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diff --git a/crates/proc_macro_srv/src/proc_macro/mod.rs b/crates/proc_macro_srv/src/proc_macro/mod.rs
new file mode 100644
index 000000000..ee0dc9722
--- /dev/null
+++ b/crates/proc_macro_srv/src/proc_macro/mod.rs
@@ -0,0 +1,926 @@
+//! lib-proc-macro main module
+//!
+//! Copy from https://github.com/rust-lang/rust/blob/6050e523bae6de61de4e060facc43dc512adaccd/src/libproc_macro/lib.rs
+//! augmented with removing unstable features
+
+// NOTE(@edwin0cheng):
+// Because we just copy the bridge module from rustc for ABI compatible
+// There are some unused stuffs inside it.
+// We suppress these warning here.
+#[doc(hidden)]
+#[allow(unused_macros)]
+#[allow(unused_variables)]
+pub mod bridge;
+
+mod diagnostic;
+
+pub use diagnostic::{Diagnostic, Level, MultiSpan};
+
+use std::ops::{Bound, RangeBounds};
+use std::path::PathBuf;
+use std::str::FromStr;
+use std::{fmt, iter, mem};
+
+/// The main type provided by this crate, representing an abstract stream of
+/// tokens, or, more specifically, a sequence of token trees.
+/// The type provide 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.
+#[derive(Clone)]
+pub struct TokenStream(bridge::client::TokenStream);
+
+/// Error returned from `TokenStream::from_str`
+#[derive(Debug)]
+pub struct LexError {
+    _inner: (),
+}
+
+impl TokenStream {
+    /// Returns an empty `TokenStream` containing no token trees.
+    pub fn new() -> TokenStream {
+        TokenStream(bridge::client::TokenStream::new())
+    }
+
+    /// Checks if this `TokenStream` is empty.
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+}
+
+/// 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.
+impl FromStr for TokenStream {
+    type Err = LexError;
+
+    fn from_str(src: &str) -> Result<TokenStream, LexError> {
+        Ok(TokenStream(bridge::client::TokenStream::from_str(src)))
+    }
+}
+
+// N.B., the bridge only provides `to_string`, implement `fmt::Display`
+// based on it (the reverse of the usual relationship between the two).
+// impl ToString for TokenStream {
+//     fn to_string(&self) -> String {
+//         self.0.to_string()
+//     }
+// }
+
+/// 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.
+impl fmt::Display for TokenStream {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.to_string())
+    }
+}
+
+/// Prints token in a form convenient for debugging.
+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()
+    }
+}
+
+/// Creates a token stream containing a single token tree.
+impl From<TokenTree> for TokenStream {
+    fn from(tree: TokenTree) -> TokenStream {
+        TokenStream(bridge::client::TokenStream::from_token_tree(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),
+        }))
+    }
+}
+
+/// Collects a number of token trees into a single stream.
+impl iter::FromIterator<TokenTree> for TokenStream {
+    fn from_iter<I: IntoIterator<Item = TokenTree>>(trees: I) -> Self {
+        trees.into_iter().map(TokenStream::from).collect()
+    }
+}
+
+/// A "flattening" operation on token streams, collects token trees
+/// from multiple token streams into a single stream.
+impl iter::FromIterator<TokenStream> for TokenStream {
+    fn from_iter<I: IntoIterator<Item = TokenStream>>(streams: I) -> Self {
+        let mut builder = bridge::client::TokenStreamBuilder::new();
+        streams.into_iter().for_each(|stream| builder.push(stream.0));
+        TokenStream(builder.build())
+    }
+}
+
+impl Extend<TokenTree> for TokenStream {
+    fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, trees: I) {
+        self.extend(trees.into_iter().map(TokenStream::from));
+    }
+}
+
+impl Extend<TokenStream> for TokenStream {
+    fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I) {
+        // FIXME(eddyb) Use an optimized implementation if/when possible.
+        *self = iter::once(mem::replace(self, Self::new())).chain(streams).collect();
+    }
+}
+
+/// Public implementation details for the `TokenStream` type, such as iterators.
+pub mod token_stream {
+    use crate::proc_macro::{bridge, Group, Ident, Literal, Punct, TokenStream, TokenTree};
+
+    /// 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)]
+    pub struct IntoIter(bridge::client::TokenStreamIter);
+
+    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)),
+            })
+        }
+    }
+
+    impl IntoIterator for TokenStream {
+        type Item = TokenTree;
+        type IntoIter = IntoIter;
+
+        fn into_iter(self) -> IntoIter {
+            IntoIter(self.0.into_iter())
+        }
+    }
+}
+
+/// A region of source code, along with macro expansion information.
+#[derive(Copy, Clone)]
+pub struct Span(bridge::client::Span);
+
+macro_rules! diagnostic_method {
+    ($name:ident, $level:expr) => {
+        /// Creates a new `Diagnostic` with the given `message` at the span
+        /// `self`.
+        pub fn $name<T: Into<String>>(self, message: T) -> Diagnostic {
+            Diagnostic::spanned(self, $level, message)
+        }
+    };
+}
+
+impl Span {
+    /// A span that resolves at the macro definition site.
+    pub fn def_site() -> Span {
+        Span(bridge::client::Span::def_site())
+    }
+
+    /// The span of the invocation of the current procedural macro.
+    /// Identifiers created with this span will be resolved as if they were written
+    /// directly at the macro call location (call-site hygiene) and other code
+    /// at the macro call site will be able to refer to them as well.
+    pub fn call_site() -> Span {
+        Span(bridge::client::Span::call_site())
+    }
+
+    /// A span that represents `macro_rules` hygiene, and sometimes resolves at the macro
+    /// definition site (local variables, labels, `$crate`) and sometimes at the macro
+    /// call site (everything else).
+    /// The span location is taken from the call-site.
+    pub fn mixed_site() -> Span {
+        Span(bridge::client::Span::mixed_site())
+    }
+
+    /// The original source file into which this span points.
+    pub fn source_file(&self) -> SourceFile {
+        SourceFile(self.0.source_file())
+    }
+
+    /// The `Span` for the tokens in the previous macro expansion from which
+    /// `self` was generated from, if any.
+    pub fn parent(&self) -> Option<Span> {
+        self.0.parent().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`.
+    pub fn source(&self) -> Span {
+        Span(self.0.source())
+    }
+
+    /// Gets the starting line/column in the source file for this span.
+    pub fn start(&self) -> LineColumn {
+        self.0.start()
+    }
+
+    /// Gets the ending line/column in the source file for this span.
+    pub fn end(&self) -> LineColumn {
+        self.0.end()
+    }
+
+    /// Creates a new span encompassing `self` and `other`.
+    ///
+    /// Returns `None` if `self` and `other` are from different files.
+    pub fn join(&self, other: Span) -> Option<Span> {
+        self.0.join(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`.
+    pub fn resolved_at(&self, other: Span) -> Span {
+        Span(self.0.resolved_at(other.0))
+    }
+
+    /// Creates a new span with the same name resolution behavior as `self` but
+    /// with the line/column information of `other`.
+    pub fn located_at(&self, other: Span) -> Span {
+        other.resolved_at(*self)
+    }
+
+    /// Compares to spans to see if they're equal.
+    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.
+    pub fn source_text(&self) -> Option<String> {
+        self.0.source_text()
+    }
+
+    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.
+impl fmt::Debug for Span {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(f)
+    }
+}
+
+/// A line-column pair representing the start or end of a `Span`.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct LineColumn {
+    /// The 1-indexed line in the source file on which the span starts or ends (inclusive).
+    pub line: usize,
+    /// The 0-indexed column (in UTF-8 characters) in the source file on which
+    /// the span starts or ends (inclusive).
+    pub column: usize,
+}
+
+/// The source file of a given `Span`.
+#[derive(Clone)]
+pub struct SourceFile(bridge::client::SourceFile);
+
+impl SourceFile {
+    /// Gets the path to this source file.
+    ///
+    /// ### Note
+    /// If the code span associated with this `SourceFile` was generated by an external macro, this
+    /// macro, this may not be an actual path on the filesystem. Use [`is_real`] to check.
+    ///
+    /// Also note that even if `is_real` returns `true`, if `--remap-path-prefix` was passed on
+    /// the command line, the path as given may not actually be valid.
+    ///
+    /// [`is_real`]: #method.is_real
+    pub fn path(&self) -> PathBuf {
+        PathBuf::from(self.0.path())
+    }
+
+    /// Returns `true` if this source file is a real source file, and not generated by an external
+    /// macro's expansion.
+    pub fn is_real(&self) -> bool {
+        // This is a hack until intercrate spans are implemented and we can have real source files
+        // for spans generated in external macros.
+        // https://github.com/rust-lang/rust/pull/43604#issuecomment-333334368
+        self.0.is_real()
+    }
+}
+
+impl fmt::Debug for SourceFile {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("SourceFile")
+            .field("path", &self.path())
+            .field("is_real", &self.is_real())
+            .finish()
+    }
+}
+
+impl PartialEq for SourceFile {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.eq(&other.0)
+    }
+}
+
+impl Eq for SourceFile {}
+
+/// A single token or a delimited sequence of token trees (e.g., `[1, (), ..]`).
+#[derive(Clone)]
+pub enum TokenTree {
+    /// A token stream surrounded by bracket delimiters.
+    Group(Group),
+    /// An identifier.
+    Ident(Ident),
+    /// A single punctuation character (`+`, `,`, `$`, etc.).
+    Punct(Punct),
+    /// A literal character (`'a'`), string (`"hello"`), number (`2.3`), etc.
+    Literal(Literal),
+}
+
+impl TokenTree {
+    /// Returns the span of this tree, delegating to the `span` method of
+    /// the contained token or a delimited stream.
+    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.
+    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.
+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),
+        }
+    }
+}
+
+impl From<Group> for TokenTree {
+    fn from(g: Group) -> TokenTree {
+        TokenTree::Group(g)
+    }
+}
+
+impl From<Ident> for TokenTree {
+    fn from(g: Ident) -> TokenTree {
+        TokenTree::Ident(g)
+    }
+}
+
+impl From<Punct> for TokenTree {
+    fn from(g: Punct) -> TokenTree {
+        TokenTree::Punct(g)
+    }
+}
+
+impl From<Literal> for TokenTree {
+    fn from(g: Literal) -> TokenTree {
+        TokenTree::Literal(g)
+    }
+}
+
+// N.B., the bridge only provides `to_string`, implement `fmt::Display`
+// based on it (the reverse of the usual relationship between the two).
+// impl ToString for TokenTree {
+//     fn to_string(&self) -> String {
+//         match *self {
+//             TokenTree::Group(ref t) => t.to_string(),
+//             TokenTree::Ident(ref t) => t.to_string(),
+//             TokenTree::Punct(ref t) => t.to_string(),
+//             TokenTree::Literal(ref t) => t.to_string(),
+//         }
+//     }
+// }
+
+/// 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.
+impl fmt::Display for TokenTree {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.to_string())
+    }
+}
+
+/// A delimited token stream.
+///
+/// A `Group` internally contains a `TokenStream` which is surrounded by `Delimiter`s.
+#[derive(Clone)]
+pub struct Group(bridge::client::Group);
+
+/// Describes how a sequence of token trees is delimited.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum Delimiter {
+    /// `( ... )`
+    Parenthesis,
+    /// `{ ... }`
+    Brace,
+    /// `[ ... ]`
+    Bracket,
+    /// `Ø ... Ø`
+    /// An implicit 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`.
+    /// Implicit delimiters may not survive roundtrip of a token stream through a string.
+    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.
+    pub fn new(delimiter: Delimiter, stream: TokenStream) -> Group {
+        Group(bridge::client::Group::new(delimiter, stream.0))
+    }
+
+    /// Returns the delimiter of this `Group`
+    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.
+    pub fn stream(&self) -> TokenStream {
+        TokenStream(self.0.stream())
+    }
+
+    /// Returns the span for the delimiters of this token stream, spanning the
+    /// entire `Group`.
+    ///
+    /// ```text
+    /// pub fn span(&self) -> Span {
+    ///            ^^^^^^^
+    /// ```
+    pub fn span(&self) -> Span {
+        Span(self.0.span())
+    }
+
+    /// Returns the span pointing to the opening delimiter of this group.
+    ///
+    /// ```text
+    /// pub fn span_open(&self) -> Span {
+    ///                 ^
+    /// ```
+    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 {
+    ///                        ^
+    /// ```
+    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`.
+    pub fn set_span(&mut self, span: Span) {
+        self.0.set_span(span.0);
+    }
+}
+
+// N.B., the bridge only provides `to_string`, implement `fmt::Display`
+// based on it (the reverse of the usual relationship between the two).
+// impl ToString for Group {
+//     fn to_string(&self) -> String {
+//         TokenStream::from(TokenTree::from(self.clone())).to_string()
+//     }
+// }
+
+/// 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.
+impl fmt::Display for Group {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.to_string())
+    }
+}
+
+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()
+    }
+}
+
+/// An `Punct` is an single punctuation character like `+`, `-` or `#`.
+///
+/// Multi-character operators like `+=` are represented as two instances of `Punct` with different
+/// forms of `Spacing` returned.
+#[derive(Clone)]
+pub struct Punct(bridge::client::Punct);
+
+/// Whether an `Punct` is followed immediately by another `Punct` or
+/// followed by another token or whitespace.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum Spacing {
+    /// e.g., `+` is `Alone` in `+ =`, `+ident` or `+()`.
+    Alone,
+    /// e.g., `+` is `Joint` in `+=` or `'#`.
+    /// Additionally, single quote `'` can join with identifiers to form lifetimes `'ident`.
+    Joint,
+}
+
+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.
+    pub fn new(ch: char, spacing: Spacing) -> Punct {
+        Punct(bridge::client::Punct::new(ch, spacing))
+    }
+
+    /// Returns the value of this punctuation character as `char`.
+    pub fn as_char(&self) -> char {
+        self.0.as_char()
+    }
+
+    /// Returns the spacing of this punctuation character, indicating whether it's immediately
+    /// followed by another `Punct` in the token stream, so they can potentially be combined into
+    /// a multi-character operator (`Joint`), or it's followed by some other token or whitespace
+    /// (`Alone`) so the operator has certainly ended.
+    pub fn spacing(&self) -> Spacing {
+        self.0.spacing()
+    }
+
+    /// Returns the span for this punctuation character.
+    pub fn span(&self) -> Span {
+        Span(self.0.span())
+    }
+
+    /// Configure the span for this punctuation character.
+    pub fn set_span(&mut self, span: Span) {
+        self.0 = self.0.with_span(span.0);
+    }
+}
+
+// N.B., the bridge only provides `to_string`, implement `fmt::Display`
+// based on it (the reverse of the usual relationship between the two).
+// impl ToString for Punct {
+//     fn to_string(&self) -> String {
+//         TokenStream::from(TokenTree::from(self.clone())).to_string()
+//     }
+// }
+
+/// Prints the punctuation character as a string that should be losslessly convertible
+/// back into the same character.
+impl fmt::Display for Punct {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.to_string())
+    }
+}
+
+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()
+    }
+}
+
+/// An identifier (`ident`).
+#[derive(Clone, PartialEq, Eq, Hash)]
+pub struct Ident(bridge::client::Ident);
+
+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, otherwise the function will panic.
+    ///
+    /// 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.
+    pub fn new(string: &str, span: Span) -> Ident {
+        Ident(bridge::client::Ident::new(string, span.0, false))
+    }
+
+    /// Same as `Ident::new`, but creates a raw identifier (`r#ident`).
+    pub fn new_raw(string: &str, span: Span) -> Ident {
+        Ident(bridge::client::Ident::new(string, span.0, true))
+    }
+
+    /// Returns the span of this `Ident`, encompassing the entire string returned
+    /// by `as_str`.
+    pub fn span(&self) -> Span {
+        Span(self.0.span())
+    }
+
+    /// Configures the span of this `Ident`, possibly changing its hygiene context.
+    pub fn set_span(&mut self, span: Span) {
+        self.0 = self.0.with_span(span.0);
+    }
+}
+
+// N.B., the bridge only provides `to_string`, implement `fmt::Display`
+// based on it (the reverse of the usual relationship between the two).
+// impl ToString for Ident {
+//     fn to_string(&self) -> String {
+//         TokenStream::from(TokenTree::from(self.clone())).to_string()
+//     }
+// }
+
+/// Prints the identifier as a string that should be losslessly convertible
+/// back into the same identifier.
+impl fmt::Display for Ident {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.to_string())
+    }
+}
+
+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"`),
+/// 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)]
+pub struct Literal(bridge::client::Literal);
+
+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 may 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.
+        pub fn $name(n: $kind) -> Literal {
+            Literal(bridge::client::Literal::typed_integer(&n.to_string(), stringify!($kind)))
+        }
+    )*)
+}
+
+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 may 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.
+        pub fn $name(n: $kind) -> Literal {
+            Literal(bridge::client::Literal::integer(&n.to_string()))
+        }
+    )*)
+}
+
+impl Literal {
+    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 may 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.
+    pub fn f32_unsuffixed(n: f32) -> Literal {
+        if !n.is_finite() {
+            panic!("Invalid float literal {}", n);
+        }
+        Literal(bridge::client::Literal::float(&n.to_string()))
+    }
+
+    /// 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 may 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.
+    pub fn f32_suffixed(n: f32) -> Literal {
+        if !n.is_finite() {
+            panic!("Invalid float literal {}", n);
+        }
+        Literal(bridge::client::Literal::f32(&n.to_string()))
+    }
+
+    /// 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 may 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.
+    pub fn f64_unsuffixed(n: f64) -> Literal {
+        if !n.is_finite() {
+            panic!("Invalid float literal {}", n);
+        }
+        Literal(bridge::client::Literal::float(&n.to_string()))
+    }
+
+    /// 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 may 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.
+    pub fn f64_suffixed(n: f64) -> Literal {
+        if !n.is_finite() {
+            panic!("Invalid float literal {}", n);
+        }
+        Literal(bridge::client::Literal::f64(&n.to_string()))
+    }
+
+    /// String literal.
+    pub fn string(string: &str) -> Literal {
+        Literal(bridge::client::Literal::string(string))
+    }
+
+    /// Character literal.
+    pub fn character(ch: char) -> Literal {
+        Literal(bridge::client::Literal::character(ch))
+    }
+
+    /// Byte string literal.
+    pub fn byte_string(bytes: &[u8]) -> Literal {
+        Literal(bridge::client::Literal::byte_string(bytes))
+    }
+
+    /// Returns the span encompassing this literal.
+    pub fn span(&self) -> Span {
+        Span(self.0.span())
+    }
+
+    /// Configures the span associated for this literal.
+    pub fn set_span(&mut self, span: Span) {
+        self.0.set_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}'.
+    pub fn subspan<R: RangeBounds<usize>>(&self, range: R) -> Option<Span> {
+        // HACK(eddyb) something akin to `Option::cloned`, but for `Bound<&T>`.
+        fn cloned_bound<T: Clone>(bound: Bound<&T>) -> Bound<T> {
+            match bound {
+                Bound::Included(x) => Bound::Included(x.clone()),
+                Bound::Excluded(x) => Bound::Excluded(x.clone()),
+                Bound::Unbounded => Bound::Unbounded,
+            }
+        }
+
+        self.0.subspan(cloned_bound(range.start_bound()), cloned_bound(range.end_bound())).map(Span)
+    }
+}
+
+// N.B., the bridge only provides `to_string`, implement `fmt::Display`
+// based on it (the reverse of the usual relationship between the two).
+// impl ToString for Literal {
+//     fn to_string(&self) -> String {
+//         TokenStream::from(TokenTree::from(self.clone())).to_string()
+//     }
+// }
+
+/// Prints the literal as a string that should be losslessly convertible
+/// back into the same literal (except for possible rounding for floating point literals).
+impl fmt::Display for Literal {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.to_string())
+    }
+}
+
+impl fmt::Debug for Literal {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        // FIXME(eddyb) `Literal` should not expose internal `Debug` impls.
+        self.0.fmt(f)
+    }
+}