src/expr.rs

use super::*;
use proc_macro2::{Span, TokenStream};
use punctuated::Punctuated;
#[cfg(feature = "extra-traits")]
use std::hash::{Hash, Hasher};
#[cfg(all(feature = "parsing", feature = "full"))]
use std::mem;
#[cfg(feature = "extra-traits")]
use tt::TokenStreamHelper;

ast_enum_of_structs! {
    /// A Rust expression.
    ///
    /// *This type is available if Syn is built with the `"derive"` or `"full"`
    /// feature.*
    ///
    /// # Syntax tree enums
    ///
    /// This type is a syntax tree enum. In Syn this and other syntax tree enums
    /// are designed to be traversed using the following rebinding idiom.
    ///
    /// ```edition2018
    /// # use syn::Expr;
    /// #
    /// # fn example(expr: Expr) {
    /// # const IGNORE: &str = stringify! {
    /// let expr: Expr = /* ... */;
    /// # };
    /// match expr {
    ///     Expr::MethodCall(expr) => {
    ///         /* ... */
    ///     }
    ///     Expr::Cast(expr) => {
    ///         /* ... */
    ///     }
    ///     Expr::If(expr) => {
    ///         /* ... */
    ///     }
    ///     /* ... */
    ///     # _ => {}
    /// }
    /// # }
    /// ```
    ///
    /// We begin with a variable `expr` of type `Expr` that has no fields
    /// (because it is an enum), and by matching on it and rebinding a variable
    /// with the same name `expr` we effectively imbue our variable with all of
    /// the data fields provided by the variant that it turned out to be. So for
    /// example above if we ended up in the `MethodCall` case then we get to use
    /// `expr.receiver`, `expr.args` etc; if we ended up in the `If` case we get
    /// to use `expr.cond`, `expr.then_branch`, `expr.else_branch`.
    ///
    /// The pattern is similar if the input expression is borrowed:
    ///
    /// ```edition2018
    /// # use syn::Expr;
    /// #
    /// # fn example(expr: &Expr) {
    /// match *expr {
    ///     Expr::MethodCall(ref expr) => {
    /// #   }
    /// #   _ => {}
    /// # }
    /// # }
    /// ```
    ///
    /// This approach avoids repeating the variant names twice on every line.
    ///
    /// ```edition2018
    /// # use syn::{Expr, ExprMethodCall};
    /// #
    /// # fn example(expr: Expr) {
    /// # match expr {
    /// Expr::MethodCall(ExprMethodCall { method, args, .. }) => { // repetitive
    /// # }
    /// # _ => {}
    /// # }
    /// # }
    /// ```
    ///
    /// In general, the name to which a syntax tree enum variant is bound should
    /// be a suitable name for the complete syntax tree enum type.
    ///
    /// ```edition2018
    /// # use syn::{Expr, ExprField};
    /// #
    /// # fn example(discriminant: &ExprField) {
    /// // Binding is called `base` which is the name I would use if I were
    /// // assigning `*discriminant.base` without an `if let`.
    /// if let Expr::Tuple(ref base) = *discriminant.base {
    /// # }
    /// # }
    /// ```
    ///
    /// A sign that you may not be choosing the right variable names is if you
    /// see names getting repeated in your code, like accessing
    /// `receiver.receiver` or `pat.pat` or `cond.cond`.
    pub enum Expr {
        /// A box expression: `box f`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Box(ExprBox #full {
            pub attrs: Vec<Attribute>,
            pub box_token: Token![box],
            pub expr: Box<Expr>,
        }),

        /// A placement expression: `place <- value`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub InPlace(ExprInPlace #full {
            pub attrs: Vec<Attribute>,
            pub place: Box<Expr>,
            pub arrow_token: Token![<-],
            pub value: Box<Expr>,
        }),

        /// A slice literal expression: `[a, b, c, d]`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Array(ExprArray #full {
            pub attrs: Vec<Attribute>,
            pub bracket_token: token::Bracket,
            pub elems: Punctuated<Expr, Token![,]>,
        }),

        /// A function call expression: `invoke(a, b)`.
        ///
        /// *This type is available if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        pub Call(ExprCall {
            pub attrs: Vec<Attribute>,
            pub func: Box<Expr>,
            pub paren_token: token::Paren,
            pub args: Punctuated<Expr, Token![,]>,
        }),

        /// A method call expression: `x.foo::<T>(a, b)`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub MethodCall(ExprMethodCall #full {
            pub attrs: Vec<Attribute>,
            pub receiver: Box<Expr>,
            pub dot_token: Token![.],
            pub method: Ident,
            pub turbofish: Option<MethodTurbofish>,
            pub paren_token: token::Paren,
            pub args: Punctuated<Expr, Token![,]>,
        }),

        /// A tuple expression: `(a, b, c, d)`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Tuple(ExprTuple #full {
            pub attrs: Vec<Attribute>,
            pub paren_token: token::Paren,
            pub elems: Punctuated<Expr, Token![,]>,
        }),

        /// A binary operation: `a + b`, `a * b`.
        ///
        /// *This type is available if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        pub Binary(ExprBinary {
            pub attrs: Vec<Attribute>,
            pub left: Box<Expr>,
            pub op: BinOp,
            pub right: Box<Expr>,
        }),

        /// A unary operation: `!x`, `*x`.
        ///
        /// *This type is available if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        pub Unary(ExprUnary {
            pub attrs: Vec<Attribute>,
            pub op: UnOp,
            pub expr: Box<Expr>,
        }),

        /// A literal in place of an expression: `1`, `"foo"`.
        ///
        /// *This type is available if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        pub Lit(ExprLit {
            pub attrs: Vec<Attribute>,
            pub lit: Lit,
        }),

        /// A cast expression: `foo as f64`.
        ///
        /// *This type is available if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        pub Cast(ExprCast {
            pub attrs: Vec<Attribute>,
            pub expr: Box<Expr>,
            pub as_token: Token![as],
            pub ty: Box<Type>,
        }),

        /// A type ascription expression: `foo: f64`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Type(ExprType #full {
            pub attrs: Vec<Attribute>,
            pub expr: Box<Expr>,
            pub colon_token: Token![:],
            pub ty: Box<Type>,
        }),

        /// A `let` guard: `let Some(x) = opt`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Let(ExprLet #full {
            pub attrs: Vec<Attribute>,
            pub let_token: Token![let],
            pub pats: Punctuated<Pat, Token![|]>,
            pub eq_token: Token![=],
            pub expr: Box<Expr>,
        }),

        /// An `if` expression with an optional `else` block: `if expr { ... }
        /// else { ... }`.
        ///
        /// The `else` branch expression may only be an `If` or `Block`
        /// expression, not any of the other types of expression.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub If(ExprIf #full {
            pub attrs: Vec<Attribute>,
            pub if_token: Token![if],
            pub cond: Box<Expr>,
            pub then_branch: Block,
            pub else_branch: Option<(Token![else], Box<Expr>)>,
        }),

        /// A while loop: `while expr { ... }`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub While(ExprWhile #full {
            pub attrs: Vec<Attribute>,
            pub label: Option<Label>,
            pub while_token: Token![while],
            pub cond: Box<Expr>,
            pub body: Block,
        }),

        /// A for loop: `for pat in expr { ... }`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub ForLoop(ExprForLoop #full {
            pub attrs: Vec<Attribute>,
            pub label: Option<Label>,
            pub for_token: Token![for],
            pub pat: Box<Pat>,
            pub in_token: Token![in],
            pub expr: Box<Expr>,
            pub body: Block,
        }),

        /// Conditionless loop: `loop { ... }`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Loop(ExprLoop #full {
            pub attrs: Vec<Attribute>,
            pub label: Option<Label>,
            pub loop_token: Token![loop],
            pub body: Block,
        }),

        /// A `match` expression: `match n { Some(n) => {}, None => {} }`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Match(ExprMatch #full {
            pub attrs: Vec<Attribute>,
            pub match_token: Token![match],
            pub expr: Box<Expr>,
            pub brace_token: token::Brace,
            pub arms: Vec<Arm>,
        }),

        /// A closure expression: `|a, b| a + b`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Closure(ExprClosure #full {
            pub attrs: Vec<Attribute>,
            pub asyncness: Option<Token![async]>,
            pub movability: Option<Token![static]>,
            pub capture: Option<Token![move]>,
            pub or1_token: Token![|],
            pub inputs: Punctuated<FnArg, Token![,]>,
            pub or2_token: Token![|],
            pub output: ReturnType,
            pub body: Box<Expr>,
        }),

        /// An unsafe block: `unsafe { ... }`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Unsafe(ExprUnsafe #full {
            pub attrs: Vec<Attribute>,
            pub unsafe_token: Token![unsafe],
            pub block: Block,
        }),

        /// A blocked scope: `{ ... }`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Block(ExprBlock #full {
            pub attrs: Vec<Attribute>,
            pub label: Option<Label>,
            pub block: Block,
        }),

        /// An assignment expression: `a = compute()`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Assign(ExprAssign #full {
            pub attrs: Vec<Attribute>,
            pub left: Box<Expr>,
            pub eq_token: Token![=],
            pub right: Box<Expr>,
        }),

        /// A compound assignment expression: `counter += 1`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub AssignOp(ExprAssignOp #full {
            pub attrs: Vec<Attribute>,
            pub left: Box<Expr>,
            pub op: BinOp,
            pub right: Box<Expr>,
        }),

        /// Access of a named struct field (`obj.k`) or unnamed tuple struct
        /// field (`obj.0`).
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Field(ExprField {
            pub attrs: Vec<Attribute>,
            pub base: Box<Expr>,
            pub dot_token: Token![.],
            pub member: Member,
        }),

        /// A square bracketed indexing expression: `vector[2]`.
        ///
        /// *This type is available if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        pub Index(ExprIndex {
            pub attrs: Vec<Attribute>,
            pub expr: Box<Expr>,
            pub bracket_token: token::Bracket,
            pub index: Box<Expr>,
        }),

        /// A range expression: `1..2`, `1..`, `..2`, `1..=2`, `..=2`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Range(ExprRange #full {
            pub attrs: Vec<Attribute>,
            pub from: Option<Box<Expr>>,
            pub limits: RangeLimits,
            pub to: Option<Box<Expr>>,
        }),

        /// A path like `std::mem::replace` possibly containing generic
        /// parameters and a qualified self-type.
        ///
        /// A plain identifier like `x` is a path of length 1.
        ///
        /// *This type is available if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        pub Path(ExprPath {
            pub attrs: Vec<Attribute>,
            pub qself: Option<QSelf>,
            pub path: Path,
        }),

        /// A referencing operation: `&a` or `&mut a`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Reference(ExprReference #full {
            pub attrs: Vec<Attribute>,
            pub and_token: Token![&],
            pub mutability: Option<Token![mut]>,
            pub expr: Box<Expr>,
        }),

        /// A `break`, with an optional label to break and an optional
        /// expression.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Break(ExprBreak #full {
            pub attrs: Vec<Attribute>,
            pub break_token: Token![break],
            pub label: Option<Lifetime>,
            pub expr: Option<Box<Expr>>,
        }),

        /// A `continue`, with an optional label.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Continue(ExprContinue #full {
            pub attrs: Vec<Attribute>,
            pub continue_token: Token![continue],
            pub label: Option<Lifetime>,
        }),

        /// A `return`, with an optional value to be returned.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Return(ExprReturn #full {
            pub attrs: Vec<Attribute>,
            pub return_token: Token![return],
            pub expr: Option<Box<Expr>>,
        }),

        /// A macro invocation expression: `format!("{}", q)`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Macro(ExprMacro #full {
            pub attrs: Vec<Attribute>,
            pub mac: Macro,
        }),

        /// A struct literal expression: `Point { x: 1, y: 1 }`.
        ///
        /// The `rest` provides the value of the remaining fields as in `S { a:
        /// 1, b: 1, ..rest }`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Struct(ExprStruct #full {
            pub attrs: Vec<Attribute>,
            pub path: Path,
            pub brace_token: token::Brace,
            pub fields: Punctuated<FieldValue, Token![,]>,
            pub dot2_token: Option<Token![..]>,
            pub rest: Option<Box<Expr>>,
        }),

        /// An array literal constructed from one repeated element: `[0u8; N]`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Repeat(ExprRepeat #full {
            pub attrs: Vec<Attribute>,
            pub bracket_token: token::Bracket,
            pub expr: Box<Expr>,
            pub semi_token: Token![;],
            pub len: Box<Expr>,
        }),

        /// A parenthesized expression: `(a + b)`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Paren(ExprParen {
            pub attrs: Vec<Attribute>,
            pub paren_token: token::Paren,
            pub expr: Box<Expr>,
        }),

        /// An expression contained within invisible delimiters.
        ///
        /// This variant is important for faithfully representing the precedence
        /// of expressions and is related to `None`-delimited spans in a
        /// `TokenStream`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Group(ExprGroup #full {
            pub attrs: Vec<Attribute>,
            pub group_token: token::Group,
            pub expr: Box<Expr>,
        }),

        /// A try-expression: `expr?`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Try(ExprTry #full {
            pub attrs: Vec<Attribute>,
            pub expr: Box<Expr>,
            pub question_token: Token![?],
        }),

        /// An async block: `async { ... }`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Async(ExprAsync #full {
            pub attrs: Vec<Attribute>,
            pub async_token: Token![async],
            pub capture: Option<Token![move]>,
            pub block: Block,
        }),

        /// A try block: `try { ... }`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub TryBlock(ExprTryBlock #full {
            pub attrs: Vec<Attribute>,
            pub try_token: Token![try],
            pub block: Block,
        }),

        /// A yield expression: `yield expr`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Yield(ExprYield #full {
            pub attrs: Vec<Attribute>,
            pub yield_token: Token![yield],
            pub expr: Option<Box<Expr>>,
        }),

        /// Tokens in expression position not interpreted by Syn.
        ///
        /// *This type is available if Syn is built with the `"derive"` or
        /// `"full"` feature.*
        pub Verbatim(ExprVerbatim #manual_extra_traits {
            pub tts: TokenStream,
        }),
    }
}

#[cfg(feature = "extra-traits")]
impl Eq for ExprVerbatim {}

#[cfg(feature = "extra-traits")]
impl PartialEq for ExprVerbatim {
    fn eq(&self, other: &Self) -> bool {
        TokenStreamHelper(&self.tts) == TokenStreamHelper(&other.tts)
    }
}

#[cfg(feature = "extra-traits")]
impl Hash for ExprVerbatim {
    fn hash<H>(&self, state: &mut H)
    where
        H: Hasher,
    {
        TokenStreamHelper(&self.tts).hash(state);
    }
}

impl Expr {
    #[cfg(all(feature = "parsing", feature = "full"))]
    fn replace_attrs(&mut self, new: Vec<Attribute>) -> Vec<Attribute> {
        match *self {
            Expr::Box(ExprBox { ref mut attrs, .. })
            | Expr::InPlace(ExprInPlace { ref mut attrs, .. })
            | Expr::Array(ExprArray { ref mut attrs, .. })
            | Expr::Call(ExprCall { ref mut attrs, .. })
            | Expr::MethodCall(ExprMethodCall { ref mut attrs, .. })
            | Expr::Tuple(ExprTuple { ref mut attrs, .. })
            | Expr::Binary(ExprBinary { ref mut attrs, .. })
            | Expr::Unary(ExprUnary { ref mut attrs, .. })
            | Expr::Lit(ExprLit { ref mut attrs, .. })
            | Expr::Cast(ExprCast { ref mut attrs, .. })
            | Expr::Type(ExprType { ref mut attrs, .. })
            | Expr::Let(ExprLet { ref mut attrs, .. })
            | Expr::If(ExprIf { ref mut attrs, .. })
            | Expr::While(ExprWhile { ref mut attrs, .. })
            | Expr::ForLoop(ExprForLoop { ref mut attrs, .. })
            | Expr::Loop(ExprLoop { ref mut attrs, .. })
            | Expr::Match(ExprMatch { ref mut attrs, .. })
            | Expr::Closure(ExprClosure { ref mut attrs, .. })
            | Expr::Unsafe(ExprUnsafe { ref mut attrs, .. })
            | Expr::Block(ExprBlock { ref mut attrs, .. })
            | Expr::Assign(ExprAssign { ref mut attrs, .. })
            | Expr::AssignOp(ExprAssignOp { ref mut attrs, .. })
            | Expr::Field(ExprField { ref mut attrs, .. })
            | Expr::Index(ExprIndex { ref mut attrs, .. })
            | Expr::Range(ExprRange { ref mut attrs, .. })
            | Expr::Path(ExprPath { ref mut attrs, .. })
            | Expr::Reference(ExprReference { ref mut attrs, .. })
            | Expr::Break(ExprBreak { ref mut attrs, .. })
            | Expr::Continue(ExprContinue { ref mut attrs, .. })
            | Expr::Return(ExprReturn { ref mut attrs, .. })
            | Expr::Macro(ExprMacro { ref mut attrs, .. })
            | Expr::Struct(ExprStruct { ref mut attrs, .. })
            | Expr::Repeat(ExprRepeat { ref mut attrs, .. })
            | Expr::Paren(ExprParen { ref mut attrs, .. })
            | Expr::Group(ExprGroup { ref mut attrs, .. })
            | Expr::Try(ExprTry { ref mut attrs, .. })
            | Expr::Async(ExprAsync { ref mut attrs, .. })
            | Expr::TryBlock(ExprTryBlock { ref mut attrs, .. })
            | Expr::Yield(ExprYield { ref mut attrs, .. }) => mem::replace(attrs, new),
            Expr::Verbatim(_) => Vec::new(),
        }
    }
}

ast_enum! {
    /// A struct or tuple struct field accessed in a struct literal or field
    /// expression.
    ///
    /// *This type is available if Syn is built with the `"derive"` or `"full"`
    /// feature.*
    pub enum Member {
        /// A named field like `self.x`.
        Named(Ident),
        /// An unnamed field like `self.0`.
        Unnamed(Index),
    }
}

ast_struct! {
    /// The index of an unnamed tuple struct field.
    ///
    /// *This type is available if Syn is built with the `"derive"` or `"full"`
    /// feature.*
    pub struct Index #manual_extra_traits {
        pub index: u32,
        pub span: Span,
    }
}

impl From<usize> for Index {
    fn from(index: usize) -> Index {
        assert!(index < u32::max_value() as usize);
        Index {
            index: index as u32,
            span: Span::call_site(),
        }
    }
}

#[cfg(feature = "extra-traits")]
impl Eq for Index {}

#[cfg(feature = "extra-traits")]
impl PartialEq for Index {
    fn eq(&self, other: &Self) -> bool {
        self.index == other.index
    }
}

#[cfg(feature = "extra-traits")]
impl Hash for Index {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.index.hash(state);
    }
}

#[cfg(feature = "full")]
ast_struct! {
    /// The `::<>` explicit type parameters passed to a method call:
    /// `parse::<u64>()`.
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    pub struct MethodTurbofish {
        pub colon2_token: Token![::],
        pub lt_token: Token![<],
        pub args: Punctuated<GenericMethodArgument, Token![,]>,
        pub gt_token: Token![>],
    }
}

#[cfg(feature = "full")]
ast_enum! {
    /// An individual generic argument to a method, like `T`.
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    pub enum GenericMethodArgument {
        /// A type argument.
        Type(Type),
        /// A const expression. Must be inside of a block.
        ///
        /// NOTE: Identity expressions are represented as Type arguments, as
        /// they are indistinguishable syntactically.
        Const(Expr),
    }
}

#[cfg(feature = "full")]
ast_struct! {
    /// A field-value pair in a struct literal.
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    pub struct FieldValue {
        /// Attributes tagged on the field.
        pub attrs: Vec<Attribute>,

        /// Name or index of the field.
        pub member: Member,

        /// The colon in `Struct { x: x }`. If written in shorthand like
        /// `Struct { x }`, there is no colon.
        pub colon_token: Option<Token![:]>,

        /// Value of the field.
        pub expr: Expr,
    }
}

#[cfg(feature = "full")]
ast_struct! {
    /// A lifetime labeling a `for`, `while`, or `loop`.
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    pub struct Label {
        pub name: Lifetime,
        pub colon_token: Token![:],
    }
}

#[cfg(feature = "full")]
ast_struct! {
    /// A braced block containing Rust statements.
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    pub struct Block {
        pub brace_token: token::Brace,
        /// Statements in a block
        pub stmts: Vec<Stmt>,
    }
}

#[cfg(feature = "full")]
ast_enum! {
    /// A statement, usually ending in a semicolon.
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    pub enum Stmt {
        /// A local (let) binding.
        Local(Local),

        /// An item definition.
        Item(Item),

        /// Expr without trailing semicolon.
        Expr(Expr),

        /// Expression with trailing semicolon.
        Semi(Expr, Token![;]),
    }
}

#[cfg(feature = "full")]
ast_struct! {
    /// A local `let` binding: `let x: u64 = s.parse()?`.
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    pub struct Local {
        pub attrs: Vec<Attribute>,
        pub let_token: Token![let],
        pub pats: Punctuated<Pat, Token![|]>,
        pub ty: Option<(Token![:], Box<Type>)>,
        pub init: Option<(Token![=], Box<Expr>)>,
        pub semi_token: Token![;],
    }
}

#[cfg(feature = "full")]
ast_enum_of_structs! {
    /// A pattern in a local binding, function signature, match expression, or
    /// various other places.
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    ///
    /// # Syntax tree enum
    ///
    /// This type is a [syntax tree enum].
    ///
    /// [syntax tree enum]: enum.Expr.html#syntax-tree-enums
    pub enum Pat {
        /// A pattern that matches any value: `_`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Wild(PatWild {
            pub underscore_token: Token![_],
        }),

        /// A pattern that binds a new variable: `ref mut binding @ SUBPATTERN`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Ident(PatIdent {
            pub by_ref: Option<Token![ref]>,
            pub mutability: Option<Token![mut]>,
            pub ident: Ident,
            pub subpat: Option<(Token![@], Box<Pat>)>,
        }),

        /// A struct or struct variant pattern: `Variant { x, y, .. }`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Struct(PatStruct {
            pub path: Path,
            pub brace_token: token::Brace,
            pub fields: Punctuated<FieldPat, Token![,]>,
            pub dot2_token: Option<Token![..]>,
        }),

        /// A tuple struct or tuple variant pattern: `Variant(x, y, .., z)`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub TupleStruct(PatTupleStruct {
            pub path: Path,
            pub pat: PatTuple,
        }),

        /// A path pattern like `Color::Red`, optionally qualified with a
        /// self-type.
        ///
        /// Unqualified path patterns can legally refer to variants, structs,
        /// constants or associated constants. Qualified path patterns like
        /// `<A>::B::C` and `<A as Trait>::B::C` can only legally refer to
        /// associated constants.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Path(PatPath {
            pub qself: Option<QSelf>,
            pub path: Path,
        }),

        /// A tuple pattern: `(a, b)`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Tuple(PatTuple {
            pub paren_token: token::Paren,
            pub front: Punctuated<Pat, Token![,]>,
            pub dot2_token: Option<Token![..]>,
            pub comma_token: Option<Token![,]>,
            pub back: Punctuated<Pat, Token![,]>,
        }),

        /// A box pattern: `box v`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Box(PatBox {
            pub box_token: Token![box],
            pub pat: Box<Pat>,
        }),

        /// A reference pattern: `&mut (first, second)`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Ref(PatRef {
            pub and_token: Token![&],
            pub mutability: Option<Token![mut]>,
            pub pat: Box<Pat>,
        }),

        /// A literal pattern: `0`.
        ///
        /// This holds an `Expr` rather than a `Lit` because negative numbers
        /// are represented as an `Expr::Unary`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Lit(PatLit {
            pub expr: Box<Expr>,
        }),

        /// A range pattern: `1..=2`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Range(PatRange {
            pub lo: Box<Expr>,
            pub limits: RangeLimits,
            pub hi: Box<Expr>,
        }),

        /// A dynamically sized slice pattern: `[a, b, i.., y, z]`.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Slice(PatSlice {
            pub bracket_token: token::Bracket,
            pub front: Punctuated<Pat, Token![,]>,
            pub middle: Option<Box<Pat>>,
            pub dot2_token: Option<Token![..]>,
            pub comma_token: Option<Token![,]>,
            pub back: Punctuated<Pat, Token![,]>,
        }),

        /// A macro in expression position.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Macro(PatMacro {
            pub mac: Macro,
        }),

        /// Tokens in pattern position not interpreted by Syn.
        ///
        /// *This type is available if Syn is built with the `"full"` feature.*
        pub Verbatim(PatVerbatim #manual_extra_traits {
            pub tts: TokenStream,
        }),
    }
}

#[cfg(all(feature = "full", feature = "extra-traits"))]
impl Eq for PatVerbatim {}

#[cfg(all(feature = "full", feature = "extra-traits"))]
impl PartialEq for PatVerbatim {
    fn eq(&self, other: &Self) -> bool {
        TokenStreamHelper(&self.tts) == TokenStreamHelper(&other.tts)
    }
}

#[cfg(all(feature = "full", feature = "extra-traits"))]
impl Hash for PatVerbatim {
    fn hash<H>(&self, state: &mut H)
    where
        H: Hasher,
    {
        TokenStreamHelper(&self.tts).hash(state);
    }
}

#[cfg(feature = "full")]
ast_struct! {
    /// One arm of a `match` expression: `0...10 => { return true; }`.
    ///
    /// As in:
    ///
    /// ```edition2018
    /// # fn f() -> bool {
    /// #     let n = 0;
    /// match n {
    ///     0...10 => {
    ///         return true;
    ///     }
    ///     // ...
    ///     # _ => {}
    /// }
    /// #   false
    /// # }
    /// ```
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    pub struct Arm {
        pub attrs: Vec<Attribute>,
        pub leading_vert: Option<Token![|]>,
        pub pats: Punctuated<Pat, Token![|]>,
        pub guard: Option<(Token![if], Box<Expr>)>,
        pub fat_arrow_token: Token![=>],
        pub body: Box<Expr>,
        pub comma: Option<Token![,]>,
    }
}

#[cfg(feature = "full")]
ast_enum! {
    /// Limit types of a range, inclusive or exclusive.
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    #[cfg_attr(feature = "clone-impls", derive(Copy))]
    pub enum RangeLimits {
        /// Inclusive at the beginning, exclusive at the end.
        HalfOpen(Token![..]),
        /// Inclusive at the beginning and end.
        Closed(Token![..=]),
    }
}

#[cfg(feature = "full")]
ast_struct! {
    /// A single field in a struct pattern.
    ///
    /// Patterns like the fields of Foo `{ x, ref y, ref mut z }` are treated
    /// the same as `x: x, y: ref y, z: ref mut z` but there is no colon token.
    ///
    /// *This type is available if Syn is built with the `"full"` feature.*
    pub struct FieldPat {
        pub attrs: Vec<Attribute>,
        pub member: Member,
        pub colon_token: Option<Token![:]>,
        pub pat: Box<Pat>,
    }
}

#[cfg(any(feature = "parsing", feature = "printing"))]
#[cfg(feature = "full")]
fn requires_terminator(expr: &Expr) -> bool {
    // see https://github.com/rust-lang/rust/blob/eb8f2586e/src/libsyntax/parse/classify.rs#L17-L37
    match *expr {
        Expr::Unsafe(..)
        | Expr::Block(..)
        | Expr::If(..)
        | Expr::Match(..)
        | Expr::While(..)
        | Expr::Loop(..)
        | Expr::ForLoop(..)
        | Expr::Async(..)
        | Expr::TryBlock(..) => false,
        _ => true,
    }
}

#[cfg(feature = "parsing")]
pub mod parsing {
    use super::*;

    #[cfg(feature = "full")]
    use ext::IdentExt;
    use parse::{Parse, ParseStream, Result};
    use path;

    // When we're parsing expressions which occur before blocks, like in an if
    // statement's condition, we cannot parse a struct literal.
    //
    // Struct literals are ambiguous in certain positions
    // https://github.com/rust-lang/rfcs/pull/92
    #[derive(Copy, Clone)]
    pub struct AllowStruct(bool);

    #[derive(Copy, Clone, PartialEq, PartialOrd)]
    enum Precedence {
        Any,
        Assign,
        Placement,
        Range,
        Or,
        And,
        Compare,
        BitOr,
        BitXor,
        BitAnd,
        Shift,
        Arithmetic,
        Term,
        Cast,
    }

    impl Precedence {
        fn of(op: &BinOp) -> Self {
            match *op {
                BinOp::Add(_) | BinOp::Sub(_) => Precedence::Arithmetic,
                BinOp::Mul(_) | BinOp::Div(_) | BinOp::Rem(_) => Precedence::Term,
                BinOp::And(_) => Precedence::And,
                BinOp::Or(_) => Precedence::Or,
                BinOp::BitXor(_) => Precedence::BitXor,
                BinOp::BitAnd(_) => Precedence::BitAnd,
                BinOp::BitOr(_) => Precedence::BitOr,
                BinOp::Shl(_) | BinOp::Shr(_) => Precedence::Shift,
                BinOp::Eq(_)
                | BinOp::Lt(_)
                | BinOp::Le(_)
                | BinOp::Ne(_)
                | BinOp::Ge(_)
                | BinOp::Gt(_) => Precedence::Compare,
                BinOp::AddEq(_)
                | BinOp::SubEq(_)
                | BinOp::MulEq(_)
                | BinOp::DivEq(_)
                | BinOp::RemEq(_)
                | BinOp::BitXorEq(_)
                | BinOp::BitAndEq(_)
                | BinOp::BitOrEq(_)
                | BinOp::ShlEq(_)
                | BinOp::ShrEq(_) => Precedence::Assign,
            }
        }
    }

    impl Parse for Expr {
        fn parse(input: ParseStream) -> Result<Self> {
            ambiguous_expr(input, AllowStruct(true))
        }
    }

    #[cfg(feature = "full")]
    fn expr_no_struct(input: ParseStream) -> Result<Expr> {
        ambiguous_expr(input, AllowStruct(false))
    }

    #[cfg(feature = "full")]
    fn parse_expr(
        input: ParseStream,
        mut lhs: Expr,
        allow_struct: AllowStruct,
        base: Precedence,
    ) -> Result<Expr> {
        loop {
            if input
                .fork()
                .parse::<BinOp>()
                .ok()
                .map_or(false, |op| Precedence::of(&op) >= base)
            {
                let op: BinOp = input.parse()?;
                let precedence = Precedence::of(&op);
                let mut rhs = unary_expr(input, allow_struct)?;
                loop {
                    let next = peek_precedence(input);
                    if next > precedence || next == precedence && precedence == Precedence::Assign {
                        rhs = parse_expr(input, rhs, allow_struct, next)?;
                    } else {
                        break;
                    }
                }
                lhs = if precedence == Precedence::Assign {
                    Expr::AssignOp(ExprAssignOp {
                        attrs: Vec::new(),
                        left: Box::new(lhs),
                        op: op,
                        right: Box::new(rhs),
                    })
                } else {
                    Expr::Binary(ExprBinary {
                        attrs: Vec::new(),
                        left: Box::new(lhs),
                        op: op,
                        right: Box::new(rhs),
                    })
                };
            } else if Precedence::Assign >= base
                && input.peek(Token![=])
                && !input.peek(Token![==])
                && !input.peek(Token![=>])
            {
                let eq_token: Token![=] = input.parse()?;
                let mut rhs = unary_expr(input, allow_struct)?;
                loop {
                    let next = peek_precedence(input);
                    if next >= Precedence::Assign {
                        rhs = parse_expr(input, rhs, allow_struct, next)?;
                    } else {
                        break;
                    }
                }
                lhs = Expr::Assign(ExprAssign {
                    attrs: Vec::new(),
                    left: Box::new(lhs),
                    eq_token: eq_token,
                    right: Box::new(rhs),
                });
            } else if Precedence::Placement >= base && input.peek(Token![<-]) {
                let arrow_token: Token![<-] = input.parse()?;
                let mut rhs = unary_expr(input, allow_struct)?;
                loop {
                    let next = peek_precedence(input);
                    if next > Precedence::Placement {
                        rhs = parse_expr(input, rhs, allow_struct, next)?;
                    } else {
                        break;
                    }
                }
                lhs = Expr::InPlace(ExprInPlace {
                    attrs: Vec::new(),
                    place: Box::new(lhs),
                    arrow_token: arrow_token,
                    value: Box::new(rhs),
                });
            } else if Precedence::Range >= base && input.peek(Token![..]) {
                let limits: RangeLimits = input.parse()?;
                let rhs = if input.is_empty()
                    || input.peek(Token![,])
                    || input.peek(Token![;])
                    || !allow_struct.0 && input.peek(token::Brace)
                {
                    None
                } else {
                    let mut rhs = unary_expr(input, allow_struct)?;
                    loop {
                        let next = peek_precedence(input);
                        if next > Precedence::Range {
                            rhs = parse_expr(input, rhs, allow_struct, next)?;
                        } else {
                            break;
                        }
                    }
                    Some(rhs)
                };
                lhs = Expr::Range(ExprRange {
                    attrs: Vec::new(),
                    from: Some(Box::new(lhs)),
                    limits: limits,
                    to: rhs.map(Box::new),
                });
            } else if Precedence::Cast >= base && input.peek(Token![as]) {
                let as_token: Token![as] = input.parse()?;
                let ty = input.call(Type::without_plus)?;
                lhs = Expr::Cast(ExprCast {
                    attrs: Vec::new(),
                    expr: Box::new(lhs),
                    as_token: as_token,
                    ty: Box::new(ty),
                });
            } else if Precedence::Cast >= base && input.peek(Token![:]) && !input.peek(Token![::]) {
                let colon_token: Token![:] = input.parse()?;
                let ty = input.call(Type::without_plus)?;
                lhs = Expr::Type(ExprType {
                    attrs: Vec::new(),
                    expr: Box::new(lhs),
                    colon_token: colon_token,
                    ty: Box::new(ty),
                });
            } else {
                break;
            }
        }
        Ok(lhs)
    }

    #[cfg(not(feature = "full"))]
    fn parse_expr(
        input: ParseStream,
        mut lhs: Expr,
        allow_struct: AllowStruct,
        base: Precedence,
    ) -> Result<Expr> {
        loop {
            if input
                .fork()
                .parse::<BinOp>()
                .ok()
                .map_or(false, |op| Precedence::of(&op) >= base)
            {
                let op: BinOp = input.parse()?;
                let precedence = Precedence::of(&op);
                let mut rhs = unary_expr(input, allow_struct)?;
                loop {
                    let next = peek_precedence(input);
                    if next > precedence || next == precedence && precedence == Precedence::Assign {
                        rhs = parse_expr(input, rhs, allow_struct, next)?;
                    } else {
                        break;
                    }
                }
                lhs = Expr::Binary(ExprBinary {
                    attrs: Vec::new(),
                    left: Box::new(lhs),
                    op: op,
                    right: Box::new(rhs),
                });
            } else if Precedence::Cast >= base && input.peek(Token![as]) {
                let as_token: Token![as] = input.parse()?;
                let ty = input.call(Type::without_plus)?;
                lhs = Expr::Cast(ExprCast {
                    attrs: Vec::new(),
                    expr: Box::new(lhs),
                    as_token: as_token,
                    ty: Box::new(ty),
                });
            } else {
                break;
            }
        }
        Ok(lhs)
    }

    fn peek_precedence(input: ParseStream) -> Precedence {
        if let Ok(op) = input.fork().parse() {
            Precedence::of(&op)
        } else if input.peek(Token![=]) && !input.peek(Token![=>]) {
            Precedence::Assign
        } else if input.peek(Token![<-]) {
            Precedence::Placement
        } else if input.peek(Token![..]) {
            Precedence::Range
        } else if input.peek(Token![as]) || input.peek(Token![:]) && !input.peek(Token![::]) {
            Precedence::Cast
        } else {
            Precedence::Any
        }
    }

    // Parse an arbitrary expression.
    fn ambiguous_expr(input: ParseStream, allow_struct: AllowStruct) -> Result<Expr> {
        let lhs = unary_expr(input, allow_struct)?;
        parse_expr(input, lhs, allow_struct, Precedence::Any)
    }

    // <UnOp> <trailer>
    // & <trailer>
    // &mut <trailer>
    // box <trailer>
    #[cfg(feature = "full")]
    fn unary_expr(input: ParseStream, allow_struct: AllowStruct) -> Result<Expr> {
        let ahead = input.fork();
        ahead.call(Attribute::parse_outer)?;
        if ahead.peek(Token![&])
            || ahead.peek(Token![box])
            || ahead.peek(Token![*])
            || ahead.peek(Token![!])
            || ahead.peek(Token![-])
        {
            let attrs = input.call(Attribute::parse_outer)?;
            if input.peek(Token![&]) {
                Ok(Expr::Reference(ExprReference {
                    attrs: attrs,
                    and_token: input.parse()?,
                    mutability: input.parse()?,
                    expr: Box::new(unary_expr(input, allow_struct)?),
                }))
            } else if input.peek(Token![box]) {
                Ok(Expr::Box(ExprBox {
                    attrs: attrs,
                    box_token: input.parse()?,
                    expr: Box::new(unary_expr(input, allow_struct)?),
                }))
            } else {
                Ok(Expr::Unary(ExprUnary {
                    attrs: attrs,
                    op: input.parse()?,
                    expr: Box::new(unary_expr(input, allow_struct)?),
                }))
            }
        } else {
            trailer_expr(input, allow_struct)
        }
    }

    #[cfg(not(feature = "full"))]
    fn unary_expr(input: ParseStream, allow_struct: AllowStruct) -> Result<Expr> {
        let ahead = input.fork();
        ahead.call(Attribute::parse_outer)?;
        if ahead.peek(Token![*]) || ahead.peek(Token![!]) || ahead.peek(Token![-]) {
            Ok(Expr::Unary(ExprUnary {
                attrs: input.call(Attribute::parse_outer)?,
                op: input.parse()?,
                expr: Box::new(unary_expr(input, allow_struct)?),
            }))
        } else {
            trailer_expr(input, allow_struct)
        }
    }

    // <atom> (..<args>) ...
    // <atom> . <ident> (..<args>) ...
    // <atom> . <ident> ...
    // <atom> . <lit> ...
    // <atom> [ <expr> ] ...
    // <atom> ? ...
    #[cfg(feature = "full")]
    fn trailer_expr(input: ParseStream, allow_struct: AllowStruct) -> Result<Expr> {
        if input.peek(token::Group) {
            return input.call(expr_group).map(Expr::Group);
        }

        let outer_attrs = input.call(Attribute::parse_outer)?;

        let atom = atom_expr(input, allow_struct)?;
        let mut e = trailer_helper(input, atom)?;

        let inner_attrs = e.replace_attrs(Vec::new());
        let attrs = private::attrs(outer_attrs, inner_attrs);
        e.replace_attrs(attrs);
        Ok(e)
    }

    #[cfg(feature = "full")]
    fn trailer_helper(input: ParseStream, mut e: Expr) -> Result<Expr> {
        loop {
            if input.peek(token::Paren) {
                let content;
                e = Expr::Call(ExprCall {
                    attrs: Vec::new(),
                    func: Box::new(e),
                    paren_token: parenthesized!(content in input),
                    args: content.parse_terminated(Expr::parse)?,
                });
            } else if input.peek(Token![.]) && !input.peek(Token![..]) {
                let dot_token: Token![.] = input.parse()?;
                let member: Member = input.parse()?;
                let turbofish = if member.is_named() && input.peek(Token![::]) {
                    Some(MethodTurbofish {
                        colon2_token: input.parse()?,
                        lt_token: input.parse()?,
                        args: {
                            let mut args = Punctuated::new();
                            loop {
                                if input.peek(Token![>]) {
                                    break;
                                }
                                let value = input.call(generic_method_argument)?;
                                args.push_value(value);
                                if input.peek(Token![>]) {
                                    break;
                                }
                                let punct = input.parse()?;
                                args.push_punct(punct);
                            }
                            args
                        },
                        gt_token: input.parse()?,
                    })
                } else {
                    None
                };

                if turbofish.is_some() || input.peek(token::Paren) {
                    if let Member::Named(method) = member {
                        let content;
                        e = Expr::MethodCall(ExprMethodCall {
                            attrs: Vec::new(),
                            receiver: Box::new(e),
                            dot_token: dot_token,
                            method: method,
                            turbofish: turbofish,
                            paren_token: parenthesized!(content in input),
                            args: content.parse_terminated(Expr::parse)?,
                        });
                        continue;
                    }
                }

                e = Expr::Field(ExprField {
                    attrs: Vec::new(),
                    base: Box::new(e),
                    dot_token: dot_token,
                    member: member,
                });
            } else if input.peek(token::Bracket) {
                let content;
                e = Expr::Index(ExprIndex {
                    attrs: Vec::new(),
                    expr: Box::new(e),
                    bracket_token: bracketed!(content in input),
                    index: content.parse()?,
                });
            } else if input.peek(Token![?]) {
                e = Expr::Try(ExprTry {
                    attrs: Vec::new(),
                    expr: Box::new(e),
                    question_token: input.parse()?,
                });
            } else {
                break;
            }
        }
        Ok(e)
    }

    #[cfg(not(feature = "full"))]
    fn trailer_expr(input: ParseStream, allow_struct: AllowStruct) -> Result<Expr> {
        let mut e = atom_expr(input, allow_struct)?;

        loop {
            if input.peek(token::Paren) {
                let content;
                e = Expr::Call(ExprCall {
                    attrs: Vec::new(),
                    func: Box::new(e),
                    paren_token: parenthesized!(content in input),
                    args: content.parse_terminated(Expr::parse)?,
                });
            } else if input.peek(Token![.]) {
                e = Expr::Field(ExprField {
                    attrs: Vec::new(),
                    base: Box::new(e),
                    dot_token: input.parse()?,
                    member: input.parse()?,
                });
            } else if input.peek(token::Bracket) {
                let content;
                e = Expr::Index(ExprIndex {
                    attrs: Vec::new(),
                    expr: Box::new(e),
                    bracket_token: bracketed!(content in input),
                    index: content.parse()?,
                });
            } else {
                break;
            }
        }

        Ok(e)
    }

    // Parse all atomic expressions which don't have to worry about precedence
    // interactions, as they are fully contained.
    #[cfg(feature = "full")]
    fn atom_expr(input: ParseStream, allow_struct: AllowStruct) -> Result<Expr> {
        if input.peek(token::Group) {
            input.call(expr_group).map(Expr::Group)
        } else if input.peek(Lit) {
            input.parse().map(Expr::Lit)
        } else if input.peek(Token![async])
            && (input.peek2(token::Brace) || input.peek2(Token![move]) && input.peek3(token::Brace))
        {
            input.call(expr_async).map(Expr::Async)
        } else if input.peek(Token![try]) && input.peek2(token::Brace) {
            input.call(expr_try_block).map(Expr::TryBlock)
        } else if input.peek(Token![|])
            || input.peek(Token![async]) && (input.peek2(Token![|]) || input.peek2(Token![move]))
            || input.peek(Token![static])
            || input.peek(Token![move])
        {
            expr_closure(input, allow_struct).map(Expr::Closure)
        } else if input.peek(Ident)
            || input.peek(Token![::])
            || input.peek(Token![<])
            || input.peek(Token![self])
            || input.peek(Token![Self])
            || input.peek(Token![super])
            || input.peek(Token![extern])
            || input.peek(Token![crate])
        {
            path_or_macro_or_struct(input, allow_struct)
        } else if input.peek(token::Paren) {
            paren_or_tuple(input)
        } else if input.peek(Token![break]) {
            expr_break(input, allow_struct).map(Expr::Break)
        } else if input.peek(Token![continue]) {
            input.call(expr_continue).map(Expr::Continue)
        } else if input.peek(Token![return]) {
            expr_ret(input, allow_struct).map(Expr::Return)
        } else if input.peek(token::Bracket) {
            array_or_repeat(input)
        } else if input.peek(Token![let]) {
            input.call(expr_let).map(Expr::Let)
        } else if input.peek(Token![if]) {
            input.parse().map(Expr::If)
        } else if input.peek(Token![while]) {
            input.parse().map(Expr::While)
        } else if input.peek(Token![for]) {
            input.parse().map(Expr::ForLoop)
        } else if input.peek(Token![loop]) {
            input.parse().map(Expr::Loop)
        } else if input.peek(Token![match]) {
            input.parse().map(Expr::Match)
        } else if input.peek(Token![yield]) {
            input.call(expr_yield).map(Expr::Yield)
        } else if input.peek(Token![unsafe]) {
            input.call(expr_unsafe).map(Expr::Unsafe)
        } else if input.peek(token::Brace) {
            input.call(expr_block).map(Expr::Block)
        } else if input.peek(Token![..]) {
            expr_range(input, allow_struct).map(Expr::Range)
        } else if input.peek(Lifetime) {
            let the_label: Label = input.parse()?;
            let mut expr = if input.peek(Token![while]) {
                Expr::While(input.parse()?)
            } else if input.peek(Token![for]) {
                Expr::ForLoop(input.parse()?)
            } else if input.peek(Token![loop]) {
                Expr::Loop(input.parse()?)
            } else if input.peek(token::Brace) {
                Expr::Block(input.call(expr_block)?)
            } else {
                return Err(input.error("expected loop or block expression"));
            };
            match expr {
                Expr::While(ExprWhile { ref mut label, .. })
                | Expr::ForLoop(ExprForLoop { ref mut label, .. })
                | Expr::Loop(ExprLoop { ref mut label, .. })
                | Expr::Block(ExprBlock { ref mut label, .. }) => *label = Some(the_label),
                _ => unreachable!(),
            }
            Ok(expr)
        } else {
            Err(input.error("expected expression"))
        }
    }

    #[cfg(not(feature = "full"))]
    fn atom_expr(input: ParseStream, _allow_struct: AllowStruct) -> Result<Expr> {
        if input.peek(Lit) {
            input.parse().map(Expr::Lit)
        } else if input.peek(token::Paren) {
            input.call(expr_paren).map(Expr::Paren)
        } else if input.peek(Ident)
            || input.peek(Token![::])
            || input.peek(Token![<])
            || input.peek(Token![self])
            || input.peek(Token![Self])
            || input.peek(Token![super])
            || input.peek(Token![extern])
            || input.peek(Token![crate])
        {
            input.parse().map(Expr::Path)
        } else {
            Err(input.error("unsupported expression; enable syn's features=[\"full\"]"))
        }
    }

    #[cfg(feature = "full")]
    fn path_or_macro_or_struct(input: ParseStream, allow_struct: AllowStruct) -> Result<Expr> {
        let expr: ExprPath = input.parse()?;
        if expr.qself.is_some() {
            return Ok(Expr::Path(expr));
        }

        if input.peek(Token![!]) && !input.peek(Token![!=]) {
            let mut contains_arguments = false;
            for segment in &expr.path.segments {
                match segment.arguments {
                    PathArguments::None => {}
                    PathArguments::AngleBracketed(_) | PathArguments::Parenthesized(_) => {
                        contains_arguments = true;
                    }
                }
            }

            if !contains_arguments {
                let bang_token: Token![!] = input.parse()?;
                let (delimiter, tts) = mac::parse_delimiter(input)?;
                return Ok(Expr::Macro(ExprMacro {
                    attrs: Vec::new(),
                    mac: Macro {
                        path: expr.path,
                        bang_token: bang_token,
                        delimiter: delimiter,
                        tts: tts,
                    },
                }));
            }
        }

        if allow_struct.0 && input.peek(token::Brace) {
            let outer_attrs = Vec::new();
            expr_struct_helper(input, outer_attrs, expr.path).map(Expr::Struct)
        } else {
            Ok(Expr::Path(expr))
        }
    }

    #[cfg(feature = "full")]
    fn paren_or_tuple(input: ParseStream) -> Result<Expr> {
        let content;
        let paren_token = parenthesized!(content in input);
        let inner_attrs = content.call(Attribute::parse_inner)?;
        if content.is_empty() {
            return Ok(Expr::Tuple(ExprTuple {
                attrs: inner_attrs,
                paren_token: paren_token,
                elems: Punctuated::new(),
            }));
        }

        let first: Expr = content.parse()?;
        if content.is_empty() {
            return Ok(Expr::Paren(ExprParen {
                attrs: inner_attrs,
                paren_token: paren_token,
                expr: Box::new(first),
            }));
        }

        let mut elems = Punctuated::new();
        elems.push_value(first);
        while !content.is_empty() {
            let punct = content.parse()?;
            elems.push_punct(punct);
            if content.is_empty() {
                break;
            }
            let value = content.parse()?;
            elems.push_value(value);
        }
        Ok(Expr::Tuple(ExprTuple {
            attrs: inner_attrs,
            paren_token: paren_token,
            elems: elems,
        }))
    }

    #[cfg(feature = "full")]
    fn array_or_repeat(input: ParseStream) -> Result<Expr> {
        let content;
        let bracket_token = bracketed!(content in input);
        let inner_attrs = content.call(Attribute::parse_inner)?;
        if content.is_empty() {
            return Ok(Expr::Array(ExprArray {
                attrs: inner_attrs,
                bracket_token: bracket_token,
                elems: Punctuated::new(),
            }));
        }

        let first: Expr = content.parse()?;
        if content.is_empty() || content.peek(Token![,]) {
            let mut elems = Punctuated::new();
            elems.push_value(first);
            while !content.is_empty() {
                let punct = content.parse()?;
                elems.push_punct(punct);
                if content.is_empty() {
                    break;
                }
                let value = content.parse()?;
                elems.push_value(value);
            }
            Ok(Expr::Array(ExprArray {
                attrs: inner_attrs,
                bracket_token: bracket_token,
                elems: elems,
            }))
        } else if content.peek(Token![;]) {
            let semi_token: Token![;] = content.parse()?;
            let len: Expr = content.parse()?;
            Ok(Expr::Repeat(ExprRepeat {
                attrs: inner_attrs,
                bracket_token: bracket_token,
                expr: Box::new(first),
                semi_token: semi_token,
                len: Box::new(len),
            }))
        } else {
            Err(content.error("expected `,` or `;`"))
        }
    }

    #[cfg(feature = "full")]
    fn expr_early(input: ParseStream) -> Result<Expr> {
        let mut attrs = input.call(Attribute::parse_outer)?;
        let mut expr = if input.peek(Token![if]) {
            Expr::If(input.parse()?)
        } else if input.peek(Token![while]) {
            Expr::While(input.parse()?)
        } else if input.peek(Token![for]) {
            Expr::ForLoop(input.parse()?)
        } else if input.peek(Token![loop]) {
            Expr::Loop(input.parse()?)
        } else if input.peek(Token![match]) {
            Expr::Match(input.parse()?)
        } else if input.peek(Token![try]) && input.peek2(token::Brace) {
            Expr::TryBlock(input.call(expr_try_block)?)
        } else if input.peek(Token![unsafe]) {
            Expr::Unsafe(input.call(expr_unsafe)?)
        } else if input.peek(token::Brace) {
            Expr::Block(input.call(expr_block)?)
        } else {
            let allow_struct = AllowStruct(true);
            let mut expr = unary_expr(input, allow_struct)?;

            attrs.extend(expr.replace_attrs(Vec::new()));
            expr.replace_attrs(attrs);

            return parse_expr(input, expr, allow_struct, Precedence::Any);
        };

        if input.peek(Token![.]) || input.peek(Token![?]) {
            expr = trailer_helper(input, expr)?;

            attrs.extend(expr.replace_attrs(Vec::new()));
            expr.replace_attrs(attrs);

            let allow_struct = AllowStruct(true);
            return parse_expr(input, expr, allow_struct, Precedence::Any);
        }

        attrs.extend(expr.replace_attrs(Vec::new()));
        expr.replace_attrs(attrs);
        Ok(expr)
    }

    impl Parse for ExprLit {
        fn parse(input: ParseStream) -> Result<Self> {
            Ok(ExprLit {
                attrs: Vec::new(),
                lit: input.parse()?,
            })
        }
    }

    #[cfg(feature = "full")]
    fn expr_group(input: ParseStream) -> Result<ExprGroup> {
        let group = private::parse_group(input)?;
        Ok(ExprGroup {
            attrs: Vec::new(),
            group_token: group.token,
            expr: group.content.parse()?,
        })
    }

    #[cfg(not(feature = "full"))]
    fn expr_paren(input: ParseStream) -> Result<ExprParen> {
        let content;
        Ok(ExprParen {
            attrs: Vec::new(),
            paren_token: parenthesized!(content in input),
            expr: content.parse()?,
        })
    }

    #[cfg(feature = "full")]
    fn generic_method_argument(input: ParseStream) -> Result<GenericMethodArgument> {
        // TODO parse const generics as well
        input.parse().map(GenericMethodArgument::Type)
    }

    #[cfg(feature = "full")]
    fn expr_let(input: ParseStream) -> Result<ExprLet> {
        Ok(ExprLet {
            attrs: Vec::new(),
            let_token: input.parse()?,
            pats: {
                let mut pats = Punctuated::new();
                input.parse::<Option<Token![|]>>()?;
                let value: Pat = input.parse()?;
                pats.push_value(value);
                while input.peek(Token![|]) && !input.peek(Token![||]) && !input.peek(Token![|=]) {
                    let punct = input.parse()?;
                    pats.push_punct(punct);
                    let value: Pat = input.parse()?;
                    pats.push_value(value);
                }
                pats
            },
            eq_token: input.parse()?,
            expr: Box::new(input.call(expr_no_struct)?),
        })
    }

    #[cfg(feature = "full")]
    impl Parse for ExprIf {
        fn parse(input: ParseStream) -> Result<Self> {
            Ok(ExprIf {
                attrs: Vec::new(),
                if_token: input.parse()?,
                cond: Box::new(input.call(expr_no_struct)?),
                then_branch: input.parse()?,
                else_branch: {
                    if input.peek(Token![else]) {
                        Some(input.call(else_block)?)
                    } else {
                        None
                    }
                },
            })
        }
    }

    #[cfg(feature = "full")]
    fn else_block(input: ParseStream) -> Result<(Token![else], Box<Expr>)> {
        let else_token: Token![else] = input.parse()?;

        let lookahead = input.lookahead1();
        let else_branch = if input.peek(Token![if]) {
            input.parse().map(Expr::If)?
        } else if input.peek(token::Brace) {
            Expr::Block(ExprBlock {
                attrs: Vec::new(),
                label: None,
                block: input.parse()?,
            })
        } else {
            return Err(lookahead.error());
        };

        Ok((else_token, Box::new(else_branch)))
    }

    #[cfg(feature = "full")]
    impl Parse for ExprForLoop {
        fn parse(input: ParseStream) -> Result<Self> {
            let label: Option<Label> = input.parse()?;
            let for_token: Token![for] = input.parse()?;
            let pat: Pat = input.parse()?;
            let in_token: Token![in] = input.parse()?;
            let expr: Expr = input.call(expr_no_struct)?;

            let content;
            let brace_token = braced!(content in input);
            let inner_attrs = content.call(Attribute::parse_inner)?;
            let stmts = content.call(Block::parse_within)?;

            Ok(ExprForLoop {
                attrs: inner_attrs,
                label: label,
                for_token: for_token,
                pat: Box::new(pat),
                in_token: in_token,
                expr: Box::new(expr),
                body: Block {
                    brace_token: brace_token,
                    stmts: stmts,
                },
            })
        }
    }

    #[cfg(feature = "full")]
    impl Parse for ExprLoop {
        fn parse(input: ParseStream) -> Result<Self> {
            let label: Option<Label> = input.parse()?;
            let loop_token: Token![loop] = input.parse()?;

            let content;
            let brace_token = braced!(content in input);
            let inner_attrs = content.call(Attribute::parse_inner)?;
            let stmts = content.call(Block::parse_within)?;

            Ok(ExprLoop {
                attrs: inner_attrs,
                label: label,
                loop_token: loop_token,
                body: Block {
                    brace_token: brace_token,
                    stmts: stmts,
                },
            })
        }
    }

    #[cfg(feature = "full")]
    impl Parse for ExprMatch {
        fn parse(input: ParseStream) -> Result<Self> {
            let match_token: Token![match] = input.parse()?;
            let expr = expr_no_struct(input)?;

            let content;
            let brace_token = braced!(content in input);
            let inner_attrs = content.call(Attribute::parse_inner)?;

            let mut arms = Vec::new();
            while !content.is_empty() {
                arms.push(content.call(Arm::parse)?);
            }

            Ok(ExprMatch {
                attrs: inner_attrs,
                match_token: match_token,
                expr: Box::new(expr),
                brace_token: brace_token,
                arms: arms,
            })
        }
    }

    macro_rules! impl_by_parsing_expr {
        ($expr_type:ty, $variant:ident, $msg:expr) => (
            #[cfg(all(feature = "full", feature = "printing"))]
            impl Parse for $expr_type {
                fn parse(input: ParseStream) -> Result<Self> {
                    let expr: Expr = input.parse()?;
                    match expr {
                        Expr::$variant(inner) => Ok(inner),
                        _ => Err(Error::new_spanned(expr, $msg))
                    }
                }
            }
        )
    }

    impl_by_parsing_expr!(ExprBox, Box, "expected box expression");
    impl_by_parsing_expr!(ExprInPlace, InPlace, "expected placement expression");
    impl_by_parsing_expr!(ExprArray, Array, "expected slice literal expression");
    impl_by_parsing_expr!(ExprCall, Call, "expected function call expression");
    impl_by_parsing_expr!(ExprMethodCall, MethodCall, "expected method call expression");
    impl_by_parsing_expr!(ExprTuple, Tuple, "expected tuple expression");
    impl_by_parsing_expr!(ExprBinary, Binary, "expected binary operation");
    impl_by_parsing_expr!(ExprUnary, Unary, "expected unary operation");
    impl_by_parsing_expr!(ExprCast, Cast, "expected cast expression");
    impl_by_parsing_expr!(ExprType, Type, "expected type ascription expression");
    impl_by_parsing_expr!(ExprLet, Let, "expected let guard");
    impl_by_parsing_expr!(ExprClosure, Closure, "expected closure expression");
    impl_by_parsing_expr!(ExprUnsafe, Unsafe, "expected unsafe block");
    impl_by_parsing_expr!(ExprBlock, Block, "expected blocked scope");
    impl_by_parsing_expr!(ExprAssign, Assign, "expected assignment expression");
    impl_by_parsing_expr!(ExprAssignOp, AssignOp, "expected compound assignment expression");
    impl_by_parsing_expr!(ExprField, Field, "expected struct field access");
    impl_by_parsing_expr!(ExprIndex, Index, "expected indexing expression");
    impl_by_parsing_expr!(ExprRange, Range, "expected range expression");
    impl_by_parsing_expr!(ExprReference, Reference, "expected referencing operation");
    impl_by_parsing_expr!(ExprBreak, Break, "expected break expression");
    impl_by_parsing_expr!(ExprContinue, Continue, "expected continue expression");
    impl_by_parsing_expr!(ExprReturn, Return, "expected return expression");
    impl_by_parsing_expr!(ExprMacro, Macro, "expected macro invocation expression");
    impl_by_parsing_expr!(ExprStruct, Struct, "expected struct literal expression");
    impl_by_parsing_expr!(ExprRepeat, Repeat, "expected array literal constructed from one repeated element");
    impl_by_parsing_expr!(ExprParen, Paren, "expected parenthesized expression");
    impl_by_parsing_expr!(ExprTry, Try, "expected try expression");
    impl_by_parsing_expr!(ExprAsync, Async, "expected async block");
    impl_by_parsing_expr!(ExprTryBlock, TryBlock, "expected try block");
    impl_by_parsing_expr!(ExprYield, Yield, "expected yield expression");

    #[cfg(feature = "full")]
    fn expr_try_block(input: ParseStream) -> Result<ExprTryBlock> {
        Ok(ExprTryBlock {
            attrs: Vec::new(),
            try_token: input.parse()?,
            block: input.parse()?,
        })
    }

    #[cfg(feature = "full")]
    fn expr_yield(input: ParseStream) -> Result<ExprYield> {
        Ok(ExprYield {
            attrs: Vec::new(),
            yield_token: input.parse()?,
            expr: {
                if !input.is_empty() && !input.peek(Token![,]) && !input.peek(Token![;]) {
                    Some(input.parse()?)
                } else {
                    None
                }
            },
        })
    }

    #[cfg(feature = "full")]
    fn expr_closure(input: ParseStream, allow_struct: AllowStruct) -> Result<ExprClosure> {
        let asyncness: Option<Token![async]> = input.parse()?;
        let movability: Option<Token![static]> = if asyncness.is_none() {
            input.parse()?
        } else {
            None
        };
        let capture: Option<Token![move]> = input.parse()?;
        let or1_token: Token![|] = input.parse()?;

        let mut inputs = Punctuated::new();
        loop {
            if input.peek(Token![|]) {
                break;
            }
            let value = fn_arg(input)?;
            inputs.push_value(value);
            if input.peek(Token![|]) {
                break;
            }
            let punct: Token![,] = input.parse()?;
            inputs.push_punct(punct);
        }

        let or2_token: Token![|] = input.parse()?;

        let (output, body) = if input.peek(Token![->]) {
            let arrow_token: Token![->] = input.parse()?;
            let ty: Type = input.parse()?;
            let body: Block = input.parse()?;
            let output = ReturnType::Type(arrow_token, Box::new(ty));
            let block = Expr::Block(ExprBlock {
                attrs: Vec::new(),
                label: None,
                block: body,
            });
            (output, block)
        } else {
            let body = ambiguous_expr(input, allow_struct)?;
            (ReturnType::Default, body)
        };

        Ok(ExprClosure {
            attrs: Vec::new(),
            asyncness: asyncness,
            movability: movability,
            capture: capture,
            or1_token: or1_token,
            inputs: inputs,
            or2_token: or2_token,
            output: output,
            body: Box::new(body),
        })
    }

    #[cfg(feature = "full")]
    fn expr_async(input: ParseStream) -> Result<ExprAsync> {
        Ok(ExprAsync {
            attrs: Vec::new(),
            async_token: input.parse()?,
            capture: input.parse()?,
            block: input.parse()?,
        })
    }

    #[cfg(feature = "full")]
    fn fn_arg(input: ParseStream) -> Result<FnArg> {
        let pat: Pat = input.parse()?;

        if input.peek(Token![:]) {
            Ok(FnArg::Captured(ArgCaptured {
                pat: pat,
                colon_token: input.parse()?,
                ty: input.parse()?,
            }))
        } else {
            Ok(FnArg::Inferred(pat))
        }
    }

    #[cfg(feature = "full")]
    impl Parse for ExprWhile {
        fn parse(input: ParseStream) -> Result<Self> {
            let label: Option<Label> = input.parse()?;
            let while_token: Token![while] = input.parse()?;
            let cond = expr_no_struct(input)?;

            let content;
            let brace_token = braced!(content in input);
            let inner_attrs = content.call(Attribute::parse_inner)?;
            let stmts = content.call(Block::parse_within)?;

            Ok(ExprWhile {
                attrs: inner_attrs,
                label: label,
                while_token: while_token,
                cond: Box::new(cond),
                body: Block {
                    brace_token: brace_token,
                    stmts: stmts,
                },
            })
        }
    }

    #[cfg(feature = "full")]
    impl Parse for Label {
        fn parse(input: ParseStream) -> Result<Self> {
            Ok(Label {
                name: input.parse()?,
                colon_token: input.parse()?,
            })
        }
    }

    #[cfg(feature = "full")]
    impl Parse for Option<Label> {
        fn parse(input: ParseStream) -> Result<Self> {
            if input.peek(Lifetime) {
                input.parse().map(Some)
            } else {
                Ok(None)
            }
        }
    }

    #[cfg(feature = "full")]
    fn expr_continue(input: ParseStream) -> Result<ExprContinue> {
        Ok(ExprContinue {
            attrs: Vec::new(),
            continue_token: input.parse()?,
            label: input.parse()?,
        })
    }

    #[cfg(feature = "full")]
    fn expr_break(input: ParseStream, allow_struct: AllowStruct) -> Result<ExprBreak> {
        Ok(ExprBreak {
            attrs: Vec::new(),
            break_token: input.parse()?,
            label: input.parse()?,
            expr: {
                if input.is_empty()
                    || input.peek(Token![,])
                    || input.peek(Token![;])
                    || !allow_struct.0 && input.peek(token::Brace)
                {
                    None
                } else {
                    let expr = ambiguous_expr(input, allow_struct)?;
                    Some(Box::new(expr))
                }
            },
        })
    }

    #[cfg(feature = "full")]
    fn expr_ret(input: ParseStream, allow_struct: AllowStruct) -> Result<ExprReturn> {
        Ok(ExprReturn {
            attrs: Vec::new(),
            return_token: input.parse()?,
            expr: {
                if input.is_empty() || input.peek(Token![,]) || input.peek(Token![;]) {
                    None
                } else {
                    // NOTE: return is greedy and eats blocks after it even when in a
                    // position where structs are not allowed, such as in if statement
                    // conditions. For example:
                    //
                    // if return { println!("A") } {} // Prints "A"
                    let expr = ambiguous_expr(input, allow_struct)?;
                    Some(Box::new(expr))
                }
            },
        })
    }

    #[cfg(feature = "full")]
    impl Parse for FieldValue {
        fn parse(input: ParseStream) -> Result<Self> {
            let member: Member = input.parse()?;
            let (colon_token, value) = if input.peek(Token![:]) || !member.is_named() {
                let colon_token: Token![:] = input.parse()?;
                let value: Expr = input.parse()?;
                (Some(colon_token), value)
            } else if let Member::Named(ref ident) = member {
                let value = Expr::Path(ExprPath {
                    attrs: Vec::new(),
                    qself: None,
                    path: Path::from(ident.clone()),
                });
                (None, value)
            } else {
                unreachable!()
            };

            Ok(FieldValue {
                attrs: Vec::new(),
                member: member,
                colon_token: colon_token,
                expr: value,
            })
        }
    }

    #[cfg(feature = "full")]
    fn expr_struct_helper(
        input: ParseStream,
        outer_attrs: Vec<Attribute>,
        path: Path,
    ) -> Result<ExprStruct> {
        let content;
        let brace_token = braced!(content in input);
        let inner_attrs = content.call(Attribute::parse_inner)?;

        let mut fields = Punctuated::new();
        loop {
            let attrs = content.call(Attribute::parse_outer)?;
            if content.fork().parse::<Member>().is_err() {
                if attrs.is_empty() {
                    break;
                } else {
                    return Err(content.error("expected struct field"));
                }
            }

            fields.push(FieldValue {
                attrs: attrs,
                ..content.parse()?
            });

            if !content.peek(Token![,]) {
                break;
            }
            let punct: Token![,] = content.parse()?;
            fields.push_punct(punct);
        }

        let (dot2_token, rest) = if fields.empty_or_trailing() && content.peek(Token![..]) {
            let dot2_token: Token![..] = content.parse()?;
            let rest: Expr = content.parse()?;
            (Some(dot2_token), Some(Box::new(rest)))
        } else {
            (None, None)
        };

        Ok(ExprStruct {
            attrs: private::attrs(outer_attrs, inner_attrs),
            brace_token: brace_token,
            path: path,
            fields: fields,
            dot2_token: dot2_token,
            rest: rest,
        })
    }

    #[cfg(feature = "full")]
    fn expr_unsafe(input: ParseStream) -> Result<ExprUnsafe> {
        let unsafe_token: Token![unsafe] = input.parse()?;

        let content;
        let brace_token = braced!(content in input);
        let inner_attrs = content.call(Attribute::parse_inner)?;
        let stmts = content.call(Block::parse_within)?;

        Ok(ExprUnsafe {
            attrs: inner_attrs,
            unsafe_token: unsafe_token,
            block: Block {
                brace_token: brace_token,
                stmts: stmts,
            },
        })
    }

    #[cfg(feature = "full")]
    pub fn expr_block(input: ParseStream) -> Result<ExprBlock> {
        let label: Option<Label> = input.parse()?;

        let content;
        let brace_token = braced!(content in input);
        let inner_attrs = content.call(Attribute::parse_inner)?;
        let stmts = content.call(Block::parse_within)?;

        Ok(ExprBlock {
            attrs: inner_attrs,
            label: label,
            block: Block {
                brace_token: brace_token,
                stmts: stmts,
            },
        })
    }

    #[cfg(feature = "full")]
    fn expr_range(input: ParseStream, allow_struct: AllowStruct) -> Result<ExprRange> {
        Ok(ExprRange {
            attrs: Vec::new(),
            from: None,
            limits: input.parse()?,
            to: {
                if input.is_empty()
                    || input.peek(Token![,])
                    || input.peek(Token![;])
                    || !allow_struct.0 && input.peek(token::Brace)
                {
                    None
                } else {
                    let to = ambiguous_expr(input, allow_struct)?;
                    Some(Box::new(to))
                }
            },
        })
    }

    #[cfg(feature = "full")]
    impl Parse for RangeLimits {
        fn parse(input: ParseStream) -> Result<Self> {
            let lookahead = input.lookahead1();
            if lookahead.peek(Token![..=]) {
                input.parse().map(RangeLimits::Closed)
            } else if lookahead.peek(Token![...]) {
                let dot3: Token![...] = input.parse()?;
                Ok(RangeLimits::Closed(Token![..=](dot3.spans)))
            } else if lookahead.peek(Token![..]) {
                input.parse().map(RangeLimits::HalfOpen)
            } else {
                Err(lookahead.error())
            }
        }
    }

    impl Parse for ExprPath {
        fn parse(input: ParseStream) -> Result<Self> {
            #[cfg(not(feature = "full"))]
            let attrs = Vec::new();
            #[cfg(feature = "full")]
            let attrs = input.call(Attribute::parse_outer)?;

            let (qself, path) = path::parsing::qpath(input, true)?;

            Ok(ExprPath {
                attrs: attrs,
                qself: qself,
                path: path,
            })
        }
    }

    #[cfg(feature = "full")]
    impl Parse for Block {
        fn parse(input: ParseStream) -> Result<Self> {
            let content;
            Ok(Block {
                brace_token: braced!(content in input),
                stmts: content.call(Block::parse_within)?,
            })
        }
    }

    #[cfg(feature = "full")]
    impl Block {
        /// Parse the body of a block as zero or more statements, possibly
        /// including one trailing expression.
        ///
        /// *This function is available if Syn is built with the `"parsing"`
        /// feature.*
        ///
        /// # Example
        ///
        /// ```edition2018
        /// use syn::{braced, token, Attribute, Block, Ident, Result, Stmt, Token};
        /// use syn::parse::{Parse, ParseStream};
        ///
        /// // Parse a function with no generics or parameter list.
        /// //
        /// //     fn playground {
        /// //         let mut x = 1;
        /// //         x += 1;
        /// //         println!("{}", x);
        /// //     }
        /// struct MiniFunction {
        ///     attrs: Vec<Attribute>,
        ///     fn_token: Token![fn],
        ///     name: Ident,
        ///     brace_token: token::Brace,
        ///     stmts: Vec<Stmt>,
        /// }
        ///
        /// impl Parse for MiniFunction {
        ///     fn parse(input: ParseStream) -> Result<Self> {
        ///         let outer_attrs = input.call(Attribute::parse_outer)?;
        ///         let fn_token: Token![fn] = input.parse()?;
        ///         let name: Ident = input.parse()?;
        ///
        ///         let content;
        ///         let brace_token = braced!(content in input);
        ///         let inner_attrs = content.call(Attribute::parse_inner)?;
        ///         let stmts = content.call(Block::parse_within)?;
        ///
        ///         Ok(MiniFunction {
        ///             attrs: {
        ///                 let mut attrs = outer_attrs;
        ///                 attrs.extend(inner_attrs);
        ///                 attrs
        ///             },
        ///             fn_token: fn_token,
        ///             name: name,
        ///             brace_token: brace_token,
        ///             stmts: stmts,
        ///         })
        ///     }
        /// }
        /// ```
        pub fn parse_within(input: ParseStream) -> Result<Vec<Stmt>> {
            let mut stmts = Vec::new();
            loop {
                while input.peek(Token![;]) {
                    input.parse::<Token![;]>()?;
                }
                if input.is_empty() {
                    break;
                }
                let s = parse_stmt(input, true)?;
                let requires_semicolon = if let Stmt::Expr(ref s) = s {
                    requires_terminator(s)
                } else {
                    false
                };
                stmts.push(s);
                if input.is_empty() {
                    break;
                } else if requires_semicolon {
                    return Err(input.error("unexpected token"));
                }
            }
            Ok(stmts)
        }
    }

    #[cfg(feature = "full")]
    impl Parse for Stmt {
        fn parse(input: ParseStream) -> Result<Self> {
            parse_stmt(input, false)
        }
    }

    #[cfg(feature = "full")]
    fn parse_stmt(input: ParseStream, allow_nosemi: bool) -> Result<Stmt> {
        let ahead = input.fork();
        ahead.call(Attribute::parse_outer)?;

        if {
            let ahead = ahead.fork();
            // Only parse braces here; paren and bracket will get parsed as
            // expression statements
            ahead.call(Path::parse_mod_style).is_ok()
                && ahead.parse::<Token![!]>().is_ok()
                && (ahead.peek(token::Brace) || ahead.peek(Ident))
        } {
            stmt_mac(input)
        } else if ahead.peek(Token![let]) {
            stmt_local(input).map(Stmt::Local)
        } else if ahead.peek(Token![pub])
            || ahead.peek(Token![crate]) && !ahead.peek2(Token![::])
            || ahead.peek(Token![extern]) && !ahead.peek2(Token![::])
            || ahead.peek(Token![use])
            || ahead.peek(Token![static]) && (ahead.peek2(Token![mut]) || ahead.peek2(Ident))
            || ahead.peek(Token![const])
            || ahead.peek(Token![unsafe]) && !ahead.peek2(token::Brace)
            || ahead.peek(Token![async]) && (ahead.peek2(Token![extern]) || ahead.peek2(Token![fn]))
            || ahead.peek(Token![fn])
            || ahead.peek(Token![mod])
            || ahead.peek(Token![type])
            || ahead.peek(Token![existential]) && ahead.peek2(Token![type])
            || ahead.peek(Token![struct])
            || ahead.peek(Token![enum])
            || ahead.peek(Token![union]) && ahead.peek2(Ident)
            || ahead.peek(Token![auto]) && ahead.peek2(Token![trait])
            || ahead.peek(Token![trait])
            || ahead.peek(Token![default])
                && (ahead.peek2(Token![unsafe]) || ahead.peek2(Token![impl]))
            || ahead.peek(Token![impl])
            || ahead.peek(Token![macro])
        {
            input.parse().map(Stmt::Item)
        } else {
            stmt_expr(input, allow_nosemi)
        }
    }

    #[cfg(feature = "full")]
    fn stmt_mac(input: ParseStream) -> Result<Stmt> {
        let attrs = input.call(Attribute::parse_outer)?;
        let path = input.call(Path::parse_mod_style)?;
        let bang_token: Token![!] = input.parse()?;
        let ident: Option<Ident> = input.parse()?;
        let (delimiter, tts) = mac::parse_delimiter(input)?;
        let semi_token: Option<Token![;]> = input.parse()?;

        Ok(Stmt::Item(Item::Macro(ItemMacro {
            attrs: attrs,
            ident: ident,
            mac: Macro {
                path: path,
                bang_token: bang_token,
                delimiter: delimiter,
                tts: tts,
            },
            semi_token: semi_token,
        })))
    }

    #[cfg(feature = "full")]
    fn stmt_local(input: ParseStream) -> Result<Local> {
        Ok(Local {
            attrs: input.call(Attribute::parse_outer)?,
            let_token: input.parse()?,
            pats: {
                let mut pats = Punctuated::new();
                let value: Pat = input.parse()?;
                pats.push_value(value);
                while input.peek(Token![|]) && !input.peek(Token![||]) && !input.peek(Token![|=]) {
                    let punct = input.parse()?;
                    pats.push_punct(punct);
                    let value: Pat = input.parse()?;
                    pats.push_value(value);
                }
                pats
            },
            ty: {
                if input.peek(Token![:]) {
                    let colon_token: Token![:] = input.parse()?;
                    let ty: Type = input.parse()?;
                    Some((colon_token, Box::new(ty)))
                } else {
                    None
                }
            },
            init: {
                if input.peek(Token![=]) {
                    let eq_token: Token![=] = input.parse()?;
                    let init: Expr = input.parse()?;
                    Some((eq_token, Box::new(init)))
                } else {
                    None
                }
            },
            semi_token: input.parse()?,
        })
    }

    #[cfg(feature = "full")]
    fn stmt_expr(input: ParseStream, allow_nosemi: bool) -> Result<Stmt> {
        let mut attrs = input.call(Attribute::parse_outer)?;
        let mut e = expr_early(input)?;

        attrs.extend(e.replace_attrs(Vec::new()));
        e.replace_attrs(attrs);

        if input.peek(Token![;]) {
            return Ok(Stmt::Semi(e, input.parse()?));
        }

        if allow_nosemi || !requires_terminator(&e) {
            Ok(Stmt::Expr(e))
        } else {
            Err(input.error("expected semicolon"))
        }
    }

    #[cfg(feature = "full")]
    impl Parse for Pat {
        fn parse(input: ParseStream) -> Result<Self> {
            let lookahead = input.lookahead1();
            if lookahead.peek(Token![_]) {
                input.call(pat_wild).map(Pat::Wild)
            } else if lookahead.peek(Token![box]) {
                input.call(pat_box).map(Pat::Box)
            } else if lookahead.peek(Token![-]) || lookahead.peek(Lit) {
                pat_lit_or_range(input)
            } else if input.peek(Ident)
                && ({
                    input.peek2(Token![::])
                        || input.peek2(Token![!])
                        || input.peek2(token::Brace)
                        || input.peek2(token::Paren)
                        || input.peek2(Token![..])
                            && !{
                                let ahead = input.fork();
                                ahead.parse::<Ident>()?;
                                ahead.parse::<RangeLimits>()?;
                                ahead.is_empty() || ahead.peek(Token![,])
                            }
                })
                || input.peek(Token![self]) && input.peek2(Token![::])
                || input.peek(Token![::])
                || input.peek(Token![<])
                || input.peek(Token![Self])
                || input.peek(Token![super])
                || input.peek(Token![extern])
                || input.peek(Token![crate])
            {
                pat_path_or_macro_or_struct_or_range(input)
            } else if input.peek(Token![ref])
                || input.peek(Token![mut])
                || input.peek(Token![self])
                || input.peek(Ident)
            {
                input.call(pat_ident).map(Pat::Ident)
            } else if lookahead.peek(token::Paren) {
                input.call(pat_tuple).map(Pat::Tuple)
            } else if lookahead.peek(Token![&]) {
                input.call(pat_ref).map(Pat::Ref)
            } else if lookahead.peek(token::Bracket) {
                input.call(pat_slice).map(Pat::Slice)
            } else {
                Err(lookahead.error())
            }
        }
    }

    #[cfg(feature = "full")]
    fn pat_path_or_macro_or_struct_or_range(input: ParseStream) -> Result<Pat> {
        let (qself, path) = path::parsing::qpath(input, true)?;

        if input.peek(Token![..]) {
            return pat_range(input, qself, path).map(Pat::Range);
        }

        if qself.is_some() {
            return Ok(Pat::Path(PatPath {
                qself: qself,
                path: path,
            }));
        }

        if input.peek(Token![!]) && !input.peek(Token![!=]) {
            let mut contains_arguments = false;
            for segment in &path.segments {
                match segment.arguments {
                    PathArguments::None => {}
                    PathArguments::AngleBracketed(_) | PathArguments::Parenthesized(_) => {
                        contains_arguments = true;
                    }
                }
            }

            if !contains_arguments {
                let bang_token: Token![!] = input.parse()?;
                let (delimiter, tts) = mac::parse_delimiter(input)?;
                return Ok(Pat::Macro(PatMacro {
                    mac: Macro {
                        path: path,
                        bang_token: bang_token,
                        delimiter: delimiter,
                        tts: tts,
                    },
                }));
            }
        }

        if input.peek(token::Brace) {
            pat_struct(input, path).map(Pat::Struct)
        } else if input.peek(token::Paren) {
            pat_tuple_struct(input, path).map(Pat::TupleStruct)
        } else if input.peek(Token![..]) {
            pat_range(input, qself, path).map(Pat::Range)
        } else {
            Ok(Pat::Path(PatPath {
                qself: qself,
                path: path,
            }))
        }
    }

    #[cfg(feature = "full")]
    fn pat_wild(input: ParseStream) -> Result<PatWild> {
        Ok(PatWild {
            underscore_token: input.parse()?,
        })
    }

    #[cfg(feature = "full")]
    fn pat_box(input: ParseStream) -> Result<PatBox> {
        Ok(PatBox {
            box_token: input.parse()?,
            pat: input.parse()?,
        })
    }

    #[cfg(feature = "full")]
    fn pat_ident(input: ParseStream) -> Result<PatIdent> {
        Ok(PatIdent {
            by_ref: input.parse()?,
            mutability: input.parse()?,
            ident: input.call(Ident::parse_any)?,
            subpat: {
                if input.peek(Token![@]) {
                    let at_token: Token![@] = input.parse()?;
                    let subpat: Pat = input.parse()?;
                    Some((at_token, Box::new(subpat)))
                } else {
                    None
                }
            },
        })
    }

    #[cfg(feature = "full")]
    fn pat_tuple_struct(input: ParseStream, path: Path) -> Result<PatTupleStruct> {
        Ok(PatTupleStruct {
            path: path,
            pat: input.call(pat_tuple)?,
        })
    }

    #[cfg(feature = "full")]
    fn pat_struct(input: ParseStream, path: Path) -> Result<PatStruct> {
        let content;
        let brace_token = braced!(content in input);

        let mut fields = Punctuated::new();
        while !content.is_empty() && !content.peek(Token![..]) {
            let value = content.call(field_pat)?;
            fields.push_value(value);
            if !content.peek(Token![,]) {
                break;
            }
            let punct: Token![,] = content.parse()?;
            fields.push_punct(punct);
        }

        let dot2_token = if fields.empty_or_trailing() && content.peek(Token![..]) {
            Some(content.parse()?)
        } else {
            None
        };

        Ok(PatStruct {
            path: path,
            brace_token: brace_token,
            fields: fields,
            dot2_token: dot2_token,
        })
    }

    #[cfg(feature = "full")]
    fn field_pat(input: ParseStream) -> Result<FieldPat> {
        let boxed: Option<Token![box]> = input.parse()?;
        let by_ref: Option<Token![ref]> = input.parse()?;
        let mutability: Option<Token![mut]> = input.parse()?;
        let member: Member = input.parse()?;

        if boxed.is_none() && by_ref.is_none() && mutability.is_none() && input.peek(Token![:])
            || member.is_unnamed()
        {
            return Ok(FieldPat {
                attrs: Vec::new(),
                member: member,
                colon_token: input.parse()?,
                pat: input.parse()?,
            });
        }

        let ident = match member {
            Member::Named(ident) => ident,
            Member::Unnamed(_) => unreachable!(),
        };

        let mut pat = Pat::Ident(PatIdent {
            by_ref: by_ref,
            mutability: mutability,
            ident: ident.clone(),
            subpat: None,
        });

        if let Some(boxed) = boxed {
            pat = Pat::Box(PatBox {
                pat: Box::new(pat),
                box_token: boxed,
            });
        }

        Ok(FieldPat {
            member: Member::Named(ident),
            pat: Box::new(pat),
            attrs: Vec::new(),
            colon_token: None,
        })
    }

    impl Parse for Member {
        fn parse(input: ParseStream) -> Result<Self> {
            if input.peek(Ident) {
                input.parse().map(Member::Named)
            } else if input.peek(LitInt) {
                input.parse().map(Member::Unnamed)
            } else {
                Err(input.error("expected identifier or integer"))
            }
        }
    }

    #[cfg(feature = "full")]
    impl Parse for Arm {
        fn parse(input: ParseStream) -> Result<Arm> {
            let requires_comma;
            Ok(Arm {
                attrs: input.call(Attribute::parse_outer)?,
                leading_vert: input.parse()?,
                pats: {
                    let mut pats = Punctuated::new();
                    let value: Pat = input.parse()?;
                    pats.push_value(value);
                    loop {
                        if !input.peek(Token![|]) {
                            break;
                        }
                        let punct = input.parse()?;
                        pats.push_punct(punct);
                        let value: Pat = input.parse()?;
                        pats.push_value(value);
                    }
                    pats
                },
                guard: {
                    if input.peek(Token![if]) {
                        let if_token: Token![if] = input.parse()?;
                        let guard: Expr = input.parse()?;
                        Some((if_token, Box::new(guard)))
                    } else {
                        None
                    }
                },
                fat_arrow_token: input.parse()?,
                body: {
                    let body = input.call(expr_early)?;
                    requires_comma = requires_terminator(&body);
                    Box::new(body)
                },
                comma: {
                    if requires_comma && !input.is_empty() {
                        Some(input.parse()?)
                    } else {
                        input.parse()?
                    }
                },
            })
        }
    }

    impl Parse for Index {
        fn parse(input: ParseStream) -> Result<Self> {
            let lit: LitInt = input.parse()?;
            if let IntSuffix::None = lit.suffix() {
                Ok(Index {
                    index: lit.value() as u32,
                    span: lit.span(),
                })
            } else {
                Err(Error::new(lit.span(), "expected unsuffixed integer"))
            }
        }
    }

    #[cfg(feature = "full")]
    fn pat_range(input: ParseStream, qself: Option<QSelf>, path: Path) -> Result<PatRange> {
        Ok(PatRange {
            lo: Box::new(Expr::Path(ExprPath {
                attrs: Vec::new(),
                qself: qself,
                path: path,
            })),
            limits: input.parse()?,
            hi: input.call(pat_lit_expr)?,
        })
    }

    #[cfg(feature = "full")]
    fn pat_tuple(input: ParseStream) -> Result<PatTuple> {
        let content;
        let paren_token = parenthesized!(content in input);

        let mut front = Punctuated::new();
        let mut dot2_token = None::<Token![..]>;
        let mut comma_token = None::<Token![,]>;
        loop {
            if content.is_empty() {
                break;
            }
            if content.peek(Token![..]) {
                dot2_token = Some(content.parse()?);
                comma_token = content.parse()?;
                break;
            }
            let value: Pat = content.parse()?;
            front.push_value(value);
            if content.is_empty() {
                break;
            }
            let punct = content.parse()?;
            front.push_punct(punct);
        }

        let mut back = Punctuated::new();
        while !content.is_empty() {
            let value: Pat = content.parse()?;
            back.push_value(value);
            if content.is_empty() {
                break;
            }
            let punct = content.parse()?;
            back.push_punct(punct);
        }

        Ok(PatTuple {
            paren_token: paren_token,
            front: front,
            dot2_token: dot2_token,
            comma_token: comma_token,
            back: back,
        })
    }

    #[cfg(feature = "full")]
    fn pat_ref(input: ParseStream) -> Result<PatRef> {
        Ok(PatRef {
            and_token: input.parse()?,
            mutability: input.parse()?,
            pat: input.parse()?,
        })
    }

    #[cfg(feature = "full")]
    fn pat_lit_or_range(input: ParseStream) -> Result<Pat> {
        let lo = input.call(pat_lit_expr)?;
        if input.peek(Token![..]) {
            Ok(Pat::Range(PatRange {
                lo: lo,
                limits: input.parse()?,
                hi: input.call(pat_lit_expr)?,
            }))
        } else {
            Ok(Pat::Lit(PatLit { expr: lo }))
        }
    }

    #[cfg(feature = "full")]
    fn pat_lit_expr(input: ParseStream) -> Result<Box<Expr>> {
        let neg: Option<Token![-]> = input.parse()?;

        let lookahead = input.lookahead1();
        let expr = if lookahead.peek(Lit) {
            Expr::Lit(input.parse()?)
        } else if lookahead.peek(Ident)
            || lookahead.peek(Token![::])
            || lookahead.peek(Token![<])
            || lookahead.peek(Token![self])
            || lookahead.peek(Token![Self])
            || lookahead.peek(Token![super])
            || lookahead.peek(Token![extern])
            || lookahead.peek(Token![crate])
        {
            Expr::Path(input.parse()?)
        } else {
            return Err(lookahead.error());
        };

        Ok(Box::new(if let Some(neg) = neg {
            Expr::Unary(ExprUnary {
                attrs: Vec::new(),
                op: UnOp::Neg(neg),
                expr: Box::new(expr),
            })
        } else {
            expr
        }))
    }

    #[cfg(feature = "full")]
    fn pat_slice(input: ParseStream) -> Result<PatSlice> {
        let content;
        let bracket_token = bracketed!(content in input);

        let mut front = Punctuated::new();
        let mut middle = None;
        loop {
            if content.is_empty() || content.peek(Token![..]) {
                break;
            }
            let value: Pat = content.parse()?;
            if content.peek(Token![..]) {
                middle = Some(Box::new(value));
                break;
            }
            front.push_value(value);
            if content.is_empty() {
                break;
            }
            let punct = content.parse()?;
            front.push_punct(punct);
        }

        let dot2_token: Option<Token![..]> = content.parse()?;
        let mut comma_token = None::<Token![,]>;
        let mut back = Punctuated::new();
        if dot2_token.is_some() {
            comma_token = content.parse()?;
            if comma_token.is_some() {
                loop {
                    if content.is_empty() {
                        break;
                    }
                    let value: Pat = content.parse()?;
                    back.push_value(value);
                    if content.is_empty() {
                        break;
                    }
                    let punct = content.parse()?;
                    back.push_punct(punct);
                }
            }
        }

        Ok(PatSlice {
            bracket_token: bracket_token,
            front: front,
            middle: middle,
            dot2_token: dot2_token,
            comma_token: comma_token,
            back: back,
        })
    }

    #[cfg(feature = "full")]
    impl Member {
        fn is_named(&self) -> bool {
            match *self {
                Member::Named(_) => true,
                Member::Unnamed(_) => false,
            }
        }

        fn is_unnamed(&self) -> bool {
            match *self {
                Member::Named(_) => false,
                Member::Unnamed(_) => true,
            }
        }
    }
}

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

    use proc_macro2::{Literal, TokenStream};
    use quote::{ToTokens, TokenStreamExt};

    #[cfg(feature = "full")]
    use attr::FilterAttrs;
    #[cfg(feature = "full")]
    use print::TokensOrDefault;

    // If the given expression is a bare `ExprStruct`, wraps it in parenthesis
    // before appending it to `TokenStream`.
    #[cfg(feature = "full")]
    fn wrap_bare_struct(tokens: &mut TokenStream, e: &Expr) {
        if let Expr::Struct(_) = *e {
            token::Paren::default().surround(tokens, |tokens| {
                e.to_tokens(tokens);
            });
        } else {
            e.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    fn outer_attrs_to_tokens(attrs: &[Attribute], tokens: &mut TokenStream) {
        tokens.append_all(attrs.outer());
    }

    #[cfg(feature = "full")]
    fn inner_attrs_to_tokens(attrs: &[Attribute], tokens: &mut TokenStream) {
        tokens.append_all(attrs.inner());
    }

    #[cfg(not(feature = "full"))]
    fn outer_attrs_to_tokens(_attrs: &[Attribute], _tokens: &mut TokenStream) {}

    #[cfg(not(feature = "full"))]
    fn inner_attrs_to_tokens(_attrs: &[Attribute], _tokens: &mut TokenStream) {}

    #[cfg(feature = "full")]
    impl ToTokens for ExprBox {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.box_token.to_tokens(tokens);
            self.expr.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprInPlace {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.place.to_tokens(tokens);
            self.arrow_token.to_tokens(tokens);
            self.value.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprArray {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.bracket_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                self.elems.to_tokens(tokens);
            })
        }
    }

    impl ToTokens for ExprCall {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.func.to_tokens(tokens);
            self.paren_token.surround(tokens, |tokens| {
                self.args.to_tokens(tokens);
            })
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprMethodCall {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.receiver.to_tokens(tokens);
            self.dot_token.to_tokens(tokens);
            self.method.to_tokens(tokens);
            self.turbofish.to_tokens(tokens);
            self.paren_token.surround(tokens, |tokens| {
                self.args.to_tokens(tokens);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for MethodTurbofish {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.colon2_token.to_tokens(tokens);
            self.lt_token.to_tokens(tokens);
            self.args.to_tokens(tokens);
            self.gt_token.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for GenericMethodArgument {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            match *self {
                GenericMethodArgument::Type(ref t) => t.to_tokens(tokens),
                GenericMethodArgument::Const(ref c) => c.to_tokens(tokens),
            }
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprTuple {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.paren_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                self.elems.to_tokens(tokens);
                // If we only have one argument, we need a trailing comma to
                // distinguish ExprTuple from ExprParen.
                if self.elems.len() == 1 && !self.elems.trailing_punct() {
                    <Token![,]>::default().to_tokens(tokens);
                }
            })
        }
    }

    impl ToTokens for ExprBinary {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.left.to_tokens(tokens);
            self.op.to_tokens(tokens);
            self.right.to_tokens(tokens);
        }
    }

    impl ToTokens for ExprUnary {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.op.to_tokens(tokens);
            self.expr.to_tokens(tokens);
        }
    }

    impl ToTokens for ExprLit {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.lit.to_tokens(tokens);
        }
    }

    impl ToTokens for ExprCast {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.expr.to_tokens(tokens);
            self.as_token.to_tokens(tokens);
            self.ty.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprType {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.expr.to_tokens(tokens);
            self.colon_token.to_tokens(tokens);
            self.ty.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    fn maybe_wrap_else(tokens: &mut TokenStream, else_: &Option<(Token![else], Box<Expr>)>) {
        if let Some((ref else_token, ref else_)) = *else_ {
            else_token.to_tokens(tokens);

            // If we are not one of the valid expressions to exist in an else
            // clause, wrap ourselves in a block.
            match **else_ {
                Expr::If(_) | Expr::Block(_) => {
                    else_.to_tokens(tokens);
                }
                _ => {
                    token::Brace::default().surround(tokens, |tokens| {
                        else_.to_tokens(tokens);
                    });
                }
            }
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprLet {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.let_token.to_tokens(tokens);
            self.pats.to_tokens(tokens);
            self.eq_token.to_tokens(tokens);
            wrap_bare_struct(tokens, &self.expr);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprIf {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.if_token.to_tokens(tokens);
            wrap_bare_struct(tokens, &self.cond);
            self.then_branch.to_tokens(tokens);
            maybe_wrap_else(tokens, &self.else_branch);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprWhile {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.label.to_tokens(tokens);
            self.while_token.to_tokens(tokens);
            wrap_bare_struct(tokens, &self.cond);
            self.body.brace_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                tokens.append_all(&self.body.stmts);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprForLoop {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.label.to_tokens(tokens);
            self.for_token.to_tokens(tokens);
            self.pat.to_tokens(tokens);
            self.in_token.to_tokens(tokens);
            wrap_bare_struct(tokens, &self.expr);
            self.body.brace_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                tokens.append_all(&self.body.stmts);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprLoop {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.label.to_tokens(tokens);
            self.loop_token.to_tokens(tokens);
            self.body.brace_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                tokens.append_all(&self.body.stmts);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprMatch {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.match_token.to_tokens(tokens);
            wrap_bare_struct(tokens, &self.expr);
            self.brace_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                for (i, arm) in self.arms.iter().enumerate() {
                    arm.to_tokens(tokens);
                    // Ensure that we have a comma after a non-block arm, except
                    // for the last one.
                    let is_last = i == self.arms.len() - 1;
                    if !is_last && requires_terminator(&arm.body) && arm.comma.is_none() {
                        <Token![,]>::default().to_tokens(tokens);
                    }
                }
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprAsync {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.async_token.to_tokens(tokens);
            self.capture.to_tokens(tokens);
            self.block.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprTryBlock {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.try_token.to_tokens(tokens);
            self.block.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprYield {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.yield_token.to_tokens(tokens);
            self.expr.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprClosure {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.asyncness.to_tokens(tokens);
            self.movability.to_tokens(tokens);
            self.capture.to_tokens(tokens);
            self.or1_token.to_tokens(tokens);
            for input in self.inputs.pairs() {
                match **input.value() {
                    FnArg::Captured(ArgCaptured {
                        ref pat,
                        ty: Type::Infer(_),
                        ..
                    }) => {
                        pat.to_tokens(tokens);
                    }
                    _ => input.value().to_tokens(tokens),
                }
                input.punct().to_tokens(tokens);
            }
            self.or2_token.to_tokens(tokens);
            self.output.to_tokens(tokens);
            self.body.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprUnsafe {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.unsafe_token.to_tokens(tokens);
            self.block.brace_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                tokens.append_all(&self.block.stmts);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprBlock {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.label.to_tokens(tokens);
            self.block.brace_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                tokens.append_all(&self.block.stmts);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprAssign {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.left.to_tokens(tokens);
            self.eq_token.to_tokens(tokens);
            self.right.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprAssignOp {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.left.to_tokens(tokens);
            self.op.to_tokens(tokens);
            self.right.to_tokens(tokens);
        }
    }

    impl ToTokens for ExprField {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.base.to_tokens(tokens);
            self.dot_token.to_tokens(tokens);
            self.member.to_tokens(tokens);
        }
    }

    impl ToTokens for Member {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            match *self {
                Member::Named(ref ident) => ident.to_tokens(tokens),
                Member::Unnamed(ref index) => index.to_tokens(tokens),
            }
        }
    }

    impl ToTokens for Index {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            let mut lit = Literal::i64_unsuffixed(i64::from(self.index));
            lit.set_span(self.span);
            tokens.append(lit);
        }
    }

    impl ToTokens for ExprIndex {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.expr.to_tokens(tokens);
            self.bracket_token.surround(tokens, |tokens| {
                self.index.to_tokens(tokens);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprRange {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.from.to_tokens(tokens);
            match self.limits {
                RangeLimits::HalfOpen(ref t) => t.to_tokens(tokens),
                RangeLimits::Closed(ref t) => t.to_tokens(tokens),
            }
            self.to.to_tokens(tokens);
        }
    }

    impl ToTokens for ExprPath {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            private::print_path(tokens, &self.qself, &self.path);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprReference {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.and_token.to_tokens(tokens);
            self.mutability.to_tokens(tokens);
            self.expr.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprBreak {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.break_token.to_tokens(tokens);
            self.label.to_tokens(tokens);
            self.expr.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprContinue {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.continue_token.to_tokens(tokens);
            self.label.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprReturn {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.return_token.to_tokens(tokens);
            self.expr.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprMacro {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.mac.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprStruct {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.path.to_tokens(tokens);
            self.brace_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                self.fields.to_tokens(tokens);
                if self.rest.is_some() {
                    TokensOrDefault(&self.dot2_token).to_tokens(tokens);
                    self.rest.to_tokens(tokens);
                }
            })
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprRepeat {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.bracket_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                self.expr.to_tokens(tokens);
                self.semi_token.to_tokens(tokens);
                self.len.to_tokens(tokens);
            })
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprGroup {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.group_token.surround(tokens, |tokens| {
                self.expr.to_tokens(tokens);
            });
        }
    }

    impl ToTokens for ExprParen {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.paren_token.surround(tokens, |tokens| {
                inner_attrs_to_tokens(&self.attrs, tokens);
                self.expr.to_tokens(tokens);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for ExprTry {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.expr.to_tokens(tokens);
            self.question_token.to_tokens(tokens);
        }
    }

    impl ToTokens for ExprVerbatim {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.tts.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for Label {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.name.to_tokens(tokens);
            self.colon_token.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for FieldValue {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.member.to_tokens(tokens);
            if let Some(ref colon_token) = self.colon_token {
                colon_token.to_tokens(tokens);
                self.expr.to_tokens(tokens);
            }
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for Arm {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            tokens.append_all(&self.attrs);
            self.leading_vert.to_tokens(tokens);
            self.pats.to_tokens(tokens);
            if let Some((ref if_token, ref guard)) = self.guard {
                if_token.to_tokens(tokens);
                guard.to_tokens(tokens);
            }
            self.fat_arrow_token.to_tokens(tokens);
            self.body.to_tokens(tokens);
            self.comma.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatWild {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.underscore_token.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatIdent {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.by_ref.to_tokens(tokens);
            self.mutability.to_tokens(tokens);
            self.ident.to_tokens(tokens);
            if let Some((ref at_token, ref subpat)) = self.subpat {
                at_token.to_tokens(tokens);
                subpat.to_tokens(tokens);
            }
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatStruct {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.path.to_tokens(tokens);
            self.brace_token.surround(tokens, |tokens| {
                self.fields.to_tokens(tokens);
                // NOTE: We need a comma before the dot2 token if it is present.
                if !self.fields.empty_or_trailing() && self.dot2_token.is_some() {
                    <Token![,]>::default().to_tokens(tokens);
                }
                self.dot2_token.to_tokens(tokens);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatTupleStruct {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.path.to_tokens(tokens);
            self.pat.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatPath {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            private::print_path(tokens, &self.qself, &self.path);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatTuple {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.paren_token.surround(tokens, |tokens| {
                self.front.to_tokens(tokens);
                if let Some(ref dot2_token) = self.dot2_token {
                    if !self.front.empty_or_trailing() {
                        // Ensure there is a comma before the .. token.
                        <Token![,]>::default().to_tokens(tokens);
                    }
                    dot2_token.to_tokens(tokens);
                    self.comma_token.to_tokens(tokens);
                    if self.comma_token.is_none() && !self.back.is_empty() {
                        // Ensure there is a comma after the .. token.
                        <Token![,]>::default().to_tokens(tokens);
                    }
                }
                self.back.to_tokens(tokens);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatBox {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.box_token.to_tokens(tokens);
            self.pat.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatRef {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.and_token.to_tokens(tokens);
            self.mutability.to_tokens(tokens);
            self.pat.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatLit {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.expr.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatRange {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.lo.to_tokens(tokens);
            match self.limits {
                RangeLimits::HalfOpen(ref t) => t.to_tokens(tokens),
                RangeLimits::Closed(ref t) => Token![...](t.spans).to_tokens(tokens),
            }
            self.hi.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatSlice {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.bracket_token.surround(tokens, |tokens| {
                self.front.to_tokens(tokens);

                // If we need a comma before the middle or standalone .. token,
                // then make sure it's present.
                if !self.front.empty_or_trailing()
                    && (self.middle.is_some() || self.dot2_token.is_some())
                {
                    <Token![,]>::default().to_tokens(tokens);
                }

                // If we have an identifier, we always need a .. token.
                if self.middle.is_some() {
                    self.middle.to_tokens(tokens);
                    TokensOrDefault(&self.dot2_token).to_tokens(tokens);
                } else if self.dot2_token.is_some() {
                    self.dot2_token.to_tokens(tokens);
                }

                // Make sure we have a comma before the back half.
                if !self.back.is_empty() {
                    TokensOrDefault(&self.comma_token).to_tokens(tokens);
                    self.back.to_tokens(tokens);
                } else {
                    self.comma_token.to_tokens(tokens);
                }
            })
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatMacro {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.mac.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for PatVerbatim {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.tts.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for FieldPat {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            if let Some(ref colon_token) = self.colon_token {
                self.member.to_tokens(tokens);
                colon_token.to_tokens(tokens);
            }
            self.pat.to_tokens(tokens);
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for Block {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            self.brace_token.surround(tokens, |tokens| {
                tokens.append_all(&self.stmts);
            });
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for Stmt {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            match *self {
                Stmt::Local(ref local) => local.to_tokens(tokens),
                Stmt::Item(ref item) => item.to_tokens(tokens),
                Stmt::Expr(ref expr) => expr.to_tokens(tokens),
                Stmt::Semi(ref expr, ref semi) => {
                    expr.to_tokens(tokens);
                    semi.to_tokens(tokens);
                }
            }
        }
    }

    #[cfg(feature = "full")]
    impl ToTokens for Local {
        fn to_tokens(&self, tokens: &mut TokenStream) {
            outer_attrs_to_tokens(&self.attrs, tokens);
            self.let_token.to_tokens(tokens);
            self.pats.to_tokens(tokens);
            if let Some((ref colon_token, ref ty)) = self.ty {
                colon_token.to_tokens(tokens);
                ty.to_tokens(tokens);
            }
            if let Some((ref eq_token, ref init)) = self.init {
                eq_token.to_tokens(tokens);
                init.to_tokens(tokens);
            }
            self.semi_token.to_tokens(tokens);
        }
    }
}