<! DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source to the Rust file `/Users/rseymour/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-0.14.7/src/lib.rs`. "><meta name="keywords" content="rust, rustlang, rust-lang"><title>lib.rs.html -- source</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script></head><body class="rustdoc source"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">&#9776;</div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’  for more options…" type="search"><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><pre class="line-numbers"><span id="1">  1</span>
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</pre><pre class="rust ">
<span class="comment">// Copyright 2018 Syn Developers</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 &lt;LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0&gt; or the MIT license</span>
<span class="comment">// &lt;LICENSE-MIT or http://opensource.org/licenses/MIT&gt;, at your</span>
<span class="comment">// option.  This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>

<span class="doccomment">//!  Syn is a parsing library for parsing a stream of Rust tokens into a syntax</span>
<span class="doccomment">//!  tree of Rust source code.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  Currently this library is geared toward the [custom derive] use case but</span>
<span class="doccomment">//!  contains some APIs that may be useful for Rust procedural macros more</span>
<span class="doccomment">//!  generally.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [ custom derive]: https://github.com/rust-lang/rfcs/blob/master/text/1681-macros-1.1.md</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! - ** Data structures** — Syn provides a complete syntax tree that can</span>
<span class="doccomment">//!    represent any valid Rust source code.  The syntax tree is rooted at</span>
<span class="doccomment">//!    [`syn::File`] which represents a full source file, but there are other</span>
<span class="doccomment">//!    entry points that may be useful to procedural macros including</span>
<span class="doccomment">//!    [`syn::Item`], [`syn::Expr`] and [`syn::Type`].</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! - ** Custom derives** — Of particular interest to custom derives is</span>
<span class="doccomment">//!    [`syn::DeriveInput`] which is any of the three legal input items to a</span>
<span class="doccomment">//!    derive macro.  An example below shows using this type in a library that can</span>
<span class="doccomment">//!    derive implementations of a trait of your own.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! - ** Parser combinators** — Parsing in Syn is built on a suite of public</span>
<span class="doccomment">//!    parser combinator macros that you can use for parsing any token-based</span>
<span class="doccomment">//!    syntax you dream up within a `functionlike!(...) ` procedural macro.  Every</span>
<span class="doccomment">//!    syntax tree node defined by Syn is individually parsable and may be used</span>
<span class="doccomment">//!    as a building block for custom syntaxes, or you may do it all yourself</span>
<span class="doccomment">//!    working from the most primitive tokens.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! - ** Location information** — Every token parsed by Syn is associated with a</span>
<span class="doccomment">//!    `Span` that tracks line and column information back to the source of that</span>
<span class="doccomment">//!    token.  These spans allow a procedural macro to display detailed error</span>
<span class="doccomment">//!    messages pointing to all the right places in the user&#39;s code.  There is an</span>
<span class="doccomment">//!    example of this below.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! - ** Feature flags** — Functionality is aggressively feature gated so your</span>
<span class="doccomment">//!    procedural macros enable only what they need, and do not pay in compile</span>
<span class="doccomment">//!    time for all the rest.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [ `syn::File`]: struct. File.html</span>
<span class="doccomment">//! [ `syn::Item`]: enum. Item.html</span>
<span class="doccomment">//! [ `syn::Expr`]: enum. Expr.html</span>
<span class="doccomment">//! [ `syn::Type`]: enum. Type.html</span>
<span class="doccomment">//! [ `syn::DeriveInput`]: struct. DeriveInput.html</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! * Version requirement: Syn supports any compiler version back to Rust&#39;s very</span>
<span class="doccomment">//!  first support for procedural macros in Rust 1.15.0.  Some features especially</span>
<span class="doccomment">//!  around error reporting are only available in newer compilers or on the</span>
<span class="doccomment">//!  nightly channel.*</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ##  Example of a custom derive</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  The canonical custom derive using Syn looks like this.  We write an ordinary</span>
<span class="doccomment">//!  Rust function tagged with a `proc_macro_derive` attribute and the name of</span>
<span class="doccomment">//!  the trait we are deriving.  Any time that derive appears in the user&#39;s code,</span>
<span class="doccomment">//!  the Rust compiler passes their data structure as tokens into our macro.  We</span>
<span class="doccomment">//!  get to execute arbitrary Rust code to figure out what to do with those</span>
<span class="doccomment">//!  tokens, then hand some tokens back to the compiler to compile into the</span>
<span class="doccomment">//!  user&#39;s crate.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [ `TokenStream`]: https://doc.rust-lang.org/proc_macro/struct.TokenStream.html</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  ```toml</span>
<span class="doccomment">//! [ dependencies]</span>
<span class="doccomment">//!  syn = &quot;0.14&quot;</span>
<span class="doccomment">//!  quote = &quot;0.6&quot;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [ lib]</span>
<span class="doccomment">//!  proc-macro = true</span>
<span class="doccomment">//!  ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  ```rust</span>
<span class="doccomment">//!  extern crate proc_macro;</span>
<span class="doccomment">//!  extern crate syn;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! #[ macro_use]</span>
<span class="doccomment">//!  extern crate quote;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  use proc_macro::TokenStream;</span>
<span class="doccomment">//!  use syn::DeriveInput;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! #  const IGNORE_TOKENS: &amp;str = stringify! { </span>
<span class="doccomment">//! #[ proc_macro_derive(MyMacro)]</span>
<span class="doccomment">//! # }; </span>
<span class="doccomment">//!  pub fn my_macro(input: TokenStream) -&gt; TokenStream {</span>
<span class="doccomment">//!      // Parse the input tokens into a syntax tree</span>
<span class="doccomment">//!      let input: DeriveInput = syn::parse(input).unwrap();</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!      // Build the output, possibly using quasi-quotation</span>
<span class="doccomment">//!      let expanded = quote! { </span>
<span class="doccomment">//!          // ...</span>
<span class="doccomment">//!      };</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!      // Hand the output tokens back to the compiler</span>
<span class="doccomment">//!      expanded.into()</span>
<span class="doccomment">//! } </span>
<span class="doccomment">//! # </span>
<span class="doccomment">//! #  fn main() {}</span>
<span class="doccomment">//!  ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  The [`heapsize`] example directory shows a complete working Macros 1.1</span>
<span class="doccomment">//!  implementation of a custom derive.  It works on any Rust compiler \&gt;=1.15.0.</span>
<span class="doccomment">//!  The example derives a `HeapSize` trait which computes an estimate of the</span>
<span class="doccomment">//!  amount of heap memory owned by a value.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [ `heapsize`]: https://github.com/dtolnay/syn/tree/master/examples/heapsize</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  ```rust</span>
<span class="doccomment">//!  pub trait HeapSize {</span>
<span class="doccomment">//!      /// Total number of bytes of heap memory owned by `self`.</span>
<span class="doccomment">//!      fn heap_size_of_children(&amp;self) -&gt; usize;</span>
<span class="doccomment">//! } </span>
<span class="doccomment">//!  ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  The custom derive allows users to write `#[derive(HeapSize)]` on data</span>
<span class="doccomment">//!  structures in their program.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  ```rust</span>
<span class="doccomment">//! #  const IGNORE_TOKENS: &amp;str = stringify! { </span>
<span class="doccomment">//! #[ derive(HeapSize)]</span>
<span class="doccomment">//! # }; </span>
<span class="doccomment">//!  struct Demo&lt;&#39;a, T: ? Sized&gt; {</span>
<span class="doccomment">//!      a: Box&lt;T&gt;,</span>
<span class="doccomment">//!      b: u8,</span>
<span class="doccomment">//!      c: &amp;&#39;a str,</span>
<span class="doccomment">//!      d: String,</span>
<span class="doccomment">//! } </span>
<span class="doccomment">//!  ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ##  Spans and error reporting</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  The [`heapsize2`] example directory is an extension of the `heapsize`</span>
<span class="doccomment">//!  example that demonstrates some of the hygiene and error reporting properties</span>
<span class="doccomment">//!  of Macros 2.0.  This example currently requires a nightly Rust compiler</span>
<span class="doccomment">//!  \&gt;=1.24.0-nightly but we are working to stabilize all of the APIs involved.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [ `heapsize2`]: https://github.com/dtolnay/syn/tree/master/examples/heapsize2</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  The token-based procedural macro API provides great control over where the</span>
<span class="doccomment">//!  compiler&#39;s error messages are displayed in user code.  Consider the error the</span>
<span class="doccomment">//!  user sees if one of their field types does not implement `HeapSize`.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  ```rust</span>
<span class="doccomment">//! #  const IGNORE_TOKENS: &amp;str = stringify! { </span>
<span class="doccomment">//! #[ derive(HeapSize)]</span>
<span class="doccomment">//! # }; </span>
<span class="doccomment">//!  struct Broken {</span>
<span class="doccomment">//!      ok: String,</span>
<span class="doccomment">//!      bad: std::thread::Thread,</span>
<span class="doccomment">//! } </span>
<span class="doccomment">//!  ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  In the Macros 1.1 string-based procedural macro world, the resulting error</span>
<span class="doccomment">//!  would point unhelpfully to the invocation of the derive macro and not to the</span>
<span class="doccomment">//!  actual problematic field.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  ```text</span>
<span class="doccomment">//!  error[E0599]: no method named `heap_size_of_children` found for type `std::thread::Thread` in the current scope</span>
<span class="doccomment">//!   --&gt; src/main.rs:4:10</span>
<span class="doccomment">//!    |</span>
<span class="doccomment">//!  4 | #[derive(HeapSize)]</span>
<span class="doccomment">//!    |          ^^^^^^^^</span>
<span class="doccomment">//!  ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  By tracking span information all the way through the expansion of a</span>
<span class="doccomment">//!  procedural macro as shown in the `heapsize2` example, token-based macros in</span>
<span class="doccomment">//!  Syn are able to trigger errors that directly pinpoint the source of the</span>
<span class="doccomment">//!  problem.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  ```text</span>
<span class="doccomment">//!  error[E0277]: the trait bound `std::thread::Thread: HeapSize` is not satisfied</span>
<span class="doccomment">//!   --&gt; src/main.rs:7:5</span>
<span class="doccomment">//!    |</span>
<span class="doccomment">//!  7 |     bad: std::thread::Thread,</span>
<span class="doccomment">//!    |     ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `HeapSize` is not implemented for `Thread`</span>
<span class="doccomment">//!  ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ##  Parsing a custom syntax using combinators</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  The [`lazy-static`] example directory shows the implementation of a</span>
<span class="doccomment">//!  `functionlike!(...) ` procedural macro in which the input tokens are parsed</span>
<span class="doccomment">//!  using [`nom`]-style parser combinators.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [ `lazy-static`]: https://github.com/dtolnay/syn/tree/master/examples/lazy-static</span>
<span class="doccomment">//! [ `nom`]: https://github.com/Geal/nom</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  The example reimplements the popular `lazy_static` crate from crates.io as a</span>
<span class="doccomment">//!  procedural macro.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  ```</span>
<span class="doccomment">//! #  macro_rules!  lazy_static {</span>
<span class="doccomment">//! #      ($($tt:tt)*) =&gt; {}</span>
<span class="doccomment">//! # } </span>
<span class="doccomment">//! # </span>
<span class="doccomment">//!  lazy_static! { </span>
<span class="doccomment">//!      static ref USERNAME: Regex = Regex::new(&quot;^[a-z0-9_-]{3,16}$&quot;).unwrap();</span>
<span class="doccomment">//! } </span>
<span class="doccomment">//!  ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  The implementation shows how to trigger custom warnings and error messages</span>
<span class="doccomment">//!  on the macro input.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  ```text</span>
<span class="doccomment">//!  warning: come on, pick a more creative name</span>
<span class="doccomment">//!    --&gt; src/main.rs:10:16</span>
<span class="doccomment">//!     |</span>
<span class="doccomment">//!  10 |     static ref FOO: String = &quot;lazy_static&quot;.to_owned();</span>
<span class="doccomment">//!     |                ^^^</span>
<span class="doccomment">//!  ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ##  Debugging</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  When developing a procedural macro it can be helpful to look at what the</span>
<span class="doccomment">//!  generated code looks like.  Use `cargo rustc -- -Zunstable-options</span>
<span class="doccomment">//!  --pretty=expanded` or the [`cargo expand`] subcommand.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [ `cargo expand`]: https://github.com/dtolnay/cargo-expand</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  To show the expanded code for some crate that uses your procedural macro,</span>
<span class="doccomment">//!  run `cargo expand` from that crate.  To show the expanded code for one of</span>
<span class="doccomment">//!  your own test cases, run `cargo expand --test the_test_case` where the last</span>
<span class="doccomment">//!  argument is the name of the test file without the `.rs` extension.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  This write-up by Brandon W Maister discusses debugging in more detail:</span>
<span class="doccomment">//! [ Debugging Rust&#39;s new Custom Derive system][debugging].</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [ debugging]: https://quodlibetor.github.io/posts/debugging-rusts-new-custom-derive-system/</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ##  Optional features</span>
<span class="doccomment">//!</span>
<span class="doccomment">//!  Syn puts a lot of functionality behind optional features in order to</span>
<span class="doccomment">//!  optimize compile time for the most common use cases.  The following features</span>
<span class="doccomment">//!  are available.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! - ** `derive`** *(enabled by default)* — Data structures for representing the</span>
<span class="doccomment">//!    possible input to a custom derive, including structs and enums and types.</span>
<span class="doccomment">//! - ** `full`** — Data structures for representing the syntax tree of all valid</span>
<span class="doccomment">//!    Rust source code, including items and expressions.</span>
<span class="doccomment">//! - ** `parsing`** *(enabled by default)* — Ability to parse input tokens into</span>
<span class="doccomment">//!    a syntax tree node of a chosen type.</span>
<span class="doccomment">//! - ** `printing`** *(enabled by default)* — Ability to print a syntax tree</span>
<span class="doccomment">//!    node as tokens of Rust source code.</span>
<span class="doccomment">//! - ** `visit`** — Trait for traversing a syntax tree.</span>
<span class="doccomment">//! - ** `visit-mut`** — Trait for traversing and mutating in place a syntax</span>
<span class="doccomment">//!    tree.</span>
<span class="doccomment">//! - ** `fold`** — Trait for transforming an owned syntax tree.</span>
<span class="doccomment">//! - ** `clone-impls`** *(enabled by default)* — Clone impls for all syntax tree</span>
<span class="doccomment">//!    types.</span>
<span class="doccomment">//! - ** `extra-traits`** — Debug, Eq, PartialEq, Hash impls for all syntax tree</span>
<span class="doccomment">//!    types.</span>
<span class="doccomment">//! - ** `proc-macro`** *(enabled by default)* — Runtime dependency on the</span>
<span class="doccomment">//!    dynamic library libproc_macro from rustc toolchain.</span>

<span class="comment">// Syn types in rustdoc of other crates get linked to here.</span>
<span class="attribute">#![<span class="ident">doc</span>(<span class="ident">html_root_url</span> <span class="op">=</span> <span class="string">&quot;https://docs.rs/syn/0.14.7&quot;</span>)]</span>
<span class="attribute">#![<span class="ident">cfg_attr</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;cargo-clippy&quot;</span>, <span class="ident">deny</span>(<span class="ident">clippy</span>, <span class="ident">clippy_pedantic</span>))]</span>
<span class="comment">// Ignored clippy lints.</span>
<span class="attribute">#![<span class="ident">cfg_attr</span>(
    <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;cargo-clippy&quot;</span>,
    <span class="ident">allow</span>(
        <span class="ident">const_static_lifetime</span>,
        <span class="ident">doc_markdown</span>,
        <span class="ident">large_enum_variant</span>,
        <span class="ident">match_bool</span>,
        <span class="ident">redundant_closure</span>,
        <span class="ident">needless_pass_by_value</span>,
        <span class="ident">redundant_field_names</span>,
        <span class="ident">trivially_copy_pass_by_ref</span>
    )
)]</span>
<span class="comment">// Ignored clippy_pedantic lints.</span>
<span class="attribute">#![<span class="ident">cfg_attr</span>(
    <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;cargo-clippy&quot;</span>,
    <span class="ident">allow</span>(
        <span class="ident">cast_possible_truncation</span>,
        <span class="ident">cast_possible_wrap</span>,
        <span class="ident">if_not_else</span>,
        <span class="ident">indexing_slicing</span>,
        <span class="ident">items_after_statements</span>,
        <span class="ident">similar_names</span>,
        <span class="ident">single_match_else</span>,
        <span class="ident">stutter</span>,
        <span class="ident">unseparated_literal_suffix</span>,
        <span class="ident">use_self</span>,
        <span class="ident">used_underscore_binding</span>
    )
)]</span>

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;proc-macro&quot;</span>)]</span>
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">proc_macro</span>;
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">proc_macro2</span>;
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">unicode_xid</span>;

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;printing&quot;</span>)]</span>
<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">quote</span>;

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>)]</span>
<span class="attribute">#[<span class="ident">macro_use</span>]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">parsers</span>;

<span class="attribute">#[<span class="ident">macro_use</span>]</span>
<span class="kw">mod</span> <span class="ident">macros</span>;

<span class="attribute">#[<span class="ident">macro_use</span>]</span>
<span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">token</span>;

<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">proc_macro2</span>::<span class="ident">Ident</span>;

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">attr</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">attr</span>::{<span class="ident">AttrStyle</span>, <span class="ident">Attribute</span>, <span class="ident">Meta</span>, <span class="ident">MetaList</span>, <span class="ident">MetaNameValue</span>, <span class="ident">NestedMeta</span>};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">data</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">data</span>::{
    <span class="ident">Field</span>, <span class="ident">Fields</span>, <span class="ident">FieldsNamed</span>, <span class="ident">FieldsUnnamed</span>, <span class="ident">Variant</span>, <span class="ident">VisCrate</span>, <span class="ident">VisPublic</span>, <span class="ident">VisRestricted</span>,
    <span class="ident">Visibility</span>,
};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">expr</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">expr</span>::{
    <span class="ident">Expr</span>, <span class="ident">ExprArray</span>, <span class="ident">ExprAssign</span>, <span class="ident">ExprAssignOp</span>, <span class="ident">ExprBinary</span>, <span class="ident">ExprBlock</span>, <span class="ident">ExprBox</span>, <span class="ident">ExprBreak</span>, <span class="ident">ExprCall</span>,
    <span class="ident">ExprCast</span>, <span class="ident">ExprCatch</span>, <span class="ident">ExprClosure</span>, <span class="ident">ExprContinue</span>, <span class="ident">ExprField</span>, <span class="ident">ExprForLoop</span>, <span class="ident">ExprGroup</span>, <span class="ident">ExprIf</span>,
    <span class="ident">ExprIfLet</span>, <span class="ident">ExprInPlace</span>, <span class="ident">ExprIndex</span>, <span class="ident">ExprLit</span>, <span class="ident">ExprLoop</span>, <span class="ident">ExprMacro</span>, <span class="ident">ExprMatch</span>, <span class="ident">ExprMethodCall</span>,
    <span class="ident">ExprParen</span>, <span class="ident">ExprPath</span>, <span class="ident">ExprRange</span>, <span class="ident">ExprReference</span>, <span class="ident">ExprRepeat</span>, <span class="ident">ExprReturn</span>, <span class="ident">ExprStruct</span>, <span class="ident">ExprTry</span>,
    <span class="ident">ExprTuple</span>, <span class="ident">ExprType</span>, <span class="ident">ExprUnary</span>, <span class="ident">ExprUnsafe</span>, <span class="ident">ExprVerbatim</span>, <span class="ident">ExprWhile</span>, <span class="ident">ExprWhileLet</span>, <span class="ident">ExprYield</span>,
    <span class="ident">Index</span>, <span class="ident">Member</span>,
};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">expr</span>::{
    <span class="ident">Arm</span>, <span class="ident">Block</span>, <span class="ident">FieldPat</span>, <span class="ident">FieldValue</span>, <span class="ident">GenericMethodArgument</span>, <span class="ident">Label</span>, <span class="ident">Local</span>, <span class="ident">MethodTurbofish</span>, <span class="ident">Pat</span>,
    <span class="ident">PatBox</span>, <span class="ident">PatIdent</span>, <span class="ident">PatLit</span>, <span class="ident">PatMacro</span>, <span class="ident">PatPath</span>, <span class="ident">PatRange</span>, <span class="ident">PatRef</span>, <span class="ident">PatSlice</span>, <span class="ident">PatStruct</span>, <span class="ident">PatTuple</span>,
    <span class="ident">PatTupleStruct</span>, <span class="ident">PatVerbatim</span>, <span class="ident">PatWild</span>, <span class="ident">RangeLimits</span>, <span class="ident">Stmt</span>,
};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">generics</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">generics</span>::{
    <span class="ident">BoundLifetimes</span>, <span class="ident">ConstParam</span>, <span class="ident">GenericParam</span>, <span class="ident">Generics</span>, <span class="ident">LifetimeDef</span>, <span class="ident">PredicateEq</span>,
    <span class="ident">PredicateLifetime</span>, <span class="ident">PredicateType</span>, <span class="ident">TraitBound</span>, <span class="ident">TraitBoundModifier</span>, <span class="ident">TypeParam</span>, <span class="ident">TypeParamBound</span>,
    <span class="ident">WhereClause</span>, <span class="ident">WherePredicate</span>,
};
<span class="attribute">#[<span class="ident">cfg</span>(
    <span class="ident">all</span>(
        <span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>),
        <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;printing&quot;</span>
    )
)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">generics</span>::{<span class="ident">ImplGenerics</span>, <span class="ident">Turbofish</span>, <span class="ident">TypeGenerics</span>};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>)]</span>
<span class="kw">mod</span> <span class="ident">item</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">item</span>::{
    <span class="ident">ArgCaptured</span>, <span class="ident">ArgSelf</span>, <span class="ident">ArgSelfRef</span>, <span class="ident">FnArg</span>, <span class="ident">FnDecl</span>, <span class="ident">ForeignItem</span>, <span class="ident">ForeignItemFn</span>, <span class="ident">ForeignItemStatic</span>,
    <span class="ident">ForeignItemType</span>, <span class="ident">ForeignItemVerbatim</span>, <span class="ident">ImplItem</span>, <span class="ident">ImplItemConst</span>, <span class="ident">ImplItemMacro</span>, <span class="ident">ImplItemMethod</span>,
    <span class="ident">ImplItemType</span>, <span class="ident">ImplItemVerbatim</span>, <span class="ident">Item</span>, <span class="ident">ItemConst</span>, <span class="ident">ItemEnum</span>, <span class="ident">ItemExternCrate</span>, <span class="ident">ItemFn</span>,
    <span class="ident">ItemForeignMod</span>, <span class="ident">ItemImpl</span>, <span class="ident">ItemMacro</span>, <span class="ident">ItemMacro2</span>, <span class="ident">ItemMod</span>, <span class="ident">ItemStatic</span>, <span class="ident">ItemStruct</span>, <span class="ident">ItemTrait</span>,
    <span class="ident">ItemType</span>, <span class="ident">ItemUnion</span>, <span class="ident">ItemUse</span>, <span class="ident">ItemVerbatim</span>, <span class="ident">MethodSig</span>, <span class="ident">TraitItem</span>, <span class="ident">TraitItemConst</span>,
    <span class="ident">TraitItemMacro</span>, <span class="ident">TraitItemMethod</span>, <span class="ident">TraitItemType</span>, <span class="ident">TraitItemVerbatim</span>, <span class="ident">UseGlob</span>, <span class="ident">UseGroup</span>, <span class="ident">UseName</span>,
    <span class="ident">UsePath</span>, <span class="ident">UseRename</span>, <span class="ident">UseTree</span>,
};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>)]</span>
<span class="kw">mod</span> <span class="ident">file</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">file</span>::<span class="ident">File</span>;

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">lifetime</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">lifetime</span>::<span class="ident">Lifetime</span>;

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">lit</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">lit</span>::{
    <span class="ident">FloatSuffix</span>, <span class="ident">IntSuffix</span>, <span class="ident">Lit</span>, <span class="ident">LitBool</span>, <span class="ident">LitByte</span>, <span class="ident">LitByteStr</span>, <span class="ident">LitChar</span>, <span class="ident">LitFloat</span>, <span class="ident">LitInt</span>, <span class="ident">LitStr</span>,
    <span class="ident">LitVerbatim</span>, <span class="ident">StrStyle</span>,
};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">mac</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">mac</span>::{<span class="ident">Macro</span>, <span class="ident">MacroDelimiter</span>};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">derive</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">derive</span>::{<span class="ident">Data</span>, <span class="ident">DataEnum</span>, <span class="ident">DataStruct</span>, <span class="ident">DataUnion</span>, <span class="ident">DeriveInput</span>};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">op</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">op</span>::{<span class="ident">BinOp</span>, <span class="ident">UnOp</span>};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">ty</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">ty</span>::{
    <span class="ident">Abi</span>, <span class="ident">BareFnArg</span>, <span class="ident">BareFnArgName</span>, <span class="ident">ReturnType</span>, <span class="ident">Type</span>, <span class="ident">TypeArray</span>, <span class="ident">TypeBareFn</span>, <span class="ident">TypeGroup</span>,
    <span class="ident">TypeImplTrait</span>, <span class="ident">TypeInfer</span>, <span class="ident">TypeMacro</span>, <span class="ident">TypeNever</span>, <span class="ident">TypeParen</span>, <span class="ident">TypePath</span>, <span class="ident">TypePtr</span>, <span class="ident">TypeReference</span>,
    <span class="ident">TypeSlice</span>, <span class="ident">TypeTraitObject</span>, <span class="ident">TypeTuple</span>, <span class="ident">TypeVerbatim</span>,
};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">path</span>;
<span class="attribute">#[<span class="ident">cfg</span>(
    <span class="ident">all</span>(
        <span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>),
        <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;printing&quot;</span>
    )
)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">path</span>::<span class="ident">PathTokens</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">path</span>::{
    <span class="ident">AngleBracketedGenericArguments</span>, <span class="ident">Binding</span>, <span class="ident">GenericArgument</span>, <span class="ident">ParenthesizedGenericArguments</span>, <span class="ident">Path</span>,
    <span class="ident">PathArguments</span>, <span class="ident">PathSegment</span>, <span class="ident">QSelf</span>,
};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">buffer</span>;
<span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">punctuated</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">synom</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">tt</span>;

<span class="comment">// Not public API except the `parse_quote! ` macro.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">parse_quote</span>;

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">all</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;printing&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">spanned</span>;

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">all</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>))]</span>
<span class="kw">mod</span> <span class="ident">verbatim</span>;

<span class="kw">mod</span> <span class="ident">gen</span> {
    <span class="doccomment">/// Syntax tree traversal to walk a shared borrow of a syntax tree.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Each method of the [`Visit`] trait is a hook that can be overridden to</span>
    <span class="doccomment">/// customize the behavior when visiting the corresponding type of node.  By</span>
    <span class="doccomment">/// default, every method recursively visits the substructure of the input</span>
    <span class="doccomment">/// by invoking the right visitor method of each of its fields.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// [`Visit`]: trait. Visit.html</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```rust</span>
    <span class="doccomment">/// # use syn::{Attribute, BinOp, Expr, ExprBinary};</span>
    <span class="doccomment">/// #</span>
    <span class="doccomment">/// pub trait Visit&lt;&#39;ast&gt; {</span>
    <span class="doccomment">///     /* ... */</span>
    <span class="doccomment">///</span>
    <span class="doccomment">///     fn visit_expr_binary(&amp;mut self, node: &amp;&#39;ast ExprBinary) {</span>
    <span class="doccomment">///         for attr in &amp;node.attrs {</span>
    <span class="doccomment">///             self.visit_attribute(attr);</span>
    <span class="doccomment">///         }</span>
    <span class="doccomment">///         self.visit_expr(&amp;*node.left);</span>
    <span class="doccomment">///         self.visit_bin_op(&amp;node.op);</span>
    <span class="doccomment">///         self.visit_expr(&amp;*node.right);</span>
    <span class="doccomment">///     }</span>
    <span class="doccomment">///</span>
    <span class="doccomment">///     /* ... */</span>
    <span class="doccomment">///     # fn visit_attribute(&amp;mut self, node: &amp;&#39;ast Attribute);</span>
    <span class="doccomment">///     # fn visit_expr(&amp;mut self, node: &amp;&#39;ast Expr);</span>
    <span class="doccomment">///     # fn visit_bin_op(&amp;mut self, node: &amp;&#39;ast BinOp);</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// *This module is available if Syn is built with the `&quot;visit&quot;` feature.*</span>
    <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;visit&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">visit</span>;

    <span class="doccomment">/// Syntax tree traversal to mutate an exclusive borrow of a syntax tree in</span>
    <span class="doccomment">/// place.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Each method of the [`VisitMut`] trait is a hook that can be overridden</span>
    <span class="doccomment">/// to customize the behavior when mutating the corresponding type of node.</span>
    <span class="doccomment">/// By default, every method recursively visits the substructure of the</span>
    <span class="doccomment">/// input by invoking the right visitor method of each of its fields.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// [`VisitMut`]: trait. VisitMut.html</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```rust</span>
    <span class="doccomment">/// # use syn::{Attribute, BinOp, Expr, ExprBinary};</span>
    <span class="doccomment">/// #</span>
    <span class="doccomment">/// pub trait VisitMut {</span>
    <span class="doccomment">///     /* ... */</span>
    <span class="doccomment">///</span>
    <span class="doccomment">///     fn visit_expr_binary_mut(&amp;mut self, node: &amp;mut ExprBinary) {</span>
    <span class="doccomment">///         for attr in &amp;mut node.attrs {</span>
    <span class="doccomment">///             self.visit_attribute_mut(attr);</span>
    <span class="doccomment">///         }</span>
    <span class="doccomment">///         self.visit_expr_mut(&amp;mut *node.left);</span>
    <span class="doccomment">///         self.visit_bin_op_mut(&amp;mut node.op);</span>
    <span class="doccomment">///         self.visit_expr_mut(&amp;mut *node.right);</span>
    <span class="doccomment">///     }</span>
    <span class="doccomment">///</span>
    <span class="doccomment">///     /* ... */</span>
    <span class="doccomment">///     # fn visit_attribute_mut(&amp;mut self, node: &amp;mut Attribute);</span>
    <span class="doccomment">///     # fn visit_expr_mut(&amp;mut self, node: &amp;mut Expr);</span>
    <span class="doccomment">///     # fn visit_bin_op_mut(&amp;mut self, node: &amp;mut BinOp);</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// *This module is available if Syn is built with the `&quot;visit-mut&quot;`</span>
    <span class="doccomment">/// feature.*</span>
    <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;visit-mut&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">visit_mut</span>;

    <span class="doccomment">/// Syntax tree traversal to transform the nodes of an owned syntax tree.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Each method of the [`Fold`] trait is a hook that can be overridden to</span>
    <span class="doccomment">/// customize the behavior when transforming the corresponding type of node.</span>
    <span class="doccomment">/// By default, every method recursively visits the substructure of the</span>
    <span class="doccomment">/// input by invoking the right visitor method of each of its fields.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// [`Fold`]: trait. Fold.html</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```rust</span>
    <span class="doccomment">/// # use syn::{Attribute, BinOp, Expr, ExprBinary};</span>
    <span class="doccomment">/// #</span>
    <span class="doccomment">/// pub trait Fold {</span>
    <span class="doccomment">///     /* ... */</span>
    <span class="doccomment">///</span>
    <span class="doccomment">///     fn fold_expr_binary(&amp;mut self, node: ExprBinary) -&gt; ExprBinary {</span>
    <span class="doccomment">///         ExprBinary {</span>
    <span class="doccomment">///             attrs: node.attrs</span>
    <span class="doccomment">///                        .into_iter()</span>
    <span class="doccomment">///                        .map(|attr| self.fold_attribute(attr))</span>
    <span class="doccomment">///                        .collect(),</span>
    <span class="doccomment">///             left: Box::new(self.fold_expr(*node.left)),</span>
    <span class="doccomment">///             op: self.fold_bin_op(node.op),</span>
    <span class="doccomment">///             right: Box::new(self.fold_expr(*node.right)),</span>
    <span class="doccomment">///         }</span>
    <span class="doccomment">///     }</span>
    <span class="doccomment">///</span>
    <span class="doccomment">///     /* ... */</span>
    <span class="doccomment">///     # fn fold_attribute(&amp;mut self, node: Attribute) -&gt; Attribute;</span>
    <span class="doccomment">///     # fn fold_expr(&amp;mut self, node: Expr) -&gt; Expr;</span>
    <span class="doccomment">///     # fn fold_bin_op(&amp;mut self, node: BinOp) -&gt; BinOp;</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// *This module is available if Syn is built with the `&quot;fold&quot;` feature.*</span>
    <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;fold&quot;</span>)]</span>
    <span class="kw">pub</span> <span class="kw">mod</span> <span class="ident">fold</span>;

    <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>))]</span>
    <span class="attribute">#[<span class="ident">path</span> <span class="op">=</span> <span class="string">&quot;../gen_helper.rs&quot;</span>]</span>
    <span class="kw">mod</span> <span class="ident">helper</span>;
}
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">gen</span>::<span class="kw-2">*</span>;

<span class="comment">////////////////////////////////////////////////////////////////////////////////</span>

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>)]</span>
<span class="kw">use</span> <span class="ident">synom</span>::{<span class="ident">Parser</span>, <span class="ident">Synom</span>};

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>)]</span>
<span class="kw">mod</span> <span class="ident">error</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>)]</span>
<span class="kw">use</span> <span class="ident">error</span>::<span class="ident">ParseError</span>;

<span class="comment">// Not public API.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">error</span>::<span class="ident">parse_error</span>;

<span class="doccomment">/// Parse tokens of source code into the chosen syntax tree node.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is preferred over parsing a string because tokens are able to preserve</span>
<span class="doccomment">/// information about where in the user&#39;s code they were originally written (the</span>
<span class="doccomment">/// &quot;span&quot; of the token), possibly allowing the compiler to produce better error</span>
<span class="doccomment">/// messages.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function parses a `proc_macro::TokenStream` which is the type used for</span>
<span class="doccomment">/// interop with the compiler in a procedural macro.  To parse a</span>
<span class="doccomment">/// `proc_macro2::TokenStream`, use [`syn::parse2`] instead.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`syn::parse2`]: fn.parse2.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *This function is available if Syn is built with both the `&quot;parsing&quot;` and</span>
<span class="doccomment">/// `&quot;proc-macro&quot;` features.*</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```rust</span>
<span class="doccomment">/// extern crate proc_macro;</span>
<span class="doccomment">/// use proc_macro::TokenStream;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// extern crate syn;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// #[macro_use]</span>
<span class="doccomment">/// extern crate quote;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// use syn::DeriveInput;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # const IGNORE_TOKENS: &amp;str = stringify! { </span>
<span class="doccomment">/// #[proc_macro_derive(MyMacro)]</span>
<span class="doccomment">/// # };</span>
<span class="doccomment">/// pub fn my_macro(input: TokenStream) -&gt; TokenStream {</span>
<span class="doccomment">///     // Parse the tokens into a syntax tree</span>
<span class="doccomment">///     let ast: DeriveInput = syn::parse(input).unwrap();</span>
<span class="doccomment">///</span>
<span class="doccomment">///     // Build the output, possibly using quasi-quotation</span>
<span class="doccomment">///     let expanded = quote! { </span>
<span class="doccomment">///         /* ... */</span>
<span class="doccomment">///     };</span>
<span class="doccomment">///</span>
<span class="doccomment">///     // Convert into a token stream and return it</span>
<span class="doccomment">///     expanded.into()</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// #</span>
<span class="doccomment">/// # fn main() {}</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">all</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;proc-macro&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">parse</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>(<span class="ident">tokens</span>: <span class="ident">proc_macro</span>::<span class="ident">TokenStream</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">ParseError</span><span class="op">&gt;</span>
<span class="kw">where</span>
    <span class="ident">T</span>: <span class="ident">Synom</span>,
{
    <span class="ident">parse2</span>(<span class="ident">tokens</span>.<span class="ident">into</span>())
}

<span class="doccomment">/// Parse a proc-macro2 token stream into the chosen syntax tree node.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function parses a `proc_macro2::TokenStream` which is commonly useful</span>
<span class="doccomment">/// when the input comes from a node of the Syn syntax tree, for example the tts</span>
<span class="doccomment">/// of a [`Macro`] node.  When in a procedural macro parsing the</span>
<span class="doccomment">/// `proc_macro::TokenStream` provided by the compiler, use [`syn::parse`]</span>
<span class="doccomment">/// instead.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Macro`]: struct. Macro.html</span>
<span class="doccomment">/// [`syn::parse`]: fn.parse.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *This function is available if Syn is built with the `&quot;parsing&quot;` feature.*</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">parse2</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>(<span class="ident">tokens</span>: <span class="ident">proc_macro2</span>::<span class="ident">TokenStream</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">ParseError</span><span class="op">&gt;</span>
<span class="kw">where</span>
    <span class="ident">T</span>: <span class="ident">Synom</span>,
{
    <span class="kw">let</span> <span class="ident">parser</span> <span class="op">=</span> <span class="ident">T</span>::<span class="ident">parse</span>;
    <span class="ident">parser</span>.<span class="ident">parse2</span>(<span class="ident">tokens</span>).<span class="ident">map_err</span>(<span class="op">|</span><span class="ident">err</span><span class="op">|</span> <span class="kw">match</span> <span class="ident">T</span>::<span class="ident">description</span>() {
        <span class="prelude-val">Some</span>(<span class="ident">s</span>) <span class="op">=&gt;</span> <span class="ident">ParseError</span>::<span class="ident">new</span>(<span class="macro">format</span><span class="macro">!</span>(<span class="string">&quot;failed to parse {}: {}&quot;</span>, <span class="ident">s</span>, <span class="ident">err</span>)),
        <span class="prelude-val">None</span> <span class="op">=&gt;</span> <span class="ident">err</span>,
    })
}

<span class="doccomment">/// Parse a string of Rust code into the chosen syntax tree node.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *This function is available if Syn is built with the `&quot;parsing&quot;` feature.*</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Hygiene</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Every span in the resulting syntax tree will be set to resolve at the macro</span>
<span class="doccomment">/// call site.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```rust</span>
<span class="doccomment">/// extern crate syn;</span>
<span class="doccomment">/// #</span>
<span class="doccomment">/// #</span>
<span class="doccomment">/// # type Result&lt;T&gt; = std::result::Result&lt;T, Box&lt;std::error::Error&gt;&gt;;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// use syn::Expr;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn run() -&gt; Result&lt;()&gt; {</span>
<span class="doccomment">///     let code = &quot;assert_eq!(u8::max_value(), 255)&quot;;</span>
<span class="doccomment">///     let expr = syn::parse_str::&lt;Expr&gt;(code)?;</span>
<span class="doccomment">///     println!(&quot;{:#?}&quot;, expr);</span>
<span class="doccomment">///     Ok(())</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// #</span>
<span class="doccomment">/// # fn main() { run().unwrap() }</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">parse_str</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="ident">Synom</span><span class="op">&gt;</span>(<span class="ident">s</span>: <span class="kw-2">&amp;</span><span class="ident">str</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">T</span>, <span class="ident">ParseError</span><span class="op">&gt;</span> {
    <span class="kw">match</span> <span class="ident">s</span>.<span class="ident">parse</span>() {
        <span class="prelude-val">Ok</span>(<span class="ident">tts</span>) <span class="op">=&gt;</span> <span class="ident">parse2</span>(<span class="ident">tts</span>),
        <span class="prelude-val">Err</span>(<span class="kw">_</span>) <span class="op">=&gt;</span> <span class="prelude-val">Err</span>(<span class="ident">ParseError</span>::<span class="ident">new</span>(<span class="string">&quot;error while lexing input string&quot;</span>)),
    }
}

<span class="comment">// FIXME the name parse_file makes it sound like you might pass in a path to a</span>
<span class="comment">// file, rather than the content.</span>
<span class="doccomment">/// Parse the content of a file of Rust code.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is different from `syn::parse_str::&lt;File&gt;(content)` in two ways:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// - It discards a leading byte order mark `\u{FEFF}` if the file has one.</span>
<span class="doccomment">/// - It preserves the shebang line of the file, such as `#! /usr/bin/env rustx`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If present, either of these would be an error using `from_str`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// *This function is available if Syn is built with the `&quot;parsing&quot;` and `&quot;full&quot;` features.*</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```rust,no_run</span>
<span class="doccomment">/// extern crate syn;</span>
<span class="doccomment">/// #</span>
<span class="doccomment">/// #</span>
<span class="doccomment">/// # type Result&lt;T&gt; = std::result::Result&lt;T, Box&lt;std::error::Error&gt;&gt;;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// use std::fs::File;</span>
<span class="doccomment">/// use std::io::Read;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn run() -&gt; Result&lt;()&gt; {</span>
<span class="doccomment">///     let mut file = File::open(&quot;path/to/code.rs&quot;)?;</span>
<span class="doccomment">///     let mut content = String::new();</span>
<span class="doccomment">///     file.read_to_string(&amp;mut content)?;</span>
<span class="doccomment">///</span>
<span class="doccomment">///     let ast = syn::parse_file(&amp;content)?;</span>
<span class="doccomment">///     if let Some(shebang) = ast.shebang {</span>
<span class="doccomment">///         println!(&quot;{}&quot;, shebang);</span>
<span class="doccomment">///     }</span>
<span class="doccomment">///     println!(&quot;{} items&quot;, ast.items.len());</span>
<span class="doccomment">///</span>
<span class="doccomment">///     Ok(())</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// #</span>
<span class="doccomment">/// # fn main() { run().unwrap() }</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">all</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;parsing&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">parse_file</span>(<span class="kw-2">mut</span> <span class="ident">content</span>: <span class="kw-2">&amp;</span><span class="ident">str</span>) <span class="op">-&gt;</span> <span class="prelude-ty">Result</span><span class="op">&lt;</span><span class="ident">File</span>, <span class="ident">ParseError</span><span class="op">&gt;</span> {
    <span class="comment">// Strip the BOM if it is present</span>
    <span class="kw">const</span> <span class="ident">BOM</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;static</span> <span class="ident">str</span> <span class="op">=</span> <span class="string">&quot;\u{feff}&quot;</span>;
    <span class="kw">if</span> <span class="ident">content</span>.<span class="ident">starts_with</span>(<span class="ident">BOM</span>) {
        <span class="ident">content</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="ident">content</span>[<span class="ident">BOM</span>.<span class="ident">len</span>()..];
    }

    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">shebang</span> <span class="op">=</span> <span class="prelude-val">None</span>;
    <span class="kw">if</span> <span class="ident">content</span>.<span class="ident">starts_with</span>(<span class="string">&quot;#!&quot;</span>) <span class="op">&amp;&amp;</span> <span class="op">!</span><span class="ident">content</span>.<span class="ident">starts_with</span>(<span class="string">&quot;#![&quot;</span>) {
        <span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">idx</span>) <span class="op">=</span> <span class="ident">content</span>.<span class="ident">find</span>(<span class="string">&#39;\n&#39;</span>) {
            <span class="ident">shebang</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">content</span>[..<span class="ident">idx</span>].<span class="ident">to_string</span>());
            <span class="ident">content</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="ident">content</span>[<span class="ident">idx</span>..];
        } <span class="kw">else</span> {
            <span class="ident">shebang</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">content</span>.<span class="ident">to_string</span>());
            <span class="ident">content</span> <span class="op">=</span> <span class="string">&quot;&quot;</span>;
        }
    }

    <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">file</span>: <span class="ident">File</span> <span class="op">=</span> <span class="ident">parse_str</span>(<span class="ident">content</span>)<span class="question-mark">?</span>;
    <span class="ident">file</span>.<span class="ident">shebang</span> <span class="op">=</span> <span class="ident">shebang</span>;
    <span class="prelude-val">Ok</span>(<span class="ident">file</span>)
}

<span class="attribute">#[<span class="ident">cfg</span>(
    <span class="ident">all</span>(
        <span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>),
        <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;printing&quot;</span>
    )
)]</span>
<span class="kw">struct</span> <span class="ident">TokensOrDefault</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span>: <span class="lifetime">&#39;a</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>);

<span class="attribute">#[<span class="ident">cfg</span>(
    <span class="ident">all</span>(
        <span class="ident">any</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;full&quot;</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;derive&quot;</span>),
        <span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;printing&quot;</span>
    )
)]</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span><span class="op">&gt;</span> <span class="ident">quote</span>::<span class="ident">ToTokens</span> <span class="kw">for</span> <span class="ident">TokensOrDefault</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span><span class="op">&gt;</span>
<span class="kw">where</span>
    <span class="ident">T</span>: <span class="ident">quote</span>::<span class="ident">ToTokens</span> <span class="op">+</span> <span class="ident">Default</span>,
{
    <span class="kw">fn</span> <span class="ident">to_tokens</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">tokens</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">proc_macro2</span>::<span class="ident">TokenStream</span>) {
        <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="number">0</span> {
            <span class="prelude-val">Some</span>(<span class="kw-2">ref</span> <span class="ident">t</span>) <span class="op">=&gt;</span> <span class="ident">t</span>.<span class="ident">to_tokens</span>(<span class="ident">tokens</span>),
            <span class="prelude-val">None</span> <span class="op">=&gt;</span> <span class="ident">T</span>::<span class="ident">default</span>().<span class="ident">to_tokens</span>(<span class="ident">tokens</span>),
        }
    }
}
</pre>
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