Merge "Upgrade proc-macro2 to 1.0.47" am: 625c45bf46 am: 7e2af67865

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/proc-macro2/+/2346146

Change-Id: If596a9c1f1538d9cfc26de59bb00586563b99752
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

18 files changed, 622 insertions, 230 deletions

diff --git a/.cargo_vcs_info.json b/.cargo_vcs_info.json
index 59bd97e..99281c2 100644
--- a/.cargo_vcs_info.json
+++ b/.cargo_vcs_info.json
@@ -1,6 +1,6 @@
 {
   "git": {
-    "sha1": "7ecea3b88fe72672ca4270631b5d4585c0f7c715"
+    "sha1": "47c91c8525088a055bbfec5df6ea4cd131d01504"
   },
   "path_in_vcs": ""
 }
\ No newline at end of file
diff --git a/.github/FUNDING.yml b/.github/FUNDING.yml
new file mode 100644
index 0000000..7507077
--- /dev/null
+++ b/.github/FUNDING.yml
@@ -0,0 +1 @@
+github: dtolnay
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2063a5c..32773a6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,6 +5,12 @@ on:
   pull_request:
   schedule: [cron: "40 1 * * *"]
 
+permissions:
+  contents: read
+
+env:
+  RUSTFLAGS: -Dwarnings
+
 jobs:
   test:
     name: Rust ${{matrix.rust}}
@@ -14,57 +20,92 @@ jobs:
       matrix:
         rust: [1.31.0, stable, beta]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{matrix.rust}}
       - run: cargo test
       - run: cargo test --no-default-features
       - run: cargo test --features span-locations
-      - run: RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo test
-      - run: RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo test --no-default-features
+      - name: RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo test
+        run: cargo test
+        env:
+          RUSTFLAGS: --cfg procmacro2_semver_exempt ${{env.RUSTFLAGS}}
+      - name: RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo test --no-default-features
+        run: cargo test --no-default-features
+        env:
+          RUSTFLAGS: --cfg procmacro2_semver_exempt ${{env.RUSTFLAGS}}
 
   nightly:
     name: Rust nightly
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@nightly
       - run: cargo test
       - run: cargo test --no-default-features
       - run: cargo test --no-default-features -- --ignored # run the ignored test to make sure the `proc-macro` feature is disabled
       - run: cargo test --features span-locations
       - run: cargo test --manifest-path tests/ui/Cargo.toml
-      - run: RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo test
-      - run: RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo test --no-default-features
-      - run: RUSTFLAGS='-Z allow-features=' cargo test
+      - name: RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo test
+        run: cargo test
+        env:
+          RUSTFLAGS: --cfg procmacro2_semver_exempt ${{env.RUSTFLAGS}}
+      - name: RUSTFLAGS='--cfg procmacro2_semver_exempt' cargo test --no-default-features
+        run: cargo test --no-default-features
+        env:
+          RUSTFLAGS: --cfg procmacro2_semver_exempt ${{env.RUSTFLAGS}}
+      - name: RUSTFLAGS='-Z allow-features=' cargo test
+        run: cargo test
+        env:
+          RUSTFLAGS: -Z allow-features= ${{env.RUSTFLAGS}}
       - run: cargo update -Z minimal-versions && cargo build
 
   webassembly:
     name: WebAssembly
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@nightly
         with:
           target: wasm32-unknown-unknown
       - run: cargo test --target wasm32-unknown-unknown --no-run
 
+  fuzz:
+    name: Fuzz
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@nightly
+      - uses: dtolnay/install@cargo-fuzz
+      - run: cargo fuzz build -O
+
   clippy:
     name: Clippy
     runs-on: ubuntu-latest
     if: github.event_name != 'pull_request'
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@clippy
       - run: cargo clippy --tests -- -Dclippy::all -Dclippy::pedantic
       - run: cargo clippy --tests --all-features -- -Dclippy::all -Dclippy::pedantic
 
+  miri:
+    name: Miri
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@miri
+      - run: cargo miri test
+        env:
+          MIRIFLAGS: -Zmiri-strict-provenance
+
   outdated:
     name: Outdated
     runs-on: ubuntu-latest
     if: github.event_name != 'pull_request'
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: dtolnay/install@cargo-outdated
-      - run: cargo outdated --exit-code 1
+      - run: cargo outdated --workspace --exit-code 1
+      - run: cargo outdated --manifest-path fuzz/Cargo.toml --exit-code 1
diff --git a/Android.bp b/Android.bp
index 410a4f4..58461ea 100644
--- a/Android.bp
+++ b/Android.bp
@@ -41,7 +41,7 @@ rust_library_host {
     name: "libproc_macro2",
     crate_name: "proc_macro2",
     cargo_env_compat: true,
-    cargo_pkg_version: "1.0.36",
+    cargo_pkg_version: "1.0.47",
     srcs: ["src/lib.rs"],
     edition: "2018",
     features: [
@@ -50,21 +50,26 @@ rust_library_host {
         "span-locations",
     ],
     cfgs: [
+        "proc_macro_span",
         "span_locations",
         "use_proc_macro",
         "wrap_proc_macro",
     ],
     rustlibs: [
-        "libunicode_xid",
+        "libunicode_ident",
     ],
     compile_multilib: "first",
+    apex_available: [
+        "//apex_available:platform",
+        "//apex_available:anyapex",
+    ],
 }
 
 rust_defaults {
     name: "proc-macro2_test_defaults",
     crate_name: "proc_macro2",
     cargo_env_compat: true,
-    cargo_pkg_version: "1.0.36",
+    cargo_pkg_version: "1.0.47",
     test_suites: ["general-tests"],
     auto_gen_config: true,
     edition: "2018",
@@ -74,6 +79,7 @@ rust_defaults {
         "span-locations",
     ],
     cfgs: [
+        "proc_macro_span",
         "span_locations",
         "use_proc_macro",
         "wrap_proc_macro",
@@ -81,7 +87,7 @@ rust_defaults {
     rustlibs: [
         "libproc_macro2",
         "libquote",
-        "libunicode_xid",
+        "libunicode_ident",
     ],
 }
 
diff --git a/Cargo.toml b/Cargo.toml
index 1272f37..1bda7e3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,25 +13,42 @@
 edition = "2018"
 rust-version = "1.31"
 name = "proc-macro2"
-version = "1.0.36"
-authors = ["David Tolnay <dtolnay@gmail.com>", "Alex Crichton <alex@alexcrichton.com>"]
+version = "1.0.47"
+authors = [
+    "David Tolnay <dtolnay@gmail.com>",
+    "Alex Crichton <alex@alexcrichton.com>",
+]
 autobenches = false
-description = "A substitute implementation of the compiler's `proc_macro` API to decouple\ntoken-based libraries from the procedural macro use case.\n"
+description = "A substitute implementation of the compiler's `proc_macro` API to decouple token-based libraries from the procedural macro use case."
 documentation = "https://docs.rs/proc-macro2"
 readme = "README.md"
-keywords = ["macros"]
+keywords = [
+    "macros",
+    "syn",
+]
 categories = ["development-tools::procedural-macro-helpers"]
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/dtolnay/proc-macro2"
+
 [package.metadata.docs.rs]
-rustc-args = ["--cfg", "procmacro2_semver_exempt"]
-rustdoc-args = ["--cfg", "procmacro2_semver_exempt", "--cfg", "doc_cfg"]
+rustc-args = [
+    "--cfg",
+    "procmacro2_semver_exempt",
+]
+rustdoc-args = [
+    "--cfg",
+    "procmacro2_semver_exempt",
+    "--cfg",
+    "doc_cfg",
+]
 targets = ["x86_64-unknown-linux-gnu"]
 
 [package.metadata.playground]
 features = ["span-locations"]
-[dependencies.unicode-xid]
-version = "0.2"
+
+[dependencies.unicode-ident]
+version = "1.0"
+
 [dev-dependencies.quote]
 version = "1.0"
 default_features = false
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
index 401bfaf..273683a 100644
--- a/Cargo.toml.orig
+++ b/Cargo.toml.orig
@@ -1,20 +1,16 @@
 [package]
 name = "proc-macro2"
-version = "1.0.36" # remember to update html_root_url
+version = "1.0.47" # remember to update html_root_url
 authors = ["David Tolnay <dtolnay@gmail.com>", "Alex Crichton <alex@alexcrichton.com>"]
-license = "MIT OR Apache-2.0"
-readme = "README.md"
-keywords = ["macros"]
-repository = "https://github.com/dtolnay/proc-macro2"
-documentation = "https://docs.rs/proc-macro2"
+autobenches = false
 categories = ["development-tools::procedural-macro-helpers"]
+description = "A substitute implementation of the compiler's `proc_macro` API to decouple token-based libraries from the procedural macro use case."
+documentation = "https://docs.rs/proc-macro2"
 edition = "2018"
-autobenches = false
+keywords = ["macros", "syn"]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/dtolnay/proc-macro2"
 rust-version = "1.31"
-description = """
-A substitute implementation of the compiler's `proc_macro` API to decouple
-token-based libraries from the procedural macro use case.
-"""
 
 [package.metadata.docs.rs]
 rustc-args = ["--cfg", "procmacro2_semver_exempt"]
@@ -25,7 +21,7 @@ targets = ["x86_64-unknown-linux-gnu"]
 features = ["span-locations"]
 
 [dependencies]
-unicode-xid = "0.2"
+unicode-ident = "1.0"
 
 [dev-dependencies]
 quote = { version = "1.0", default_features = false }
diff --git a/METADATA b/METADATA
index e2ded2b..ffab613 100644
--- a/METADATA
+++ b/METADATA
@@ -1,3 +1,7 @@
+# This project was upgraded with external_updater.
+# Usage: tools/external_updater/updater.sh update rust/crates/proc-macro2
+# For more info, check https://cs.android.com/android/platform/superproject/+/master:tools/external_updater/README.md
+
 name: "proc-macro2"
 description: "A substitute implementation of the compiler\'s `proc_macro` API to decouple token-based libraries from the procedural macro use case."
 third_party {
@@ -7,13 +11,13 @@ third_party {
   }
   url {
     type: ARCHIVE
-    value: "https://static.crates.io/crates/proc-macro2/proc-macro2-1.0.36.crate"
+    value: "https://static.crates.io/crates/proc-macro2/proc-macro2-1.0.47.crate"
   }
-  version: "1.0.36"
+  version: "1.0.47"
   license_type: NOTICE
   last_upgrade_date {
     year: 2022
-    month: 3
-    day: 1
+    month: 12
+    day: 13
   }
 }
diff --git a/README.md b/README.md
index 35e1876..70b6c86 100644
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@
 
 [<img alt="github" src="https://img.shields.io/badge/github-dtolnay/proc--macro2-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/proc-macro2)
 [<img alt="crates.io" src="https://img.shields.io/crates/v/proc-macro2.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/proc-macro2)
-[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-proc--macro2-66c2a5?style=for-the-badge&labelColor=555555&logoColor=white&logo=data:image/svg+xml;base64,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" height="20">](https://docs.rs/proc-macro2)
+[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-proc--macro2-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/proc-macro2)
 [<img alt="build status" src="https://img.shields.io/github/workflow/status/dtolnay/proc-macro2/CI/master?style=for-the-badge" height="20">](https://github.com/dtolnay/proc-macro2/actions?query=branch%3Amaster)
 
 A wrapper around the procedural macro API of the compiler's `proc_macro` crate.
diff --git a/build.rs b/build.rs
index 946be6e..b69d813 100644
--- a/build.rs
+++ b/build.rs
@@ -41,7 +41,6 @@
 //     1.57+.
 
 use std::env;
-use std::iter;
 use std::process::{self, Command};
 use std::str;
 
@@ -85,6 +84,10 @@ fn main() {
         println!("cargo:rustc-cfg=no_hygiene");
     }
 
+    if version.minor < 47 {
+        println!("cargo:rustc-cfg=no_ident_new_raw");
+    }
+
     if version.minor < 54 {
         println!("cargo:rustc-cfg=no_literal_from_str");
     }
@@ -108,7 +111,10 @@ fn main() {
         println!("cargo:rustc-cfg=wrap_proc_macro");
     }
 
-    if version.nightly && feature_allowed("proc_macro_span") {
+    if version.nightly
+        && feature_allowed("proc_macro_span")
+        && feature_allowed("proc_macro_span_shrink")
+    {
         println!("cargo:rustc-cfg=proc_macro_span");
     }
 
@@ -154,23 +160,13 @@ fn feature_allowed(feature: &str) -> bool {
 
     let flags_var;
     let flags_var_string;
-    let mut flags_var_split;
-    let mut flags_none;
-    let flags: &mut dyn Iterator<Item = &str> =
-        if let Some(encoded_rustflags) = env::var_os("CARGO_ENCODED_RUSTFLAGS") {
-            flags_var = encoded_rustflags;
-            flags_var_string = flags_var.to_string_lossy();
-            flags_var_split = flags_var_string.split('\x1f');
-            &mut flags_var_split
-        } else if let Some(rustflags) = env::var_os("RUSTFLAGS") {
-            flags_var = rustflags;
-            flags_var_string = flags_var.to_string_lossy();
-            flags_var_split = flags_var_string.split(' ');
-            &mut flags_var_split
-        } else {
-            flags_none = iter::empty();
-            &mut flags_none
-        };
+    let flags = if let Some(encoded_rustflags) = env::var_os("CARGO_ENCODED_RUSTFLAGS") {
+        flags_var = encoded_rustflags;
+        flags_var_string = flags_var.to_string_lossy();
+        flags_var_string.split('\x1f')
+    } else {
+        return true;
+    };
 
     for mut flag in flags {
         if flag.starts_with("-Z") {
diff --git a/src/detection.rs b/src/detection.rs
index d139b73..beba7b2 100644
--- a/src/detection.rs
+++ b/src/detection.rs
@@ -1,4 +1,4 @@
-use std::sync::atomic::{AtomicUsize, Ordering};
+use core::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Once;
 
 static WORKS: AtomicUsize = AtomicUsize::new(0);
diff --git a/src/fallback.rs b/src/fallback.rs
index ac5437d..fe4f248 100644
--- a/src/fallback.rs
+++ b/src/fallback.rs
@@ -1,19 +1,19 @@
 use crate::parse::{self, Cursor};
+use crate::rcvec::{RcVec, RcVecBuilder, RcVecIntoIter, RcVecMut};
 use crate::{Delimiter, Spacing, TokenTree};
 #[cfg(span_locations)]
-use std::cell::RefCell;
+use core::cell::RefCell;
 #[cfg(span_locations)]
-use std::cmp;
-use std::fmt::{self, Debug, Display};
-use std::iter::FromIterator;
-use std::mem;
-use std::ops::RangeBounds;
+use core::cmp;
+use core::fmt::{self, Debug, Display, Write};
+use core::iter::FromIterator;
+use core::mem::ManuallyDrop;
+use core::ops::RangeBounds;
+use core::ptr;
+use core::str::FromStr;
 #[cfg(procmacro2_semver_exempt)]
 use std::path::Path;
 use std::path::PathBuf;
-use std::str::FromStr;
-use std::vec;
-use unicode_xid::UnicodeXID;
 
 /// Force use of proc-macro2's fallback implementation of the API for now, even
 /// if the compiler's implementation is available.
@@ -31,7 +31,7 @@ pub fn unforce() {
 
 #[derive(Clone)]
 pub(crate) struct TokenStream {
-    inner: Vec<TokenTree>,
+    inner: RcVec<TokenTree>,
 }
 
 #[derive(Debug)]
@@ -53,71 +53,69 @@ impl LexError {
 
 impl TokenStream {
     pub fn new() -> Self {
-        TokenStream { inner: Vec::new() }
+        TokenStream {
+            inner: RcVecBuilder::new().build(),
+        }
     }
 
     pub fn is_empty(&self) -> bool {
         self.inner.len() == 0
     }
 
-    fn take_inner(&mut self) -> Vec<TokenTree> {
-        mem::replace(&mut self.inner, Vec::new())
+    fn take_inner(self) -> RcVecBuilder<TokenTree> {
+        let nodrop = ManuallyDrop::new(self);
+        unsafe { ptr::read(&nodrop.inner) }.make_owned()
     }
+}
 
-    fn push_token(&mut self, token: TokenTree) {
-        // https://github.com/dtolnay/proc-macro2/issues/235
-        match token {
-            #[cfg(not(no_bind_by_move_pattern_guard))]
-            TokenTree::Literal(crate::Literal {
-                #[cfg(wrap_proc_macro)]
-                    inner: crate::imp::Literal::Fallback(literal),
-                #[cfg(not(wrap_proc_macro))]
-                    inner: literal,
-                ..
-            }) if literal.repr.starts_with('-') => {
-                push_negative_literal(self, literal);
-            }
-            #[cfg(no_bind_by_move_pattern_guard)]
-            TokenTree::Literal(crate::Literal {
-                #[cfg(wrap_proc_macro)]
-                    inner: crate::imp::Literal::Fallback(literal),
-                #[cfg(not(wrap_proc_macro))]
-                    inner: literal,
-                ..
-            }) => {
-                if literal.repr.starts_with('-') {
-                    push_negative_literal(self, literal);
-                } else {
-                    self.inner
-                        .push(TokenTree::Literal(crate::Literal::_new_stable(literal)));
-                }
-            }
-            _ => self.inner.push(token),
+fn push_token_from_proc_macro(mut vec: RcVecMut<TokenTree>, token: TokenTree) {
+    // https://github.com/dtolnay/proc-macro2/issues/235
+    match token {
+        #[cfg(not(no_bind_by_move_pattern_guard))]
+        TokenTree::Literal(crate::Literal {
+            #[cfg(wrap_proc_macro)]
+                inner: crate::imp::Literal::Fallback(literal),
+            #[cfg(not(wrap_proc_macro))]
+                inner: literal,
+            ..
+        }) if literal.repr.starts_with('-') => {
+            push_negative_literal(vec, literal);
         }
-
-        #[cold]
-        fn push_negative_literal(stream: &mut TokenStream, mut literal: Literal) {
-            literal.repr.remove(0);
-            let mut punct = crate::Punct::new('-', Spacing::Alone);
-            punct.set_span(crate::Span::_new_stable(literal.span));
-            stream.inner.push(TokenTree::Punct(punct));
-            stream
-                .inner
-                .push(TokenTree::Literal(crate::Literal::_new_stable(literal)));
+        #[cfg(no_bind_by_move_pattern_guard)]
+        TokenTree::Literal(crate::Literal {
+            #[cfg(wrap_proc_macro)]
+                inner: crate::imp::Literal::Fallback(literal),
+            #[cfg(not(wrap_proc_macro))]
+                inner: literal,
+            ..
+        }) => {
+            if literal.repr.starts_with('-') {
+                push_negative_literal(vec, literal);
+            } else {
+                vec.push(TokenTree::Literal(crate::Literal::_new_stable(literal)));
+            }
         }
+        _ => vec.push(token),
     }
-}
 
-impl From<Vec<TokenTree>> for TokenStream {
-    fn from(inner: Vec<TokenTree>) -> Self {
-        TokenStream { inner }
+    #[cold]
+    fn push_negative_literal(mut vec: RcVecMut<TokenTree>, mut literal: Literal) {
+        literal.repr.remove(0);
+        let mut punct = crate::Punct::new('-', Spacing::Alone);
+        punct.set_span(crate::Span::_new_stable(literal.span));
+        vec.push(TokenTree::Punct(punct));
+        vec.push(TokenTree::Literal(crate::Literal::_new_stable(literal)));
     }
 }
 
 // Nonrecursive to prevent stack overflow.
 impl Drop for TokenStream {
     fn drop(&mut self) {
-        while let Some(token) = self.inner.pop() {
+        let mut inner = match self.inner.get_mut() {
+            Some(inner) => inner,
+            None => return,
+        };
+        while let Some(token) = inner.pop() {
             let group = match token {
                 TokenTree::Group(group) => group.inner,
                 _ => continue,
@@ -127,8 +125,35 @@ impl Drop for TokenStream {
                 crate::imp::Group::Fallback(group) => group,
                 crate::imp::Group::Compiler(_) => continue,
             };
-            let mut group = group;
-            self.inner.extend(group.stream.take_inner());
+            inner.extend(group.stream.take_inner());
+        }
+    }
+}
+
+pub(crate) struct TokenStreamBuilder {
+    inner: RcVecBuilder<TokenTree>,
+}
+
+impl TokenStreamBuilder {
+    pub fn new() -> Self {
+        TokenStreamBuilder {
+            inner: RcVecBuilder::new(),
+        }
+    }
+
+    pub fn with_capacity(cap: usize) -> Self {
+        TokenStreamBuilder {
+            inner: RcVecBuilder::with_capacity(cap),
+        }
+    }
+
+    pub fn push_token_from_parser(&mut self, tt: TokenTree) {
+        self.inner.push(tt);
+    }
+
+    pub fn build(self) -> TokenStream {
+        TokenStream {
+            inner: self.inner.build(),
         }
     }
 }
@@ -157,7 +182,13 @@ impl FromStr for TokenStream {
 
     fn from_str(src: &str) -> Result<TokenStream, LexError> {
         // Create a dummy file & add it to the source map
-        let cursor = get_cursor(src);
+        let mut cursor = get_cursor(src);
+
+        // Strip a byte order mark if present
+        const BYTE_ORDER_MARK: &str = "\u{feff}";
+        if cursor.starts_with(BYTE_ORDER_MARK) {
+            cursor = cursor.advance(BYTE_ORDER_MARK.len());
+        }
 
         parse::token_stream(cursor)
     }
@@ -221,9 +252,11 @@ impl From<TokenStream> for proc_macro::TokenStream {
 
 impl From<TokenTree> for TokenStream {
     fn from(tree: TokenTree) -> TokenStream {
-        let mut stream = TokenStream::new();
-        stream.push_token(tree);
-        stream
+        let mut stream = RcVecBuilder::new();
+        push_token_from_proc_macro(stream.as_mut(), tree);
+        TokenStream {
+            inner: stream.build(),
+        }
     }
 }
 
@@ -237,35 +270,38 @@ impl FromIterator<TokenTree> for TokenStream {
 
 impl FromIterator<TokenStream> for TokenStream {
     fn from_iter<I: IntoIterator<Item = TokenStream>>(streams: I) -> Self {
-        let mut v = Vec::new();
+        let mut v = RcVecBuilder::new();
 
-        for mut stream in streams {
+        for stream in streams {
             v.extend(stream.take_inner());
         }
 
-        TokenStream { inner: v }
+        TokenStream { inner: v.build() }
     }
 }
 
 impl Extend<TokenTree> for TokenStream {
     fn extend<I: IntoIterator<Item = TokenTree>>(&mut self, tokens: I) {
-        tokens.into_iter().for_each(|token| self.push_token(token));
+        let mut vec = self.inner.make_mut();
+        tokens
+            .into_iter()
+            .for_each(|token| push_token_from_proc_macro(vec.as_mut(), token));
     }
 }
 
 impl Extend<TokenStream> for TokenStream {
     fn extend<I: IntoIterator<Item = TokenStream>>(&mut self, streams: I) {
-        self.inner.extend(streams.into_iter().flatten());
+        self.inner.make_mut().extend(streams.into_iter().flatten());
     }
 }
 
-pub(crate) type TokenTreeIter = vec::IntoIter<TokenTree>;
+pub(crate) type TokenTreeIter = RcVecIntoIter<TokenTree>;
 
 impl IntoIterator for TokenStream {
     type Item = TokenTree;
     type IntoIter = TokenTreeIter;
 
-    fn into_iter(mut self) -> TokenTreeIter {
+    fn into_iter(self) -> TokenTreeIter {
         self.take_inner().into_iter()
     }
 }
@@ -384,7 +420,7 @@ impl SourceMap {
     fn add_file(&mut self, name: &str, src: &str) -> Span {
         let (len, lines) = lines_offsets(src);
         let lo = self.next_start_pos();
-        // XXX(nika): Shouild we bother doing a checked cast or checked add here?
+        // XXX(nika): Should we bother doing a checked cast or checked add here?
         let span = Span {
             lo,
             hi: lo + (len as u32),
@@ -482,6 +518,26 @@ impl Span {
         })
     }
 
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn before(&self) -> Span {
+        Span {
+            #[cfg(span_locations)]
+            lo: self.lo,
+            #[cfg(span_locations)]
+            hi: self.lo,
+        }
+    }
+
+    #[cfg(procmacro2_semver_exempt)]
+    pub fn after(&self) -> Span {
+        Span {
+            #[cfg(span_locations)]
+            lo: self.hi,
+            #[cfg(span_locations)]
+            hi: self.hi,
+        }
+    }
+
     #[cfg(not(span_locations))]
     pub fn join(&self, _other: Span) -> Option<Span> {
         Some(Span {})
@@ -639,7 +695,7 @@ pub(crate) struct Ident {
 
 impl Ident {
     fn _new(string: &str, raw: bool, span: Span) -> Self {
-        validate_ident(string);
+        validate_ident(string, raw);
 
         Ident {
             sym: string.to_owned(),
@@ -666,27 +722,19 @@ impl Ident {
 }
 
 pub(crate) fn is_ident_start(c: char) -> bool {
-    ('a' <= c && c <= 'z')
-        || ('A' <= c && c <= 'Z')
-        || c == '_'
-        || (c > '\x7f' && UnicodeXID::is_xid_start(c))
+    c == '_' || unicode_ident::is_xid_start(c)
 }
 
 pub(crate) fn is_ident_continue(c: char) -> bool {
-    ('a' <= c && c <= 'z')
-        || ('A' <= c && c <= 'Z')
-        || c == '_'
-        || ('0' <= c && c <= '9')
-        || (c > '\x7f' && UnicodeXID::is_xid_continue(c))
+    unicode_ident::is_xid_continue(c)
 }
 
-fn validate_ident(string: &str) {
-    let validate = string;
-    if validate.is_empty() {
+fn validate_ident(string: &str, raw: bool) {
+    if string.is_empty() {
         panic!("Ident is not allowed to be empty; use Option<Ident>");
     }
 
-    if validate.bytes().all(|digit| digit >= b'0' && digit <= b'9') {
+    if string.bytes().all(|digit| digit >= b'0' && digit <= b'9') {
         panic!("Ident cannot be a number; use Literal instead");
     }
 
@@ -704,9 +752,18 @@ fn validate_ident(string: &str) {
         true
     }
 
-    if !ident_ok(validate) {
+    if !ident_ok(string) {
         panic!("{:?} is not a valid Ident", string);
     }
+
+    if raw {
+        match string {
+            "_" | "super" | "self" | "Self" | "crate" => {
+                panic!("`r#{}` cannot be a raw identifier", string);
+            }
+            _ => {}
+        }
+    }
 }
 
 impl PartialEq for Ident {
@@ -883,7 +940,9 @@ impl Literal {
                 b'"' => escaped.push_str("\\\""),
                 b'\\' => escaped.push_str("\\\\"),
                 b'\x20'..=b'\x7E' => escaped.push(*b as char),
-                _ => escaped.push_str(&format!("\\x{:02X}", b)),
+                _ => {
+                    let _ = write!(escaped, "\\x{:02X}", b);
+                }
             }
         }
         escaped.push('"');
diff --git a/src/lib.rs b/src/lib.rs
index 6edaf42..3fda02d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,7 +2,7 @@
 //!
 //! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
 //! [crates-io]: https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust
-//! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logoColor=white&logo=data:image/svg+xml;base64,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
+//! [docs-rs]: https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs
 //!
 //! <br>
 //!
@@ -86,8 +86,11 @@
 //! a different thread.
 
 // Proc-macro2 types in rustdoc of other crates get linked to here.
-#![doc(html_root_url = "https://docs.rs/proc-macro2/1.0.36")]
-#![cfg_attr(any(proc_macro_span, super_unstable), feature(proc_macro_span))]
+#![doc(html_root_url = "https://docs.rs/proc-macro2/1.0.47")]
+#![cfg_attr(
+    any(proc_macro_span, super_unstable),
+    feature(proc_macro_span, proc_macro_span_shrink)
+)]
 #![cfg_attr(super_unstable, feature(proc_macro_def_site))]
 #![cfg_attr(doc_cfg, feature(doc_cfg))]
 #![allow(
@@ -120,6 +123,7 @@ extern crate proc_macro;
 
 mod marker;
 mod parse;
+mod rcvec;
 
 #[cfg(wrap_proc_macro)]
 mod detection;
@@ -136,15 +140,15 @@ use crate::fallback as imp;
 mod imp;
 
 use crate::marker::Marker;
-use std::cmp::Ordering;
+use core::cmp::Ordering;
+use core::fmt::{self, Debug, Display};
+use core::hash::{Hash, Hasher};
+use core::iter::FromIterator;
+use core::ops::RangeBounds;
+use core::str::FromStr;
 use std::error::Error;
-use std::fmt::{self, Debug, Display};
-use std::hash::{Hash, Hasher};
-use std::iter::FromIterator;
-use std::ops::RangeBounds;
 #[cfg(procmacro2_semver_exempt)]
 use std::path::PathBuf;
-use std::str::FromStr;
 
 /// An abstract stream of tokens, or more concretely a sequence of token trees.
 ///
@@ -508,6 +512,24 @@ impl Span {
         LineColumn { line, column }
     }
 
+    /// Creates an empty span pointing to directly before this span.
+    ///
+    /// This method is semver exempt and not exposed by default.
+    #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
+    #[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
+    pub fn before(&self) -> Span {
+        Span::_new(self.inner.before())
+    }
+
+    /// Creates an empty span pointing to directly after this span.
+    ///
+    /// This method is semver exempt and not exposed by default.
+    #[cfg(all(procmacro2_semver_exempt, any(not(wrap_proc_macro), super_unstable)))]
+    #[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
+    pub fn after(&self) -> Span {
+        Span::_new(self.inner.after())
+    }
+
     /// Create a new span encompassing `self` and `other`.
     ///
     /// Returns `None` if `self` and `other` are from different files.
@@ -952,11 +974,11 @@ impl Ident {
         Ident::_new(imp::Ident::new(string, span.inner))
     }
 
-    /// Same as `Ident::new`, but creates a raw identifier (`r#ident`).
-    ///
-    /// This method is semver exempt and not exposed by default.
-    #[cfg(procmacro2_semver_exempt)]
-    #[cfg_attr(doc_cfg, doc(cfg(procmacro2_semver_exempt)))]
+    /// Same as `Ident::new`, but creates a raw identifier (`r#ident`). The
+    /// `string` argument must 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.
     pub fn new_raw(string: &str, span: Span) -> Self {
         Ident::_new_raw(string, span)
     }
@@ -1128,9 +1150,9 @@ impl 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).
+    /// Literals created from negative numbers may not survive round-trips
+    /// through `TokenStream` or strings and may be broken into two tokens (`-`
+    /// and positive literal).
     ///
     /// # Panics
     ///
@@ -1147,7 +1169,7 @@ impl Literal {
     /// 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
+    /// round-trips through `TokenStream` or strings and may be broken into two
     /// tokens (`-` and positive literal).
     ///
     /// # Panics
@@ -1164,9 +1186,9 @@ impl 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).
+    /// Literals created from negative numbers may not survive round-trips
+    /// through `TokenStream` or strings and may be broken into two tokens (`-`
+    /// and positive literal).
     ///
     /// # Panics
     ///
@@ -1183,7 +1205,7 @@ impl Literal {
     /// 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
+    /// round-trips through `TokenStream` or strings and may be broken into two
     /// tokens (`-` and positive literal).
     ///
     /// # Panics
@@ -1270,7 +1292,7 @@ impl Display for Literal {
 pub mod token_stream {
     use crate::marker::Marker;
     use crate::{imp, TokenTree};
-    use std::fmt::{self, Debug};
+    use core::fmt::{self, Debug};
 
     pub use crate::TokenStream;
 
@@ -1290,11 +1312,16 @@ pub mod token_stream {
         fn next(&mut self) -> Option<TokenTree> {
             self.inner.next()
         }
+
+        fn size_hint(&self) -> (usize, Option<usize>) {
+            self.inner.size_hint()
+        }
     }
 
     impl Debug for IntoIter {
         fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-            Debug::fmt(&self.inner, f)
+            f.write_str("TokenStream ")?;
+            f.debug_list().entries(self.clone()).finish()
         }
     }
 
diff --git a/src/marker.rs b/src/marker.rs
index 58729ba..59fd096 100644
--- a/src/marker.rs
+++ b/src/marker.rs
@@ -1,4 +1,4 @@
-use std::marker::PhantomData;
+use core::marker::PhantomData;
 use std::panic::{RefUnwindSafe, UnwindSafe};
 use std::rc::Rc;
 
@@ -9,7 +9,7 @@ pub(crate) type Marker = PhantomData<ProcMacroAutoTraits>;
 pub(crate) use self::value::*;
 
 mod value {
-    pub(crate) use std::marker::PhantomData as Marker;
+    pub(crate) use core::marker::PhantomData as Marker;
 }
 
 pub(crate) struct ProcMacroAutoTraits(Rc<()>);
diff --git a/src/parse.rs b/src/parse.rs
index f77213a..307e065 100644
--- a/src/parse.rs
+++ b/src/parse.rs
@@ -1,9 +1,10 @@
 use crate::fallback::{
     is_ident_continue, is_ident_start, Group, LexError, Literal, Span, TokenStream,
+    TokenStreamBuilder,
 };
 use crate::{Delimiter, Punct, Spacing, TokenTree};
-use std::char;
-use std::str::{Bytes, CharIndices, Chars};
+use core::char;
+use core::str::{Bytes, CharIndices, Chars};
 
 #[derive(Copy, Clone, Eq, PartialEq)]
 pub(crate) struct Cursor<'a> {
@@ -13,7 +14,7 @@ pub(crate) struct Cursor<'a> {
 }
 
 impl<'a> Cursor<'a> {
-    fn advance(&self, bytes: usize) -> Cursor<'a> {
+    pub fn advance(&self, bytes: usize) -> Cursor<'a> {
         let (_front, rest) = self.rest.split_at(bytes);
         Cursor {
             rest,
@@ -22,7 +23,7 @@ impl<'a> Cursor<'a> {
         }
     }
 
-    fn starts_with(&self, s: &str) -> bool {
+    pub fn starts_with(&self, s: &str) -> bool {
         self.rest.starts_with(s)
     }
 
@@ -115,9 +116,9 @@ fn block_comment(input: Cursor) -> PResult<&str> {
         return Err(Reject);
     }
 
-    let mut depth = 0;
+    let mut depth = 0usize;
     let bytes = input.as_bytes();
-    let mut i = 0;
+    let mut i = 0usize;
     let upper = bytes.len() - 1;
 
     while i < upper {
@@ -150,14 +151,13 @@ fn word_break(input: Cursor) -> Result<Cursor, Reject> {
 }
 
 pub(crate) fn token_stream(mut input: Cursor) -> Result<TokenStream, LexError> {
-    let mut trees = Vec::new();
+    let mut trees = TokenStreamBuilder::new();
     let mut stack = Vec::new();
 
     loop {
         input = skip_whitespace(input);
 
-        if let Ok((rest, tt)) = doc_comment(input) {
-            trees.extend(tt);
+        if let Ok((rest, ())) = doc_comment(input, &mut trees) {
             input = rest;
             continue;
         }
@@ -168,7 +168,7 @@ pub(crate) fn token_stream(mut input: Cursor) -> Result<TokenStream, LexError> {
         let first = match input.bytes().next() {
             Some(first) => first,
             None => match stack.last() {
-                None => return Ok(TokenStream::from(trees)),
+                None => return Ok(trees.build()),
                 #[cfg(span_locations)]
                 Some((lo, _frame)) => {
                     return Err(LexError {
@@ -191,7 +191,7 @@ pub(crate) fn token_stream(mut input: Cursor) -> Result<TokenStream, LexError> {
             #[cfg(span_locations)]
             let frame = (lo, frame);
             stack.push(frame);
-            trees = Vec::new();
+            trees = TokenStreamBuilder::new();
         } else if let Some(close_delimiter) = match first {
             b')' => Some(Delimiter::Parenthesis),
             b']' => Some(Delimiter::Bracket),
@@ -209,7 +209,7 @@ pub(crate) fn token_stream(mut input: Cursor) -> Result<TokenStream, LexError> {
                 return Err(lex_error(input));
             }
             input = input.advance(1);
-            let mut g = Group::new(open_delimiter, TokenStream::from(trees));
+            let mut g = Group::new(open_delimiter, trees.build());
             g.set_span(Span {
                 #[cfg(span_locations)]
                 lo,
@@ -217,7 +217,7 @@ pub(crate) fn token_stream(mut input: Cursor) -> Result<TokenStream, LexError> {
                 hi: input.off,
             });
             trees = outer;
-            trees.push(TokenTree::Group(crate::Group::_new_stable(g)));
+            trees.push_token_from_parser(TokenTree::Group(crate::Group::_new_stable(g)));
         } else {
             let (rest, mut tt) = match leaf_token(input) {
                 Ok((rest, tt)) => (rest, tt),
@@ -229,7 +229,7 @@ pub(crate) fn token_stream(mut input: Cursor) -> Result<TokenStream, LexError> {
                 #[cfg(span_locations)]
                 hi: rest.off,
             }));
-            trees.push(tt);
+            trees.push_token_from_parser(tt);
             input = rest;
         }
     }
@@ -283,8 +283,9 @@ fn ident_any(input: Cursor) -> PResult<crate::Ident> {
         return Ok((rest, ident));
     }
 
-    if sym == "_" {
-        return Err(Reject);
+    match sym {
+        "_" | "super" | "self" | "Self" | "crate" => return Err(Reject),
+        _ => {}
     }
 
     let ident = crate::Ident::_new_raw(sym, crate::Span::call_site());
@@ -786,7 +787,7 @@ fn punct_char(input: Cursor) -> PResult<char> {
     }
 }
 
-fn doc_comment(input: Cursor) -> PResult<Vec<TokenTree>> {
+fn doc_comment<'a>(input: Cursor<'a>, trees: &mut TokenStreamBuilder) -> PResult<'a, ()> {
     #[cfg(span_locations)]
     let lo = input.off;
     let (rest, (comment, inner)) = doc_comment_contents(input)?;
@@ -806,25 +807,31 @@ fn doc_comment(input: Cursor) -> PResult<Vec<TokenTree>> {
         scan_for_bare_cr = rest;
     }
 
-    let mut trees = Vec::new();
-    trees.push(TokenTree::Punct(Punct::new('#', Spacing::Alone)));
+    let mut pound = Punct::new('#', Spacing::Alone);
+    pound.set_span(span);
+    trees.push_token_from_parser(TokenTree::Punct(pound));
+
     if inner {
-        trees.push(Punct::new('!', Spacing::Alone).into());
-    }
-    let mut stream = vec![
-        TokenTree::Ident(crate::Ident::new("doc", span)),
-        TokenTree::Punct(Punct::new('=', Spacing::Alone)),
-        TokenTree::Literal(crate::Literal::string(comment)),
-    ];
-    for tt in &mut stream {
-        tt.set_span(span);
-    }
-    let group = Group::new(Delimiter::Bracket, TokenStream::from(stream));
-    trees.push(crate::Group::_new_stable(group).into());
-    for tt in &mut trees {
-        tt.set_span(span);
-    }
-    Ok((rest, trees))
+        let mut bang = Punct::new('!', Spacing::Alone);
+        bang.set_span(span);
+        trees.push_token_from_parser(TokenTree::Punct(bang));
+    }
+
+    let doc_ident = crate::Ident::new("doc", span);
+    let mut equal = Punct::new('=', Spacing::Alone);
+    equal.set_span(span);
+    let mut literal = crate::Literal::string(comment);
+    literal.set_span(span);
+    let mut bracketed = TokenStreamBuilder::with_capacity(3);
+    bracketed.push_token_from_parser(TokenTree::Ident(doc_ident));
+    bracketed.push_token_from_parser(TokenTree::Punct(equal));
+    bracketed.push_token_from_parser(TokenTree::Literal(literal));
+    let group = Group::new(Delimiter::Bracket, bracketed.build());
+    let mut group = crate::Group::_new_stable(group);
+    group.set_span(span);
+    trees.push_token_from_parser(TokenTree::Group(group));
+
+    Ok((rest, ()))
 }
 
 fn doc_comment_contents(input: Cursor) -> PResult<(&str, bool)> {
diff --git a/src/rcvec.rs b/src/rcvec.rs
new file mode 100644
index 0000000..86ca7d8
--- /dev/null
+++ b/src/rcvec.rs
@@ -0,0 +1,142 @@
+use core::mem;
+use core::slice;
+use std::rc::Rc;
+use std::vec;
+
+pub(crate) struct RcVec<T> {
+    inner: Rc<Vec<T>>,
+}
+
+pub(crate) struct RcVecBuilder<T> {
+    inner: Vec<T>,
+}
+
+pub(crate) struct RcVecMut<'a, T> {
+    inner: &'a mut Vec<T>,
+}
+
+#[derive(Clone)]
+pub(crate) struct RcVecIntoIter<T> {
+    inner: vec::IntoIter<T>,
+}
+
+impl<T> RcVec<T> {
+    pub fn is_empty(&self) -> bool {
+        self.inner.is_empty()
+    }
+
+    pub fn len(&self) -> usize {
+        self.inner.len()
+    }
+
+    pub fn iter(&self) -> slice::Iter<T> {
+        self.inner.iter()
+    }
+
+    pub fn make_mut(&mut self) -> RcVecMut<T>
+    where
+        T: Clone,
+    {
+        RcVecMut {
+            inner: Rc::make_mut(&mut self.inner),
+        }
+    }
+
+    pub fn get_mut(&mut self) -> Option<RcVecMut<T>> {
+        let inner = Rc::get_mut(&mut self.inner)?;
+        Some(RcVecMut { inner })
+    }
+
+    pub fn make_owned(mut self) -> RcVecBuilder<T>
+    where
+        T: Clone,
+    {
+        let vec = if let Some(owned) = Rc::get_mut(&mut self.inner) {
+            mem::replace(owned, Vec::new())
+        } else {
+            Vec::clone(&self.inner)
+        };
+        RcVecBuilder { inner: vec }
+    }
+}
+
+impl<T> RcVecBuilder<T> {
+    pub fn new() -> Self {
+        RcVecBuilder { inner: Vec::new() }
+    }
+
+    pub fn with_capacity(cap: usize) -> Self {
+        RcVecBuilder {
+            inner: Vec::with_capacity(cap),
+        }
+    }
+
+    pub fn push(&mut self, element: T) {
+        self.inner.push(element);
+    }
+
+    pub fn extend(&mut self, iter: impl IntoIterator<Item = T>) {
+        self.inner.extend(iter);
+    }
+
+    pub fn as_mut(&mut self) -> RcVecMut<T> {
+        RcVecMut {
+            inner: &mut self.inner,
+        }
+    }
+
+    pub fn build(self) -> RcVec<T> {
+        RcVec {
+            inner: Rc::new(self.inner),
+        }
+    }
+}
+
+impl<'a, T> RcVecMut<'a, T> {
+    pub fn push(&mut self, element: T) {
+        self.inner.push(element);
+    }
+
+    pub fn extend(&mut self, iter: impl IntoIterator<Item = T>) {
+        self.inner.extend(iter);
+    }
+
+    pub fn pop(&mut self) -> Option<T> {
+        self.inner.pop()
+    }
+
+    pub fn as_mut(&mut self) -> RcVecMut<T> {
+        RcVecMut { inner: self.inner }
+    }
+}
+
+impl<T> Clone for RcVec<T> {
+    fn clone(&self) -> Self {
+        RcVec {
+            inner: Rc::clone(&self.inner),
+        }
+    }
+}
+
+impl<T> IntoIterator for RcVecBuilder<T> {
+    type Item = T;
+    type IntoIter = RcVecIntoIter<T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        RcVecIntoIter {
+            inner: self.inner.into_iter(),
+        }
+    }
+}
+
+impl<T> Iterator for RcVecIntoIter<T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
diff --git a/src/wrapper.rs b/src/wrapper.rs
index 2ba76cc..47d1494 100644
--- a/src/wrapper.rs
+++ b/src/wrapper.rs
@@ -1,12 +1,12 @@
 use crate::detection::inside_proc_macro;
 use crate::{fallback, Delimiter, Punct, Spacing, TokenTree};
-use std::fmt::{self, Debug, Display};
-use std::iter::FromIterator;
-use std::ops::RangeBounds;
+use core::fmt::{self, Debug, Display};
+use core::iter::FromIterator;
+use core::ops::RangeBounds;
+use core::str::FromStr;
 use std::panic;
 #[cfg(super_unstable)]
 use std::path::PathBuf;
-use std::str::FromStr;
 
 #[derive(Clone)]
 pub(crate) enum TokenStream {
@@ -350,12 +350,6 @@ impl Iterator for TokenTreeIter {
     }
 }
 
-impl Debug for TokenTreeIter {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.debug_struct("TokenTreeIter").finish()
-    }
-}
-
 #[derive(Clone, PartialEq, Eq)]
 #[cfg(super_unstable)]
 pub(crate) enum SourceFile {
@@ -511,6 +505,22 @@ impl Span {
         }
     }
 
+    #[cfg(super_unstable)]
+    pub fn before(&self) -> Span {
+        match self {
+            Span::Compiler(s) => Span::Compiler(s.before()),
+            Span::Fallback(s) => Span::Fallback(s.before()),
+        }
+    }
+
+    #[cfg(super_unstable)]
+    pub fn after(&self) -> Span {
+        match self {
+            Span::Compiler(s) => Span::Compiler(s.after()),
+            Span::Fallback(s) => Span::Fallback(s.after()),
+        }
+    }
+
     pub fn join(&self, other: Span) -> Option<Span> {
         let ret = match (self, other) {
             #[cfg(proc_macro_span)]
@@ -694,16 +704,26 @@ impl Ident {
 
     pub fn new_raw(string: &str, span: Span) -> Self {
         match span {
+            #[cfg(not(no_ident_new_raw))]
+            Span::Compiler(s) => Ident::Compiler(proc_macro::Ident::new_raw(string, s)),
+            #[cfg(no_ident_new_raw)]
             Span::Compiler(s) => {
-                let p: proc_macro::TokenStream = string.parse().unwrap();
-                let ident = match p.into_iter().next() {
-                    Some(proc_macro::TokenTree::Ident(mut i)) => {
-                        i.set_span(s);
-                        i
+                let _ = proc_macro::Ident::new(string, s);
+                // At this point the un-r#-prefixed string is known to be a
+                // valid identifier. Try to produce a valid raw identifier by
+                // running the `TokenStream` parser, and unwrapping the first
+                // token as an `Ident`.
+                let raw_prefixed = format!("r#{}", string);
+                if let Ok(ts) = raw_prefixed.parse::<proc_macro::TokenStream>() {
+                    let mut iter = ts.into_iter();
+                    if let (Some(proc_macro::TokenTree::Ident(mut id)), None) =
+                        (iter.next(), iter.next())
+                    {
+                        id.set_span(s);
+                        return Ident::Compiler(id);
                     }
-                    _ => panic!(),
-                };
-                Ident::Compiler(ident)
+                }
+                panic!("not allowed as a raw identifier: `{}`", raw_prefixed)
             }
             Span::Fallback(s) => Ident::Fallback(fallback::Ident::new_raw(string, s)),
         }
diff --git a/tests/comments.rs b/tests/comments.rs
index 7174108..4f7236d 100644
--- a/tests/comments.rs
+++ b/tests/comments.rs
@@ -1,3 +1,5 @@
+#![allow(clippy::assertions_on_result_states)]
+
 use proc_macro2::{Delimiter, Literal, Spacing, TokenStream, TokenTree};
 
 // #[doc = "..."] -> "..."
diff --git a/tests/test.rs b/tests/test.rs
index ab82390..8f5624d 100644
--- a/tests/test.rs
+++ b/tests/test.rs
@@ -1,4 +1,4 @@
-#![allow(clippy::non_ascii_literal)]
+#![allow(clippy::assertions_on_result_states, clippy::non_ascii_literal)]
 
 use proc_macro2::{Ident, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
 use std::panic;
@@ -15,14 +15,24 @@ fn idents() {
 }
 
 #[test]
-#[cfg(procmacro2_semver_exempt)]
 fn raw_idents() {
     assert_eq!(
         Ident::new_raw("String", Span::call_site()).to_string(),
         "r#String"
     );
     assert_eq!(Ident::new_raw("fn", Span::call_site()).to_string(), "r#fn");
-    assert_eq!(Ident::new_raw("_", Span::call_site()).to_string(), "r#_");
+}
+
+#[test]
+#[should_panic(expected = "`r#_` cannot be a raw identifier")]
+fn ident_raw_underscore() {
+    Ident::new_raw("_", Span::call_site());
+}
+
+#[test]
+#[should_panic(expected = "`r#super` cannot be a raw identifier")]
+fn ident_raw_reserved() {
+    Ident::new_raw("super", Span::call_site());
 }
 
 #[test]
@@ -107,6 +117,15 @@ fn literal_raw_string() {
 }
 
 #[test]
+fn literal_byte_string() {
+    assert_eq!(Literal::byte_string(b"").to_string(), "b\"\"");
+    assert_eq!(
+        Literal::byte_string(b"\0\t\n\r\"\\2\x10").to_string(),
+        "b\"\\0\\t\\n\\r\\\"\\\\2\\x10\"",
+    );
+}
+
+#[test]
 fn literal_character() {
     assert_eq!(Literal::character('x').to_string(), "'x'");
     assert_eq!(Literal::character('\'').to_string(), "'\\''");
@@ -114,8 +133,43 @@ fn literal_character() {
 }
 
 #[test]
+fn literal_integer() {
+    assert_eq!(Literal::u8_suffixed(10).to_string(), "10u8");
+    assert_eq!(Literal::u16_suffixed(10).to_string(), "10u16");
+    assert_eq!(Literal::u32_suffixed(10).to_string(), "10u32");
+    assert_eq!(Literal::u64_suffixed(10).to_string(), "10u64");
+    assert_eq!(Literal::u128_suffixed(10).to_string(), "10u128");
+    assert_eq!(Literal::usize_suffixed(10).to_string(), "10usize");
+
+    assert_eq!(Literal::i8_suffixed(10).to_string(), "10i8");
+    assert_eq!(Literal::i16_suffixed(10).to_string(), "10i16");
+    assert_eq!(Literal::i32_suffixed(10).to_string(), "10i32");
+    assert_eq!(Literal::i64_suffixed(10).to_string(), "10i64");
+    assert_eq!(Literal::i128_suffixed(10).to_string(), "10i128");
+    assert_eq!(Literal::isize_suffixed(10).to_string(), "10isize");
+
+    assert_eq!(Literal::u8_unsuffixed(10).to_string(), "10");
+    assert_eq!(Literal::u16_unsuffixed(10).to_string(), "10");
+    assert_eq!(Literal::u32_unsuffixed(10).to_string(), "10");
+    assert_eq!(Literal::u64_unsuffixed(10).to_string(), "10");
+    assert_eq!(Literal::u128_unsuffixed(10).to_string(), "10");
+    assert_eq!(Literal::usize_unsuffixed(10).to_string(), "10");
+
+    assert_eq!(Literal::i8_unsuffixed(10).to_string(), "10");
+    assert_eq!(Literal::i16_unsuffixed(10).to_string(), "10");
+    assert_eq!(Literal::i32_unsuffixed(10).to_string(), "10");
+    assert_eq!(Literal::i64_unsuffixed(10).to_string(), "10");
+    assert_eq!(Literal::i128_unsuffixed(10).to_string(), "10");
+    assert_eq!(Literal::isize_unsuffixed(10).to_string(), "10");
+}
+
+#[test]
 fn literal_float() {
+    assert_eq!(Literal::f32_suffixed(10.0).to_string(), "10f32");
+    assert_eq!(Literal::f64_suffixed(10.0).to_string(), "10f64");
+
     assert_eq!(Literal::f32_unsuffixed(10.0).to_string(), "10.0");
+    assert_eq!(Literal::f64_unsuffixed(10.0).to_string(), "10.0");
 }
 
 #[test]
@@ -494,6 +548,13 @@ fn default_tokenstream_is_empty() {
 }
 
 #[test]
+fn tokenstream_size_hint() {
+    let tokens = "a b (c d) e".parse::<TokenStream>().unwrap();
+
+    assert_eq!(tokens.into_iter().size_hint(), (4, Some(4)));
+}
+
+#[test]
 fn tuple_indexing() {
     // This behavior may change depending on https://github.com/rust-lang/rust/pull/71322
     let mut tokens = "tuple.0.0".parse::<TokenStream>().unwrap().into_iter();
@@ -569,3 +630,16 @@ fn check_spans_internal(ts: TokenStream, lines: &mut &[(usize, usize, usize, usi
         }
     }
 }
+
+#[test]
+fn byte_order_mark() {
+    let string = "\u{feff}foo";
+    let tokens = string.parse::<TokenStream>().unwrap();
+    match tokens.into_iter().next().unwrap() {
+        TokenTree::Ident(ident) => assert_eq!(ident, "foo"),
+        _ => unreachable!(),
+    }
+
+    let string = "foo\u{feff}";
+    string.parse::<TokenStream>().unwrap_err();
+}