rust: syn: import crate

This is a subset of the Rust `syn` crate, version 2.0.106 (released
2025-08-16), licensed under "Apache-2.0 OR MIT", from:

    https://github.com/dtolnay/syn/raw/2.0.106/src

The files are copied as-is, with no modifications whatsoever (not even
adding the SPDX identifiers).

For copyright details, please see:

    https://github.com/dtolnay/syn/blob/2.0.106/README.md#license
    https://github.com/dtolnay/syn/blob/2.0.106/LICENSE-APACHE
    https://github.com/dtolnay/syn/blob/2.0.106/LICENSE-MIT

The next two patches modify these files as needed for use within the
kernel. This patch split allows reviewers to double-check the import
and to clearly see the differences introduced.

The following script may be used to verify the contents:

    for path in $(cd rust/syn/ && find . -type f -name '*.rs'); do
        curl --silent --show-error --location \
            https://github.com/dtolnay/syn/raw/2.0.106/src/$path \
            | diff --unified rust/syn/$path - && echo $path: OK
    done

Reviewed-by: Gary Guo <gary@garyguo.net>
Tested-by: Gary Guo <gary@garyguo.net>
Tested-by: Jesung Yang <y.j3ms.n@gmail.com>
Link: https://patch.msgid.link/20251124151837.2184382-16-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 1271 insertions, 0 deletions

diff --git a/rust/syn/ty.rs b/rust/syn/ty.rs
new file mode 100644
index 000000000000..c093f5877b3c
--- /dev/null
+++ b/rust/syn/ty.rs
@@ -0,0 +1,1271 @@
+use crate::attr::Attribute;
+use crate::expr::Expr;
+use crate::generics::{BoundLifetimes, TypeParamBound};
+use crate::ident::Ident;
+use crate::lifetime::Lifetime;
+use crate::lit::LitStr;
+use crate::mac::Macro;
+use crate::path::{Path, QSelf};
+use crate::punctuated::Punctuated;
+use crate::token;
+use proc_macro2::TokenStream;
+
+ast_enum_of_structs! {
+    /// The possible types that a Rust value could have.
+    ///
+    /// # Syntax tree enum
+    ///
+    /// This type is a [syntax tree enum].
+    ///
+    /// [syntax tree enum]: crate::expr::Expr#syntax-tree-enums
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    #[non_exhaustive]
+    pub enum Type {
+        /// A fixed size array type: `[T; n]`.
+        Array(TypeArray),
+
+        /// A bare function type: `fn(usize) -> bool`.
+        BareFn(TypeBareFn),
+
+        /// A type contained within invisible delimiters.
+        Group(TypeGroup),
+
+        /// An `impl Bound1 + Bound2 + Bound3` type where `Bound` is a trait or
+        /// a lifetime.
+        ImplTrait(TypeImplTrait),
+
+        /// Indication that a type should be inferred by the compiler: `_`.
+        Infer(TypeInfer),
+
+        /// A macro in the type position.
+        Macro(TypeMacro),
+
+        /// The never type: `!`.
+        Never(TypeNever),
+
+        /// A parenthesized type equivalent to the inner type.
+        Paren(TypeParen),
+
+        /// A path like `std::slice::Iter`, optionally qualified with a
+        /// self-type as in `<Vec<T> as SomeTrait>::Associated`.
+        Path(TypePath),
+
+        /// A raw pointer type: `*const T` or `*mut T`.
+        Ptr(TypePtr),
+
+        /// A reference type: `&'a T` or `&'a mut T`.
+        Reference(TypeReference),
+
+        /// A dynamically sized slice type: `[T]`.
+        Slice(TypeSlice),
+
+        /// A trait object type `dyn Bound1 + Bound2 + Bound3` where `Bound` is a
+        /// trait or a lifetime.
+        TraitObject(TypeTraitObject),
+
+        /// A tuple type: `(A, B, C, String)`.
+        Tuple(TypeTuple),
+
+        /// Tokens in type position not interpreted by Syn.
+        Verbatim(TokenStream),
+
+        // For testing exhaustiveness in downstream code, use the following idiom:
+        //
+        //     match ty {
+        //         #![cfg_attr(test, deny(non_exhaustive_omitted_patterns))]
+        //
+        //         Type::Array(ty) => {...}
+        //         Type::BareFn(ty) => {...}
+        //         ...
+        //         Type::Verbatim(ty) => {...}
+        //
+        //         _ => { /* some sane fallback */ }
+        //     }
+        //
+        // This way we fail your tests but don't break your library when adding
+        // a variant. You will be notified by a test failure when a variant is
+        // added, so that you can add code to handle it, but your library will
+        // continue to compile and work for downstream users in the interim.
+    }
+}
+
+ast_struct! {
+    /// A fixed size array type: `[T; n]`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeArray {
+        pub bracket_token: token::Bracket,
+        pub elem: Box<Type>,
+        pub semi_token: Token![;],
+        pub len: Expr,
+    }
+}
+
+ast_struct! {
+    /// A bare function type: `fn(usize) -> bool`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeBareFn {
+        pub lifetimes: Option<BoundLifetimes>,
+        pub unsafety: Option<Token![unsafe]>,
+        pub abi: Option<Abi>,
+        pub fn_token: Token![fn],
+        pub paren_token: token::Paren,
+        pub inputs: Punctuated<BareFnArg, Token![,]>,
+        pub variadic: Option<BareVariadic>,
+        pub output: ReturnType,
+    }
+}
+
+ast_struct! {
+    /// A type contained within invisible delimiters.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeGroup {
+        pub group_token: token::Group,
+        pub elem: Box<Type>,
+    }
+}
+
+ast_struct! {
+    /// An `impl Bound1 + Bound2 + Bound3` type where `Bound` is a trait or
+    /// a lifetime.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeImplTrait {
+        pub impl_token: Token![impl],
+        pub bounds: Punctuated<TypeParamBound, Token![+]>,
+    }
+}
+
+ast_struct! {
+    /// Indication that a type should be inferred by the compiler: `_`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeInfer {
+        pub underscore_token: Token![_],
+    }
+}
+
+ast_struct! {
+    /// A macro in the type position.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeMacro {
+        pub mac: Macro,
+    }
+}
+
+ast_struct! {
+    /// The never type: `!`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeNever {
+        pub bang_token: Token![!],
+    }
+}
+
+ast_struct! {
+    /// A parenthesized type equivalent to the inner type.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeParen {
+        pub paren_token: token::Paren,
+        pub elem: Box<Type>,
+    }
+}
+
+ast_struct! {
+    /// A path like `std::slice::Iter`, optionally qualified with a
+    /// self-type as in `<Vec<T> as SomeTrait>::Associated`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypePath {
+        pub qself: Option<QSelf>,
+        pub path: Path,
+    }
+}
+
+ast_struct! {
+    /// A raw pointer type: `*const T` or `*mut T`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypePtr {
+        pub star_token: Token![*],
+        pub const_token: Option<Token![const]>,
+        pub mutability: Option<Token![mut]>,
+        pub elem: Box<Type>,
+    }
+}
+
+ast_struct! {
+    /// A reference type: `&'a T` or `&'a mut T`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeReference {
+        pub and_token: Token![&],
+        pub lifetime: Option<Lifetime>,
+        pub mutability: Option<Token![mut]>,
+        pub elem: Box<Type>,
+    }
+}
+
+ast_struct! {
+    /// A dynamically sized slice type: `[T]`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeSlice {
+        pub bracket_token: token::Bracket,
+        pub elem: Box<Type>,
+    }
+}
+
+ast_struct! {
+    /// A trait object type `dyn Bound1 + Bound2 + Bound3` where `Bound` is a
+    /// trait or a lifetime.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeTraitObject {
+        pub dyn_token: Option<Token![dyn]>,
+        pub bounds: Punctuated<TypeParamBound, Token![+]>,
+    }
+}
+
+ast_struct! {
+    /// A tuple type: `(A, B, C, String)`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct TypeTuple {
+        pub paren_token: token::Paren,
+        pub elems: Punctuated<Type, Token![,]>,
+    }
+}
+
+ast_struct! {
+    /// The binary interface of a function: `extern "C"`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct Abi {
+        pub extern_token: Token![extern],
+        pub name: Option<LitStr>,
+    }
+}
+
+ast_struct! {
+    /// An argument in a function type: the `usize` in `fn(usize) -> bool`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct BareFnArg {
+        pub attrs: Vec<Attribute>,
+        pub name: Option<(Ident, Token![:])>,
+        pub ty: Type,
+    }
+}
+
+ast_struct! {
+    /// The variadic argument of a function pointer like `fn(usize, ...)`.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub struct BareVariadic {
+        pub attrs: Vec<Attribute>,
+        pub name: Option<(Ident, Token![:])>,
+        pub dots: Token![...],
+        pub comma: Option<Token![,]>,
+    }
+}
+
+ast_enum! {
+    /// Return type of a function signature.
+    #[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
+    pub enum ReturnType {
+        /// Return type is not specified.
+        ///
+        /// Functions default to `()` and closures default to type inference.
+        Default,
+        /// A particular type is returned.
+        Type(Token![->], Box<Type>),
+    }
+}
+
+#[cfg(feature = "parsing")]
+pub(crate) mod parsing {
+    use crate::attr::Attribute;
+    use crate::error::{self, Result};
+    use crate::ext::IdentExt as _;
+    use crate::generics::{BoundLifetimes, TraitBound, TraitBoundModifier, TypeParamBound};
+    use crate::ident::Ident;
+    use crate::lifetime::Lifetime;
+    use crate::mac::{self, Macro};
+    use crate::parse::{Parse, ParseStream};
+    use crate::path;
+    use crate::path::{Path, PathArguments, QSelf};
+    use crate::punctuated::Punctuated;
+    use crate::token;
+    use crate::ty::{
+        Abi, BareFnArg, BareVariadic, ReturnType, Type, TypeArray, TypeBareFn, TypeGroup,
+        TypeImplTrait, TypeInfer, TypeMacro, TypeNever, TypeParen, TypePath, TypePtr,
+        TypeReference, TypeSlice, TypeTraitObject, TypeTuple,
+    };
+    use crate::verbatim;
+    use proc_macro2::Span;
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for Type {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let allow_plus = true;
+            let allow_group_generic = true;
+            ambig_ty(input, allow_plus, allow_group_generic)
+        }
+    }
+
+    impl Type {
+        /// In some positions, types may not contain the `+` character, to
+        /// disambiguate them. For example in the expression `1 as T`, T may not
+        /// contain a `+` character.
+        ///
+        /// This parser does not allow a `+`, while the default parser does.
+        #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+        pub fn without_plus(input: ParseStream) -> Result<Self> {
+            let allow_plus = false;
+            let allow_group_generic = true;
+            ambig_ty(input, allow_plus, allow_group_generic)
+        }
+    }
+
+    pub(crate) fn ambig_ty(
+        input: ParseStream,
+        allow_plus: bool,
+        allow_group_generic: bool,
+    ) -> Result<Type> {
+        let begin = input.fork();
+
+        if input.peek(token::Group) {
+            let mut group: TypeGroup = input.parse()?;
+            if input.peek(Token![::]) && input.peek3(Ident::peek_any) {
+                if let Type::Path(mut ty) = *group.elem {
+                    Path::parse_rest(input, &mut ty.path, false)?;
+                    return Ok(Type::Path(ty));
+                } else {
+                    return Ok(Type::Path(TypePath {
+                        qself: Some(QSelf {
+                            lt_token: Token![<](group.group_token.span),
+                            position: 0,
+                            as_token: None,
+                            gt_token: Token![>](group.group_token.span),
+                            ty: group.elem,
+                        }),
+                        path: Path::parse_helper(input, false)?,
+                    }));
+                }
+            } else if input.peek(Token![<]) && allow_group_generic
+                || input.peek(Token![::]) && input.peek3(Token![<])
+            {
+                if let Type::Path(mut ty) = *group.elem {
+                    let arguments = &mut ty.path.segments.last_mut().unwrap().arguments;
+                    if arguments.is_none() {
+                        *arguments = PathArguments::AngleBracketed(input.parse()?);
+                        Path::parse_rest(input, &mut ty.path, false)?;
+                        return Ok(Type::Path(ty));
+                    } else {
+                        group.elem = Box::new(Type::Path(ty));
+                    }
+                }
+            }
+            return Ok(Type::Group(group));
+        }
+
+        let mut lifetimes = None::<BoundLifetimes>;
+        let mut lookahead = input.lookahead1();
+        if lookahead.peek(Token![for]) {
+            lifetimes = input.parse()?;
+            lookahead = input.lookahead1();
+            if !lookahead.peek(Ident)
+                && !lookahead.peek(Token![fn])
+                && !lookahead.peek(Token![unsafe])
+                && !lookahead.peek(Token![extern])
+                && !lookahead.peek(Token![super])
+                && !lookahead.peek(Token![self])
+                && !lookahead.peek(Token![Self])
+                && !lookahead.peek(Token![crate])
+                || input.peek(Token![dyn])
+            {
+                return Err(lookahead.error());
+            }
+        }
+
+        if lookahead.peek(token::Paren) {
+            let content;
+            let paren_token = parenthesized!(content in input);
+            if content.is_empty() {
+                return Ok(Type::Tuple(TypeTuple {
+                    paren_token,
+                    elems: Punctuated::new(),
+                }));
+            }
+            if content.peek(Lifetime) {
+                return Ok(Type::Paren(TypeParen {
+                    paren_token,
+                    elem: Box::new(Type::TraitObject(content.parse()?)),
+                }));
+            }
+            if content.peek(Token![?]) {
+                return Ok(Type::TraitObject(TypeTraitObject {
+                    dyn_token: None,
+                    bounds: {
+                        let mut bounds = Punctuated::new();
+                        bounds.push_value(TypeParamBound::Trait(TraitBound {
+                            paren_token: Some(paren_token),
+                            ..content.parse()?
+                        }));
+                        while let Some(plus) = input.parse()? {
+                            bounds.push_punct(plus);
+                            bounds.push_value({
+                                let allow_precise_capture = false;
+                                let allow_const = false;
+                                TypeParamBound::parse_single(
+                                    input,
+                                    allow_precise_capture,
+                                    allow_const,
+                                )?
+                            });
+                        }
+                        bounds
+                    },
+                }));
+            }
+            let mut first: Type = content.parse()?;
+            if content.peek(Token![,]) {
+                return Ok(Type::Tuple(TypeTuple {
+                    paren_token,
+                    elems: {
+                        let mut elems = Punctuated::new();
+                        elems.push_value(first);
+                        elems.push_punct(content.parse()?);
+                        while !content.is_empty() {
+                            elems.push_value(content.parse()?);
+                            if content.is_empty() {
+                                break;
+                            }
+                            elems.push_punct(content.parse()?);
+                        }
+                        elems
+                    },
+                }));
+            }
+            if allow_plus && input.peek(Token![+]) {
+                loop {
+                    let first = match first {
+                        Type::Path(TypePath { qself: None, path }) => {
+                            TypeParamBound::Trait(TraitBound {
+                                paren_token: Some(paren_token),
+                                modifier: TraitBoundModifier::None,
+                                lifetimes: None,
+                                path,
+                            })
+                        }
+                        Type::TraitObject(TypeTraitObject {
+                            dyn_token: None,
+                            bounds,
+                        }) => {
+                            if bounds.len() > 1 || bounds.trailing_punct() {
+                                first = Type::TraitObject(TypeTraitObject {
+                                    dyn_token: None,
+                                    bounds,
+                                });
+                                break;
+                            }
+                            match bounds.into_iter().next().unwrap() {
+                                TypeParamBound::Trait(trait_bound) => {
+                                    TypeParamBound::Trait(TraitBound {
+                                        paren_token: Some(paren_token),
+                                        ..trait_bound
+                                    })
+                                }
+                                other @ (TypeParamBound::Lifetime(_)
+                                | TypeParamBound::PreciseCapture(_)
+                                | TypeParamBound::Verbatim(_)) => other,
+                            }
+                        }
+                        _ => break,
+                    };
+                    return Ok(Type::TraitObject(TypeTraitObject {
+                        dyn_token: None,
+                        bounds: {
+                            let mut bounds = Punctuated::new();
+                            bounds.push_value(first);
+                            while let Some(plus) = input.parse()? {
+                                bounds.push_punct(plus);
+                                bounds.push_value({
+                                    let allow_precise_capture = false;
+                                    let allow_const = false;
+                                    TypeParamBound::parse_single(
+                                        input,
+                                        allow_precise_capture,
+                                        allow_const,
+                                    )?
+                                });
+                            }
+                            bounds
+                        },
+                    }));
+                }
+            }
+            Ok(Type::Paren(TypeParen {
+                paren_token,
+                elem: Box::new(first),
+            }))
+        } else if lookahead.peek(Token![fn])
+            || lookahead.peek(Token![unsafe])
+            || lookahead.peek(Token![extern])
+        {
+            let mut bare_fn: TypeBareFn = input.parse()?;
+            bare_fn.lifetimes = lifetimes;
+            Ok(Type::BareFn(bare_fn))
+        } else if lookahead.peek(Ident)
+            || input.peek(Token![super])
+            || input.peek(Token![self])
+            || input.peek(Token![Self])
+            || input.peek(Token![crate])
+            || lookahead.peek(Token![::])
+            || lookahead.peek(Token![<])
+        {
+            let ty: TypePath = input.parse()?;
+            if ty.qself.is_some() {
+                return Ok(Type::Path(ty));
+            }
+
+            if input.peek(Token![!]) && !input.peek(Token![!=]) && ty.path.is_mod_style() {
+                let bang_token: Token![!] = input.parse()?;
+                let (delimiter, tokens) = mac::parse_delimiter(input)?;
+                return Ok(Type::Macro(TypeMacro {
+                    mac: Macro {
+                        path: ty.path,
+                        bang_token,
+                        delimiter,
+                        tokens,
+                    },
+                }));
+            }
+
+            if lifetimes.is_some() || allow_plus && input.peek(Token![+]) {
+                let mut bounds = Punctuated::new();
+                bounds.push_value(TypeParamBound::Trait(TraitBound {
+                    paren_token: None,
+                    modifier: TraitBoundModifier::None,
+                    lifetimes,
+                    path: ty.path,
+                }));
+                if allow_plus {
+                    while input.peek(Token![+]) {
+                        bounds.push_punct(input.parse()?);
+                        if !(input.peek(Ident::peek_any)
+                            || input.peek(Token![::])
+                            || input.peek(Token![?])
+                            || input.peek(Lifetime)
+                            || input.peek(token::Paren))
+                        {
+                            break;
+                        }
+                        bounds.push_value({
+                            let allow_precise_capture = false;
+                            let allow_const = false;
+                            TypeParamBound::parse_single(input, allow_precise_capture, allow_const)?
+                        });
+                    }
+                }
+                return Ok(Type::TraitObject(TypeTraitObject {
+                    dyn_token: None,
+                    bounds,
+                }));
+            }
+
+            Ok(Type::Path(ty))
+        } else if lookahead.peek(Token![dyn]) {
+            let dyn_token: Token![dyn] = input.parse()?;
+            let dyn_span = dyn_token.span;
+            let star_token: Option<Token![*]> = input.parse()?;
+            let bounds = TypeTraitObject::parse_bounds(dyn_span, input, allow_plus)?;
+            Ok(if star_token.is_some() {
+                Type::Verbatim(verbatim::between(&begin, input))
+            } else {
+                Type::TraitObject(TypeTraitObject {
+                    dyn_token: Some(dyn_token),
+                    bounds,
+                })
+            })
+        } else if lookahead.peek(token::Bracket) {
+            let content;
+            let bracket_token = bracketed!(content in input);
+            let elem: Type = content.parse()?;
+            if content.peek(Token![;]) {
+                Ok(Type::Array(TypeArray {
+                    bracket_token,
+                    elem: Box::new(elem),
+                    semi_token: content.parse()?,
+                    len: content.parse()?,
+                }))
+            } else {
+                Ok(Type::Slice(TypeSlice {
+                    bracket_token,
+                    elem: Box::new(elem),
+                }))
+            }
+        } else if lookahead.peek(Token![*]) {
+            input.parse().map(Type::Ptr)
+        } else if lookahead.peek(Token![&]) {
+            input.parse().map(Type::Reference)
+        } else if lookahead.peek(Token![!]) && !input.peek(Token![=]) {
+            input.parse().map(Type::Never)
+        } else if lookahead.peek(Token![impl]) {
+            TypeImplTrait::parse(input, allow_plus).map(Type::ImplTrait)
+        } else if lookahead.peek(Token![_]) {
+            input.parse().map(Type::Infer)
+        } else if lookahead.peek(Lifetime) {
+            input.parse().map(Type::TraitObject)
+        } else {
+            Err(lookahead.error())
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypeSlice {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let content;
+            Ok(TypeSlice {
+                bracket_token: bracketed!(content in input),
+                elem: content.parse()?,
+            })
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypeArray {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let content;
+            Ok(TypeArray {
+                bracket_token: bracketed!(content in input),
+                elem: content.parse()?,
+                semi_token: content.parse()?,
+                len: content.parse()?,
+            })
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypePtr {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let star_token: Token![*] = input.parse()?;
+
+            let lookahead = input.lookahead1();
+            let (const_token, mutability) = if lookahead.peek(Token![const]) {
+                (Some(input.parse()?), None)
+            } else if lookahead.peek(Token![mut]) {
+                (None, Some(input.parse()?))
+            } else {
+                return Err(lookahead.error());
+            };
+
+            Ok(TypePtr {
+                star_token,
+                const_token,
+                mutability,
+                elem: Box::new(input.call(Type::without_plus)?),
+            })
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypeReference {
+        fn parse(input: ParseStream) -> Result<Self> {
+            Ok(TypeReference {
+                and_token: input.parse()?,
+                lifetime: input.parse()?,
+                mutability: input.parse()?,
+                // & binds tighter than +, so we don't allow + here.
+                elem: Box::new(input.call(Type::without_plus)?),
+            })
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypeBareFn {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let args;
+            let mut variadic = None;
+
+            Ok(TypeBareFn {
+                lifetimes: input.parse()?,
+                unsafety: input.parse()?,
+                abi: input.parse()?,
+                fn_token: input.parse()?,
+                paren_token: parenthesized!(args in input),
+                inputs: {
+                    let mut inputs = Punctuated::new();
+
+                    while !args.is_empty() {
+                        let attrs = args.call(Attribute::parse_outer)?;
+
+                        if inputs.empty_or_trailing()
+                            && (args.peek(Token![...])
+                                || (args.peek(Ident) || args.peek(Token![_]))
+                                    && args.peek2(Token![:])
+                                    && args.peek3(Token![...]))
+                        {
+                            variadic = Some(parse_bare_variadic(&args, attrs)?);
+                            break;
+                        }
+
+                        let allow_self = inputs.is_empty();
+                        let arg = parse_bare_fn_arg(&args, allow_self)?;
+                        inputs.push_value(BareFnArg { attrs, ..arg });
+                        if args.is_empty() {
+                            break;
+                        }
+
+                        let comma = args.parse()?;
+                        inputs.push_punct(comma);
+                    }
+
+                    inputs
+                },
+                variadic,
+                output: input.call(ReturnType::without_plus)?,
+            })
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypeNever {
+        fn parse(input: ParseStream) -> Result<Self> {
+            Ok(TypeNever {
+                bang_token: input.parse()?,
+            })
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypeInfer {
+        fn parse(input: ParseStream) -> Result<Self> {
+            Ok(TypeInfer {
+                underscore_token: input.parse()?,
+            })
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypeTuple {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let content;
+            let paren_token = parenthesized!(content in input);
+
+            if content.is_empty() {
+                return Ok(TypeTuple {
+                    paren_token,
+                    elems: Punctuated::new(),
+                });
+            }
+
+            let first: Type = content.parse()?;
+            Ok(TypeTuple {
+                paren_token,
+                elems: {
+                    let mut elems = Punctuated::new();
+                    elems.push_value(first);
+                    elems.push_punct(content.parse()?);
+                    while !content.is_empty() {
+                        elems.push_value(content.parse()?);
+                        if content.is_empty() {
+                            break;
+                        }
+                        elems.push_punct(content.parse()?);
+                    }
+                    elems
+                },
+            })
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypeMacro {
+        fn parse(input: ParseStream) -> Result<Self> {
+            Ok(TypeMacro {
+                mac: input.parse()?,
+            })
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypePath {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let expr_style = false;
+            let (qself, path) = path::parsing::qpath(input, expr_style)?;
+            Ok(TypePath { qself, path })
+        }
+    }
+
+    impl ReturnType {
+        #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+        pub fn without_plus(input: ParseStream) -> Result<Self> {
+            let allow_plus = false;
+            Self::parse(input, allow_plus)
+        }
+
+        pub(crate) fn parse(input: ParseStream, allow_plus: bool) -> Result<Self> {
+            if input.peek(Token![->]) {
+                let arrow = input.parse()?;
+                let allow_group_generic = true;
+                let ty = ambig_ty(input, allow_plus, allow_group_generic)?;
+                Ok(ReturnType::Type(arrow, Box::new(ty)))
+            } else {
+                Ok(ReturnType::Default)
+            }
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for ReturnType {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let allow_plus = true;
+            Self::parse(input, allow_plus)
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypeTraitObject {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let allow_plus = true;
+            Self::parse(input, allow_plus)
+        }
+    }
+
+    impl TypeTraitObject {
+        #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+        pub fn without_plus(input: ParseStream) -> Result<Self> {
+            let allow_plus = false;
+            Self::parse(input, allow_plus)
+        }
+
+        // Only allow multiple trait references if allow_plus is true.
+        pub(crate) fn parse(input: ParseStream, allow_plus: bool) -> Result<Self> {
+            let dyn_token: Option<Token![dyn]> = input.parse()?;
+            let dyn_span = match &dyn_token {
+                Some(token) => token.span,
+                None => input.span(),
+            };
+            let bounds = Self::parse_bounds(dyn_span, input, allow_plus)?;
+            Ok(TypeTraitObject { dyn_token, bounds })
+        }
+
+        fn parse_bounds(
+            dyn_span: Span,
+            input: ParseStream,
+            allow_plus: bool,
+        ) -> Result<Punctuated<TypeParamBound, Token![+]>> {
+            let allow_precise_capture = false;
+            let allow_const = false;
+            let bounds = TypeParamBound::parse_multiple(
+                input,
+                allow_plus,
+                allow_precise_capture,
+                allow_const,
+            )?;
+            let mut last_lifetime_span = None;
+            let mut at_least_one_trait = false;
+            for bound in &bounds {
+                match bound {
+                    TypeParamBound::Trait(_) => {
+                        at_least_one_trait = true;
+                        break;
+                    }
+                    TypeParamBound::Lifetime(lifetime) => {
+                        last_lifetime_span = Some(lifetime.ident.span());
+                    }
+                    TypeParamBound::PreciseCapture(_) | TypeParamBound::Verbatim(_) => {
+                        unreachable!()
+                    }
+                }
+            }
+            // Just lifetimes like `'a + 'b` is not a TraitObject.
+            if !at_least_one_trait {
+                let msg = "at least one trait is required for an object type";
+                return Err(error::new2(dyn_span, last_lifetime_span.unwrap(), msg));
+            }
+            Ok(bounds)
+        }
+    }
+
+    #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+    impl Parse for TypeImplTrait {
+        fn parse(input: ParseStream) -> Result<Self> {
+            let allow_plus = true;
+            Self::parse(input, allow_plus)
+        }
+    }
+
+    impl TypeImplTrait {
+        #[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
+        pub fn without_plus(input: ParseStream) -> Result<Self> {
+            let allow_plus = false;
+            Self::parse(input, allow_plus)
+        }
+
+        pub(crate) fn parse(input: ParseStream, allow_plus: bool) -> Result<Self> {
+            let impl_token: Token![impl] = input.parse()?;
+            let allow_precise_capture = true;
+            let allow_const = true;
+            let bounds = TypeParamBound::parse_multiple(
+                input,
+                allow_plus,
+                allow_precise_capture,
+                allow_const,
+            )?;
+            let mut last_nontrait_span = None;
+            let mut at_least_one_trait = false;
+            for bound in &bounds {
+                match bound {
+                    TypeParamBound::Trait(_) => {
+                        at_least_one_trait = true;
+                        break;
+                    }
+                    TypeParamBound::Lifetime(lifetime) => {
+                        last_nontrait_span = Some(lifetime.ident.span());
+                    }
+                    TypeParamBound::PreciseCapture(precise_capture) => {
+                        #[cfg(feature = "full")]
+                        {
+                            last_nontrait_span = Some(precise_capture.gt_token.span);