rustc_proc_macro/

lib.rs

//! A support library for macro authors when defining new macros.
//!
//! This library, provided by the standard distribution, provides the types
//! consumed in the interfaces of procedurally defined macro definitions such as
//! function-like macros `#[proc_macro]`, macro attributes `#[proc_macro_attribute]` and
//! custom derive attributes `#[proc_macro_derive]`.
//!
//! See [the book] for more.
//!
//! [the book]: ../book/ch19-06-macros.html#procedural-macros-for-generating-code-from-attributes

#![stable(feature = "proc_macro_lib", since = "1.15.0")]
#![deny(missing_docs)]
#![doc(
    html_playground_url = "https://play.rust-lang.org/",
    issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
    test(no_crate_inject, attr(deny(warnings))),
    test(attr(allow(dead_code, deprecated, unused_variables, unused_mut)))
)]
#![doc(rust_logo)]
#![feature(rustdoc_internals)]
#![feature(staged_api)]
#![feature(allow_internal_unstable)]
#![feature(decl_macro)]
#![feature(negative_impls)]
#![feature(panic_can_unwind)]
#![feature(restricted_std)]
#![feature(rustc_attrs)]
#![feature(extend_one)]
#![feature(mem_conjure_zst)]
#![recursion_limit = "256"]
#![allow(internal_features)]
#![deny(ffi_unwind_calls)]
#![allow(rustc::internal)] // Can't use FxHashMap when compiled as part of the standard library
#![warn(rustdoc::unescaped_backticks)]
#![warn(unreachable_pub)]
#![deny(unsafe_op_in_unsafe_fn)]

#[unstable(feature = "proc_macro_internals", issue = "27812")]
#[doc(hidden)]
pub mod bridge;

mod diagnostic;
mod escape;
mod to_tokens;

use core::ops::BitOr;
use std::ffi::CStr;
use std::ops::{Range, RangeBounds};
use std::path::PathBuf;
use std::str::FromStr;
use std::{error, fmt};

#[unstable(feature = "proc_macro_diagnostic", issue = "54140")]
pub use diagnostic::{Diagnostic, Level, MultiSpan};
#[unstable(feature = "proc_macro_value", issue = "136652")]
pub use rustc_literal_escaper::EscapeError;
use rustc_literal_escaper::{
    MixedUnit, unescape_byte, unescape_byte_str, unescape_c_str, unescape_char, unescape_str,
};
#[unstable(feature = "proc_macro_totokens", issue = "130977")]
pub use to_tokens::ToTokens;

use crate::bridge::client::Methods as BridgeMethods;
use crate::escape::{EscapeOptions, escape_bytes};

/// Errors returned when trying to retrieve a literal unescaped value.
#[unstable(feature = "proc_macro_value", issue = "136652")]
#[derive(Debug, PartialEq, Eq)]
pub enum ConversionErrorKind {
    /// The literal failed to be escaped, take a look at [`EscapeError`] for more information.
    FailedToUnescape(EscapeError),
    /// Trying to convert a literal with the wrong type.
    InvalidLiteralKind,
}

/// Determines whether proc_macro has been made accessible to the currently
/// running program.
///
/// The proc_macro crate is only intended for use inside the implementation of
/// procedural macros. All the functions in this crate panic if invoked from
/// outside of a procedural macro, such as from a build script or unit test or
/// ordinary Rust binary.
///
/// With consideration for Rust libraries that are designed to support both
/// macro and non-macro use cases, `proc_macro::is_available()` provides a
/// non-panicking way to detect whether the infrastructure required to use the
/// API of proc_macro is presently available. Returns true if invoked from
/// inside of a procedural macro, false if invoked from any other binary.
#[stable(feature = "proc_macro_is_available", since = "1.57.0")]
pub fn is_available() -> bool {
    bridge::client::is_available()
}

/// The main type provided by this crate, representing an abstract stream of
/// tokens, or, more specifically, a sequence of token trees.
/// The type provides interfaces for iterating over those token trees and, conversely,
/// collecting a number of token trees into one stream.
///
/// This is both the input and output of `#[proc_macro]`, `#[proc_macro_attribute]`
/// and `#[proc_macro_derive]` definitions.
#[cfg_attr(feature = "rustc-dep-of-std", rustc_diagnostic_item = "TokenStream")]
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
#[derive(Clone)]
pub struct TokenStream(Option<bridge::client::TokenStream>);

#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl !Send for TokenStream {}
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl !Sync for TokenStream {}

/// Error returned from `TokenStream::from_str`.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
#[non_exhaustive]
#[derive(Debug)]
pub struct LexError;

#[stable(feature = "proc_macro_lexerror_impls", since = "1.44.0")]
impl fmt::Display for LexError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str("cannot parse string into token stream")
    }
}

#[stable(feature = "proc_macro_lexerror_impls", since = "1.44.0")]
impl error::Error for LexError {}

#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl !Send for LexError {}
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl !Sync for LexError {}

/// Error returned from `TokenStream::expand_expr`.
#[unstable(feature = "proc_macro_expand", issue = "90765")]
#[non_exhaustive]
#[derive(Debug)]
pub struct ExpandError;

#[unstable(feature = "proc_macro_expand", issue = "90765")]
impl fmt::Display for ExpandError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str("macro expansion failed")
    }
}

#[unstable(feature = "proc_macro_expand", issue = "90765")]
impl error::Error for ExpandError {}

#[unstable(feature = "proc_macro_expand", issue = "90765")]
impl !Send for ExpandError {}

#[unstable(feature = "proc_macro_expand", issue = "90765")]
impl !Sync for ExpandError {}

impl TokenStream {
    /// Returns an empty `TokenStream` containing no token trees.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn new() -> TokenStream {
        TokenStream(None)
    }

    /// Checks if this `TokenStream` is empty.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn is_empty(&self) -> bool {
        self.0.as_ref().map(|h| BridgeMethods::ts_is_empty(h)).unwrap_or(true)
    }

    /// Parses this `TokenStream` as an expression and attempts to expand any
    /// macros within it. Returns the expanded `TokenStream`.
    ///
    /// Currently only expressions expanding to literals will succeed, although
    /// this may be relaxed in the future.
    ///
    /// NOTE: In error conditions, `expand_expr` may leave macros unexpanded,
    /// report an error, failing compilation, and/or return an `Err(..)`. The
    /// specific behavior for any error condition, and what conditions are
    /// considered errors, is unspecified and may change in the future.
    #[unstable(feature = "proc_macro_expand", issue = "90765")]
    pub fn expand_expr(&self) -> Result<TokenStream, ExpandError> {
        let stream = self.0.as_ref().ok_or(ExpandError)?;
        match BridgeMethods::ts_expand_expr(stream) {
            Ok(stream) => Ok(TokenStream(Some(stream))),
            Err(_) => Err(ExpandError),
        }
    }
}

/// Attempts to break the string into tokens and parse those tokens into a token stream.
/// May fail for a number of reasons, for example, if the string contains unbalanced delimiters
/// or characters not existing in the language.
/// All tokens in the parsed stream get `Span::call_site()` spans.
///
/// NOTE: some errors may cause panics instead of returning `LexError`. We reserve the right to
/// change these errors into `LexError`s later.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl FromStr for TokenStream {
    type Err = LexError;

    fn from_str(src: &str) -> Result<TokenStream, LexError> {
        Ok(TokenStream(Some(BridgeMethods::ts_from_str(src))))
    }
}

/// Prints the token stream as a string that is supposed to be losslessly convertible back
/// into the same token stream (modulo spans), except for possibly `TokenTree::Group`s
/// with `Delimiter::None` delimiters and negative numeric literals.
///
/// Note: the exact form of the output is subject to change, e.g. there might
/// be changes in the whitespace used between tokens. Therefore, you should
/// *not* do any kind of simple substring matching on the output string (as
/// produced by `to_string`) to implement a proc macro, because that matching
/// might stop working if such changes happen. Instead, you should work at the
/// `TokenTree` level, e.g. matching against `TokenTree::Ident`,
/// `TokenTree::Punct`, or `TokenTree::Literal`.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl fmt::Display for TokenStream {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match &self.0 {
            Some(ts) => write!(f, "{}", BridgeMethods::ts_to_string(ts)),
            None => Ok(()),
        }
    }
}

/// Prints tokens in a form convenient for debugging.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl fmt::Debug for TokenStream {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str("TokenStream ")?;
        f.debug_list().entries(self.clone()).finish()
    }
}

#[stable(feature = "proc_macro_token_stream_default", since = "1.45.0")]
impl Default for TokenStream {
    fn default() -> Self {
        TokenStream::new()
    }
}

#[unstable(feature = "proc_macro_quote", issue = "54722")]
pub use quote::{HasIterator, RepInterp, ThereIsNoIteratorInRepetition, ext, quote, quote_span};

fn tree_to_bridge_tree(
    tree: TokenTree,
) -> bridge::TokenTree<bridge::client::TokenStream, bridge::client::Span, bridge::client::Symbol> {
    match tree {
        TokenTree::Group(tt) => bridge::TokenTree::Group(tt.0),
        TokenTree::Punct(tt) => bridge::TokenTree::Punct(tt.0),
        TokenTree::Ident(tt) => bridge::TokenTree::Ident(tt.0),
        TokenTree::Literal(tt) => bridge::TokenTree::Literal(tt.0),
    }
}

/// Creates a token stream containing a single token tree.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl From<TokenTree> for TokenStream {
    fn from(tree: TokenTree) -> TokenStream {
        TokenStream(Some(BridgeMethods::ts_from_token_tree(tree_to_bridge_tree(tree))))
    }
}

/// Non-generic helper for implementing `FromIterator<TokenTree>` and
/// `Extend<TokenTree>` with less monomorphization in calling crates.
struct ConcatTreesHelper {
    trees: Vec<
        bridge::TokenTree<
            bridge::client::TokenStream,
            bridge::client::Span,
            bridge::client::Symbol,
        >,
    >,
}

impl ConcatTreesHelper {
    fn new(capacity: usize) -> Self {
        ConcatTreesHelper { trees: Vec::with_capacity(capacity) }
    }

    fn push(&mut self, tree: TokenTree) {
        self.trees.push(tree_to_bridge_tree(tree));
    }

    fn build(self) -> TokenStream {
        if self.trees.is_empty() {
            TokenStream(None)
        } else {
            TokenStream(Some(BridgeMethods::ts_concat_trees(None, self.trees)))
        }
    }

    fn append_to(self, stream: &mut TokenStream) {
        if self.trees.is_empty() {
            return;
        }
        stream.0 = Some(BridgeMethods::ts_concat_trees(stream.0.take(), self.trees))
    }
}

/// Non-generic helper for implementing `FromIterator<TokenStream>` and
/// `Extend<TokenStream>` with less monomorphization in calling crates.
struct ConcatStreamsHelper {
    streams: Vec<bridge::client::TokenStream>,
}

impl ConcatStreamsHelper {
    fn new(capacity: usize) -> Self {
        ConcatStreamsHelper { streams: Vec::with_capacity(capacity) }
    }

    fn push(&mut self, stream: TokenStream) {
        if let Some(stream) = stream.0 {
            self.streams.push(stream);
        }
    }

    fn build(mut self) -> TokenStream {
        if self.streams.len() <= 1 {
            TokenStream(self.streams.pop())
        } else {
            TokenStream(Some(BridgeMethods::ts_concat_streams(None, self.streams)))
        }
    }

    fn append_to(mut self, stream: &mut TokenStream) {
        if self.streams.is_empty() {
            return;
        }
        let base = stream.0.take();
        if base.is_none() && self.streams.len() == 1 {
            stream.0 = self.streams.pop();
        } else {
            stream.0 = Some(BridgeMethods::ts_concat_streams(base, self.streams));
        }
    }
}

/// Collects a number of token trees into a single stream.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl FromIterator<TokenTree> for TokenStream {
    fn from_iter<I: IntoIterator<Item = TokenTree>>(trees: I) -> Self {
        let iter = trees.into_iter();
        let mut builder = ConcatTreesHelper::new(iter.size_hint().0);
        iter.for_each(|tree| builder.push(tree));
        builder.build()
    }
}

/// A "flattening" operation on token streams, collects token trees
/// from multiple token streams into a single stream.
#[stable(feature = "proc_macro_lib", since = "1.15.0")]
impl FromIterator<TokenStream> for TokenStream {
    fn from_iter<I: IntoIterator<Item = TokenStream>>(streams: I) -> Self {
        let iter = streams.into_iter();
        let mut builder = ConcatStreamsHelper::new(iter.size_hint().0);
        iter.for_each(|stream| builder.push(stream));
        builder.build()
    }
}

#[stable(feature = "token_stream_extend", since = "1.30.0")]
impl Extend<TokenTree> for TokenStream {
    fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, trees: I) {
        let iter = trees.into_iter();
        let mut builder = ConcatTreesHelper::new(iter.size_hint().0);
        iter.for_each(|tree| builder.push(tree));
        builder.append_to(self);
    }
}

#[stable(feature = "token_stream_extend", since = "1.30.0")]
impl Extend<TokenStream> for TokenStream {
    fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I) {
        let iter = streams.into_iter();
        let mut builder = ConcatStreamsHelper::new(iter.size_hint().0);
        iter.for_each(|stream| builder.push(stream));
        builder.append_to(self);
    }
}

macro_rules! extend_items {
    ($($item:ident)*) => {
        $(
            #[stable(feature = "token_stream_extend_ts_items", since = "1.92.0")]
            impl Extend<$item> for TokenStream {
                fn extend<T: IntoIterator<Item = $item>>(&mut self, iter: T) {
                    self.extend(iter.into_iter().map(TokenTree::$item));
                }
            }
        )*
    };
}

extend_items!(Group Literal Punct Ident);

/// Public implementation details for the `TokenStream` type, such as iterators.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub mod token_stream {
    use crate::{BridgeMethods, Group, Ident, Literal, Punct, TokenStream, TokenTree, bridge};

    /// An iterator over `TokenStream`'s `TokenTree`s.
    /// The iteration is "shallow", e.g., the iterator doesn't recurse into delimited groups,
    /// and returns whole groups as token trees.
    #[derive(Clone)]
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub struct IntoIter(
        std::vec::IntoIter<
            bridge::TokenTree<
                bridge::client::TokenStream,
                bridge::client::Span,
                bridge::client::Symbol,
            >,
        >,
    );

    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    impl Iterator for IntoIter {
        type Item = TokenTree;

        fn next(&mut self) -> Option<TokenTree> {
            self.0.next().map(|tree| match tree {
                bridge::TokenTree::Group(tt) => TokenTree::Group(Group(tt)),
                bridge::TokenTree::Punct(tt) => TokenTree::Punct(Punct(tt)),
                bridge::TokenTree::Ident(tt) => TokenTree::Ident(Ident(tt)),
                bridge::TokenTree::Literal(tt) => TokenTree::Literal(Literal(tt)),
            })
        }

        fn size_hint(&self) -> (usize, Option<usize>) {
            self.0.size_hint()
        }

        fn count(self) -> usize {
            self.0.count()
        }
    }

    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    impl IntoIterator for TokenStream {
        type Item = TokenTree;
        type IntoIter = IntoIter;

        fn into_iter(self) -> IntoIter {
            IntoIter(
                self.0.map(|v| BridgeMethods::ts_into_trees(v)).unwrap_or_default().into_iter(),
            )
        }
    }
}

/// `quote!(..)` accepts arbitrary tokens and expands into a `TokenStream` describing the input.
/// For example, `quote!(a + b)` will produce an expression, that, when evaluated, constructs
/// the `TokenStream` `[Ident("a"), Punct('+', Alone), Ident("b")]`.
///
/// Unquoting is done with `$`, and works by taking the single next ident as the unquoted term.
/// To quote `$` itself, use `$$`.
#[unstable(feature = "proc_macro_quote", issue = "54722")]
#[allow_internal_unstable(proc_macro_def_site, proc_macro_internals, proc_macro_totokens)]
#[rustc_builtin_macro]
pub macro quote($($t:tt)*) {
    /* compiler built-in */
}

#[unstable(feature = "proc_macro_internals", issue = "27812")]
#[doc(hidden)]
mod quote;

/// A region of source code, along with macro expansion information.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
#[derive(Copy, Clone)]
pub struct Span(bridge::client::Span);

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Send for Span {}
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Sync for Span {}

macro_rules! diagnostic_method {
    ($name:ident, $level:expr) => {
        /// Creates a new `Diagnostic` with the given `message` at the span
        /// `self`.
        #[unstable(feature = "proc_macro_diagnostic", issue = "54140")]
        pub fn $name<T: Into<String>>(self, message: T) -> Diagnostic {
            Diagnostic::spanned(self, $level, message)
        }
    };
}

impl Span {
    /// A span that resolves at the macro definition site.
    #[unstable(feature = "proc_macro_def_site", issue = "54724")]
    pub fn def_site() -> Span {
        Span(bridge::client::Span::def_site())
    }

    /// The span of the invocation of the current procedural macro.
    /// Identifiers created with this span will be resolved as if they were written
    /// directly at the macro call location (call-site hygiene) and other code
    /// at the macro call site will be able to refer to them as well.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn call_site() -> Span {
        Span(bridge::client::Span::call_site())
    }

    /// A span that represents `macro_rules` hygiene, and sometimes resolves at the macro
    /// definition site (local variables, labels, `$crate`) and sometimes at the macro
    /// call site (everything else).
    /// The span location is taken from the call-site.
    #[stable(feature = "proc_macro_mixed_site", since = "1.45.0")]
    pub fn mixed_site() -> Span {
        Span(bridge::client::Span::mixed_site())
    }

    /// The `Span` for the tokens in the previous macro expansion from which
    /// `self` was generated from, if any.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn parent(&self) -> Option<Span> {
        BridgeMethods::span_parent(self.0).map(Span)
    }

    /// The span for the origin source code that `self` was generated from. If
    /// this `Span` wasn't generated from other macro expansions then the return
    /// value is the same as `*self`.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn source(&self) -> Span {
        Span(BridgeMethods::span_source(self.0))
    }

    /// Returns the span's byte position range in the source file.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn byte_range(&self) -> Range<usize> {
        BridgeMethods::span_byte_range(self.0)
    }

    /// Creates an empty span pointing to directly before this span.
    #[stable(feature = "proc_macro_span_location", since = "1.88.0")]
    pub fn start(&self) -> Span {
        Span(BridgeMethods::span_start(self.0))
    }

    /// Creates an empty span pointing to directly after this span.
    #[stable(feature = "proc_macro_span_location", since = "1.88.0")]
    pub fn end(&self) -> Span {
        Span(BridgeMethods::span_end(self.0))
    }

    /// The one-indexed line of the source file where the span starts.
    ///
    /// To obtain the line of the span's end, use `span.end().line()`.
    #[stable(feature = "proc_macro_span_location", since = "1.88.0")]
    pub fn line(&self) -> usize {
        BridgeMethods::span_line(self.0)
    }

    /// The one-indexed column of the source file where the span starts.
    ///
    /// To obtain the column of the span's end, use `span.end().column()`.
    #[stable(feature = "proc_macro_span_location", since = "1.88.0")]
    pub fn column(&self) -> usize {
        BridgeMethods::span_column(self.0)
    }

    /// The path to the source file in which this span occurs, for display purposes.
    ///
    /// This might not correspond to a valid file system path.
    /// It might be remapped (e.g. `"/src/lib.rs"`) or an artificial path (e.g. `"<command line>"`).
    #[stable(feature = "proc_macro_span_file", since = "1.88.0")]
    pub fn file(&self) -> String {
        BridgeMethods::span_file(self.0)
    }

    /// The path to the source file in which this span occurs on the local file system.
    ///
    /// This is the actual path on disk. It is unaffected by path remapping.
    ///
    /// This path should not be embedded in the output of the macro; prefer `file()` instead.
    #[stable(feature = "proc_macro_span_file", since = "1.88.0")]
    pub fn local_file(&self) -> Option<PathBuf> {
        BridgeMethods::span_local_file(self.0).map(PathBuf::from)
    }

    /// Creates a new span encompassing `self` and `other`.
    ///
    /// Returns `None` if `self` and `other` are from different files.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn join(&self, other: Span) -> Option<Span> {
        BridgeMethods::span_join(self.0, other.0).map(Span)
    }

    /// Creates a new span with the same line/column information as `self` but
    /// that resolves symbols as though it were at `other`.
    #[stable(feature = "proc_macro_span_resolved_at", since = "1.45.0")]
    pub fn resolved_at(&self, other: Span) -> Span {
        Span(BridgeMethods::span_resolved_at(self.0, other.0))
    }

    /// Creates a new span with the same name resolution behavior as `self` but
    /// with the line/column information of `other`.
    #[stable(feature = "proc_macro_span_located_at", since = "1.45.0")]
    pub fn located_at(&self, other: Span) -> Span {
        other.resolved_at(*self)
    }

    /// Compares two spans to see if they're equal.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn eq(&self, other: &Span) -> bool {
        self.0 == other.0
    }

    /// Returns the source text behind a span. This preserves the original source
    /// code, including spaces and comments. It only returns a result if the span
    /// corresponds to real source code.
    ///
    /// Note: The observable result of a macro should only rely on the tokens and
    /// not on this source text. The result of this function is a best effort to
    /// be used for diagnostics only.
    #[stable(feature = "proc_macro_source_text", since = "1.66.0")]
    pub fn source_text(&self) -> Option<String> {
        BridgeMethods::span_source_text(self.0)
    }

    // Used by the implementation of `Span::quote`
    #[doc(hidden)]
    #[unstable(feature = "proc_macro_internals", issue = "27812")]
    pub fn save_span(&self) -> usize {
        BridgeMethods::span_save_span(self.0)
    }

    // Used by the implementation of `Span::quote`
    #[doc(hidden)]
    #[unstable(feature = "proc_macro_internals", issue = "27812")]
    pub fn recover_proc_macro_span(id: usize) -> Span {
        Span(BridgeMethods::span_recover_proc_macro_span(id))
    }

    diagnostic_method!(error, Level::Error);
    diagnostic_method!(warning, Level::Warning);
    diagnostic_method!(note, Level::Note);
    diagnostic_method!(help, Level::Help);
}

/// Prints a span in a form convenient for debugging.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Debug for Span {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.0.fmt(f)
    }
}

/// A single token or a delimited sequence of token trees (e.g., `[1, (), ..]`).
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
#[derive(Clone)]
pub enum TokenTree {
    /// A token stream surrounded by bracket delimiters.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Group(#[stable(feature = "proc_macro_lib2", since = "1.29.0")] Group),
    /// An identifier.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Ident(#[stable(feature = "proc_macro_lib2", since = "1.29.0")] Ident),
    /// A single punctuation character (`+`, `,`, `$`, etc.).
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Punct(#[stable(feature = "proc_macro_lib2", since = "1.29.0")] Punct),
    /// A literal character (`'a'`), string (`"hello"`), number (`2.3`), etc.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Literal(#[stable(feature = "proc_macro_lib2", since = "1.29.0")] Literal),
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Send for TokenTree {}
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Sync for TokenTree {}

impl TokenTree {
    /// Returns the span of this tree, delegating to the `span` method of
    /// the contained token or a delimited stream.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn span(&self) -> Span {
        match *self {
            TokenTree::Group(ref t) => t.span(),
            TokenTree::Ident(ref t) => t.span(),
            TokenTree::Punct(ref t) => t.span(),
            TokenTree::Literal(ref t) => t.span(),
        }
    }

    /// Configures the span for *only this token*.
    ///
    /// Note that if this token is a `Group` then this method will not configure
    /// the span of each of the internal tokens, this will simply delegate to
    /// the `set_span` method of each variant.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn set_span(&mut self, span: Span) {
        match *self {
            TokenTree::Group(ref mut t) => t.set_span(span),
            TokenTree::Ident(ref mut t) => t.set_span(span),
            TokenTree::Punct(ref mut t) => t.set_span(span),
            TokenTree::Literal(ref mut t) => t.set_span(span),
        }
    }
}

/// Prints token tree in a form convenient for debugging.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Debug for TokenTree {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        // Each of these has the name in the struct type in the derived debug,
        // so don't bother with an extra layer of indirection
        match *self {
            TokenTree::Group(ref tt) => tt.fmt(f),
            TokenTree::Ident(ref tt) => tt.fmt(f),
            TokenTree::Punct(ref tt) => tt.fmt(f),
            TokenTree::Literal(ref tt) => tt.fmt(f),
        }
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl From<Group> for TokenTree {
    fn from(g: Group) -> TokenTree {
        TokenTree::Group(g)
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl From<Ident> for TokenTree {
    fn from(g: Ident) -> TokenTree {
        TokenTree::Ident(g)
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl From<Punct> for TokenTree {
    fn from(g: Punct) -> TokenTree {
        TokenTree::Punct(g)
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl From<Literal> for TokenTree {
    fn from(g: Literal) -> TokenTree {
        TokenTree::Literal(g)
    }
}

/// Prints the token tree as a string that is supposed to be losslessly convertible back
/// into the same token tree (modulo spans), except for possibly `TokenTree::Group`s
/// with `Delimiter::None` delimiters and negative numeric literals.
///
/// Note: the exact form of the output is subject to change, e.g. there might
/// be changes in the whitespace used between tokens. Therefore, you should
/// *not* do any kind of simple substring matching on the output string (as
/// produced by `to_string`) to implement a proc macro, because that matching
/// might stop working if such changes happen. Instead, you should work at the
/// `TokenTree` level, e.g. matching against `TokenTree::Ident`,
/// `TokenTree::Punct`, or `TokenTree::Literal`.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Display for TokenTree {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            TokenTree::Group(t) => write!(f, "{t}"),
            TokenTree::Ident(t) => write!(f, "{t}"),
            TokenTree::Punct(t) => write!(f, "{t}"),
            TokenTree::Literal(t) => write!(f, "{t}"),
        }
    }
}

/// A delimited token stream.
///
/// A `Group` internally contains a `TokenStream` which is surrounded by `Delimiter`s.
#[derive(Clone)]
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub struct Group(bridge::Group<bridge::client::TokenStream, bridge::client::Span>);

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Send for Group {}
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Sync for Group {}

/// Describes how a sequence of token trees is delimited.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub enum Delimiter {
    /// `( ... )`
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Parenthesis,
    /// `{ ... }`
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Brace,
    /// `[ ... ]`
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Bracket,
    /// `∅ ... ∅`
    /// An invisible delimiter, that may, for example, appear around tokens coming from a
    /// "macro variable" `$var`. It is important to preserve operator priorities in cases like
    /// `$var * 3` where `$var` is `1 + 2`.
    /// Invisible delimiters might not survive roundtrip of a token stream through a string.
    ///
    /// <div class="warning">
    ///
    /// Note: rustc currently can ignore the grouping of tokens delimited by `None` in the output
    /// of a proc_macro. Only `None`-delimited groups created by a macro_rules macro in the input
    /// of a proc_macro macro are preserved, and only in very specific circumstances.
    /// Any `None`-delimited groups (re)created by a proc_macro will therefore not preserve
    /// operator priorities as indicated above. The other `Delimiter` variants should be used
    /// instead in this context. This is a rustc bug. For details, see
    /// [rust-lang/rust#67062](https://github.com/rust-lang/rust/issues/67062).
    ///
    /// </div>
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    None,
}

impl Group {
    /// Creates a new `Group` with the given delimiter and token stream.
    ///
    /// This constructor will set the span for this group to
    /// `Span::call_site()`. To change the span you can use the `set_span`
    /// method below.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn new(delimiter: Delimiter, stream: TokenStream) -> Group {
        Group(bridge::Group {
            delimiter,
            stream: stream.0,
            span: bridge::DelimSpan::from_single(Span::call_site().0),
        })
    }

    /// Returns the delimiter of this `Group`
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn delimiter(&self) -> Delimiter {
        self.0.delimiter
    }

    /// Returns the `TokenStream` of tokens that are delimited in this `Group`.
    ///
    /// Note that the returned token stream does not include the delimiter
    /// returned above.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn stream(&self) -> TokenStream {
        TokenStream(self.0.stream.clone())
    }

    /// Returns the span for the delimiters of this token stream, spanning the
    /// entire `Group`.
    ///
    /// ```text
    /// pub fn span(&self) -> Span {
    ///            ^^^^^^^
    /// ```
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn span(&self) -> Span {
        Span(self.0.span.entire)
    }

    /// Returns the span pointing to the opening delimiter of this group.
    ///
    /// ```text
    /// pub fn span_open(&self) -> Span {
    ///                 ^
    /// ```
    #[stable(feature = "proc_macro_group_span", since = "1.55.0")]
    pub fn span_open(&self) -> Span {
        Span(self.0.span.open)
    }

    /// Returns the span pointing to the closing delimiter of this group.
    ///
    /// ```text
    /// pub fn span_close(&self) -> Span {
    ///                        ^
    /// ```
    #[stable(feature = "proc_macro_group_span", since = "1.55.0")]
    pub fn span_close(&self) -> Span {
        Span(self.0.span.close)
    }

    /// Configures the span for this `Group`'s delimiters, but not its internal
    /// tokens.
    ///
    /// This method will **not** set the span of all the internal tokens spanned
    /// by this group, but rather it will only set the span of the delimiter
    /// tokens at the level of the `Group`.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn set_span(&mut self, span: Span) {
        self.0.span = bridge::DelimSpan::from_single(span.0);
    }
}

/// Prints the group as a string that should be losslessly convertible back
/// into the same group (modulo spans), except for possibly `TokenTree::Group`s
/// with `Delimiter::None` delimiters.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Display for Group {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", TokenStream::from(TokenTree::from(self.clone())))
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Debug for Group {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Group")
            .field("delimiter", &self.delimiter())
            .field("stream", &self.stream())
            .field("span", &self.span())
            .finish()
    }
}

/// A `Punct` is a single punctuation character such as `+`, `-` or `#`.
///
/// Multi-character operators like `+=` are represented as two instances of `Punct` with different
/// forms of `Spacing` returned.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
#[derive(Clone)]
pub struct Punct(bridge::Punct<bridge::client::Span>);

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Send for Punct {}
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl !Sync for Punct {}

/// Indicates whether a `Punct` token can join with the following token
/// to form a multi-character operator.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub enum Spacing {
    /// A `Punct` token can join with the following token to form a multi-character operator.
    ///
    /// In token streams constructed using proc macro interfaces, `Joint` punctuation tokens can be
    /// followed by any other tokens. However, in token streams parsed from source code, the
    /// compiler will only set spacing to `Joint` in the following cases.
    /// - When a `Punct` is immediately followed by another `Punct` without a whitespace. E.g. `+`
    ///   is `Joint` in `+=` and `++`.
    /// - When a single quote `'` is immediately followed by an identifier without a whitespace.
    ///   E.g. `'` is `Joint` in `'lifetime`.
    ///
    /// This list may be extended in the future to enable more token combinations.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Joint,
    /// A `Punct` token cannot join with the following token to form a multi-character operator.
    ///
    /// `Alone` punctuation tokens can be followed by any other tokens. In token streams parsed
    /// from source code, the compiler will set spacing to `Alone` in all cases not covered by the
    /// conditions for `Joint` above. E.g. `+` is `Alone` in `+ =`, `+ident` and `+()`. In
    /// particular, tokens not followed by anything will be marked as `Alone`.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    Alone,
}

impl Punct {
    /// Creates a new `Punct` from the given character and spacing.
    /// The `ch` argument must be a valid punctuation character permitted by the language,
    /// otherwise the function will panic.
    ///
    /// The returned `Punct` will have the default span of `Span::call_site()`
    /// which can be further configured with the `set_span` method below.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn new(ch: char, spacing: Spacing) -> Punct {
        const LEGAL_CHARS: &[char] = &[
            '=', '<', '>', '!', '~', '+', '-', '*', '/', '%', '^', '&', '|', '@', '.', ',', ';',
            ':', '#', '$', '?', '\'',
        ];
        if !LEGAL_CHARS.contains(&ch) {
            panic!("unsupported character `{:?}`", ch);
        }
        Punct(bridge::Punct {
            ch: ch as u8,
            joint: spacing == Spacing::Joint,
            span: Span::call_site().0,
        })
    }

    /// Returns the value of this punctuation character as `char`.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn as_char(&self) -> char {
        self.0.ch as char
    }

    /// Returns the spacing of this punctuation character, indicating whether it can be potentially
    /// combined into a multi-character operator with the following token (`Joint`), or whether the
    /// operator has definitely ended (`Alone`).
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn spacing(&self) -> Spacing {
        if self.0.joint { Spacing::Joint } else { Spacing::Alone }
    }

    /// Returns the span for this punctuation character.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn span(&self) -> Span {
        Span(self.0.span)
    }

    /// Configure the span for this punctuation character.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn set_span(&mut self, span: Span) {
        self.0.span = span.0;
    }
}

/// Prints the punctuation character as a string that should be losslessly convertible
/// back into the same character.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Display for Punct {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", self.as_char())
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Debug for Punct {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Punct")
            .field("ch", &self.as_char())
            .field("spacing", &self.spacing())
            .field("span", &self.span())
            .finish()
    }
}

#[stable(feature = "proc_macro_punct_eq", since = "1.50.0")]
impl PartialEq<char> for Punct {
    fn eq(&self, rhs: &char) -> bool {
        self.as_char() == *rhs
    }
}

#[stable(feature = "proc_macro_punct_eq_flipped", since = "1.52.0")]
impl PartialEq<Punct> for char {
    fn eq(&self, rhs: &Punct) -> bool {
        *self == rhs.as_char()
    }
}

/// An identifier (`ident`).
#[derive(Clone)]
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub struct Ident(bridge::Ident<bridge::client::Span, bridge::client::Symbol>);

impl Ident {
    /// Creates a new `Ident` with the given `string` as well as the specified
    /// `span`.
    /// The `string` argument must be a valid identifier permitted by the
    /// language (including keywords, e.g. `self` or `fn`). Otherwise, the function will panic.
    ///
    /// The constructed identifier will be NFC-normalized. See the [Reference] for more info.
    ///
    /// Note that `span`, currently in rustc, configures the hygiene information
    /// for this identifier.
    ///
    /// As of this time `Span::call_site()` explicitly opts-in to "call-site" hygiene
    /// meaning that identifiers created with this span will be resolved as if they were written
    /// directly at the location of the macro call, and other code at the macro call site will be
    /// able to refer to them as well.
    ///
    /// Later spans like `Span::def_site()` will allow to opt-in to "definition-site" hygiene
    /// meaning that identifiers created with this span will be resolved at the location of the
    /// macro definition and other code at the macro call site will not be able to refer to them.
    ///
    /// Due to the current importance of hygiene this constructor, unlike other
    /// tokens, requires a `Span` to be specified at construction.
    ///
    /// [Reference]: https://doc.rust-lang.org/nightly/reference/identifiers.html#r-ident.normalization
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn new(string: &str, span: Span) -> Ident {
        Ident(bridge::Ident {
            sym: bridge::client::Symbol::new_ident(string, false),
            is_raw: false,
            span: span.0,
        })
    }

    /// Same as `Ident::new`, but creates a raw identifier (`r#ident`).
    /// The `string` argument be a valid identifier permitted by the language
    /// (including keywords, e.g. `fn`). Keywords which are usable in path segments
    /// (e.g. `self`, `super`) are not supported, and will cause a panic.
    #[stable(feature = "proc_macro_raw_ident", since = "1.47.0")]
    pub fn new_raw(string: &str, span: Span) -> Ident {
        Ident(bridge::Ident {
            sym: bridge::client::Symbol::new_ident(string, true),
            is_raw: true,
            span: span.0,
        })
    }

    /// Returns the span of this `Ident`, encompassing the entire string returned
    /// by [`to_string`](ToString::to_string).
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn span(&self) -> Span {
        Span(self.0.span)
    }

    /// Configures the span of this `Ident`, possibly changing its hygiene context.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn set_span(&mut self, span: Span) {
        self.0.span = span.0;
    }
}

/// Prints the identifier as a string that should be losslessly convertible back
/// into the same identifier.
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Display for Ident {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        if self.0.is_raw {
            f.write_str("r#")?;
        }
        fmt::Display::fmt(&self.0.sym, f)
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Debug for Ident {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Ident")
            .field("ident", &self.to_string())
            .field("span", &self.span())
            .finish()
    }
}

/// A literal string (`"hello"`), byte string (`b"hello"`), C string (`c"hello"`),
/// character (`'a'`), byte character (`b'a'`), an integer or floating point number
/// with or without a suffix (`1`, `1u8`, `2.3`, `2.3f32`).
/// Boolean literals like `true` and `false` do not belong here, they are `Ident`s.
#[derive(Clone)]
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
pub struct Literal(bridge::Literal<bridge::client::Span, bridge::client::Symbol>);

macro_rules! suffixed_int_literals {
    ($($name:ident => $kind:ident,)*) => ($(
        /// Creates a new suffixed integer literal with the specified value.
        ///
        /// This function will create an integer like `1u32` where the integer
        /// value specified is the first part of the token and the integral is
        /// also suffixed at the end.
        /// Literals created from negative numbers might not survive round-trips through
        /// `TokenStream` or strings and may be broken into two tokens (`-` and positive literal).
        ///
        /// Literals created through this method have the `Span::call_site()`
        /// span by default, which can be configured with the `set_span` method
        /// below.
        #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
        pub fn $name(n: $kind) -> Literal {
            Literal(bridge::Literal {
                kind: bridge::LitKind::Integer,
                symbol: bridge::client::Symbol::new(&n.to_string()),
                suffix: Some(bridge::client::Symbol::new(stringify!($kind))),
                span: Span::call_site().0,
            })
        }
    )*)
}

macro_rules! unsuffixed_int_literals {
    ($($name:ident => $kind:ident,)*) => ($(
        /// Creates a new unsuffixed integer literal with the specified value.
        ///
        /// This function will create an integer like `1` where the integer
        /// value specified is the first part of the token. No suffix is
        /// specified on this token, meaning that invocations like
        /// `Literal::i8_unsuffixed(1)` are equivalent to
        /// `Literal::u32_unsuffixed(1)`.
        /// Literals created from negative numbers might not survive rountrips through
        /// `TokenStream` or strings and may be broken into two tokens (`-` and positive literal).
        ///
        /// Literals created through this method have the `Span::call_site()`
        /// span by default, which can be configured with the `set_span` method
        /// below.
        #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
        pub fn $name(n: $kind) -> Literal {
            Literal(bridge::Literal {
                kind: bridge::LitKind::Integer,
                symbol: bridge::client::Symbol::new(&n.to_string()),
                suffix: None,
                span: Span::call_site().0,
            })
        }
    )*)
}

impl Literal {
    fn new(kind: bridge::LitKind, value: &str, suffix: Option<&str>) -> Self {
        Literal(bridge::Literal {
            kind,
            symbol: bridge::client::Symbol::new(value),
            suffix: suffix.map(bridge::client::Symbol::new),
            span: Span::call_site().0,
        })
    }

    suffixed_int_literals! {
        u8_suffixed => u8,
        u16_suffixed => u16,
        u32_suffixed => u32,
        u64_suffixed => u64,
        u128_suffixed => u128,
        usize_suffixed => usize,
        i8_suffixed => i8,
        i16_suffixed => i16,
        i32_suffixed => i32,
        i64_suffixed => i64,
        i128_suffixed => i128,
        isize_suffixed => isize,
    }

    unsuffixed_int_literals! {
        u8_unsuffixed => u8,
        u16_unsuffixed => u16,
        u32_unsuffixed => u32,
        u64_unsuffixed => u64,
        u128_unsuffixed => u128,
        usize_unsuffixed => usize,
        i8_unsuffixed => i8,
        i16_unsuffixed => i16,
        i32_unsuffixed => i32,
        i64_unsuffixed => i64,
        i128_unsuffixed => i128,
        isize_unsuffixed => isize,
    }

    /// Creates a new unsuffixed floating-point literal.
    ///
    /// This constructor is similar to those like `Literal::i8_unsuffixed` where
    /// the float's value is emitted directly into the token but no suffix is
    /// used, so it may be inferred to be a `f64` later in the compiler.
    /// Literals created from negative numbers might not survive rountrips through
    /// `TokenStream` or strings and may be broken into two tokens (`-` and positive literal).
    ///
    /// # Panics
    ///
    /// This function requires that the specified float is finite, for
    /// example if it is infinity or NaN this function will panic.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn f32_unsuffixed(n: f32) -> Literal {
        if !n.is_finite() {
            panic!("Invalid float literal {n}");
        }
        let mut repr = n.to_string();
        if !repr.contains('.') {
            repr.push_str(".0");
        }
        Literal::new(bridge::LitKind::Float, &repr, None)
    }

    /// Creates a new suffixed floating-point literal.
    ///
    /// This constructor will create a literal like `1.0f32` where the value
    /// specified is the preceding part of the token and `f32` is the suffix of
    /// the token. This token will always be inferred to be an `f32` in the
    /// compiler.
    /// Literals created from negative numbers might not survive rountrips through
    /// `TokenStream` or strings and may be broken into two tokens (`-` and positive literal).
    ///
    /// # Panics
    ///
    /// This function requires that the specified float is finite, for
    /// example if it is infinity or NaN this function will panic.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn f32_suffixed(n: f32) -> Literal {
        if !n.is_finite() {
            panic!("Invalid float literal {n}");
        }
        Literal::new(bridge::LitKind::Float, &n.to_string(), Some("f32"))
    }

    /// Creates a new unsuffixed floating-point literal.
    ///
    /// This constructor is similar to those like `Literal::i8_unsuffixed` where
    /// the float's value is emitted directly into the token but no suffix is
    /// used, so it may be inferred to be a `f64` later in the compiler.
    /// Literals created from negative numbers might not survive rountrips through
    /// `TokenStream` or strings and may be broken into two tokens (`-` and positive literal).
    ///
    /// # Panics
    ///
    /// This function requires that the specified float is finite, for
    /// example if it is infinity or NaN this function will panic.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn f64_unsuffixed(n: f64) -> Literal {
        if !n.is_finite() {
            panic!("Invalid float literal {n}");
        }
        let mut repr = n.to_string();
        if !repr.contains('.') {
            repr.push_str(".0");
        }
        Literal::new(bridge::LitKind::Float, &repr, None)
    }

    /// Creates a new suffixed floating-point literal.
    ///
    /// This constructor will create a literal like `1.0f64` where the value
    /// specified is the preceding part of the token and `f64` is the suffix of
    /// the token. This token will always be inferred to be an `f64` in the
    /// compiler.
    /// Literals created from negative numbers might not survive rountrips through
    /// `TokenStream` or strings and may be broken into two tokens (`-` and positive literal).
    ///
    /// # Panics
    ///
    /// This function requires that the specified float is finite, for
    /// example if it is infinity or NaN this function will panic.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn f64_suffixed(n: f64) -> Literal {
        if !n.is_finite() {
            panic!("Invalid float literal {n}");
        }
        Literal::new(bridge::LitKind::Float, &n.to_string(), Some("f64"))
    }

    /// String literal.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn string(string: &str) -> Literal {
        let escape = EscapeOptions {
            escape_single_quote: false,
            escape_double_quote: true,
            escape_nonascii: false,
        };
        let repr = escape_bytes(string.as_bytes(), escape);
        Literal::new(bridge::LitKind::Str, &repr, None)
    }

    /// Character literal.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn character(ch: char) -> Literal {
        let escape = EscapeOptions {
            escape_single_quote: true,
            escape_double_quote: false,
            escape_nonascii: false,
        };
        let repr = escape_bytes(ch.encode_utf8(&mut [0u8; 4]).as_bytes(), escape);
        Literal::new(bridge::LitKind::Char, &repr, None)
    }

    /// Byte character literal.
    #[stable(feature = "proc_macro_byte_character", since = "1.79.0")]
    pub fn byte_character(byte: u8) -> Literal {
        let escape = EscapeOptions {
            escape_single_quote: true,
            escape_double_quote: false,
            escape_nonascii: true,
        };
        let repr = escape_bytes(&[byte], escape);
        Literal::new(bridge::LitKind::Byte, &repr, None)
    }

    /// Byte string literal.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn byte_string(bytes: &[u8]) -> Literal {
        let escape = EscapeOptions {
            escape_single_quote: false,
            escape_double_quote: true,
            escape_nonascii: true,
        };
        let repr = escape_bytes(bytes, escape);
        Literal::new(bridge::LitKind::ByteStr, &repr, None)
    }

    /// C string literal.
    #[stable(feature = "proc_macro_c_str_literals", since = "1.79.0")]
    pub fn c_string(string: &CStr) -> Literal {
        let escape = EscapeOptions {
            escape_single_quote: false,
            escape_double_quote: true,
            escape_nonascii: false,
        };
        let repr = escape_bytes(string.to_bytes(), escape);
        Literal::new(bridge::LitKind::CStr, &repr, None)
    }

    /// Returns the span encompassing this literal.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn span(&self) -> Span {
        Span(self.0.span)
    }

    /// Configures the span associated for this literal.
    #[stable(feature = "proc_macro_lib2", since = "1.29.0")]
    pub fn set_span(&mut self, span: Span) {
        self.0.span = span.0;
    }

    /// Returns a `Span` that is a subset of `self.span()` containing only the
    /// source bytes in range `range`. Returns `None` if the would-be trimmed
    /// span is outside the bounds of `self`.
    // FIXME(SergioBenitez): check that the byte range starts and ends at a
    // UTF-8 boundary of the source. otherwise, it's likely that a panic will
    // occur elsewhere when the source text is printed.
    // FIXME(SergioBenitez): there is no way for the user to know what
    // `self.span()` actually maps to, so this method can currently only be
    // called blindly. For example, `to_string()` for the character 'c' returns
    // "'\u{63}'"; there is no way for the user to know whether the source text
    // was 'c' or whether it was '\u{63}'.
    #[unstable(feature = "proc_macro_span", issue = "54725")]
    pub fn subspan<R: RangeBounds<usize>>(&self, range: R) -> Option<Span> {
        BridgeMethods::span_subspan(
            self.0.span,
            range.start_bound().cloned(),
            range.end_bound().cloned(),
        )
        .map(Span)
    }

    fn with_symbol_and_suffix<R>(&self, f: impl FnOnce(&str, &str) -> R) -> R {
        self.0.symbol.with(|symbol| match self.0.suffix {
            Some(suffix) => suffix.with(|suffix| f(symbol, suffix)),
            None => f(symbol, ""),
        })
    }

    /// Invokes the callback with a `&[&str]` consisting of each part of the
    /// literal's representation. This is done to allow the `ToString` and
    /// `Display` implementations to borrow references to symbol values, and
    /// both be optimized to reduce overhead.
    fn with_stringify_parts<R>(&self, f: impl FnOnce(&[&str]) -> R) -> R {
        /// Returns a string containing exactly `num` '#' characters.
        /// Uses a 256-character source string literal which is always safe to
        /// index with a `u8` index.
        fn get_hashes_str(num: u8) -> &'static str {
            const HASHES: &str = "\
            ################################################################\
            ################################################################\
            ################################################################\
            ################################################################\
            ";
            const _: () = assert!(HASHES.len() == 256);
            &HASHES[..num as usize]
        }

        self.with_symbol_and_suffix(|symbol, suffix| match self.0.kind {
            bridge::LitKind::Byte => f(&["b'", symbol, "'", suffix]),
            bridge::LitKind::Char => f(&["'", symbol, "'", suffix]),
            bridge::LitKind::Str => f(&["\"", symbol, "\"", suffix]),
            bridge::LitKind::StrRaw(n) => {
                let hashes = get_hashes_str(n);
                f(&["r", hashes, "\"", symbol, "\"", hashes, suffix])
            }
            bridge::LitKind::ByteStr => f(&["b\"", symbol, "\"", suffix]),
            bridge::LitKind::ByteStrRaw(n) => {
                let hashes = get_hashes_str(n);
                f(&["br", hashes, "\"", symbol, "\"", hashes, suffix])
            }
            bridge::LitKind::CStr => f(&["c\"", symbol, "\"", suffix]),
            bridge::LitKind::CStrRaw(n) => {
                let hashes = get_hashes_str(n);
                f(&["cr", hashes, "\"", symbol, "\"", hashes, suffix])
            }

            bridge::LitKind::Integer | bridge::LitKind::Float | bridge::LitKind::ErrWithGuar => {
                f(&[symbol, suffix])
            }
        })
    }

    /// Returns the unescaped character value if the current literal is a byte character literal.
    #[unstable(feature = "proc_macro_value", issue = "136652")]
    pub fn byte_character_value(&self) -> Result<u8, ConversionErrorKind> {
        self.0.symbol.with(|symbol| match self.0.kind {
            bridge::LitKind::Char => {
                unescape_byte(symbol).map_err(ConversionErrorKind::FailedToUnescape)
            }
            _ => Err(ConversionErrorKind::InvalidLiteralKind),
        })
    }

    /// Returns the unescaped character value if the current literal is a character literal.
    #[unstable(feature = "proc_macro_value", issue = "136652")]
    pub fn character_value(&self) -> Result<char, ConversionErrorKind> {
        self.0.symbol.with(|symbol| match self.0.kind {
            bridge::LitKind::Char => {
                unescape_char(symbol).map_err(ConversionErrorKind::FailedToUnescape)
            }
            _ => Err(ConversionErrorKind::InvalidLiteralKind),
        })
    }

    /// Returns the unescaped string value if the current literal is a string or a string literal.
    #[unstable(feature = "proc_macro_value", issue = "136652")]
    pub fn str_value(&self) -> Result<String, ConversionErrorKind> {
        self.0.symbol.with(|symbol| match self.0.kind {
            bridge::LitKind::Str => {
                if symbol.contains('\\') {
                    let mut buf = String::with_capacity(symbol.len());
                    let mut error = None;
                    // Force-inlining here is aggressive but the closure is
                    // called on every char in the string, so it can be hot in
                    // programs with many long strings containing escapes.
                    unescape_str(
                        symbol,
                        #[inline(always)]
                        |_, c| match c {
                            Ok(c) => buf.push(c),
                            Err(err) => {
                                if err.is_fatal() {
                                    error = Some(ConversionErrorKind::FailedToUnescape(err));
                                }
                            }
                        },
                    );
                    if let Some(error) = error { Err(error) } else { Ok(buf) }
                } else {
                    Ok(symbol.to_string())
                }
            }
            bridge::LitKind::StrRaw(_) => Ok(symbol.to_string()),
            _ => Err(ConversionErrorKind::InvalidLiteralKind),
        })
    }

    /// Returns the unescaped string value if the current literal is a c-string or a c-string
    /// literal.
    #[unstable(feature = "proc_macro_value", issue = "136652")]
    pub fn cstr_value(&self) -> Result<Vec<u8>, ConversionErrorKind> {
        self.0.symbol.with(|symbol| match self.0.kind {
            bridge::LitKind::CStr => {
                let mut error = None;
                let mut buf = Vec::with_capacity(symbol.len());

                unescape_c_str(symbol, |_span, res| match res {
                    Ok(MixedUnit::Char(c)) => {
                        buf.extend_from_slice(c.get().encode_utf8(&mut [0; 4]).as_bytes())
                    }
                    Ok(MixedUnit::HighByte(b)) => buf.push(b.get()),
                    Err(err) => {
                        if err.is_fatal() {
                            error = Some(ConversionErrorKind::FailedToUnescape(err));
                        }
                    }
                });
                if let Some(error) = error {
                    Err(error)
                } else {
                    buf.push(0);
                    Ok(buf)
                }
            }
            bridge::LitKind::CStrRaw(_) => {
                // Raw strings have no escapes so we can convert the symbol
                // directly to a `Lrc<u8>` after appending the terminating NUL
                // char.
                let mut buf = symbol.to_owned().into_bytes();
                buf.push(0);
                Ok(buf)
            }
            _ => Err(ConversionErrorKind::InvalidLiteralKind),
        })
    }

    /// Returns the unescaped string value if the current literal is a byte string or a byte string
    /// literal.
    #[unstable(feature = "proc_macro_value", issue = "136652")]
    pub fn byte_str_value(&self) -> Result<Vec<u8>, ConversionErrorKind> {
        self.0.symbol.with(|symbol| match self.0.kind {
            bridge::LitKind::ByteStr => {
                let mut buf = Vec::with_capacity(symbol.len());
                let mut error = None;

                unescape_byte_str(symbol, |_, res| match res {
                    Ok(b) => buf.push(b),
                    Err(err) => {
                        if err.is_fatal() {
                            error = Some(ConversionErrorKind::FailedToUnescape(err));
                        }
                    }
                });
                if let Some(error) = error { Err(error) } else { Ok(buf) }
            }
            bridge::LitKind::ByteStrRaw(_) => {
                // Raw strings have no escapes so we can convert the symbol
                // directly to a `Lrc<u8>`.
                Ok(symbol.to_owned().into_bytes())
            }
            _ => Err(ConversionErrorKind::InvalidLiteralKind),
        })
    }
}

/// Parse a single literal from its stringified representation.
///
/// In order to parse successfully, the input string must not contain anything
/// but the literal token. Specifically, it must not contain whitespace or
/// comments in addition to the literal.
///
/// The resulting literal token will have a `Span::call_site()` span.
///
/// NOTE: some errors may cause panics instead of returning `LexError`. We
/// reserve the right to change these errors into `LexError`s later.
#[stable(feature = "proc_macro_literal_parse", since = "1.54.0")]
impl FromStr for Literal {
    type Err = LexError;

    fn from_str(src: &str) -> Result<Self, LexError> {
        match BridgeMethods::literal_from_str(src) {
            Ok(literal) => Ok(Literal(literal)),
            Err(()) => Err(LexError),
        }
    }
}

/// Prints the literal as a string that should be losslessly convertible
/// back into the same literal (except for possible rounding for floating point literals).
#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Display for Literal {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.with_stringify_parts(|parts| {
            for part in parts {
                fmt::Display::fmt(part, f)?;
            }
            Ok(())
        })
    }
}

#[stable(feature = "proc_macro_lib2", since = "1.29.0")]
impl fmt::Debug for Literal {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Literal")
            // format the kind on one line even in {:#?} mode
            .field("kind", &format_args!("{:?}", self.0.kind))
            .field("symbol", &self.0.symbol)
            // format `Some("...")` on one line even in {:#?} mode
            .field("suffix", &format_args!("{:?}", self.0.suffix))
            .field("span", &self.0.span)
            .finish()
    }
}

#[unstable(
    feature = "proc_macro_tracked_path",
    issue = "99515",
    implied_by = "proc_macro_tracked_env"
)]
/// Functionality for adding environment state to the build dependency info.
pub mod tracked {
    use std::env::{self, VarError};
    use std::ffi::OsStr;
    use std::path::Path;

    use crate::BridgeMethods;

    /// Retrieve an environment variable and add it to build dependency info.
    /// The build system executing the compiler will know that the variable was accessed during
    /// compilation, and will be able to rerun the build when the value of that variable changes.
    /// Besides the dependency tracking this function should be equivalent to `env::var` from the
    /// standard library, except that the argument must be UTF-8.
    #[unstable(feature = "proc_macro_tracked_env", issue = "99515")]
    pub fn env_var<K: AsRef<OsStr> + AsRef<str>>(key: K) -> Result<String, VarError> {
        let key: &str = key.as_ref();
        let value = BridgeMethods::injected_env_var(key).map_or_else(|| env::var(key), Ok);
        BridgeMethods::track_env_var(key, value.as_deref().ok());
        value
    }

    /// Track a file or directory explicitly.
    ///
    /// Commonly used for tracking asset preprocessing.
    #[unstable(feature = "proc_macro_tracked_path", issue = "99515")]
    pub fn path<P: AsRef<Path>>(path: P) {
        let path: &str = path.as_ref().to_str().unwrap();
        BridgeMethods::track_path(path);
    }
}