Add structopt dependency in version 0.3.7

This patch series replaces argparse with structopt in the argument
handling code. As a first step, we need structopt as a dependency.

Import subrepo structopt/:structopt at efbdda4753592e27bc430fb01f7b9650b2f3174d
Import subrepo bitflags/:bitflags at 30668016aca6bd3b02c766e8347e0b4080d4c296
Import subrepo clap/:clap at 784524f7eb193e35f81082cc69454c8c21b948f7
Import subrepo heck/:heck at 093d56fbf001e1506e56dbfa38631d99b1066df1
Import subrepo proc-macro-error/:proc-macro-error at 6c4cfe79a622c5de8ae68557993542be46eacae2
Import subrepo proc-macro2/:proc-macro2 at d5d48eddca4566e5438e8a2cbed4a74e049544de
Import subrepo quote/:quote at 727436c6c137b20f0f34dde5d8fda2679b9747ad
Import subrepo rustversion/:rustversion at 0c5663313516263059ce9059ef81fc7a1cf655ca
Import subrepo syn-mid/:syn-mid at 5d3d85414a9e6674e1857ec22a87b96e04a6851a
Import subrepo syn/:syn at e87c27e87f6f4ef8919d0372bdb056d53ef0d8f3
Import subrepo textwrap/:textwrap at abcd618beae3f74841032aa5b53c1086b0a57ca2
Import subrepo unicode-segmentation/:unicode-segmentation at 637c9874c4fe0c205ff27787faf150a40295c6c3
Import subrepo unicode-width/:unicode-width at 3033826f8bf05e82724140a981d5941e48fce393
Import subrepo unicode-xid/:unicode-xid at 4baae9fffb156ba229665b972a9cd5991787ceb7

7 files changed, 1920 insertions, 0 deletions

diff --git a/quote/src/ext.rs b/quote/src/ext.rs
new file mode 100644
index 0000000..9e9b4a5
--- /dev/null
+++ b/quote/src/ext.rs
@@ -0,0 +1,112 @@
+use super::ToTokens;
+
+use std::iter;
+
+use proc_macro2::{TokenStream, TokenTree};
+
+/// TokenStream extension trait with methods for appending tokens.
+///
+/// This trait is sealed and cannot be implemented outside of the `quote` crate.
+pub trait TokenStreamExt: private::Sealed {
+    /// For use by `ToTokens` implementations.
+    ///
+    /// Appends the token specified to this list of tokens.
+    fn append<U>(&mut self, token: U)
+    where
+        U: Into<TokenTree>;
+
+    /// For use by `ToTokens` implementations.
+    ///
+    /// ```
+    /// # use quote::{quote, TokenStreamExt, ToTokens};
+    /// # use proc_macro2::TokenStream;
+    /// #
+    /// struct X;
+    ///
+    /// impl ToTokens for X {
+    ///     fn to_tokens(&self, tokens: &mut TokenStream) {
+    ///         tokens.append_all(&[true, false]);
+    ///     }
+    /// }
+    ///
+    /// let tokens = quote!(#X);
+    /// assert_eq!(tokens.to_string(), "true false");
+    /// ```
+    fn append_all<I>(&mut self, iter: I)
+    where
+        I: IntoIterator,
+        I::Item: ToTokens;
+
+    /// For use by `ToTokens` implementations.
+    ///
+    /// Appends all of the items in the iterator `I`, separated by the tokens
+    /// `U`.
+    fn append_separated<I, U>(&mut self, iter: I, op: U)
+    where
+        I: IntoIterator,
+        I::Item: ToTokens,
+        U: ToTokens;
+
+    /// For use by `ToTokens` implementations.
+    ///
+    /// Appends all tokens in the iterator `I`, appending `U` after each
+    /// element, including after the last element of the iterator.
+    fn append_terminated<I, U>(&mut self, iter: I, term: U)
+    where
+        I: IntoIterator,
+        I::Item: ToTokens,
+        U: ToTokens;
+}
+
+impl TokenStreamExt for TokenStream {
+    fn append<U>(&mut self, token: U)
+    where
+        U: Into<TokenTree>,
+    {
+        self.extend(iter::once(token.into()));
+    }
+
+    fn append_all<I>(&mut self, iter: I)
+    where
+        I: IntoIterator,
+        I::Item: ToTokens,
+    {
+        for token in iter {
+            token.to_tokens(self);
+        }
+    }
+
+    fn append_separated<I, U>(&mut self, iter: I, op: U)
+    where
+        I: IntoIterator,
+        I::Item: ToTokens,
+        U: ToTokens,
+    {
+        for (i, token) in iter.into_iter().enumerate() {
+            if i > 0 {
+                op.to_tokens(self);
+            }
+            token.to_tokens(self);
+        }
+    }
+
+    fn append_terminated<I, U>(&mut self, iter: I, term: U)
+    where
+        I: IntoIterator,
+        I::Item: ToTokens,
+        U: ToTokens,
+    {
+        for token in iter {
+            token.to_tokens(self);
+            term.to_tokens(self);
+        }
+    }
+}
+
+mod private {
+    use proc_macro2::TokenStream;
+
+    pub trait Sealed {}
+
+    impl Sealed for TokenStream {}
+}
diff --git a/quote/src/format.rs b/quote/src/format.rs
new file mode 100644
index 0000000..13c8811
--- /dev/null
+++ b/quote/src/format.rs
@@ -0,0 +1,164 @@
+/// Formatting macro for constructing `Ident`s.
+///
+/// <br>
+///
+/// # Syntax
+///
+/// Syntax is copied from the [`format!`] macro, supporting both positional and
+/// named arguments.
+///
+/// Only a limited set of formatting traits are supported. The current mapping
+/// of format types to traits is:
+///
+/// * `{}` ⇒ [`IdentFragment`]
+/// * `{:o}` ⇒ [`Octal`](`std::fmt::Octal`)
+/// * `{:x}` ⇒ [`LowerHex`](`std::fmt::LowerHex`)
+/// * `{:X}` ⇒ [`UpperHex`](`std::fmt::UpperHex`)
+/// * `{:b}` ⇒ [`Binary`](`std::fmt::Binary`)
+///
+/// See [`std::fmt`] for more information.
+///
+/// <br>
+///
+/// # IdentFragment
+///
+/// Unlike `format!`, this macro uses the [`IdentFragment`] formatting trait by
+/// default. This trait is like `Display`, with a few differences:
+///
+/// * `IdentFragment` is only implemented for a limited set of types, such as
+///    unsigned integers and strings.
+/// * [`Ident`] arguments will have their `r#` prefixes stripped, if present.
+///
+/// [`Ident`]: `proc_macro2::Ident`
+///
+/// <br>
+///
+/// # Hygiene
+///
+/// The [`Span`] of the first `Ident` argument is used as the span of the final
+/// identifier, falling back to [`Span::call_site`] when no identifiers are
+/// provided.
+///
+/// ```
+/// # use quote::format_ident;
+/// # let ident = format_ident!("Ident");
+/// // If `ident` is an Ident, the span of `my_ident` will be inherited from it.
+/// let my_ident = format_ident!("My{}{}", ident, "IsCool");
+/// assert_eq!(my_ident, "MyIdentIsCool");
+/// ```
+///
+/// Alternatively, the span can be overridden by passing the `span` named
+/// argument.
+///
+/// ```
+/// # use quote::format_ident;
+/// # const IGNORE_TOKENS: &'static str = stringify! {
+/// let my_span = /* ... */;
+/// # };
+/// # let my_span = proc_macro2::Span::call_site();
+/// format_ident!("MyIdent", span = my_span);
+/// ```
+///
+/// [`Span`]: `proc_macro2::Span`
+/// [`Span::call_site`]: `proc_macro2::Span::call_site`
+///
+/// <p><br></p>
+///
+/// # Panics
+///
+/// This method will panic if the resulting formatted string is not a valid
+/// identifier.
+///
+/// <br>
+///
+/// # Examples
+///
+/// Composing raw and non-raw identifiers:
+/// ```
+/// # use quote::format_ident;
+/// let my_ident = format_ident!("My{}", "Ident");
+/// assert_eq!(my_ident, "MyIdent");
+///
+/// let raw = format_ident!("r#Raw");
+/// assert_eq!(raw, "r#Raw");
+///
+/// let my_ident_raw = format_ident!("{}Is{}", my_ident, raw);
+/// assert_eq!(my_ident_raw, "MyIdentIsRaw");
+/// ```
+///
+/// Integer formatting options:
+/// ```
+/// # use quote::format_ident;
+/// let num: u32 = 10;
+///
+/// let decimal = format_ident!("Id_{}", num);
+/// assert_eq!(decimal, "Id_10");
+///
+/// let octal = format_ident!("Id_{:o}", num);
+/// assert_eq!(octal, "Id_12");
+///
+/// let binary = format_ident!("Id_{:b}", num);
+/// assert_eq!(binary, "Id_1010");
+///
+/// let lower_hex = format_ident!("Id_{:x}", num);
+/// assert_eq!(lower_hex, "Id_a");
+///
+/// let upper_hex = format_ident!("Id_{:X}", num);
+/// assert_eq!(upper_hex, "Id_A");
+/// ```
+#[macro_export]
+macro_rules! format_ident {
+    ($fmt:expr) => {
+        $crate::format_ident_impl!([
+            ::std::option::Option::None,
+            $fmt
+        ])
+    };
+
+    ($fmt:expr, $($rest:tt)*) => {
+        $crate::format_ident_impl!([
+            ::std::option::Option::None,
+            $fmt
+        ] $($rest)*)
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! format_ident_impl {
+    // Final state
+    ([$span:expr, $($fmt:tt)*]) => {
+        $crate::__rt::mk_ident(&format!($($fmt)*), $span)
+    };
+
+    // Span argument
+    ([$old:expr, $($fmt:tt)*] span = $span:expr) => {
+        $crate::format_ident_impl!([$old, $($fmt)*] span = $span,)
+    };
+    ([$old:expr, $($fmt:tt)*] span = $span:expr, $($rest:tt)*) => {
+        $crate::format_ident_impl!([
+            ::std::option::Option::Some::<$crate::__rt::Span>($span),
+            $($fmt)*
+        ] $($rest)*)
+    };
+
+    // Named argument
+    ([$span:expr, $($fmt:tt)*] $name:ident = $arg:expr) => {
+        $crate::format_ident_impl!([$span, $($fmt)*] $name = $arg,)
+    };
+    ([$span:expr, $($fmt:tt)*] $name:ident = $arg:expr, $($rest:tt)*) => {
+        match $crate::__rt::IdentFragmentAdapter(&$arg) {
+            arg => $crate::format_ident_impl!([$span.or(arg.span()), $($fmt)*, $name = arg] $($rest)*),
+        }
+    };
+
+    // Positional argument
+    ([$span:expr, $($fmt:tt)*] $arg:expr) => {
+        $crate::format_ident_impl!([$span, $($fmt)*] $arg,)
+    };
+    ([$span:expr, $($fmt:tt)*] $arg:expr, $($rest:tt)*) => {
+        match $crate::__rt::IdentFragmentAdapter(&$arg) {
+            arg => $crate::format_ident_impl!([$span.or(arg.span()), $($fmt)*, arg] $($rest)*),
+        }
+    };
+}
diff --git a/quote/src/ident_fragment.rs b/quote/src/ident_fragment.rs
new file mode 100644
index 0000000..09ead65
--- /dev/null
+++ b/quote/src/ident_fragment.rs
@@ -0,0 +1,72 @@
+use proc_macro2::{Ident, Span};
+use std::fmt;
+
+/// Specialized formatting trait used by `format_ident!`.
+///
+/// [`Ident`] arguments formatted using this trait will have their `r#` prefix
+/// stripped, if present.
+///
+/// See [`format_ident!`] for more information.
+pub trait IdentFragment {
+    /// Format this value as an identifier fragment.
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result;
+
+    /// Span associated with this `IdentFragment`.
+    ///
+    /// If non-`None`, may be inherited by formatted identifiers.
+    fn span(&self) -> Option<Span> {
+        None
+    }
+}
+
+impl<'a, T: IdentFragment + ?Sized> IdentFragment for &'a T {
+    fn span(&self) -> Option<Span> {
+        <T as IdentFragment>::span(*self)
+    }
+
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        IdentFragment::fmt(*self, f)
+    }
+}
+
+impl<'a, T: IdentFragment + ?Sized> IdentFragment for &'a mut T {
+    fn span(&self) -> Option<Span> {
+        <T as IdentFragment>::span(*self)
+    }
+
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        IdentFragment::fmt(*self, f)
+    }
+}
+
+impl IdentFragment for Ident {
+    fn span(&self) -> Option<Span> {
+        Some(self.span())
+    }
+
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let id = self.to_string();
+        if id.starts_with("r#") {
+            fmt::Display::fmt(&id[2..], f)
+        } else {
+            fmt::Display::fmt(&id[..], f)
+        }
+    }
+}
+
+// Limited set of types which this is implemented for, as we want to avoid types
+// which will often include non-identifier characters in their `Display` impl.
+macro_rules! ident_fragment_display {
+    ($($T:ty),*) => {
+        $(
+            impl IdentFragment for $T {
+                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                    fmt::Display::fmt(self, f)
+                }
+            }
+        )*
+    }
+}
+
+ident_fragment_display!(bool, str, String);
+ident_fragment_display!(u8, u16, u32, u64, u128, usize);
diff --git a/quote/src/lib.rs b/quote/src/lib.rs
new file mode 100644
index 0000000..3341a16
--- /dev/null
+++ b/quote/src/lib.rs
@@ -0,0 +1,948 @@
+//! This crate provides the [`quote!`] macro for turning Rust syntax tree data
+//! structures into tokens of source code.
+//!
+//! [`quote!`]: macro.quote.html
+//!
+//! Procedural macros in Rust receive a stream of tokens as input, execute
+//! arbitrary Rust code to determine how to manipulate those tokens, and produce
+//! a stream of tokens to hand back to the compiler to compile into the caller's
+//! crate. Quasi-quoting is a solution to one piece of that &mdash; producing
+//! tokens to return to the compiler.
+//!
+//! The idea of quasi-quoting is that we write *code* that we treat as *data*.
+//! Within the `quote!` macro, we can write what looks like code to our text
+//! editor or IDE. We get all the benefits of the editor's brace matching,
+//! syntax highlighting, indentation, and maybe autocompletion. But rather than
+//! compiling that as code into the current crate, we can treat it as data, pass
+//! it around, mutate it, and eventually hand it back to the compiler as tokens
+//! to compile into the macro caller's crate.
+//!
+//! This crate is motivated by the procedural macro use case, but is a
+//! general-purpose Rust quasi-quoting library and is not specific to procedural
+//! macros.
+//!
+//! ```toml
+//! [dependencies]
+//! quote = "1.0"
+//! ```
+//!
+//! <br>
+//!
+//! # Example
+//!
+//! The following quasi-quoted block of code is something you might find in [a]
+//! procedural macro having to do with data structure serialization. The `#var`
+//! syntax performs interpolation of runtime variables into the quoted tokens.
+//! Check out the documentation of the [`quote!`] macro for more detail about
+//! the syntax. See also the [`quote_spanned!`] macro which is important for
+//! implementing hygienic procedural macros.
+//!
+//! [a]: https://serde.rs/
+//! [`quote_spanned!`]: macro.quote_spanned.html
+//!
+//! ```
+//! # use quote::quote;
+//! #
+//! # let generics = "";
+//! # let where_clause = "";
+//! # let field_ty = "";
+//! # let item_ty = "";
+//! # let path = "";
+//! # let value = "";
+//! #
+//! let tokens = quote! {
+//!     struct SerializeWith #generics #where_clause {
+//!         value: &'a #field_ty,
+//!         phantom: core::marker::PhantomData<#item_ty>,
+//!     }
+//!
+//!     impl #generics serde::Serialize for SerializeWith #generics #where_clause {
+//!         fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+//!         where
+//!             S: serde::Serializer,
+//!         {
+//!             #path(self.value, serializer)
+//!         }
+//!     }
+//!
+//!     SerializeWith {
+//!         value: #value,
+//!         phantom: core::marker::PhantomData::<#item_ty>,
+//!     }
+//! };
+//! ```
+
+// Quote types in rustdoc of other crates get linked to here.
+#![doc(html_root_url = "https://docs.rs/quote/1.0.2")]
+
+#[cfg(all(
+    not(all(target_arch = "wasm32", target_os = "unknown")),
+    feature = "proc-macro"
+))]
+extern crate proc_macro;
+
+mod ext;
+mod format;
+mod ident_fragment;
+mod to_tokens;
+
+// Not public API.
+#[doc(hidden)]
+#[path = "runtime.rs"]
+pub mod __rt;
+
+pub use crate::ext::TokenStreamExt;
+pub use crate::ident_fragment::IdentFragment;
+pub use crate::to_tokens::ToTokens;
+
+// Not public API.
+#[doc(hidden)]
+pub mod spanned;
+
+/// The whole point.
+///
+/// Performs variable interpolation against the input and produces it as
+/// [`proc_macro2::TokenStream`].
+///
+/// Note: for returning tokens to the compiler in a procedural macro, use
+/// `.into()` on the result to convert to [`proc_macro::TokenStream`].
+///
+/// [`TokenStream`]: https://docs.rs/proc-macro2/1.0/proc_macro2/struct.TokenStream.html
+///
+/// <br>
+///
+/// # Interpolation
+///
+/// Variable interpolation is done with `#var` (similar to `$var` in
+/// `macro_rules!` macros). This grabs the `var` variable that is currently in
+/// scope and inserts it in that location in the output tokens. Any type
+/// implementing the [`ToTokens`] trait can be interpolated. This includes most
+/// Rust primitive types as well as most of the syntax tree types from the [Syn]
+/// crate.
+///
+/// [`ToTokens`]: trait.ToTokens.html
+/// [Syn]: https://github.com/dtolnay/syn
+///
+/// Repetition is done using `#(...)*` or `#(...),*` again similar to
+/// `macro_rules!`. This iterates through the elements of any variable
+/// interpolated within the repetition and inserts a copy of the repetition body
+/// for each one. The variables in an interpolation may be a `Vec`, slice,
+/// `BTreeSet`, or any `Iterator`.
+///
+/// - `#(#var)*` — no separators
+/// - `#(#var),*` — the character before the asterisk is used as a separator
+/// - `#( struct #var; )*` — the repetition can contain other tokens
+/// - `#( #k => println!("{}", #v), )*` — even multiple interpolations
+///
+/// <br>
+///
+/// # Hygiene
+///
+/// Any interpolated tokens preserve the `Span` information provided by their
+/// `ToTokens` implementation. Tokens that originate within the `quote!`
+/// invocation are spanned with [`Span::call_site()`].
+///
+/// [`Span::call_site()`]: https://docs.rs/proc-macro2/1.0/proc_macro2/struct.Span.html#method.call_site
+///
+/// A different span can be provided through the [`quote_spanned!`] macro.
+///
+/// [`quote_spanned!`]: macro.quote_spanned.html
+///
+/// <br>
+///
+/// # Return type
+///
+/// The macro evaluates to an expression of type `proc_macro2::TokenStream`.
+/// Meanwhile Rust procedural macros are expected to return the type
+/// `proc_macro::TokenStream`.
+///
+/// The difference between the two types is that `proc_macro` types are entirely
+/// specific to procedural macros and cannot ever exist in code outside of a
+/// procedural macro, while `proc_macro2` types may exist anywhere including
+/// tests and non-macro code like main.rs and build.rs. This is why even the
+/// procedural macro ecosystem is largely built around `proc_macro2`, because
+/// that ensures the libraries are unit testable and accessible in non-macro
+/// contexts.
+///
+/// There is a [`From`]-conversion in both directions so returning the output of
+/// `quote!` from a procedural macro usually looks like `tokens.into()` or
+/// `proc_macro::TokenStream::from(tokens)`.
+///
+/// [`From`]: https://doc.rust-lang.org/std/convert/trait.From.html
+///
+/// <br>
+///
+/// # Examples
+///
+/// ### Procedural macro
+///
+/// The structure of a basic procedural macro is as follows. Refer to the [Syn]
+/// crate for further useful guidance on using `quote!` as part of a procedural
+/// macro.
+///
+/// [Syn]: https://github.com/dtolnay/syn
+///
+/// ```
+/// # #[cfg(any())]
+/// extern crate proc_macro;
+/// # extern crate proc_macro2;
+///
+/// # #[cfg(any())]
+/// use proc_macro::TokenStream;
+/// # use proc_macro2::TokenStream;
+/// use quote::quote;
+///
+/// # const IGNORE_TOKENS: &'static str = stringify! {
+/// #[proc_macro_derive(HeapSize)]
+/// # };
+/// pub fn derive_heap_size(input: TokenStream) -> TokenStream {
+///     // Parse the input and figure out what implementation to generate...
+///     # const IGNORE_TOKENS: &'static str = stringify! {
+///     let name = /* ... */;
+///     let expr = /* ... */;
+///     # };
+///     #
+///     # let name = 0;
+///     # let expr = 0;
+///
+///     let expanded = quote! {
+///         // The generated impl.
+///         impl heapsize::HeapSize for #name {
+///             fn heap_size_of_children(&self) -> usize {
+///                 #expr
+///             }
+///         }
+///     };
+///
+///     // Hand the output tokens back to the compiler.
+///     TokenStream::from(expanded)
+/// }
+/// ```
+///
+/// <p><br></p>
+///
+/// ### Combining quoted fragments
+///
+/// Usually you don't end up constructing an entire final `TokenStream` in one
+/// piece. Different parts may come from different helper functions. The tokens
+/// produced by `quote!` themselves implement `ToTokens` and so can be
+/// interpolated into later `quote!` invocations to build up a final result.
+///
+/// ```
+/// # use quote::quote;
+/// #
+/// let type_definition = quote! {...};
+/// let methods = quote! {...};
+///
+/// let tokens = quote! {
+///     #type_definition
+///     #methods
+/// };
+/// ```
+///
+/// <p><br></p>
+///
+/// ### Constructing identifiers
+///
+/// Suppose we have an identifier `ident` which came from somewhere in a macro
+/// input and we need to modify it in some way for the macro output. Let's
+/// consider prepending the identifier with an underscore.
+///
+/// Simply interpolating the identifier next to an underscore will not have the
+/// behavior of concatenating them. The underscore and the identifier will
+/// continue to be two separate tokens as if you had written `_ x`.
+///
+/// ```
+/// # use proc_macro2::{self as syn, Span};
+/// # use quote::quote;
+/// #
+/// # let ident = syn::Ident::new("i", Span::call_site());
+/// #
+/// // incorrect
+/// quote! {
+///     let mut _#ident = 0;
+/// }
+/// # ;
+/// ```
+///
+/// The solution is to build a new identifier token with the correct value. As
+/// this is such a common case, the [`format_ident!`] macro provides a
+/// convenient utility for doing so correctly.
+///
+/// ```
+/// # use proc_macro2::{Ident, Span};
+/// # use quote::{format_ident, quote};
+/// #
+/// # let ident = Ident::new("i", Span::call_site());
+/// #
+/// let varname = format_ident!("_{}", ident);
+/// quote! {
+///     let mut #varname = 0;
+/// }
+/// # ;
+/// ```
+///
+/// Alternatively, the APIs provided by Syn and proc-macro2 can be used to
+/// directly build the identifier. This is roughly equivalent to the above, but
+/// will not handle `ident` being a raw identifier.
+///
+/// ```
+/// # use proc_macro2::{self as syn, Span};
+/// # use quote::quote;
+/// #
+/// # let ident = syn::Ident::new("i", Span::call_site());
+/// #
+/// let concatenated = format!("_{}", ident);
+/// let varname = syn::Ident::new(&concatenated, ident.span());
+/// quote! {
+///     let mut #varname = 0;
+/// }
+/// # ;
+/// ```
+///
+/// <p><br></p>
+///
+/// ### Making method calls
+///
+/// Let's say our macro requires some type specified in the macro input to have
+/// a constructor called `new`. We have the type in a variable called
+/// `field_type` of type `syn::Type` and want to invoke the constructor.
+///
+/// ```
+/// # use quote::quote;
+/// #
+/// # let field_type = quote!(...);
+/// #
+/// // incorrect
+/// quote! {
+///     let value = #field_type::new();
+/// }
+/// # ;
+/// ```
+///
+/// This works only sometimes. If `field_type` is `String`, the expanded code
+/// contains `String::new()` which is fine. But if `field_type` is something
+/// like `Vec<i32>` then the expanded code is `Vec<i32>::new()` which is invalid
+/// syntax. Ordinarily in handwritten Rust we would write `Vec::<i32>::new()`
+/// but for macros often the following is more convenient.
+///
+/// ```
+/// # use quote::quote;
+/// #
+/// # let field_type = quote!(...);
+/// #
+/// quote! {
+///     let value = <#field_type>::new();
+/// }
+/// # ;
+/// ```
+///
+/// This expands to `<Vec<i32>>::new()` which behaves correctly.
+///
+/// A similar pattern is appropriate for trait methods.
+///
+/// ```
+/// # use quote::quote;
+/// #
+/// # let field_type = quote!(...);
+/// #
+/// quote! {
+///     let value = <#field_type as core::default::Default>::default();
+/// }
+/// # ;
+/// ```
+///
+/// <p><br></p>
+///
+/// ### Interpolating text inside of doc comments
+///
+/// Neither doc comments nor string literals get interpolation behavior in
+/// quote:
+///
+/// ```compile_fail
+/// quote! {
+///     /// try to interpolate: #ident
+///     ///
+///     /// ...
+/// }
+/// ```
+///
+/// ```compile_fail
+/// quote! {
+///     #[doc = "try to interpolate: #ident"]
+/// }
+/// ```
+///
+/// Macro calls in a doc attribute are not valid syntax:
+///
+/// ```compile_fail
+/// quote! {
+///     #[doc = concat!("try to interpolate: ", stringify!(#ident))]
+/// }
+/// ```
+///
+/// Instead the best way to build doc comments that involve variables is by
+/// formatting the doc string literal outside of quote.
+///
+/// ```rust
+/// # use proc_macro2::{Ident, Span};
+/// # use quote::quote;
+/// #
+/// # const IGNORE: &str = stringify! {
+/// let msg = format!(...);
+/// # };
+/// #
+/// # let ident = Ident::new("var", Span::call_site());
+/// # let msg = format!("try to interpolate: {}", ident);
+/// quote! {
+///     #[doc = #msg]
+///     ///
+///     /// ...
+/// }
+/// # ;
+/// ```
+///
+/// <p><br></p>
+///
+/// ### Indexing into a tuple struct
+///
+/// When interpolating indices of a tuple or tuple struct, we need them not to
+/// appears suffixed as integer literals by interpolating them as [`syn::Index`]
+/// instead.
+///
+/// [`syn::Index`]: https://docs.rs/syn/1.0/syn/struct.Index.html
+///
+/// ```compile_fail
+/// let i = 0usize..self.fields.len();
+///
+/// // expands to 0 + self.0usize.heap_size() + self.1usize.heap_size() + ...
+/// // which is not valid syntax
+/// quote! {
+///     0 #( + self.#i.heap_size() )*
+/// }
+/// ```
+///
+/// ```
+/// # use proc_macro2::{Ident, TokenStream};
+/// # use quote::quote;
+/// #
+/// # mod syn {
+/// #     use proc_macro2::{Literal, TokenStream};
+/// #     use quote::{ToTokens, TokenStreamExt};
+/// #
+/// #     pub struct Index(usize);
+/// #
+/// #     impl From<usize> for Index {
+/// #         fn from(i: usize) -> Self {
+/// #             Index(i)
+/// #         }
+/// #     }
+/// #
+/// #     impl ToTokens for Index {
+/// #         fn to_tokens(&self, tokens: &mut TokenStream) {
+/// #             tokens.append(Literal::usize_unsuffixed(self.0));
+/// #         }
+/// #     }
+/// # }
+/// #
+/// # struct Struct {
+/// #     fields: Vec<Ident>,
+/// # }
+/// #
+/// # impl Struct {
+/// #     fn example(&self) -> TokenStream {
+/// let i = (0..self.fields.len()).map(syn::Index::from);
+///
+/// // expands to 0 + self.0.heap_size() + self.1.heap_size() + ...
+/// quote! {
+///     0 #( + self.#i.heap_size() )*
+/// }
+/// #     }
+/// # }
+/// ```
+#[macro_export]
+macro_rules! quote {
+    ($($tt:tt)*) => {
+        $crate::quote_spanned!($crate::__rt::Span::call_site()=> $($tt)*)
+    };
+}
+
+/// Same as `quote!`, but applies a given span to all tokens originating within
+/// the macro invocation.
+///
+/// <br>
+///
+/// # Syntax
+///
+/// A span expression of type [`Span`], followed by `=>`, followed by the tokens
+/// to quote. The span expression should be brief &mdash; use a variable for
+/// anything more than a few characters. There should be no space before the
+/// `=>` token.
+///
+/// [`Span`]: https://docs.rs/proc-macro2/1.0/proc_macro2/struct.Span.html
+///
+/// ```
+/// # use proc_macro2::Span;
+/// # use quote::quote_spanned;
+/// #
+/// # const IGNORE_TOKENS: &'static str = stringify! {
+/// let span = /* ... */;
+/// # };
+/// # let span = Span::call_site();
+/// # let init = 0;
+///
+/// // On one line, use parentheses.
+/// let tokens = quote_spanned!(span=> Box::into_raw(Box::new(#init)));
+///
+/// // On multiple lines, place the span at the top and use braces.
+/// let tokens = quote_spanned! {span=>
+///     Box::into_raw(Box::new(#init))
+/// };
+/// ```
+///
+/// The lack of space before the `=>` should look jarring to Rust programmers
+/// and this is intentional. The formatting is designed to be visibly
+/// off-balance and draw the eye a particular way, due to the span expression
+/// being evaluated in the context of the procedural macro and the remaining
+/// tokens being evaluated in the generated code.
+///
+/// <br>
+///
+/// # Hygiene
+///
+/// Any interpolated tokens preserve the `Span` information provided by their
+/// `ToTokens` implementation. Tokens that originate within the `quote_spanned!`
+/// invocation are spanned with the given span argument.
+///
+/// <br>
+///
+/// # Example
+///
+/// The following procedural macro code uses `quote_spanned!` to assert that a
+/// particular Rust type implements the [`Sync`] trait so that references can be
+/// safely shared between threads.
+///
+/// [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html
+///
+/// ```
+/// # use quote::{quote_spanned, TokenStreamExt, ToTokens};
+/// # use proc_macro2::{Span, TokenStream};
+/// #
+/// # struct Type;
+/// #
+/// # impl Type {
+/// #     fn span(&self) -> Span {
+/// #         Span::call_site()
+/// #     }
+/// # }
+/// #
+/// # impl ToTokens for Type {
+/// #     fn to_tokens(&self, _tokens: &mut TokenStream) {}
+/// # }
+/// #
+/// # let ty = Type;
+/// # let call_site = Span::call_site();
+/// #
+/// let ty_span = ty.span();
+/// let assert_sync = quote_spanned! {ty_span=>
+///     struct _AssertSync where #ty: Sync;
+/// };
+/// ```
+///
+/// If the assertion fails, the user will see an error like the following. The
+/// input span of their type is hightlighted in the error.
+///
+/// ```text
+/// error[E0277]: the trait bound `*const (): std::marker::Sync` is not satisfied
+///   --> src/main.rs:10:21
+///    |
+/// 10 |     static ref PTR: *const () = &();
+///    |                     ^^^^^^^^^ `*const ()` cannot be shared between threads safely
+/// ```
+///
+/// In this example it is important for the where-clause to be spanned with the
+/// line/column information of the user's input type so that error messages are
+/// placed appropriately by the compiler.
+#[macro_export]
+macro_rules! quote_spanned {
+    ($span:expr=> $($tt:tt)*) => {{
+        let mut _s = $crate::__rt::TokenStream::new();
+        let _span: $crate::__rt::Span = $span;
+        $crate::quote_each_token!(_s _span $($tt)*);
+        _s
+    }};
+}
+
+// Extract the names of all #metavariables and pass them to the $call macro.
+//
+// in:   pounded_var_names!(then!(...) a #b c #( #d )* #e)
+// out:  then!(... b);
+//       then!(... d);
+//       then!(... e);
+#[macro_export]
+#[doc(hidden)]
+macro_rules! pounded_var_names {
+    ($call:ident! $extra:tt $($tts:tt)*) => {
+        $crate::pounded_var_names_with_context!($call! $extra
+            (@ $($tts)*)
+            ($($tts)* @)
+        )
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! pounded_var_names_with_context {
+    ($call:ident! $extra:tt ($($b1:tt)*) ($($curr:tt)*)) => {
+        $(
+            $crate::pounded_var_with_context!($call! $extra $b1 $curr);
+        )*
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! pounded_var_with_context {
+    ($call:ident! $extra:tt $b1:tt ( $($inner:tt)* )) => {
+        $crate::pounded_var_names!($call! $extra $($inner)*);
+    };
+
+    ($call:ident! $extra:tt $b1:tt [ $($inner:tt)* ]) => {
+        $crate::pounded_var_names!($call! $extra $($inner)*);
+    };
+
+    ($call:ident! $extra:tt $b1:tt { $($inner:tt)* }) => {
+        $crate::pounded_var_names!($call! $extra $($inner)*);
+    };
+
+    ($call:ident!($($extra:tt)*) # $var:ident) => {
+        $crate::$call!($($extra)* $var);
+    };
+
+    ($call:ident! $extra:tt $b1:tt $curr:tt) => {};
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! quote_bind_into_iter {
+    ($has_iter:ident $var:ident) => {
+        // `mut` may be unused if $var occurs multiple times in the list.
+        #[allow(unused_mut)]
+        let (mut $var, i) = $var.quote_into_iter();
+        let $has_iter = $has_iter | i;
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! quote_bind_next_or_break {
+    ($var:ident) => {
+        let $var = match $var.next() {
+            Some(_x) => $crate::__rt::RepInterp(_x),
+            None => break,
+        };
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! quote_each_token {
+    ($tokens:ident $span:ident $($tts:tt)*) => {
+        $crate::quote_tokens_with_context!($tokens $span
+            (@ @ @ @ @ @ $($tts)*)
+            (@ @ @ @ @ $($tts)* @)
+            (@ @ @ @ $($tts)* @ @)
+            (@ @ @ $(($tts))* @ @ @)
+            (@ @ $($tts)* @ @ @ @)
+            (@ $($tts)* @ @ @ @ @)
+            ($($tts)* @ @ @ @ @ @)
+        );
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! quote_tokens_with_context {
+    ($tokens:ident $span:ident
+        ($($b3:tt)*) ($($b2:tt)*) ($($b1:tt)*)
+        ($($curr:tt)*)
+        ($($a1:tt)*) ($($a2:tt)*) ($($a3:tt)*)
+    ) => {
+        $(
+            $crate::quote_token_with_context!($tokens $span $b3 $b2 $b1 $curr $a1 $a2 $a3);
+        )*
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! quote_token_with_context {
+    ($tokens:ident $span:ident $b3:tt $b2:tt $b1:tt @ $a1:tt $a2:tt $a3:tt) => {};
+
+    ($tokens:ident $span:ident $b3:tt $b2:tt $b1:tt (#) ( $($inner:tt)* ) * $a3:tt) => {{
+        use $crate::__rt::ext::*;
+        let has_iter = $crate::__rt::ThereIsNoIteratorInRepetition;
+        $crate::pounded_var_names!(quote_bind_into_iter!(has_iter) () $($inner)*);
+        let _: $crate::__rt::HasIterator = has_iter;
+        // This is `while true` instead of `loop` because if there are no
+        // iterators used inside of this repetition then the body would not
+        // contain any `break`, so the compiler would emit unreachable code
+        // warnings on anything below the loop. We use has_iter to detect and
+        // fail to compile when there are no iterators, so here we just work
+        // around the unneeded extra warning.
+        while true {
+            $crate::pounded_var_names!(quote_bind_next_or_break!() () $($inner)*);
+            $crate::quote_each_token!($tokens $span $($inner)*);
+        }
+    }};
+    ($tokens:ident $span:ident $b3:tt $b2:tt # (( $($inner:tt)* )) * $a2:tt $a3:tt) => {};
+    ($tokens:ident $span:ident $b3:tt # ( $($inner:tt)* ) (*) $a1:tt $a2:tt $a3:tt) => {};
+
+    ($tokens:ident $span:ident $b3:tt $b2:tt $b1:tt (#) ( $($inner:tt)* ) $sep:tt *) => {{
+        use $crate::__rt::ext::*;
+        let mut _i = 0usize;
+        let has_iter = $crate::__rt::ThereIsNoIteratorInRepetition;
+        $crate::pounded_var_names!(quote_bind_into_iter!(has_iter) () $($inner)*);
+        let _: $crate::__rt::HasIterator = has_iter;
+        while true {
+            $crate::pounded_var_names!(quote_bind_next_or_break!() () $($inner)*);
+            if _i > 0 {
+                $crate::quote_token!($tokens $span $sep);
+            }
+            _i += 1;
+            $crate::quote_each_token!($tokens $span $($inner)*);
+        }
+    }};
+    ($tokens:ident $span:ident $b3:tt $b2:tt # (( $($inner:tt)* )) $sep:tt * $a3:tt) => {};
+    ($tokens:ident $span:ident $b3:tt # ( $($inner:tt)* ) ($sep:tt) * $a2:tt $a3:tt) => {};
+    ($tokens:ident $span:ident # ( $($inner:tt)* ) * (*) $a1:tt $a2:tt $a3:tt) => {
+        // https://github.com/dtolnay/quote/issues/130
+        $crate::quote_token!($tokens $span *);
+    };
+    ($tokens:ident $span:ident # ( $($inner:tt)* ) $sep:tt (*) $a1:tt $a2:tt $a3:tt) => {};
+
+    ($tokens:ident $span:ident $b3:tt $b2:tt $b1:tt (#) $var:ident $a2:tt $a3:tt) => {
+        $crate::ToTokens::to_tokens(&$var, &mut $tokens);
+    };
+    ($tokens:ident $span:ident $b3:tt $b2:tt # ($var:ident) $a1:tt $a2:tt $a3:tt) => {};
+    ($tokens:ident $span:ident $b3:tt $b2:tt $b1:tt ($curr:tt) $a1:tt $a2:tt $a3:tt) => {
+        $crate::quote_token!($tokens $span $curr);
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! quote_token {
+    ($tokens:ident $span:ident ( $($inner:tt)* )) => {
+        $tokens.extend({
+            let mut g = $crate::__rt::Group::new(
+                $crate::__rt::Delimiter::Parenthesis,
+                $crate::quote_spanned!($span=> $($inner)*),
+            );
+            g.set_span($span);
+            Some($crate::__rt::TokenTree::from(g))
+        });
+    };
+
+    ($tokens:ident $span:ident [ $($inner:tt)* ]) => {
+        $tokens.extend({
+            let mut g = $crate::__rt::Group::new(
+                $crate::__rt::Delimiter::Bracket,
+                $crate::quote_spanned!($span=> $($inner)*),
+            );
+            g.set_span($span);
+            Some($crate::__rt::TokenTree::from(g))
+        });
+    };
+
+    ($tokens:ident $span:ident { $($inner:tt)* }) => {
+        $tokens.extend({
+            let mut g = $crate::__rt::Group::new(
+                $crate::__rt::Delimiter::Brace,
+                $crate::quote_spanned!($span=> $($inner)*),
+            );
+            g.set_span($span);
+            Some($crate::__rt::TokenTree::from(g))
+        });
+    };
+
+    ($tokens:ident $span:ident +) => {
+        $crate::__rt::push_add(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident +=) => {
+        $crate::__rt::push_add_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident &) => {
+        $crate::__rt::push_and(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident &&) => {
+        $crate::__rt::push_and_and(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident &=) => {
+        $crate::__rt::push_and_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident @) => {
+        $crate::__rt::push_at(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident !) => {
+        $crate::__rt::push_bang(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ^) => {
+        $crate::__rt::push_caret(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ^=) => {
+        $crate::__rt::push_caret_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident :) => {
+        $crate::__rt::push_colon(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ::) => {
+        $crate::__rt::push_colon2(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ,) => {
+        $crate::__rt::push_comma(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident /) => {
+        $crate::__rt::push_div(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident /=) => {
+        $crate::__rt::push_div_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident .) => {
+        $crate::__rt::push_dot(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ..) => {
+        $crate::__rt::push_dot2(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ...) => {
+        $crate::__rt::push_dot3(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ..=) => {
+        $crate::__rt::push_dot_dot_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident =) => {
+        $crate::__rt::push_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ==) => {
+        $crate::__rt::push_eq_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident >=) => {
+        $crate::__rt::push_ge(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident >) => {
+        $crate::__rt::push_gt(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident <=) => {
+        $crate::__rt::push_le(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident <) => {
+        $crate::__rt::push_lt(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident *=) => {
+        $crate::__rt::push_mul_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident !=) => {
+        $crate::__rt::push_ne(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident |) => {
+        $crate::__rt::push_or(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident |=) => {
+        $crate::__rt::push_or_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ||) => {
+        $crate::__rt::push_or_or(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident #) => {
+        $crate::__rt::push_pound(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ?) => {
+        $crate::__rt::push_question(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ->) => {
+        $crate::__rt::push_rarrow(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident <-) => {
+        $crate::__rt::push_larrow(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident %) => {
+        $crate::__rt::push_rem(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident %=) => {
+        $crate::__rt::push_rem_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident =>) => {
+        $crate::__rt::push_fat_arrow(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident ;) => {
+        $crate::__rt::push_semi(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident <<) => {
+        $crate::__rt::push_shl(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident <<=) => {
+        $crate::__rt::push_shl_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident >>) => {
+        $crate::__rt::push_shr(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident >>=) => {
+        $crate::__rt::push_shr_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident *) => {
+        $crate::__rt::push_star(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident -) => {
+        $crate::__rt::push_sub(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident -=) => {
+        $crate::__rt::push_sub_eq(&mut $tokens, $span);
+    };
+
+    ($tokens:ident $span:ident $other:tt) => {
+        $crate::__rt::parse(&mut $tokens, $span, stringify!($other));
+    };
+}
diff --git a/quote/src/runtime.rs b/quote/src/runtime.rs
new file mode 100644
index 0000000..4a1c14c
--- /dev/null
+++ b/quote/src/runtime.rs
@@ -0,0 +1,373 @@
+use crate::{IdentFragment, ToTokens, TokenStreamExt};
+use std::fmt;
+use std::ops::BitOr;
+
+pub use proc_macro2::*;
+
+pub struct HasIterator; // True
+pub struct ThereIsNoIteratorInRepetition; // False
+
+impl BitOr<ThereIsNoIteratorInRepetition> for ThereIsNoIteratorInRepetition {
+    type Output = ThereIsNoIteratorInRepetition;
+    fn bitor(self, _rhs: ThereIsNoIteratorInRepetition) -> ThereIsNoIteratorInRepetition {
+        ThereIsNoIteratorInRepetition
+    }
+}
+
+impl BitOr<ThereIsNoIteratorInRepetition> for HasIterator {
+    type Output = HasIterator;
+    fn bitor(self, _rhs: ThereIsNoIteratorInRepetition) -> HasIterator {
+        HasIterator
+    }
+}
+
+impl BitOr<HasIterator> for ThereIsNoIteratorInRepetition {
+    type Output = HasIterator;
+    fn bitor(self, _rhs: HasIterator) -> HasIterator {
+        HasIterator
+    }
+}
+
+impl BitOr<HasIterator> for HasIterator {
+    type Output = HasIterator;
+    fn bitor(self, _rhs: HasIterator) -> HasIterator {
+        HasIterator
+    }
+}
+
+/// Extension traits used by the implementation of `quote!`. These are defined
+/// in separate traits, rather than as a single trait due to ambiguity issues.
+///
+/// These traits expose a `quote_into_iter` method which should allow calling
+/// whichever impl happens to be applicable. Calling that method repeatedly on
+/// the returned value should be idempotent.
+pub mod ext {
+    use super::RepInterp;
+    use super::{HasIterator as HasIter, ThereIsNoIteratorInRepetition as DoesNotHaveIter};
+    use crate::ToTokens;
+    use std::collections::btree_set::{self, BTreeSet};
+    use std::slice;
+
+    /// Extension trait providing the `quote_into_iter` method on iterators.
+    pub trait RepIteratorExt: Iterator + Sized {
+        fn quote_into_iter(self) -> (Self, HasIter) {
+            (self, HasIter)
+        }
+    }
+
+    impl<T: Iterator> RepIteratorExt for T {}
+
+    /// Extension trait providing the `quote_into_iter` method for
+    /// non-iterable types. These types interpolate the same value in each
+    /// iteration of the repetition.
+    pub trait RepToTokensExt {
+        /// Pretend to be an iterator for the purposes of `quote_into_iter`.
+        /// This allows repeated calls to `quote_into_iter` to continue
+        /// correctly returning DoesNotHaveIter.
+        fn next(&self) -> Option<&Self> {
+            Some(self)
+        }
+
+        fn quote_into_iter(&self) -> (&Self, DoesNotHaveIter) {
+            (self, DoesNotHaveIter)
+        }
+    }
+
+    impl<T: ToTokens + ?Sized> RepToTokensExt for T {}
+
+    /// Extension trait providing the `quote_into_iter` method for types that
+    /// can be referenced as an iterator.
+    pub trait RepAsIteratorExt<'q> {
+        type Iter: Iterator;
+
+        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter);
+    }
+
+    impl<'q, 'a, T: RepAsIteratorExt<'q> + ?Sized> RepAsIteratorExt<'q> for &'a T {
+        type Iter = T::Iter;
+
+        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
+            <T as RepAsIteratorExt>::quote_into_iter(*self)
+        }
+    }
+
+    impl<'q, 'a, T: RepAsIteratorExt<'q> + ?Sized> RepAsIteratorExt<'q> for &'a mut T {
+        type Iter = T::Iter;
+
+        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
+            <T as RepAsIteratorExt>::quote_into_iter(*self)
+        }
+    }
+
+    impl<'q, T: 'q> RepAsIteratorExt<'q> for [T] {
+        type Iter = slice::Iter<'q, T>;
+
+        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
+            (self.iter(), HasIter)
+        }
+    }
+
+    impl<'q, T: 'q> RepAsIteratorExt<'q> for Vec<T> {
+        type Iter = slice::Iter<'q, T>;
+
+        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
+            (self.iter(), HasIter)
+        }
+    }
+
+    impl<'q, T: 'q> RepAsIteratorExt<'q> for BTreeSet<T> {
+        type Iter = btree_set::Iter<'q, T>;
+
+        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
+            (self.iter(), HasIter)
+        }
+    }
+
+    macro_rules! array_rep_slice {
+        ($($l:tt)*) => {
+            $(
+                impl<'q, T: 'q> RepAsIteratorExt<'q> for [T; $l] {
+                    type Iter = slice::Iter<'q, T>;
+
+                    fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
+                        (self.iter(), HasIter)
+                    }
+                }
+            )*
+        }
+    }
+
+    array_rep_slice!(
+        0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
+        17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
+    );
+
+    impl<'q, T: RepAsIteratorExt<'q>> RepAsIteratorExt<'q> for RepInterp<T> {
+        type Iter = T::Iter;
+
+        fn quote_into_iter(&'q self) -> (Self::Iter, HasIter) {
+            self.0.quote_into_iter()
+        }
+    }
+}
+
+// Helper type used within interpolations to allow for repeated binding names.
+// Implements the relevant traits, and exports a dummy `next()` method.
+#[derive(Copy, Clone)]
+pub struct RepInterp<T>(pub T);
+
+impl<T> RepInterp<T> {
+    // This method is intended to look like `Iterator::next`, and is called when
+    // a name is bound multiple times, as the previous binding will shadow the
+    // original `Iterator` object. This allows us to avoid advancing the
+    // iterator multiple times per iteration.
+    pub fn next(self) -> Option<T> {
+        Some(self.0)
+    }
+}
+
+impl<T: Iterator> Iterator for RepInterp<T> {
+    type Item = T::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.next()
+    }
+}
+
+impl<T: ToTokens> ToTokens for RepInterp<T> {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        self.0.to_tokens(tokens);
+    }
+}
+
+fn is_ident_start(c: u8) -> bool {
+    (b'a' <= c && c <= b'z') || (b'A' <= c && c <= b'Z') || c == b'_'
+}
+
+fn is_ident_continue(c: u8) -> bool {
+    (b'a' <= c && c <= b'z') || (b'A' <= c && c <= b'Z') || c == b'_' || (b'0' <= c && c <= b'9')
+}
+
+fn is_ident(token: &str) -> bool {
+    let mut iter = token.bytes();
+    let first_ok = iter.next().map(is_ident_start).unwrap_or(false);
+
+    first_ok && iter.all(is_ident_continue)
+}
+
+pub fn parse(tokens: &mut TokenStream, span: Span, s: &str) {
+    if is_ident(s) {
+        // Fast path, since idents are the most common token.
+        tokens.append(Ident::new(s, span));
+    } else {
+        let s: TokenStream = s.parse().expect("invalid token stream");
+        tokens.extend(s.into_iter().map(|mut t| {
+            t.set_span(span);
+            t
+        }));
+    }
+}
+
+macro_rules! push_punct {
+    ($name:ident $char1:tt) => {
+        pub fn $name(tokens: &mut TokenStream, span: Span) {
+            let mut punct = Punct::new($char1, Spacing::Alone);
+            punct.set_span(span);
+            tokens.append(punct);
+        }
+    };
+    ($name:ident $char1:tt $char2:tt) => {
+        pub fn $name(tokens: &mut TokenStream, span: Span) {
+            let mut punct = Punct::new($char1, Spacing::Joint);
+            punct.set_span(span);
+            tokens.append(punct);
+            let mut punct = Punct::new($char2, Spacing::Alone);
+            punct.set_span(span);
+            tokens.append(punct);
+        }
+    };
+    ($name:ident $char1:tt $char2:tt $char3:tt) => {
+        pub fn $name(tokens: &mut TokenStream, span: Span) {
+            let mut punct = Punct::new($char1, Spacing::Joint);
+            punct.set_span(span);
+            tokens.append(punct);
+            let mut punct = Punct::new($char2, Spacing::Joint);
+            punct.set_span(span);
+            tokens.append(punct);
+            let mut punct = Punct::new($char3, Spacing::Alone);
+            punct.set_span(span);
+            tokens.append(punct);
+        }
+    };
+}
+
+push_punct!(push_add '+');
+push_punct!(push_add_eq '+' '=');
+push_punct!(push_and '&');
+push_punct!(push_and_and '&' '&');
+push_punct!(push_and_eq '&' '=');
+push_punct!(push_at '@');
+push_punct!(push_bang '!');
+push_punct!(push_caret '^');
+push_punct!(push_caret_eq '^' '=');
+push_punct!(push_colon ':');
+push_punct!(push_colon2 ':' ':');
+push_punct!(push_comma ',');
+push_punct!(push_div '/');
+push_punct!(push_div_eq '/' '=');
+push_punct!(push_dot '.');
+push_punct!(push_dot2 '.' '.');
+push_punct!(push_dot3 '.' '.' '.');
+push_punct!(push_dot_dot_eq '.' '.' '=');
+push_punct!(push_eq '=');
+push_punct!(push_eq_eq '=' '=');
+push_punct!(push_ge '>' '=');
+push_punct!(push_gt '>');
+push_punct!(push_le '<' '=');
+push_punct!(push_lt '<');
+push_punct!(push_mul_eq '*' '=');
+push_punct!(push_ne '!' '=');
+push_punct!(push_or '|');
+push_punct!(push_or_eq '|' '=');
+push_punct!(push_or_or '|' '|');
+push_punct!(push_pound '#');
+push_punct!(push_question '?');
+push_punct!(push_rarrow '-' '>');
+push_punct!(push_larrow '<' '-');
+push_punct!(push_rem '%');
+push_punct!(push_rem_eq '%' '=');
+push_punct!(push_fat_arrow '=' '>');
+push_punct!(push_semi ';');
+push_punct!(push_shl '<' '<');
+push_punct!(push_shl_eq '<' '<' '=');
+push_punct!(push_shr '>' '>');
+push_punct!(push_shr_eq '>' '>' '=');
+push_punct!(push_star '*');
+push_punct!(push_sub '-');
+push_punct!(push_sub_eq '-' '=');
+
+// Helper method for constructing identifiers from the `format_ident!` macro,
+// handling `r#` prefixes.
+//
+// Directly parsing the input string may produce a valid identifier,
+// although the input string was invalid, due to ignored characters such as
+// whitespace and comments. Instead, we always create a non-raw identifier
+// to validate that the string is OK, and only parse again if needed.
+//
+// The `is_ident` method defined above is insufficient for validation, as it
+// will reject non-ASCII identifiers.
+pub fn mk_ident(id: &str, span: Option<Span>) -> Ident {
+    let span = span.unwrap_or_else(Span::call_site);
+
+    let is_raw = id.starts_with("r#");
+    let unraw = Ident::new(if is_raw { &id[2..] } else { id }, span);
+    if !is_raw {
+        return unraw;
+    }
+
+    // At this point, the identifier is raw, and the unraw-ed version of it was
+    // successfully converted into an identifier. Try to produce a valid raw
+    // identifier by running the `TokenStream` parser, and unwrapping the first
+    // token as an `Ident`.
+    //
+    // FIXME: When `Ident::new_raw` becomes stable, this method should be
+    // updated to call it when available.
+    match id.parse::<TokenStream>() {
+        Ok(ts) => {
+            let mut iter = ts.into_iter();
+            match (iter.next(), iter.next()) {
+                (Some(TokenTree::Ident(mut id)), None) => {
+                    id.set_span(span);
+                    id
+                }
+                _ => unreachable!("valid raw ident fails to parse"),
+            }
+        }
+        Err(_) => unreachable!("valid raw ident fails to parse"),
+    }
+}
+
+// Adapts from `IdentFragment` to `fmt::Display` for use by the `format_ident!`
+// macro, and exposes span information from these fragments.
+//
+// This struct also has forwarding implementations of the formatting traits
+// `Octal`, `LowerHex`, `UpperHex`, and `Binary` to allow for their use within
+// `format_ident!`.
+#[derive(Copy, Clone)]
+pub struct IdentFragmentAdapter<T: IdentFragment>(pub T);
+
+impl<T: IdentFragment> IdentFragmentAdapter<T> {
+    pub fn span(&self) -> Option<Span> {
+        self.0.span()
+    }
+}
+
+impl<T: IdentFragment> fmt::Display for IdentFragmentAdapter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        IdentFragment::fmt(&self.0, f)
+    }
+}
+
+impl<T: IdentFragment + fmt::Octal> fmt::Octal for IdentFragmentAdapter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Octal::fmt(&self.0, f)
+    }
+}
+
+impl<T: IdentFragment + fmt::LowerHex> fmt::LowerHex for IdentFragmentAdapter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::LowerHex::fmt(&self.0, f)
+    }
+}
+
+impl<T: IdentFragment + fmt::UpperHex> fmt::UpperHex for IdentFragmentAdapter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::UpperHex::fmt(&self.0, f)
+    }
+}
+
+impl<T: IdentFragment + fmt::Binary> fmt::Binary for IdentFragmentAdapter<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Binary::fmt(&self.0, f)
+    }
+}
diff --git a/quote/src/spanned.rs b/quote/src/spanned.rs
new file mode 100644
index 0000000..55168bd
--- /dev/null
+++ b/quote/src/spanned.rs
@@ -0,0 +1,42 @@
+use crate::ToTokens;
+use proc_macro2::{Span, TokenStream};
+
+pub trait Spanned {
+    fn __span(&self) -> Span;
+}
+
+impl Spanned for Span {
+    fn __span(&self) -> Span {
+        *self
+    }
+}
+
+impl<T: ?Sized + ToTokens> Spanned for T {
+    fn __span(&self) -> Span {
+        join_spans(self.into_token_stream())
+    }
+}
+
+fn join_spans(tokens: TokenStream) -> Span {
+    let mut iter = tokens.into_iter().filter_map(|tt| {
+        // FIXME: This shouldn't be required, since optimally spans should
+        // never be invalid. This filter_map can probably be removed when
+        // https://github.com/rust-lang/rust/issues/43081 is resolved.
+        let span = tt.span();
+        let debug = format!("{:?}", span);
+        if debug.ends_with("bytes(0..0)") {
+            None
+        } else {
+            Some(span)
+        }
+    });
+
+    let first = match iter.next() {
+        Some(span) => span,
+        None => return Span::call_site(),
+    };
+
+    iter.fold(None, |_prev, next| Some(next))
+        .and_then(|last| first.join(last))
+        .unwrap_or(first)
+}
diff --git a/quote/src/to_tokens.rs b/quote/src/to_tokens.rs
new file mode 100644
index 0000000..7f98083
--- /dev/null
+++ b/quote/src/to_tokens.rs
@@ -0,0 +1,209 @@
+use super::TokenStreamExt;
+
+use std::borrow::Cow;
+use std::iter;
+use std::rc::Rc;
+
+use proc_macro2::{Group, Ident, Literal, Punct, Span, TokenStream, TokenTree};
+
+/// Types that can be interpolated inside a `quote!` invocation.
+///
+/// [`quote!`]: macro.quote.html
+pub trait ToTokens {
+    /// Write `self` to the given `TokenStream`.
+    ///
+    /// The token append methods provided by the [`TokenStreamExt`] extension
+    /// trait may be useful for implementing `ToTokens`.
+    ///
+    /// [`TokenStreamExt`]: trait.TokenStreamExt.html
+    ///
+    /// # Example
+    ///
+    /// Example implementation for a struct representing Rust paths like
+    /// `std::cmp::PartialEq`:
+    ///
+    /// ```
+    /// use proc_macro2::{TokenTree, Spacing, Span, Punct, TokenStream};
+    /// use quote::{TokenStreamExt, ToTokens};
+    ///
+    /// pub struct Path {
+    ///     pub global: bool,
+    ///     pub segments: Vec<PathSegment>,
+    /// }
+    ///
+    /// impl ToTokens for Path {
+    ///     fn to_tokens(&self, tokens: &mut TokenStream) {
+    ///         for (i, segment) in self.segments.iter().enumerate() {
+    ///             if i > 0 || self.global {
+    ///                 // Double colon `::`
+    ///                 tokens.append(Punct::new(':', Spacing::Joint));
+    ///                 tokens.append(Punct::new(':', Spacing::Alone));
+    ///             }
+    ///             segment.to_tokens(tokens);
+    ///         }
+    ///     }
+    /// }
+    /// #
+    /// # pub struct PathSegment;
+    /// #
+    /// # impl ToTokens for PathSegment {
+    /// #     fn to_tokens(&self, tokens: &mut TokenStream) {
+    /// #         unimplemented!()
+    /// #     }
+    /// # }
+    /// ```
+    fn to_tokens(&self, tokens: &mut TokenStream);
+
+    /// Convert `self` directly into a `TokenStream` object.
+    ///
+    /// This method is implicitly implemented using `to_tokens`, and acts as a
+    /// convenience method for consumers of the `ToTokens` trait.
+    fn to_token_stream(&self) -> TokenStream {
+        let mut tokens = TokenStream::new();
+        self.to_tokens(&mut tokens);
+        tokens
+    }
+
+    /// Convert `self` directly into a `TokenStream` object.
+    ///
+    /// This method is implicitly implemented using `to_tokens`, and acts as a
+    /// convenience method for consumers of the `ToTokens` trait.
+    fn into_token_stream(self) -> TokenStream
+    where
+        Self: Sized,
+    {
+        self.to_token_stream()
+    }
+}
+
+impl<'a, T: ?Sized + ToTokens> ToTokens for &'a T {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        (**self).to_tokens(tokens);
+    }
+}
+
+impl<'a, T: ?Sized + ToTokens> ToTokens for &'a mut T {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        (**self).to_tokens(tokens);
+    }
+}
+
+impl<'a, T: ?Sized + ToOwned + ToTokens> ToTokens for Cow<'a, T> {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        (**self).to_tokens(tokens);
+    }
+}
+
+impl<T: ?Sized + ToTokens> ToTokens for Box<T> {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        (**self).to_tokens(tokens);
+    }
+}
+
+impl<T: ?Sized + ToTokens> ToTokens for Rc<T> {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        (**self).to_tokens(tokens);
+    }
+}
+
+impl<T: ToTokens> ToTokens for Option<T> {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        if let Some(ref t) = *self {
+            t.to_tokens(tokens);
+        }
+    }
+}
+
+impl ToTokens for str {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        tokens.append(Literal::string(self));
+    }
+}
+
+impl ToTokens for String {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        self.as_str().to_tokens(tokens);
+    }
+}
+
+macro_rules! primitive {
+    ($($t:ident => $name:ident)*) => ($(
+        impl ToTokens for $t {
+            fn to_tokens(&self, tokens: &mut TokenStream) {
+                tokens.append(Literal::$name(*self));
+            }
+        }
+    )*)
+}
+
+primitive! {
+    i8 => i8_suffixed
+    i16 => i16_suffixed
+    i32 => i32_suffixed
+    i64 => i64_suffixed
+    i128 => i128_suffixed
+    isize => isize_suffixed
+
+    u8 => u8_suffixed
+    u16 => u16_suffixed
+    u32 => u32_suffixed
+    u64 => u64_suffixed
+    u128 => u128_suffixed
+    usize => usize_suffixed
+
+    f32 => f32_suffixed
+    f64 => f64_suffixed
+}
+
+impl ToTokens for char {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        tokens.append(Literal::character(*self));
+    }
+}
+
+impl ToTokens for bool {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        let word = if *self { "true" } else { "false" };
+        tokens.append(Ident::new(word, Span::call_site()));
+    }
+}
+
+impl ToTokens for Group {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        tokens.append(self.clone());
+    }
+}
+
+impl ToTokens for Ident {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        tokens.append(self.clone());
+    }
+}
+
+impl ToTokens for Punct {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        tokens.append(self.clone());
+    }
+}
+
+impl ToTokens for Literal {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        tokens.append(self.clone());
+    }
+}
+
+impl ToTokens for TokenTree {
+    fn to_tokens(&self, dst: &mut TokenStream) {
+        dst.append(self.clone());
+    }
+}
+
+impl ToTokens for TokenStream {
+    fn to_tokens(&self, dst: &mut TokenStream) {
+        dst.extend(iter::once(self.clone()));
+    }
+
+    fn into_token_stream(self) -> TokenStream {
+        self
+    }
+}