
+//! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
+//! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs
+//!
+//! <br>
+//!
+//! Syn is a parsing library for parsing a stream of Rust tokens into a syntax
+//! tree of Rust source code.
+//!
+//! Currently this library is geared toward use in Rust procedural macros, but
+//! contains some APIs that may be useful more generally.
+//!
+//! - **Data structures** — Syn provides a complete syntax tree that can
+//!   represent any valid Rust source code. The syntax tree is rooted at
+//!   [`syn::File`] which represents a full source file, but there are other
+//!   entry points that may be useful to procedural macros including
+//!   [`syn::Item`], [`syn::Expr`] and [`syn::Type`].
+//!
+//! - **Derives** — Of particular interest to derive macros is
+//!   [`syn::DeriveInput`] which is any of the three legal input items to a
+//!   derive macro. An example below shows using this type in a library that can
+//!   derive implementations of a user-defined trait.
+//!
+//! - **Parsing** — Parsing in Syn is built around [parser functions] with the
+//!   signature `fn(ParseStream) -> Result<T>`. Every syntax tree node defined
+//!   by Syn is individually parsable and may be used as a building block for
+//!   custom syntaxes, or you may dream up your own brand new syntax without
+//!   involving any of our syntax tree types.
+//!
+//! - **Location information** — Every token parsed by Syn is associated with a
+//!   `Span` that tracks line and column information back to the source of that
+//!   token. These spans allow a procedural macro to display detailed error
+//!   messages pointing to all the right places in the user's code. There is an
+//!   example of this below.
+//!
+//! - **Feature flags** — Functionality is aggressively feature gated so your
+//!   procedural macros enable only what they need, and do not pay in compile
+//!   time for all the rest.
+//!
+//! [`syn::File`]: File
+//! [`syn::Item`]: Item
+//! [`syn::Expr`]: Expr
+//! [`syn::Type`]: Type
+//! [`syn::DeriveInput`]: DeriveInput
+//! [parser functions]: mod@parse
+//!
+//! <br>
+//!
+//! # Example of a derive macro
+//!
+//! The canonical derive macro using Syn looks like this. We write an ordinary
+//! Rust function tagged with a `proc_macro_derive` attribute and the name of
+//! the trait we are deriving. Any time that derive appears in the user's code,
+//! the Rust compiler passes their data structure as tokens into our macro. We
+//! get to execute arbitrary Rust code to figure out what to do with those
+//! tokens, then hand some tokens back to the compiler to compile into the
+//! user's crate.
+//!
+//! [`TokenStream`]: proc_macro::TokenStream
+//!
+//! ```toml
+//! [dependencies]
+//! syn = "2.0"
+//! quote = "1.0"
+//!
+//! [lib]
+//! proc-macro = true
+//! ```
+//!
+//! ```
+//! # extern crate proc_macro;
+//! #
+//! use proc_macro::TokenStream;
+//! use quote::quote;
+//! use syn::{parse_macro_input, DeriveInput};
+//!
+//! # const IGNORE_TOKENS: &str = stringify! {
+//! #[proc_macro_derive(MyMacro)]
+//! # };
+//! pub fn my_macro(input: TokenStream) -> TokenStream {
+//!     // Parse the input tokens into a syntax tree
+//!     let input = parse_macro_input!(input as DeriveInput);
+//!
+//!     // Build the output, possibly using quasi-quotation
+//!     let expanded = quote! {
+//!         // ...
+//!     };
+//!
+//!     // Hand the output tokens back to the compiler
+//!     TokenStream::from(expanded)
+//! }
+//! ```
+//!
+//! The [`heapsize`] example directory shows a complete working implementation
+//! of a derive macro. The example derives a `HeapSize` trait which computes an
+//! estimate of the amount of heap memory owned by a value.
+//!
+//! [`heapsize`]: https://github.com/dtolnay/syn/tree/master/examples/heapsize
+//!
+//! ```
+//! pub trait HeapSize {
+//!     /// Total number of bytes of heap memory owned by `self`.
+//!     fn heap_size_of_children(&self) -> usize;
+//! }
+//! ```
+//!
+//! The derive macro allows users to write `#[derive(HeapSize)]` on data
+//! structures in their program.
+//!
+//! ```
+//! # const IGNORE_TOKENS: &str = stringify! {
+//! #[derive(HeapSize)]
+//! # };
+//! struct Demo<'a, T: ?Sized> {
+//!     a: Box<T>,
+//!     b: u8,
+//!     c: &'a str,
+//!     d: String,
+//! }
+//! ```
+//!
+//! <p><br></p>
+//!
+//! # Spans and error reporting
+//!
+//! The token-based procedural macro API provides great control over where the
+//! compiler's error messages are displayed in user code. Consider the error the
+//! user sees if one of their field types does not implement `HeapSize`.
+//!
+//! ```
+//! # const IGNORE_TOKENS: &str = stringify! {
+//! #[derive(HeapSize)]
+//! # };
+//! struct Broken {
+//!     ok: String,
+//!     bad: std::thread::Thread,
+//! }
+//! ```
+//!
+//! By tracking span information all the way through the expansion of a
+//! procedural macro as shown in the `heapsize` example, token-based macros in
+//! Syn are able to trigger errors that directly pinpoint the source of the
+//! problem.
+//!
+//! ```text
+//! error[E0277]: the trait bound `std::thread::Thread: HeapSize` is not satisfied
+//!  --> src/main.rs:7:5
+//!   |
+//! 7 |     bad: std::thread::Thread,
+//!   |     ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `HeapSize` is not implemented for `Thread`
+//! ```
+//!
+//! <br>
+//!
+//! # Parsing a custom syntax
+//!
+//! The [`lazy-static`] example directory shows the implementation of a
+//! `functionlike!(...)` procedural macro in which the input tokens are parsed
+//! using Syn's parsing API.
+//!
+//! [`lazy-static`]: https://github.com/dtolnay/syn/tree/master/examples/lazy-static
+//!
+//! The example reimplements the popular `lazy_static` crate from crates.io as a
+//! procedural macro.
+//!
+//! ```
+//! # macro_rules! lazy_static {
+//! #     ($($tt:tt)*) => {}
+//! # }
+//! #
+//! lazy_static! {
+//!     static ref USERNAME: Regex = Regex::new("^[a-z0-9_-]{3,16}$").unwrap();
+//! }
+//! ```
+//!
+//! The implementation shows how to trigger custom warnings and error messages
+//! on the macro input.
+//!
+//! ```text
+//! warning: come on, pick a more creative name
+//!   --> src/main.rs:10:16
+//!    |
+//! 10 |     static ref FOO: String = "lazy_static".to_owned();
+//!    |                ^^^
+//! ```
+//!
+//! <br>
+//!
+//! # Testing
+//!
+//! When testing macros, we often care not just that the macro can be used
+//! successfully but also that when the macro is provided with invalid input it
+//! produces maximally helpful error messages. Consider using the [`trybuild`]
+//! crate to write tests for errors that are emitted by your macro or errors
+//! detected by the Rust compiler in the expanded code following misuse of the
+//! macro. Such tests help avoid regressions from later refactors that
+//! mistakenly make an error no longer trigger or be less helpful than it used
+//! to be.
+//!
+//! [`trybuild`]: https://github.com/dtolnay/trybuild
+//!
+//! <br>
+//!
+//! # Debugging
+//!
+//! When developing a procedural macro it can be helpful to look at what the
+//! generated code looks like. Use `cargo rustc -- -Zunstable-options
+//! --pretty=expanded` or the [`cargo expand`] subcommand.
+//!
+//! [`cargo expand`]: https://github.com/dtolnay/cargo-expand
+//!
+//! To show the expanded code for some crate that uses your procedural macro,
+//! run `cargo expand` from that crate. To show the expanded code for one of
+//! your own test cases, run `cargo expand --test the_test_case` where the last
+//! argument is the name of the test file without the `.rs` extension.
+//!
+//! This write-up by Brandon W Maister discusses debugging in more detail:
+//! [Debugging Rust's new Custom Derive system][debugging].
+//!
+//! [debugging]: https://quodlibetor.github.io/posts/debugging-rusts-new-custom-derive-system/
+//!
+//! <br>
+//!
+//! # Optional features
+//!
+//! Syn puts a lot of functionality behind optional features in order to
+//! optimize compile time for the most common use cases. The following features
+//! are available.
+//!
+//! - **`derive`** *(enabled by default)* — Data structures for representing the
+//!   possible input to a derive macro, including structs and enums and types.
+//! - **`full`** — Data structures for representing the syntax tree of all valid
+//!   Rust source code, including items and expressions.
+//! - **`parsing`** *(enabled by default)* — Ability to parse input tokens into
+//!   a syntax tree node of a chosen type.
+//! - **`printing`** *(enabled by default)* — Ability to print a syntax tree
+//!   node as tokens of Rust source code.
+//! - **`visit`** — Trait for traversing a syntax tree.
+//! - **`visit-mut`** — Trait for traversing and mutating in place a syntax
+//!   tree.
+//! - **`fold`** — Trait for transforming an owned syntax tree.
+//! - **`clone-impls`** *(enabled by default)* — Clone impls for all syntax tree
+//!   types.
+//! - **`extra-traits`** — Debug, Eq, PartialEq, Hash impls for all syntax tree
+//!   types.
+//! - **`proc-macro`** *(enabled by default)* — Runtime dependency on the
+//!   dynamic library libproc_macro from rustc toolchain.
+
+// Syn types in rustdoc of other crates get linked to here.
+#![doc(html_root_url = "https://docs.rs/syn/2.0.48")]
+#![cfg_attr(doc_cfg, feature(doc_cfg))]
+#![deny(unsafe_op_in_unsafe_fn)]
+#![allow(non_camel_case_types)]
+#![allow(
+    clippy::bool_to_int_with_if,
+    clippy::cast_lossless,
+    clippy::cast_possible_truncation,
+    clippy::cast_possible_wrap,
+    clippy::cast_ptr_alignment,
+    clippy::default_trait_access,
+    clippy::derivable_impls,
+    clippy::diverging_sub_expression,
+    clippy::doc_markdown,
+    clippy::expl_impl_clone_on_copy,
+    clippy::explicit_auto_deref,
+    clippy::if_not_else,
+    clippy::inherent_to_string,
+    clippy::into_iter_without_iter,
+    clippy::items_after_statements,
+    clippy::large_enum_variant,
+    clippy::let_underscore_untyped, // https://github.com/rust-lang/rust-clippy/issues/10410
+    clippy::manual_assert,
+    clippy::manual_let_else,
+    clippy::match_like_matches_macro,
+    clippy::match_on_vec_items,
+    clippy::match_same_arms,
+    clippy::match_wildcard_for_single_variants, // clippy bug: https://github.com/rust-lang/rust-clippy/issues/6984
+    clippy::missing_errors_doc,
+    clippy::missing_panics_doc,
+    clippy::module_name_repetitions,
+    clippy::must_use_candidate,
+    clippy::needless_doctest_main,
+    clippy::needless_pass_by_value,
+    clippy::never_loop,
+    clippy::range_plus_one,
+    clippy::redundant_else,
+    clippy::return_self_not_must_use,
+    clippy::similar_names,
+    clippy::single_match_else,
+    clippy::too_many_arguments,
+    clippy::too_many_lines,
+    clippy::trivially_copy_pass_by_ref,
+    clippy::uninhabited_references,
+    clippy::uninlined_format_args,
+    clippy::unnecessary_box_returns,
+    clippy::unnecessary_unwrap,
+    clippy::used_underscore_binding,
+    clippy::wildcard_imports,
+)]
+
+#[cfg(feature = "proc-macro")]
+extern crate proc_macro;
+
+#[macro_use]
+mod macros;
+
+#[cfg(feature = "parsing")]
+#[macro_use]
+mod group;
+
+#[macro_use]
+pub mod token;
+
+#[cfg(any(feature = "full", feature = "derive"))]
+mod attr;
+#[cfg(any(feature = "full", feature = "derive"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
+pub use crate::attr::{AttrStyle, Attribute, Meta, MetaList, MetaNameValue};
+
+mod bigint;
+
+#[cfg(feature = "parsing")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+pub mod buffer;
+
+mod custom_keyword;
+
+mod custom_punctuation;
+
+#[cfg(any(feature = "full", feature = "derive"))]
+mod data;
+#[cfg(any(feature = "full", feature = "derive"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
+pub use crate::data::{Field, Fields, FieldsNamed, FieldsUnnamed, Variant};
+
+#[cfg(any(feature = "full", feature = "derive"))]
+mod derive;
+#[cfg(feature = "derive")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "derive")))]
+pub use crate::derive::{Data, DataEnum, DataStruct, DataUnion, DeriveInput};
+
+mod drops;
+
+mod error;
+pub use crate::error::{Error, Result};
+
+#[cfg(any(feature = "full", feature = "derive"))]
+mod expr;
+#[cfg(feature = "full")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
+pub use crate::expr::{Arm, Label, RangeLimits};
+#[cfg(any(feature = "full", feature = "derive"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
+pub use crate::expr::{
+    Expr, ExprBinary, ExprCall, ExprCast, ExprField, ExprIndex, ExprLit, ExprMacro, ExprMethodCall,
+    ExprParen, ExprPath, ExprReference, ExprStruct, ExprUnary, FieldValue, Index, Member,
+};
+#[cfg(any(feature = "full", feature = "derive"))]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
+pub use crate::expr::{
+    ExprArray, ExprAssign, ExprAsync, ExprAwait, ExprBlock, ExprBreak, ExprClosure, ExprConst,
+    ExprContinue, ExprForLoop, ExprGroup, ExprIf, ExprInfer, ExprLet, ExprLoop, ExprMatch,
+    ExprRange, ExprRepeat, ExprReturn, ExprTry, ExprTryBlock, ExprTuple, ExprUnsafe, ExprWhile,
+    ExprYield,
+};
+
+#[cfg(feature = "parsing")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+pub mod ext;
+
+#[cfg(feature = "full")]
+mod file;
+#[cfg(feature = "full")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
+pub use crate::file::File;
+
+#[cfg(any(feature = "full", feature = "derive"))]
+mod generics;
+#[cfg(any(feature = "full", feature = "derive"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
+pub use crate::generics::{
+    BoundLifetimes, ConstParam, GenericParam, Generics, LifetimeParam, PredicateLifetime,
+    PredicateType, TraitBound, TraitBoundModifier, TypeParam, TypeParamBound, WhereClause,
+    WherePredicate,
+};
+#[cfg(all(any(feature = "full", feature = "derive"), feature = "printing"))]
+#[cfg_attr(
+    doc_cfg,
+    doc(cfg(all(any(feature = "full", feature = "derive"), feature = "printing")))
+)]
+pub use crate::generics::{ImplGenerics, Turbofish, TypeGenerics};
+
+mod ident;
+#[doc(inline)]
+pub use crate::ident::Ident;
+
+#[cfg(feature = "full")]
+mod item;
+#[cfg(feature = "full")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
+pub use crate::item::{
+    FnArg, ForeignItem, ForeignItemFn, ForeignItemMacro, ForeignItemStatic, ForeignItemType,
+    ImplItem, ImplItemConst, ImplItemFn, ImplItemMacro, ImplItemType, ImplRestriction, Item,
+    ItemConst, ItemEnum, ItemExternCrate, ItemFn, ItemForeignMod, ItemImpl, ItemMacro, ItemMod,
+    ItemStatic, ItemStruct, ItemTrait, ItemTraitAlias, ItemType, ItemUnion, ItemUse, Receiver,
+    Signature, StaticMutability, TraitItem, TraitItemConst, TraitItemFn, TraitItemMacro,
+    TraitItemType, UseGlob, UseGroup, UseName, UsePath, UseRename, UseTree, Variadic,
+};
+
+mod lifetime;
+#[doc(inline)]
+pub use crate::lifetime::Lifetime;
+
+mod lit;
+#[doc(hidden)] // https://github.com/dtolnay/syn/issues/1566
+pub use crate::lit::StrStyle;
+#[doc(inline)]
+pub use crate::lit::{Lit, LitBool, LitByte, LitByteStr, LitChar, LitFloat, LitInt, LitStr};
+
+#[cfg(feature = "parsing")]
+mod lookahead;
+
+#[cfg(any(feature = "full", feature = "derive"))]
+mod mac;
+#[cfg(any(feature = "full", feature = "derive"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
+pub use crate::mac::{Macro, MacroDelimiter};
+
+#[cfg(all(feature = "parsing", any(feature = "full", feature = "derive")))]
+#[cfg_attr(
+    doc_cfg,
+    doc(cfg(all(feature = "parsing", any(feature = "full", feature = "derive"))))
+)]
+pub mod meta;
+
+#[cfg(any(feature = "full", feature = "derive"))]
+mod op;
+#[cfg(any(feature = "full", feature = "derive"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
+pub use crate::op::{BinOp, UnOp};
+
+#[cfg(feature = "parsing")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+pub mod parse;
+
+#[cfg(all(feature = "parsing", feature = "proc-macro"))]
+mod parse_macro_input;
+
+#[cfg(all(feature = "parsing", feature = "printing"))]
+mod parse_quote;
+
+#[cfg(feature = "full")]
+mod pat;
+#[cfg(feature = "full")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
+pub use crate::expr::{
+    ExprConst as PatConst, ExprLit as PatLit, ExprMacro as PatMacro, ExprPath as PatPath,
+    ExprRange as PatRange,
+};
+#[cfg(feature = "full")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
+pub use crate::pat::{
+    FieldPat, Pat, PatIdent, PatOr, PatParen, PatReference, PatRest, PatSlice, PatStruct, PatTuple,
+    PatTupleStruct, PatType, PatWild,
+};
+
+#[cfg(any(feature = "full", feature = "derive"))]
+mod path;
+#[cfg(any(feature = "full", feature = "derive"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
+pub use crate::path::{
+    AngleBracketedGenericArguments, AssocConst, AssocType, Constraint, GenericArgument,
+    ParenthesizedGenericArguments, Path, PathArguments, PathSegment, QSelf,
+};
+
+#[cfg(all(any(feature = "full", feature = "derive"), feature = "printing"))]
+mod print;
+
+pub mod punctuated;
+
+#[cfg(any(feature = "full", feature = "derive"))]
+mod restriction;
+#[cfg(any(feature = "full", feature = "derive"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
+pub use crate::restriction::{FieldMutability, VisRestricted, Visibility};
+
+mod sealed;
+
+mod span;
+
+#[cfg(all(feature = "parsing", feature = "printing"))]
+#[cfg_attr(doc_cfg, doc(cfg(all(feature = "parsing", feature = "printing"))))]
+pub mod spanned;
+
+#[cfg(feature = "full")]
+mod stmt;
+#[cfg(feature = "full")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "full")))]
+pub use crate::stmt::{Block, Local, LocalInit, Stmt, StmtMacro};
+
+mod thread;
+
+#[cfg(all(any(feature = "full", feature = "derive"), feature = "extra-traits"))]
+mod tt;
+
+#[cfg(any(feature = "full", feature = "derive"))]
+mod ty;
+#[cfg(any(feature = "full", feature = "derive"))]
+#[cfg_attr(doc_cfg, doc(cfg(any(feature = "full", feature = "derive"))))]
+pub use crate::ty::{
+    Abi, BareFnArg, BareVariadic, ReturnType, Type, TypeArray, TypeBareFn, TypeGroup,
+    TypeImplTrait, TypeInfer, TypeMacro, TypeNever, TypeParen, TypePath, TypePtr, TypeReference,
+    TypeSlice, TypeTraitObject, TypeTuple,
+};
+
+#[cfg(all(any(feature = "full", feature = "derive"), feature = "parsing"))]
+mod verbatim;
+
+#[cfg(all(feature = "parsing", feature = "full"))]
+mod whitespace;
+
+mod gen {
+    /// Syntax tree traversal to transform the nodes of an owned syntax tree.
+    ///
+    /// Each method of the [`Fold`] trait is a hook that can be overridden to
+    /// customize the behavior when transforming the corresponding type of node.
+    /// By default, every method recursively visits the substructure of the
+    /// input by invoking the right visitor method of each of its fields.
+    ///
+    /// [`Fold`]: fold::Fold
+    ///
+    /// ```
+    /// # use syn::{Attribute, BinOp, Expr, ExprBinary};
+    /// #
+    /// pub trait Fold {
+    ///     /* ... */
+    ///
+    ///     fn fold_expr_binary(&mut self, node: ExprBinary) -> ExprBinary {
+    ///         fold_expr_binary(self, node)
+    ///     }
+    ///
+    ///     /* ... */
+    ///     # fn fold_attribute(&mut self, node: Attribute) -> Attribute;
+    ///     # fn fold_expr(&mut self, node: Expr) -> Expr;
+    ///     # fn fold_bin_op(&mut self, node: BinOp) -> BinOp;
+    /// }
+    ///
+    /// pub fn fold_expr_binary<V>(v: &mut V, node: ExprBinary) -> ExprBinary
+    /// where
+    ///     V: Fold + ?Sized,
+    /// {
+    ///     ExprBinary {
+    ///         attrs: node
+    ///             .attrs
+    ///             .into_iter()
+    ///             .map(|attr| v.fold_attribute(attr))
+    ///             .collect(),
+    ///         left: Box::new(v.fold_expr(*node.left)),
+    ///         op: v.fold_bin_op(node.op),
+    ///         right: Box::new(v.fold_expr(*node.right)),
+    ///     }
+    /// }
+    ///
+    /// /* ... */
+    /// ```
+    ///
+    /// <br>
+    ///
+    /// # Example
+    ///
+    /// This fold inserts parentheses to fully parenthesizes any expression.
+    ///
+    /// ```
+    /// // [dependencies]
+    /// // quote = "1.0"
+    /// // syn = { version = "2.0", features = ["fold", "full"] }
+    ///
+    /// use quote::quote;
+    /// use syn::fold::{fold_expr, Fold};
+    /// use syn::{token, Expr, ExprParen};
+    ///
+    /// struct ParenthesizeEveryExpr;
+    ///
+    /// impl Fold for ParenthesizeEveryExpr {
+    ///     fn fold_expr(&mut self, expr: Expr) -> Expr {
+    ///         Expr::Paren(ExprParen {
+    ///             attrs: Vec::new(),
+    ///             expr: Box::new(fold_expr(self, expr)),
+    ///             paren_token: token::Paren::default(),
+    ///         })
+    ///     }
+    /// }
+    ///
+    /// fn main() {
+    ///     let code = quote! { a() + b(1) * c.d };
+    ///     let expr: Expr = syn::parse2(code).unwrap();
+    ///     let parenthesized = ParenthesizeEveryExpr.fold_expr(expr);
+    ///     println!("{}", quote!(#parenthesized));
+    ///
+    ///     // Output: (((a)()) + (((b)((1))) * ((c).d)))
+    /// }
+    /// ```
+    #[cfg(feature = "fold")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "fold")))]
+    #[rustfmt::skip]
+    pub mod fold;
+
+    /// Syntax tree traversal to walk a shared borrow of a syntax tree.
+    ///
+    /// Each method of the [`Visit`] trait is a hook that can be overridden to
+    /// customize the behavior when visiting the corresponding type of node. By
+    /// default, every method recursively visits the substructure of the input
+    /// by invoking the right visitor method of each of its fields.
+    ///
+    /// [`Visit`]: visit::Visit
+    ///
+    /// ```
+    /// # use syn::{Attribute, BinOp, Expr, ExprBinary};
+    /// #
+    /// pub trait Visit<'ast> {
+    ///     /* ... */
+    ///
+    ///     fn visit_expr_binary(&mut self, node: &'ast ExprBinary) {
+    ///         visit_expr_binary(self, node);
+    ///     }
+    ///
+    ///     /* ... */
+    ///     # fn visit_attribute(&mut self, node: &'ast Attribute);
+    ///     # fn visit_expr(&mut self, node: &'ast Expr);
+    ///     # fn visit_bin_op(&mut self, node: &'ast BinOp);
+    /// }
+    ///
+    /// pub fn visit_expr_binary<'ast, V>(v: &mut V, node: &'ast ExprBinary)
+    /// where
+    ///     V: Visit<'ast> + ?Sized,
+    /// {
+    ///     for attr in &node.attrs {
+    ///         v.visit_attribute(attr);
+    ///     }
+    ///     v.visit_expr(&*node.left);
+    ///     v.visit_bin_op(&node.op);
+    ///     v.visit_expr(&*node.right);
+    /// }
+    ///
+    /// /* ... */
+    /// ```
+    ///
+    /// <br>
+    ///
+    /// # Example
+    ///
+    /// This visitor will print the name of every freestanding function in the
+    /// syntax tree, including nested functions.
+    ///
+    /// ```
+    /// // [dependencies]
+    /// // quote = "1.0"
+    /// // syn = { version = "2.0", features = ["full", "visit"] }
+    ///
+    /// use quote::quote;
+    /// use syn::visit::{self, Visit};
+    /// use syn::{File, ItemFn};
+    ///
+    /// struct FnVisitor;
+    ///
+    /// impl<'ast> Visit<'ast> for FnVisitor {
+    ///     fn visit_item_fn(&mut self, node: &'ast ItemFn) {
+    ///         println!("Function with name={}", node.sig.ident);
+    ///
+    ///         // Delegate to the default impl to visit any nested functions.
+    ///         visit::visit_item_fn(self, node);
+    ///     }
+    /// }
+    ///
+    /// fn main() {
+    ///     let code = quote! {
+    ///         pub fn f() {
+    ///             fn g() {}
+    ///         }
+    ///     };
+    ///
+    ///     let syntax_tree: File = syn::parse2(code).unwrap();
+    ///     FnVisitor.visit_file(&syntax_tree);
+    /// }
+    /// ```
+    ///
+    /// The `'ast` lifetime on the input references means that the syntax tree
+    /// outlives the complete recursive visit call, so the visitor is allowed to
+    /// hold on to references into the syntax tree.
+    ///
+    /// ```
+    /// use quote::quote;
+    /// use syn::visit::{self, Visit};
+    /// use syn::{File, ItemFn};
+    ///
+    /// struct FnVisitor<'ast> {
+    ///     functions: Vec<&'ast ItemFn>,
+    /// }
+    ///
+    /// impl<'ast> Visit<'ast> for FnVisitor<'ast> {
+    ///     fn visit_item_fn(&mut self, node: &'ast ItemFn) {
+    ///         self.functions.push(node);
+    ///         visit::visit_item_fn(self, node);
+    ///     }
+    /// }
+    ///
+    /// fn main() {
+    ///     let code = quote! {
+    ///         pub fn f() {
+    ///             fn g() {}
+    ///         }
+    ///     };
+    ///
+    ///     let syntax_tree: File = syn::parse2(code).unwrap();
+    ///     let mut visitor = FnVisitor { functions: Vec::new() };
+    ///     visitor.visit_file(&syntax_tree);
+    ///     for f in visitor.functions {
+    ///         println!("Function with name={}", f.sig.ident);
+    ///     }
+    /// }
+    /// ```
+    #[cfg(feature = "visit")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "visit")))]
+    #[rustfmt::skip]
+    pub mod visit;
+
+    /// Syntax tree traversal to mutate an exclusive borrow of a syntax tree in
+    /// place.
+    ///
+    /// Each method of the [`VisitMut`] trait is a hook that can be overridden
+    /// to customize the behavior when mutating the corresponding type of node.
+    /// By default, every method recursively visits the substructure of the
+    /// input by invoking the right visitor method of each of its fields.
+    ///
+    /// [`VisitMut`]: visit_mut::VisitMut
+    ///
+    /// ```
+    /// # use syn::{Attribute, BinOp, Expr, ExprBinary};
+    /// #
+    /// pub trait VisitMut {
+    ///     /* ... */
+    ///
+    ///     fn visit_expr_binary_mut(&mut self, node: &mut ExprBinary) {
+    ///         visit_expr_binary_mut(self, node);
+    ///     }
+    ///
+    ///     /* ... */
+    ///     # fn visit_attribute_mut(&mut self, node: &mut Attribute);
+    ///     # fn visit_expr_mut(&mut self, node: &mut Expr);
+    ///     # fn visit_bin_op_mut(&mut self, node: &mut BinOp);
+    /// }
+    ///
+    /// pub fn visit_expr_binary_mut<V>(v: &mut V, node: &mut ExprBinary)
+    /// where
+    ///     V: VisitMut + ?Sized,
+    /// {
+    ///     for attr in &mut node.attrs {
+    ///         v.visit_attribute_mut(attr);
+    ///     }
+    ///     v.visit_expr_mut(&mut *node.left);
+    ///     v.visit_bin_op_mut(&mut node.op);
+    ///     v.visit_expr_mut(&mut *node.right);
+    /// }
+    ///
+    /// /* ... */
+    /// ```
+    ///
+    /// <br>
+    ///
+    /// # Example
+    ///
+    /// This mut visitor replace occurrences of u256 suffixed integer literals
+    /// like `999u256` with a macro invocation `bigint::u256!(999)`.
+    ///
+    /// ```
+    /// // [dependencies]
+    /// // quote = "1.0"
+    /// // syn = { version = "2.0", features = ["full", "visit-mut"] }
+    ///
+    /// use quote::quote;
+    /// use syn::visit_mut::{self, VisitMut};
+    /// use syn::{parse_quote, Expr, File, Lit, LitInt};
+    ///
+    /// struct BigintReplace;
+    ///
+    /// impl VisitMut for BigintReplace {
+    ///     fn visit_expr_mut(&mut self, node: &mut Expr) {
+    ///         if let Expr::Lit(expr) = &node {
+    ///             if let Lit::Int(int) = &expr.lit {
+    ///                 if int.suffix() == "u256" {
+    ///                     let digits = int.base10_digits();
+    ///                     let unsuffixed: LitInt = syn::parse_str(digits).unwrap();
+    ///                     *node = parse_quote!(bigint::u256!(#unsuffixed));
+    ///                     return;
+    ///                 }
+    ///             }
+    ///         }
+    ///
+    ///         // Delegate to the default impl to visit nested expressions.
+    ///         visit_mut::visit_expr_mut(self, node);
+    ///     }
+    /// }
+    ///
+    /// fn main() {
+    ///     let code = quote! {
+    ///         fn main() {
+    ///             let _ = 999u256;
+    ///         }
+    ///     };
+    ///
+    ///     let mut syntax_tree: File = syn::parse2(code).unwrap();
+    ///     BigintReplace.visit_file_mut(&mut syntax_tree);
+    ///     println!("{}", quote!(#syntax_tree));
+    /// }
+    /// ```
+    #[cfg(feature = "visit-mut")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "visit-mut")))]
+    #[rustfmt::skip]
+    pub mod visit_mut;
+
+    #[cfg(feature = "clone-impls")]
+    #[rustfmt::skip]
+    mod clone;
+
+    #[cfg(feature = "extra-traits")]
+    #[rustfmt::skip]
+    mod debug;
+
+    #[cfg(feature = "extra-traits")]
+    #[rustfmt::skip]
+    mod eq;
+
+    #[cfg(feature = "extra-traits")]
+    #[rustfmt::skip]
+    mod hash;
+
+    #[cfg(any(feature = "full", feature = "derive"))]
+    #[path = "../gen_helper.rs"]
+    mod helper;
+}
+
+#[cfg(feature = "fold")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "fold")))]
+pub use crate::gen::fold;
+
+#[cfg(feature = "visit")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "visit")))]
+pub use crate::gen::visit;
+
+#[cfg(feature = "visit-mut")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "visit-mut")))]
+pub use crate::gen::visit_mut;
+
+// Not public API.
+#[doc(hidden)]
+#[path = "export.rs"]
+pub mod __private;
+
+/// Parse tokens of source code into the chosen syntax tree node.
+///
+/// This is preferred over parsing a string because tokens are able to preserve
+/// information about where in the user's code they were originally written (the
+/// "span" of the token), possibly allowing the compiler to produce better error
+/// messages.
+///
+/// This function parses a `proc_macro::TokenStream` which is the type used for
+/// interop with the compiler in a procedural macro. To parse a
+/// `proc_macro2::TokenStream`, use [`syn::parse2`] instead.
+///
+/// [`syn::parse2`]: parse2
+///
+/// # Examples
+///
+/// ```
+/// # extern crate proc_macro;
+/// #
+/// use proc_macro::TokenStream;
+/// use quote::quote;
+/// use syn::DeriveInput;
+///
+/// # const IGNORE_TOKENS: &str = stringify! {
+/// #[proc_macro_derive(MyMacro)]
+/// # };
+/// pub fn my_macro(input: TokenStream) -> TokenStream {
+///     // Parse the tokens into a syntax tree
+///     let ast: DeriveInput = syn::parse(input).unwrap();
+///
+///     // Build the output, possibly using quasi-quotation
+///     let expanded = quote! {
+///         /* ... */
+///     };
+///
+///     // Convert into a token stream and return it
+///     expanded.into()
+/// }
+/// ```
+#[cfg(all(feature = "parsing", feature = "proc-macro"))]
+#[cfg_attr(doc_cfg, doc(cfg(all(feature = "parsing", feature = "proc-macro"))))]
+pub fn parse<T: parse::Parse>(tokens: proc_macro::TokenStream) -> Result<T> {
+    parse::Parser::parse(T::parse, tokens)
+}
+
+/// Parse a proc-macro2 token stream into the chosen syntax tree node.
+///
+/// This function will check that the input is fully parsed. If there are
+/// any unparsed tokens at the end of the stream, an error is returned.
+///
+/// This function parses a `proc_macro2::TokenStream` which is commonly useful
+/// when the input comes from a node of the Syn syntax tree, for example the
+/// body tokens of a [`Macro`] node. When in a procedural macro parsing the
+/// `proc_macro::TokenStream` provided by the compiler, use [`syn::parse`]
+/// instead.
+///
+/// [`syn::parse`]: parse()
+#[cfg(feature = "parsing")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+pub fn parse2<T: parse::Parse>(tokens: proc_macro2::TokenStream) -> Result<T> {
+    parse::Parser::parse2(T::parse, tokens)
+}
+
+/// Parse a string of Rust code into the chosen syntax tree node.
+///
+/// # Hygiene
+///
+/// Every span in the resulting syntax tree will be set to resolve at the macro
+/// call site.
+///
+/// # Examples
+///
+/// ```
+/// use syn::{Expr, Result};
+///
+/// fn run() -> Result<()> {
+///     let code = "assert_eq!(u8::max_value(), 255)";
+///     let expr = syn::parse_str::<Expr>(code)?;
+///     println!("{:#?}", expr);
+///     Ok(())
+/// }
+/// #
+/// # run().unwrap();
+/// ```
+#[cfg(feature = "parsing")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+pub fn parse_str<T: parse::Parse>(s: &str) -> Result<T> {
+    parse::Parser::parse_str(T::parse, s)
+}
+
+// FIXME the name parse_file makes it sound like you might pass in a path to a
+// file, rather than the content.
+/// Parse the content of a file of Rust code.
+///
+/// This is different from `syn::parse_str::<File>(content)` in two ways:
+///
+/// - It discards a leading byte order mark `\u{FEFF}` if the file has one.
+/// - It preserves the shebang line of the file, such as `#!/usr/bin/env rustx`.
+///
+/// If present, either of these would be an error using `from_str`.
+///
+/// # Examples
+///
+/// ```no_run
+/// use std::error::Error;
+/// use std::fs::File;
+/// use std::io::Read;
+///
+/// fn run() -> Result<(), Box<dyn Error>> {
+///     let mut file = File::open("path/to/code.rs")?;
+///     let mut content = String::new();
+///     file.read_to_string(&mut content)?;
+///
+///     let ast = syn::parse_file(&content)?;
+///     if let Some(shebang) = ast.shebang {
+///         println!("{}", shebang);
+///     }
+///     println!("{} items", ast.items.len());
+///
+///     Ok(())
+/// }
+/// #
+/// # run().unwrap();
+/// ```
+#[cfg(all(feature = "parsing", feature = "full"))]
+#[cfg_attr(doc_cfg, doc(cfg(all(feature = "parsing", feature = "full"))))]
+pub fn parse_file(mut content: &str) -> Result<File> {
+    // Strip the BOM if it is present
+    const BOM: &str = "\u{feff}";
+    if content.starts_with(BOM) {
+        content = &content[BOM.len()..];
+    }
+
+    let mut shebang = None;
+    if content.starts_with("#!") {
+        let rest = whitespace::skip(&content[2..]);
+        if !rest.starts_with('[') {
+            if let Some(idx) = content.find('\n') {
+                shebang = Some(content[..idx].to_string());
+                content = &content[idx..];
+            } else {
+                shebang = Some(content.to_string());
+                content = "";
+            }
+        }
+    }
+
+    let mut file: File = parse_str(content)?;
+    file.shebang = shebang;
+    Ok(file)
+}