Upgrade proc-macro2 to 1.0.66 am: 5c471c4a5c am: 4801c12b7f

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/proc-macro2/+/2710373

Change-Id: I1989f77738844fc409af5ff825e128c0eec8b48d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>

21 files changed, 332 insertions, 424 deletions

diff --git a/.cargo_vcs_info.json b/.cargo_vcs_info.json
index c26dd7c..9eaf829 100644
--- a/.cargo_vcs_info.json
+++ b/.cargo_vcs_info.json
@@ -1,6 +1,6 @@
 {
   "git": {
-    "sha1": "72ee0b3b0523395e75bf71ae7702e93a7c506f1a"
+    "sha1": "64b4608278be46fcc8d63ae1138da8cb600e258a"
   },
   "path_in_vcs": ""
 }
\ No newline at end of file
diff --git a/.clippy.toml b/.clippy.toml
deleted file mode 100644
index 3d30690..0000000
--- a/.clippy.toml
+++ /dev/null
@@ -1 +0,0 @@
-msrv = "1.31.0"
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1299805..296381c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -24,13 +24,14 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [1.31.0, stable, beta]
+        rust: [1.56.0, stable, beta]
     timeout-minutes: 45
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{matrix.rust}}
+          components: rust-src
       - run: cargo test
       - run: cargo test --no-default-features
       - run: cargo test --features span-locations
@@ -52,6 +53,8 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@nightly
+        with:
+          components: rust-src
       - name: Enable type layout randomization
         run: echo RUSTFLAGS=${RUSTFLAGS}\ -Zrandomize-layout >> $GITHUB_ENV
       - run: cargo test
@@ -71,7 +74,18 @@ jobs:
         run: cargo test
         env:
           RUSTFLAGS: -Z allow-features= ${{env.RUSTFLAGS}}
-      - run: cargo update -Z minimal-versions && cargo build
+
+  minimal:
+    name: Minimal versions
+    needs: pre_ci
+    if: needs.pre_ci.outputs.continue
+    runs-on: ubuntu-latest
+    timeout-minutes: 45
+    steps:
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@nightly
+      - run: cargo generate-lockfile -Z minimal-versions
+      - run: cargo check --locked
 
   webassembly:
     name: WebAssembly
@@ -84,6 +98,7 @@ jobs:
       - uses: dtolnay/rust-toolchain@nightly
         with:
           target: wasm32-unknown-unknown
+          components: rust-src
       - run: cargo test --target wasm32-unknown-unknown --no-run
 
   fuzz:
@@ -95,14 +110,18 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@nightly
+        with:
+          components: rust-src
       - uses: dtolnay/install@cargo-fuzz
       - run: cargo fuzz check
       - run: cargo check --no-default-features --features afl
         working-directory: fuzz
       - uses: dtolnay/install@honggfuzz
       - run: sudo apt-get install binutils-dev libunwind-dev
+        continue-on-error: true # https://github.com/dtolnay/proc-macro2/issues/387
       - run: cargo hfuzz build --no-default-features --features honggfuzz
         working-directory: fuzz
+        continue-on-error: true # https://github.com/dtolnay/proc-macro2/issues/387
 
   clippy:
     name: Clippy
@@ -111,7 +130,9 @@ jobs:
     timeout-minutes: 45
     steps:
       - uses: actions/checkout@v3
-      - uses: dtolnay/rust-toolchain@clippy
+      - uses: dtolnay/rust-toolchain@nightly
+        with:
+          components: clippy, rust-src
       - run: cargo clippy --tests -- -Dclippy::all -Dclippy::pedantic
       - run: cargo clippy --tests --all-features -- -Dclippy::all -Dclippy::pedantic
 
@@ -124,6 +145,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@miri
+      - run: cargo miri setup
       - run: cargo miri test
         env:
           MIRIFLAGS: -Zmiri-strict-provenance
diff --git a/Android.bp b/Android.bp
index dea1ca2..4222426 100644
--- a/Android.bp
+++ b/Android.bp
@@ -41,18 +41,16 @@ rust_library_host {
     name: "libproc_macro2",
     crate_name: "proc_macro2",
     cargo_env_compat: true,
-    cargo_pkg_version: "1.0.56",
+    cargo_pkg_version: "1.0.66",
     srcs: ["src/lib.rs"],
-    edition: "2018",
+    edition: "2021",
     features: [
         "default",
         "proc-macro",
         "span-locations",
     ],
     cfgs: [
-        "proc_macro_span",
         "span_locations",
-        "use_proc_macro",
         "wrap_proc_macro",
     ],
     rustlibs: [
@@ -67,19 +65,17 @@ rust_defaults {
     name: "proc-macro2_test_defaults",
     crate_name: "proc_macro2",
     cargo_env_compat: true,
-    cargo_pkg_version: "1.0.56",
+    cargo_pkg_version: "1.0.66",
     test_suites: ["general-tests"],
     auto_gen_config: true,
-    edition: "2018",
+    edition: "2021",
     features: [
         "default",
         "proc-macro",
         "span-locations",
     ],
     cfgs: [
-        "proc_macro_span",
         "span_locations",
-        "use_proc_macro",
         "wrap_proc_macro",
     ],
     rustlibs: [
diff --git a/Cargo.toml b/Cargo.toml
index 76c0df6..7612f21 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -10,10 +10,10 @@
 # See Cargo.toml.orig for the original contents.
 
 [package]
-edition = "2018"
-rust-version = "1.31"
+edition = "2021"
+rust-version = "1.56"
 name = "proc-macro2"
-version = "1.0.56"
+version = "1.0.66"
 authors = [
     "David Tolnay <dtolnay@gmail.com>",
     "Alex Crichton <alex@alexcrichton.com>",
@@ -40,6 +40,7 @@ rustdoc-args = [
     "procmacro2_semver_exempt",
     "--cfg",
     "doc_cfg",
+    "--generate-link-to-definition",
 ]
 targets = ["x86_64-unknown-linux-gnu"]
 
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
index 791d5e9..b0fb8fd 100644
--- a/Cargo.toml.orig
+++ b/Cargo.toml.orig
@@ -1,20 +1,20 @@
 [package]
 name = "proc-macro2"
-version = "1.0.56" # remember to update html_root_url
+version = "1.0.66" # remember to update html_root_url
 authors = ["David Tolnay <dtolnay@gmail.com>", "Alex Crichton <alex@alexcrichton.com>"]
 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"
+edition = "2021"
 keywords = ["macros", "syn"]
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/dtolnay/proc-macro2"
-rust-version = "1.31"
+rust-version = "1.56"
 
 [package.metadata.docs.rs]
 rustc-args = ["--cfg", "procmacro2_semver_exempt"]
-rustdoc-args = ["--cfg", "procmacro2_semver_exempt", "--cfg", "doc_cfg"]
+rustdoc-args = ["--cfg", "procmacro2_semver_exempt", "--cfg", "doc_cfg", "--generate-link-to-definition"]
 targets = ["x86_64-unknown-linux-gnu"]
 
 [package.metadata.playground]
diff --git a/METADATA b/METADATA
index 66c5a87..34f90ff 100644
--- a/METADATA
+++ b/METADATA
@@ -1,6 +1,6 @@
 # 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
+# For more info, check https://cs.android.com/android/platform/superproject/+/main: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."
@@ -11,13 +11,13 @@ third_party {
   }
   url {
     type: ARCHIVE
-    value: "https://static.crates.io/crates/proc-macro2/proc-macro2-1.0.56.crate"
+    value: "https://static.crates.io/crates/proc-macro2/proc-macro2-1.0.66.crate"
   }
-  version: "1.0.56"
+  version: "1.0.66"
   license_type: NOTICE
   last_upgrade_date {
     year: 2023
-    month: 4
-    day: 3
+    month: 8
+    day: 15
   }
 }
diff --git a/README.md b/README.md
index 131ba51..e48dd47 100644
--- a/README.md
+++ b/README.md
@@ -62,7 +62,7 @@ proc-macro2 by default.
 
 To opt into the additional APIs available in the most recent nightly compiler,
 the `procmacro2_semver_exempt` config flag must be passed to rustc. We will
-polyfill those nightly-only APIs back to Rust 1.31.0. As these are unstable APIs
+polyfill those nightly-only APIs back to Rust 1.56.0. As these are unstable APIs
 that track the nightly compiler, minor versions of proc-macro2 may make breaking
 changes to them at any time.
 
diff --git a/build.rs b/build.rs
index 3ee8a9f..9f0fb51 100644
--- a/build.rs
+++ b/build.rs
@@ -1,11 +1,5 @@
 // rustc-cfg emitted by the build script:
 //
-// "use_proc_macro"
-//     Link to extern crate proc_macro. Available on any compiler and any target
-//     except wasm32. Requires "proc-macro" Cargo cfg to be enabled (default is
-//     enabled). On wasm32 we never link to proc_macro even if "proc-macro" cfg
-//     is enabled.
-//
 // "wrap_proc_macro"
 //     Wrap types from libproc_macro rather than polyfilling the whole API.
 //     Enabled on rustc 1.29+ as long as procmacro2_semver_exempt is not set,
@@ -41,21 +35,17 @@
 //     1.57+.
 
 use std::env;
-use std::process::{self, Command};
+use std::process::Command;
 use std::str;
+use std::u32;
 
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
 
-    let version = match rustc_version() {
-        Some(version) => version,
-        None => return,
-    };
-
-    if version.minor < 31 {
-        eprintln!("Minimum supported rustc version is 1.31");
-        process::exit(1);
-    }
+    let version = rustc_version().unwrap_or(RustcVersion {
+        minor: u32::MAX,
+        nightly: false,
+    });
 
     let docs_rs = env::var_os("DOCS_RS").is_some();
     let semver_exempt = cfg!(procmacro2_semver_exempt) || docs_rs;
@@ -68,38 +58,6 @@ fn main() {
         println!("cargo:rustc-cfg=span_locations");
     }
 
-    if version.minor < 32 {
-        println!("cargo:rustc-cfg=no_libprocmacro_unwind_safe");
-    }
-
-    if version.minor < 34 {
-        println!("cargo:rustc-cfg=no_try_from");
-    }
-
-    if version.minor < 39 {
-        println!("cargo:rustc-cfg=no_bind_by_move_pattern_guard");
-    }
-
-    if version.minor < 44 {
-        println!("cargo:rustc-cfg=no_lexerror_display");
-    }
-
-    if version.minor < 45 {
-        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");
-    }
-
-    if version.minor < 55 {
-        println!("cargo:rustc-cfg=no_group_open_close");
-    }
-
     if version.minor < 57 {
         println!("cargo:rustc-cfg=no_is_available");
     }
@@ -108,21 +66,15 @@ fn main() {
         println!("cargo:rustc-cfg=no_source_text");
     }
 
-    let target = env::var("TARGET").unwrap();
-    if !enable_use_proc_macro(&target) {
+    if !cfg!(feature = "proc-macro") {
         return;
     }
 
-    println!("cargo:rustc-cfg=use_proc_macro");
-
     if version.nightly || !semver_exempt {
         println!("cargo:rustc-cfg=wrap_proc_macro");
     }
 
-    if version.nightly
-        && feature_allowed("proc_macro_span")
-        && feature_allowed("proc_macro_span_shrink")
-    {
+    if version.nightly && feature_allowed("proc_macro_span") {
         println!("cargo:rustc-cfg=proc_macro_span");
     }
 
@@ -131,16 +83,6 @@ fn main() {
     }
 }
 
-fn enable_use_proc_macro(target: &str) -> bool {
-    // wasm targets don't have the `proc_macro` crate, disable this feature.
-    if target.contains("wasm32") {
-        return false;
-    }
-
-    // Otherwise, only enable it if our feature is actually enabled.
-    cfg!(feature = "proc-macro")
-}
-
 struct RustcVersion {
     minor: u32,
     nightly: bool,
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
new file mode 100644
index 0000000..20fe888
--- /dev/null
+++ b/rust-toolchain.toml
@@ -0,0 +1,2 @@
+[toolchain]
+components = ["rust-src"]
diff --git a/src/convert.rs b/src/convert.rs
deleted file mode 100644
index afc5faf..0000000
--- a/src/convert.rs
+++ /dev/null
@@ -1,19 +0,0 @@
-pub(crate) fn usize_to_u32(u: usize) -> Option<u32> {
-    #[cfg(not(no_try_from))]
-    {
-        use core::convert::TryFrom;
-
-        u32::try_from(u).ok()
-    }
-
-    #[cfg(no_try_from)]
-    {
-        use core::mem;
-
-        if mem::size_of::<usize>() <= mem::size_of::<u32>() || u <= u32::max_value() as usize {
-            Some(u as u32)
-        } else {
-            None
-        }
-    }
-}
diff --git a/src/extra.rs b/src/extra.rs
index cbce162..4a69d46 100644
--- a/src/extra.rs
+++ b/src/extra.rs
@@ -22,9 +22,7 @@ enum DelimSpanEnum {
     #[cfg(wrap_proc_macro)]
     Compiler {
         join: proc_macro::Span,
-        #[cfg(not(no_group_open_close))]
         open: proc_macro::Span,
-        #[cfg(not(no_group_open_close))]
         close: proc_macro::Span,
     },
     Fallback(fallback::Span),
@@ -36,9 +34,7 @@ impl DelimSpan {
         let inner = match group {
             imp::Group::Compiler(group) => DelimSpanEnum::Compiler {
                 join: group.span(),
-                #[cfg(not(no_group_open_close))]
                 open: group.span_open(),
-                #[cfg(not(no_group_open_close))]
                 close: group.span_close(),
             },
             imp::Group::Fallback(group) => DelimSpanEnum::Fallback(group.span()),
@@ -66,13 +62,7 @@ impl DelimSpan {
     pub fn open(&self) -> Span {
         match &self.inner {
             #[cfg(wrap_proc_macro)]
-            DelimSpanEnum::Compiler {
-                #[cfg(not(no_group_open_close))]
-                open,
-                #[cfg(no_group_open_close)]
-                    join: open,
-                ..
-            } => Span::_new(imp::Span::Compiler(*open)),
+            DelimSpanEnum::Compiler { open, .. } => Span::_new(imp::Span::Compiler(*open)),
             DelimSpanEnum::Fallback(span) => Span::_new_fallback(span.first_byte()),
         }
     }
@@ -81,13 +71,7 @@ impl DelimSpan {
     pub fn close(&self) -> Span {
         match &self.inner {
             #[cfg(wrap_proc_macro)]
-            DelimSpanEnum::Compiler {
-                #[cfg(not(no_group_open_close))]
-                close,
-                #[cfg(no_group_open_close)]
-                    join: close,
-                ..
-            } => Span::_new(imp::Span::Compiler(*close)),
+            DelimSpanEnum::Compiler { close, .. } => Span::_new(imp::Span::Compiler(*close)),
             DelimSpanEnum::Fallback(span) => Span::_new_fallback(span.last_byte()),
         }
     }
diff --git a/src/fallback.rs b/src/fallback.rs
index bbea473..daa1e17 100644
--- a/src/fallback.rs
+++ b/src/fallback.rs
@@ -8,7 +8,6 @@ use core::cell::RefCell;
 #[cfg(span_locations)]
 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;
@@ -71,7 +70,6 @@ impl TokenStream {
 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),
@@ -81,20 +79,6 @@ fn push_token_from_proc_macro(mut vec: RcVecMut<TokenTree>, token: TokenTree) {
         }) if literal.repr.starts_with('-') => {
             push_negative_literal(vec, 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_fallback(literal)));
-            }
-        }
         _ => vec.push(token),
     }
 
@@ -233,7 +217,7 @@ impl Debug for TokenStream {
     }
 }
 
-#[cfg(use_proc_macro)]
+#[cfg(feature = "proc-macro")]
 impl From<proc_macro::TokenStream> for TokenStream {
     fn from(inner: proc_macro::TokenStream) -> Self {
         inner
@@ -243,7 +227,7 @@ impl From<proc_macro::TokenStream> for TokenStream {
     }
 }
 
-#[cfg(use_proc_macro)]
+#[cfg(feature = "proc-macro")]
 impl From<TokenStream> for proc_macro::TokenStream {
     fn from(inner: TokenStream) -> Self {
         inner
@@ -479,7 +463,6 @@ impl Span {
         Span { lo: 0, hi: 0 }
     }
 
-    #[cfg(not(no_hygiene))]
     pub fn mixed_site() -> Self {
         Span::call_site()
     }
@@ -541,26 +524,6 @@ 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 {})
@@ -789,7 +752,7 @@ fn validate_ident(string: &str, raw: bool) {
         panic!("Ident is not allowed to be empty; use Option<Ident>");
     }
 
-    if string.bytes().all(|digit| digit >= b'0' && digit <= b'9') {
+    if string.bytes().all(|digit| b'0' <= digit && digit <= b'9') {
         panic!("Ident cannot be a number; use Literal instead");
     }
 
@@ -850,6 +813,7 @@ impl Display for Ident {
     }
 }
 
+#[allow(clippy::missing_fields_in_debug)]
 impl Debug for Ident {
     // Ident(proc_macro), Ident(r#union)
     #[cfg(not(span_locations))]
@@ -1039,27 +1003,26 @@ impl Literal {
 
         #[cfg(span_locations)]
         {
-            use crate::convert::usize_to_u32;
             use core::ops::Bound;
 
             let lo = match range.start_bound() {
                 Bound::Included(start) => {
-                    let start = usize_to_u32(*start)?;
+                    let start = u32::try_from(*start).ok()?;
                     self.span.lo.checked_add(start)?
                 }
                 Bound::Excluded(start) => {
-                    let start = usize_to_u32(*start)?;
+                    let start = u32::try_from(*start).ok()?;
                     self.span.lo.checked_add(start)?.checked_add(1)?
                 }
                 Bound::Unbounded => self.span.lo,
             };
             let hi = match range.end_bound() {
                 Bound::Included(end) => {
-                    let end = usize_to_u32(*end)?;
+                    let end = u32::try_from(*end).ok()?;
                     self.span.lo.checked_add(end)?.checked_add(1)?
                 }
                 Bound::Excluded(end) => {
-                    let end = usize_to_u32(*end)?;
+                    let end = u32::try_from(*end).ok()?;
                     self.span.lo.checked_add(end)?
                 }
                 Bound::Unbounded => self.span.hi,
diff --git a/src/lib.rs b/src/lib.rs
index 6ce679d..910d47b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -65,7 +65,7 @@
 //!
 //! To opt into the additional APIs available in the most recent nightly
 //! compiler, the `procmacro2_semver_exempt` config flag must be passed to
-//! rustc. We will polyfill those nightly-only APIs back to Rust 1.31.0. As
+//! rustc. We will polyfill those nightly-only APIs back to Rust 1.56.0. As
 //! these are unstable APIs that track the nightly compiler, minor versions of
 //! proc-macro2 may make breaking changes to them at any time.
 //!
@@ -86,11 +86,8 @@
 //! a different thread.
 
 // Proc-macro2 types in rustdoc of other crates get linked to here.
-#![doc(html_root_url = "https://docs.rs/proc-macro2/1.0.56")]
-#![cfg_attr(
-    any(proc_macro_span, super_unstable),
-    feature(proc_macro_span, proc_macro_span_shrink)
-)]
+#![doc(html_root_url = "https://docs.rs/proc-macro2/1.0.66")]
+#![cfg_attr(any(proc_macro_span, super_unstable), feature(proc_macro_span))]
 #![cfg_attr(super_unstable, feature(proc_macro_def_site))]
 #![cfg_attr(doc_cfg, feature(doc_cfg))]
 #![allow(
@@ -100,8 +97,10 @@
     clippy::items_after_statements,
     clippy::let_underscore_untyped,
     clippy::manual_assert,
+    clippy::manual_range_contains,
     clippy::must_use_candidate,
     clippy::needless_doctest_main,
+    clippy::new_without_default,
     clippy::return_self_not_must_use,
     clippy::shadow_unrelated,
     clippy::trivially_copy_pass_by_ref,
@@ -119,7 +118,9 @@ compile_error! {"\
     build script as well.
 "}
 
-#[cfg(use_proc_macro)]
+extern crate alloc;
+
+#[cfg(feature = "proc-macro")]
 extern crate proc_macro;
 
 mod marker;
@@ -143,8 +144,6 @@ use crate::fallback as imp;
 mod imp;
 
 #[cfg(span_locations)]
-mod convert;
-#[cfg(span_locations)]
 mod location;
 
 use crate::extra::DelimSpan;
@@ -152,7 +151,6 @@ use crate::marker::Marker;
 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;
@@ -235,14 +233,16 @@ impl FromStr for TokenStream {
     }
 }
 
-#[cfg(use_proc_macro)]
+#[cfg(feature = "proc-macro")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "proc-macro")))]
 impl From<proc_macro::TokenStream> for TokenStream {
     fn from(inner: proc_macro::TokenStream) -> Self {
         TokenStream::_new(inner.into())
     }
 }
 
-#[cfg(use_proc_macro)]
+#[cfg(feature = "proc-macro")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "proc-macro")))]
 impl From<TokenStream> for proc_macro::TokenStream {
     fn from(inner: TokenStream) -> Self {
         inner.inner.into()
@@ -402,9 +402,6 @@ impl Span {
     /// The span located at the invocation of the procedural macro, but with
     /// local variables, labels, and `$crate` resolved at the definition site
     /// of the macro. This is the same hygiene behavior as `macro_rules`.
-    ///
-    /// This function requires Rust 1.45 or later.
-    #[cfg(not(no_hygiene))]
     pub fn mixed_site() -> Self {
         Span::_new(imp::Span::mixed_site())
     }
@@ -491,24 +488,6 @@ impl Span {
         self.inner.end()
     }
 
-    /// 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.
diff --git a/src/marker.rs b/src/marker.rs
index 59fd096..e648dd2 100644
--- a/src/marker.rs
+++ b/src/marker.rs
@@ -1,6 +1,6 @@
+use alloc::rc::Rc;
 use core::marker::PhantomData;
-use std::panic::{RefUnwindSafe, UnwindSafe};
-use std::rc::Rc;
+use core::panic::{RefUnwindSafe, UnwindSafe};
 
 // Zero sized marker with the correct set of autotrait impls we want all proc
 // macro types to have.
diff --git a/src/parse.rs b/src/parse.rs
index be2425b..c084e4c 100644
--- a/src/parse.rs
+++ b/src/parse.rs
@@ -108,7 +108,7 @@ fn skip_whitespace(input: Cursor) -> Cursor {
                 s = s.advance(1);
                 continue;
             }
-            b if b <= 0x7f => {}
+            b if b.is_ascii() => {}
             _ => {
                 let ch = s.chars().next().unwrap();
                 if is_whitespace(ch) {
@@ -273,9 +273,11 @@ fn leaf_token(input: Cursor) -> PResult<TokenTree> {
 }
 
 fn ident(input: Cursor) -> PResult<crate::Ident> {
-    if ["r\"", "r#\"", "r##", "b\"", "b\'", "br\"", "br#"]
-        .iter()
-        .any(|prefix| input.starts_with(prefix))
+    if [
+        "r\"", "r#\"", "r##", "b\"", "b\'", "br\"", "br#", "c\"", "cr\"", "cr#",
+    ]
+    .iter()
+    .any(|prefix| input.starts_with(prefix))
     {
         Err(Reject)
     } else {
@@ -333,6 +335,8 @@ fn literal_nocapture(input: Cursor) -> Result<Cursor, Reject> {
         Ok(ok)
     } else if let Ok(ok) = byte_string(input) {
         Ok(ok)
+    } else if let Ok(ok) = c_string(input) {
+        Ok(ok)
     } else if let Ok(ok) = byte(input) {
         Ok(ok)
     } else if let Ok(ok) = character(input) {
@@ -363,8 +367,8 @@ fn string(input: Cursor) -> Result<Cursor, Reject> {
     }
 }
 
-fn cooked_string(input: Cursor) -> Result<Cursor, Reject> {
-    let mut chars = input.char_indices().peekable();
+fn cooked_string(mut input: Cursor) -> Result<Cursor, Reject> {
+    let mut chars = input.char_indices();
 
     while let Some((i, ch)) = chars.next() {
         match ch {
@@ -378,31 +382,16 @@ fn cooked_string(input: Cursor) -> Result<Cursor, Reject> {
             },
             '\\' => match chars.next() {
                 Some((_, 'x')) => {
-                    if !backslash_x_char(&mut chars) {
-                        break;
-                    }
+                    backslash_x_char(&mut chars)?;
                 }
-                Some((_, 'n')) | Some((_, 'r')) | Some((_, 't')) | Some((_, '\\'))
-                | Some((_, '\'')) | Some((_, '"')) | Some((_, '0')) => {}
+                Some((_, 'n' | 'r' | 't' | '\\' | '\'' | '"' | '0')) => {}
                 Some((_, 'u')) => {
-                    if !backslash_u(&mut chars) {
-                        break;
-                    }
+                    backslash_u(&mut chars)?;
                 }
-                Some((_, ch @ '\n')) | Some((_, ch @ '\r')) => {
-                    let mut last = ch;
-                    loop {
-                        if last == '\r' && chars.next().map_or(true, |(_, ch)| ch != '\n') {
-                            return Err(Reject);
-                        }
-                        match chars.peek() {
-                            Some((_, ch)) if ch.is_whitespace() => {
-                                last = *ch;
-                                chars.next();
-                            }
-                            _ => break,
-                        }
-                    }
+                Some((newline, ch @ ('\n' | '\r'))) => {
+                    input = input.advance(newline + 1);
+                    trailing_backslash(&mut input, ch as u8)?;
+                    chars = input.char_indices();
                 }
                 _ => break,
             },
@@ -412,11 +401,30 @@ fn cooked_string(input: Cursor) -> Result<Cursor, Reject> {
     Err(Reject)
 }
 
+fn raw_string(input: Cursor) -> Result<Cursor, Reject> {
+    let (input, delimiter) = delimiter_of_raw_string(input)?;
+    let mut bytes = input.bytes().enumerate();
+    while let Some((i, byte)) = bytes.next() {
+        match byte {
+            b'"' if input.rest[i + 1..].starts_with(delimiter) => {
+                let rest = input.advance(i + 1 + delimiter.len());
+                return Ok(literal_suffix(rest));
+            }
+            b'\r' => match bytes.next() {
+                Some((_, b'\n')) => {}
+                _ => break,
+            },
+            _ => {}
+        }
+    }
+    Err(Reject)
+}
+
 fn byte_string(input: Cursor) -> Result<Cursor, Reject> {
     if let Ok(input) = input.parse("b\"") {
         cooked_byte_string(input)
     } else if let Ok(input) = input.parse("br") {
-        raw_string(input)
+        raw_byte_string(input)
     } else {
         Err(Reject)
     }
@@ -436,68 +444,125 @@ fn cooked_byte_string(mut input: Cursor) -> Result<Cursor, Reject> {
             },
             b'\\' => match bytes.next() {
                 Some((_, b'x')) => {
-                    if !backslash_x_byte(&mut bytes) {
-                        break;
-                    }
+                    backslash_x_byte(&mut bytes)?;
                 }
-                Some((_, b'n')) | Some((_, b'r')) | Some((_, b't')) | Some((_, b'\\'))
-                | Some((_, b'0')) | Some((_, b'\'')) | Some((_, b'"')) => {}
-                Some((newline, b @ b'\n')) | Some((newline, b @ b'\r')) => {
-                    let mut last = b as char;
-                    let rest = input.advance(newline + 1);
-                    let mut chars = rest.char_indices();
-                    loop {
-                        if last == '\r' && chars.next().map_or(true, |(_, ch)| ch != '\n') {
-                            return Err(Reject);
-                        }
-                        match chars.next() {
-                            Some((_, ch)) if ch.is_whitespace() => last = ch,
-                            Some((offset, _)) => {
-                                input = rest.advance(offset);
-                                bytes = input.bytes().enumerate();
-                                break;
-                            }
-                            None => return Err(Reject),
-                        }
-                    }
+                Some((_, b'n' | b'r' | b't' | b'\\' | b'0' | b'\'' | b'"')) => {}
+                Some((newline, b @ (b'\n' | b'\r'))) => {
+                    input = input.advance(newline + 1);
+                    trailing_backslash(&mut input, b)?;
+                    bytes = input.bytes().enumerate();
                 }
                 _ => break,
             },
-            b if b < 0x80 => {}
+            b if b.is_ascii() => {}
             _ => break,
         }
     }
     Err(Reject)
 }
 
-fn raw_string(input: Cursor) -> Result<Cursor, Reject> {
-    let mut chars = input.char_indices();
-    let mut n = 0;
-    for (i, ch) in &mut chars {
-        match ch {
-            '"' => {
-                n = i;
-                break;
+fn delimiter_of_raw_string(input: Cursor) -> PResult<&str> {
+    for (i, byte) in input.bytes().enumerate() {
+        match byte {
+            b'"' => {
+                if i > 255 {
+                    // https://github.com/rust-lang/rust/pull/95251
+                    return Err(Reject);
+                }
+                return Ok((input.advance(i + 1), &input.rest[..i]));
             }
-            '#' => {}
-            _ => return Err(Reject),
+            b'#' => {}
+            _ => break,
         }
     }
-    if n > 255 {
-        // https://github.com/rust-lang/rust/pull/95251
-        return Err(Reject);
+    Err(Reject)
+}
+
+fn raw_byte_string(input: Cursor) -> Result<Cursor, Reject> {
+    let (input, delimiter) = delimiter_of_raw_string(input)?;
+    let mut bytes = input.bytes().enumerate();
+    while let Some((i, byte)) = bytes.next() {
+        match byte {
+            b'"' if input.rest[i + 1..].starts_with(delimiter) => {
+                let rest = input.advance(i + 1 + delimiter.len());
+                return Ok(literal_suffix(rest));
+            }
+            b'\r' => match bytes.next() {
+                Some((_, b'\n')) => {}
+                _ => break,
+            },
+            other => {
+                if !other.is_ascii() {
+                    break;
+                }
+            }
+        }
     }
+    Err(Reject)
+}
+
+fn c_string(input: Cursor) -> Result<Cursor, Reject> {
+    if let Ok(input) = input.parse("c\"") {
+        cooked_c_string(input)
+    } else if let Ok(input) = input.parse("cr") {
+        raw_c_string(input)
+    } else {
+        Err(Reject)
+    }
+}
+
+fn raw_c_string(input: Cursor) -> Result<Cursor, Reject> {
+    let (input, delimiter) = delimiter_of_raw_string(input)?;
+    let mut bytes = input.bytes().enumerate();
+    while let Some((i, byte)) = bytes.next() {
+        match byte {
+            b'"' if input.rest[i + 1..].starts_with(delimiter) => {
+                let rest = input.advance(i + 1 + delimiter.len());
+                return Ok(literal_suffix(rest));
+            }
+            b'\r' => match bytes.next() {
+                Some((_, b'\n')) => {}
+                _ => break,
+            },
+            b'\0' => break,
+            _ => {}
+        }
+    }
+    Err(Reject)
+}
+
+fn cooked_c_string(mut input: Cursor) -> Result<Cursor, Reject> {
+    let mut chars = input.char_indices();
+
     while let Some((i, ch)) = chars.next() {
         match ch {
-            '"' if input.rest[i + 1..].starts_with(&input.rest[..n]) => {
-                let rest = input.advance(i + 1 + n);
-                return Ok(literal_suffix(rest));
+            '"' => {
+                let input = input.advance(i + 1);
+                return Ok(literal_suffix(input));
             }
             '\r' => match chars.next() {
                 Some((_, '\n')) => {}
                 _ => break,
             },
-            _ => {}
+            '\\' => match chars.next() {
+                Some((_, 'x')) => {
+                    backslash_x_nonzero(&mut chars)?;
+                }
+                Some((_, 'n' | 'r' | 't' | '\\' | '\'' | '"')) => {}
+                Some((_, 'u')) => {
+                    if backslash_u(&mut chars)? == '\0' {
+                        break;
+                    }
+                }
+                Some((newline, ch @ ('\n' | '\r'))) => {
+                    input = input.advance(newline + 1);
+                    trailing_backslash(&mut input, ch as u8)?;
+                    chars = input.char_indices();
+                }
+                _ => break,
+            },
+            '\0' => break,
+            _ch => {}
         }
     }
     Err(Reject)
@@ -508,9 +573,8 @@ fn byte(input: Cursor) -> Result<Cursor, Reject> {
     let mut bytes = input.bytes().enumerate();
     let ok = match bytes.next().map(|(_, b)| b) {
         Some(b'\\') => match bytes.next().map(|(_, b)| b) {
-            Some(b'x') => backslash_x_byte(&mut bytes),
-            Some(b'n') | Some(b'r') | Some(b't') | Some(b'\\') | Some(b'0') | Some(b'\'')
-            | Some(b'"') => true,
+            Some(b'x') => backslash_x_byte(&mut bytes).is_ok(),
+            Some(b'n' | b'r' | b't' | b'\\' | b'0' | b'\'' | b'"') => true,
             _ => false,
         },
         b => b.is_some(),
@@ -531,11 +595,9 @@ fn character(input: Cursor) -> Result<Cursor, Reject> {
     let mut chars = input.char_indices();
     let ok = match chars.next().map(|(_, ch)| ch) {
         Some('\\') => match chars.next().map(|(_, ch)| ch) {
-            Some('x') => backslash_x_char(&mut chars),
-            Some('u') => backslash_u(&mut chars),
-            Some('n') | Some('r') | Some('t') | Some('\\') | Some('0') | Some('\'') | Some('"') => {
-                true
-            }
+            Some('x') => backslash_x_char(&mut chars).is_ok(),
+            Some('u') => backslash_u(&mut chars).is_ok(),
+            Some('n' | 'r' | 't' | '\\' | '0' | '\'' | '"') => true,
             _ => false,
         },
         ch => ch.is_some(),
@@ -549,36 +611,49 @@ fn character(input: Cursor) -> Result<Cursor, Reject> {
 }
 
 macro_rules! next_ch {
-    ($chars:ident @ $pat:pat $(| $rest:pat)*) => {
+    ($chars:ident @ $pat:pat) => {
         match $chars.next() {
             Some((_, ch)) => match ch {
-                $pat $(| $rest)* => ch,
-                _ => return false,
+                $pat => ch,
+                _ => return Err(Reject),
             },
-            None => return false,
+            None => return Err(Reject),
         }
     };
 }
 
-fn backslash_x_char<I>(chars: &mut I) -> bool
+fn backslash_x_char<I>(chars: &mut I) -> Result<(), Reject>
 where
     I: Iterator<Item = (usize, char)>,
 {
     next_ch!(chars @ '0'..='7');
     next_ch!(chars @ '0'..='9' | 'a'..='f' | 'A'..='F');
-    true
+    Ok(())
 }
 
-fn backslash_x_byte<I>(chars: &mut I) -> bool
+fn backslash_x_byte<I>(chars: &mut I) -> Result<(), Reject>
 where
     I: Iterator<Item = (usize, u8)>,
 {
     next_ch!(chars @ b'0'..=b'9' | b'a'..=b'f' | b'A'..=b'F');
     next_ch!(chars @ b'0'..=b'9' | b'a'..=b'f' | b'A'..=b'F');
-    true
+    Ok(())
+}
+
+fn backslash_x_nonzero<I>(chars: &mut I) -> Result<(), Reject>
+where
+    I: Iterator<Item = (usize, char)>,
+{
+    let first = next_ch!(chars @ '0'..='9' | 'a'..='f' | 'A'..='F');
+    let second = next_ch!(chars @ '0'..='9' | 'a'..='f' | 'A'..='F');
+    if first == '0' && second == '0' {
+        Err(Reject)
+    } else {
+        Ok(())
+    }
 }
 
-fn backslash_u<I>(chars: &mut I) -> bool
+fn backslash_u<I>(chars: &mut I) -> Result<char, Reject>
 where
     I: Iterator<Item = (usize, char)>,
 {
@@ -591,17 +666,36 @@ where
             'a'..='f' => 10 + ch as u8 - b'a',
             'A'..='F' => 10 + ch as u8 - b'A',
             '_' if len > 0 => continue,
-            '}' if len > 0 => return char::from_u32(value).is_some(),
-            _ => return false,
+            '}' if len > 0 => return char::from_u32(value).ok_or(Reject),
+            _ => break,
         };
         if len == 6 {
-            return false;
+            break;
         }
         value *= 0x10;
         value += u32::from(digit);
         len += 1;
     }
-    false
+    Err(Reject)
+}
+
+fn trailing_backslash(input: &mut Cursor, mut last: u8) -> Result<(), Reject> {
+    let mut whitespace = input.bytes().enumerate();
+    loop {
+        if last == b'\r' && whitespace.next().map_or(true, |(_, b)| b != b'\n') {
+            return Err(Reject);
+        }
+        match whitespace.next() {
+            Some((_, b @ (b' ' | b'\t' | b'\n' | b'\r'))) => {
+                last = b;
+            }
+            Some((offset, _)) => {
+                *input = input.advance(offset);
+                return Ok(());
+            }
+            None => return Err(Reject),
+        }
+    }
 }
 
 fn float(input: Cursor) -> Result<Cursor, Reject> {
@@ -617,7 +711,7 @@ fn float(input: Cursor) -> Result<Cursor, Reject> {
 fn float_digits(input: Cursor) -> Result<Cursor, Reject> {
     let mut chars = input.chars().peekable();
     match chars.next() {
-        Some(ch) if ch >= '0' && ch <= '9' => {}
+        Some(ch) if '0' <= ch && ch <= '9' => {}
         _ => return Err(Reject),
     }
 
diff --git a/src/rcvec.rs b/src/rcvec.rs
index 62298b4..37955af 100644
--- a/src/rcvec.rs
+++ b/src/rcvec.rs
@@ -1,8 +1,8 @@
+use alloc::rc::Rc;
+use alloc::vec;
 use core::mem;
+use core::panic::RefUnwindSafe;
 use core::slice;
-use std::panic::RefUnwindSafe;
-use std::rc::Rc;
-use std::vec;
 
 pub(crate) struct RcVec<T> {
     inner: Rc<Vec<T>>,
@@ -53,7 +53,7 @@ impl<T> RcVec<T> {
         T: Clone,
     {
         let vec = if let Some(owned) = Rc::get_mut(&mut self.inner) {
-            mem::replace(owned, Vec::new())
+            mem::take(owned)
         } else {
             Vec::clone(&self.inner)
         };
diff --git a/src/wrapper.rs b/src/wrapper.rs
index 00f67cd..860b6b7 100644
--- a/src/wrapper.rs
+++ b/src/wrapper.rs
@@ -3,7 +3,6 @@ use crate::detection::inside_proc_macro;
 use crate::location::LineColumn;
 use crate::{fallback, Delimiter, Punct, Spacing, TokenTree};
 use core::fmt::{self, Debug, Display};
-use core::iter::FromIterator;
 use core::ops::RangeBounds;
 use core::str::FromStr;
 use std::panic;
@@ -286,15 +285,7 @@ impl Debug for LexError {
 impl Display for LexError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
-            #[cfg(not(no_lexerror_display))]
             LexError::Compiler(e) => Display::fmt(e, f),
-            #[cfg(no_lexerror_display)]
-            LexError::Compiler(_e) => Display::fmt(
-                &fallback::LexError {
-                    span: fallback::Span::call_site(),
-                },
-                f,
-            ),
             LexError::Fallback(e) => Display::fmt(e, f),
         }
     }
@@ -406,7 +397,6 @@ impl Span {
         }
     }
 
-    #[cfg(not(no_hygiene))]
     pub fn mixed_site() -> Self {
         if inside_proc_macro() {
             Span::Compiler(proc_macro::Span::mixed_site())
@@ -426,13 +416,7 @@ impl Span {
 
     pub fn resolved_at(&self, other: Span) -> Span {
         match (self, other) {
-            #[cfg(not(no_hygiene))]
             (Span::Compiler(a), Span::Compiler(b)) => Span::Compiler(a.resolved_at(b)),
-
-            // Name resolution affects semantics, but location is only cosmetic
-            #[cfg(no_hygiene)]
-            (Span::Compiler(_), Span::Compiler(_)) => other,
-
             (Span::Fallback(a), Span::Fallback(b)) => Span::Fallback(a.resolved_at(b)),
             _ => mismatch(),
         }
@@ -440,13 +424,7 @@ impl Span {
 
     pub fn located_at(&self, other: Span) -> Span {
         match (self, other) {
-            #[cfg(not(no_hygiene))]
             (Span::Compiler(a), Span::Compiler(b)) => Span::Compiler(a.located_at(b)),
-
-            // Name resolution affects semantics, but location is only cosmetic
-            #[cfg(no_hygiene)]
-            (Span::Compiler(_), Span::Compiler(_)) => *self,
-
             (Span::Fallback(a), Span::Fallback(b)) => Span::Fallback(a.located_at(b)),
             _ => mismatch(),
         }
@@ -470,12 +448,6 @@ impl Span {
     #[cfg(span_locations)]
     pub fn start(&self) -> LineColumn {
         match self {
-            #[cfg(proc_macro_span)]
-            Span::Compiler(s) => {
-                let proc_macro::LineColumn { line, column } = s.start();
-                LineColumn { line, column }
-            }
-            #[cfg(not(proc_macro_span))]
             Span::Compiler(_) => LineColumn { line: 0, column: 0 },
             Span::Fallback(s) => s.start(),
         }
@@ -484,33 +456,11 @@ impl Span {
     #[cfg(span_locations)]
     pub fn end(&self) -> LineColumn {
         match self {
-            #[cfg(proc_macro_span)]
-            Span::Compiler(s) => {
-                let proc_macro::LineColumn { line, column } = s.end();
-                LineColumn { line, column }
-            }
-            #[cfg(not(proc_macro_span))]
             Span::Compiler(_) => LineColumn { line: 0, column: 0 },
             Span::Fallback(s) => s.end(),
         }
     }
 
-    #[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)]
@@ -630,20 +580,14 @@ impl Group {
 
     pub fn span_open(&self) -> Span {
         match self {
-            #[cfg(not(no_group_open_close))]
             Group::Compiler(g) => Span::Compiler(g.span_open()),
-            #[cfg(no_group_open_close)]
-            Group::Compiler(g) => Span::Compiler(g.span()),
             Group::Fallback(g) => Span::Fallback(g.span_open()),
         }
     }
 
     pub fn span_close(&self) -> Span {
         match self {
-            #[cfg(not(no_group_open_close))]
             Group::Compiler(g) => Span::Compiler(g.span_close()),
-            #[cfg(no_group_open_close)]
-            Group::Compiler(g) => Span::Compiler(g.span()),
             Group::Fallback(g) => Span::Fallback(g.span_close()),
         }
     }
@@ -704,27 +648,7 @@ 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 _ = 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!("not allowed as a raw identifier: `{}`", raw_prefixed)
-            }
             Span::Fallback(s) => Ident::Fallback(fallback::Ident::new_raw(string, s)),
         }
     }
@@ -826,7 +750,7 @@ macro_rules! unsuffixed_integers {
 impl Literal {
     pub unsafe fn from_str_unchecked(repr: &str) -> Self {
         if inside_proc_macro() {
-            Literal::Compiler(compiler_literal_from_str(repr).expect("invalid literal"))
+            Literal::Compiler(proc_macro::Literal::from_str(repr).expect("invalid literal"))
         } else {
             Literal::Fallback(fallback::Literal::from_str_unchecked(repr))
         }
@@ -949,7 +873,8 @@ impl FromStr for Literal {
 
     fn from_str(repr: &str) -> Result<Self, Self::Err> {
         if inside_proc_macro() {
-            compiler_literal_from_str(repr).map(Literal::Compiler)
+            let literal = proc_macro::Literal::from_str(repr)?;
+            Ok(Literal::Compiler(literal))
         } else {
             let literal = fallback::Literal::from_str(repr)?;
             Ok(Literal::Fallback(literal))
@@ -957,24 +882,6 @@ impl FromStr for Literal {
     }
 }
 
-fn compiler_literal_from_str(repr: &str) -> Result<proc_macro::Literal, LexError> {
-    #[cfg(not(no_literal_from_str))]
-    {
-        proc_macro::Literal::from_str(repr).map_err(LexError::Compiler)
-    }
-    #[cfg(no_literal_from_str)]
-    {
-        let tokens = proc_macro_parse(repr)?;
-        let mut iter = tokens.into_iter();
-        if let (Some(proc_macro::TokenTree::Literal(literal)), None) = (iter.next(), iter.next()) {
-            if literal.to_string().len() == repr.len() {
-                return Ok(literal);
-            }
-        }
-        Err(LexError::call_site())
-    }
-}
-
 impl Display for Literal {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
diff --git a/tests/marker.rs b/tests/marker.rs
index 5b45733..d08fbfc 100644
--- a/tests/marker.rs
+++ b/tests/marker.rs
@@ -62,7 +62,6 @@ mod semver_exempt {
     assert_impl!(SourceFile is not Send or Sync);
 }
 
-#[cfg(not(no_libprocmacro_unwind_safe))]
 mod unwind_safe {
     use proc_macro2::{
         Delimiter, Group, Ident, LexError, Literal, Punct, Spacing, Span, TokenStream, TokenTree,
diff --git a/tests/test.rs b/tests/test.rs
index 75f69e2..8e47b46 100644
--- a/tests/test.rs
+++ b/tests/test.rs
@@ -7,7 +7,6 @@
 
 use proc_macro2::{Ident, Literal, Punct, Spacing, Span, TokenStream, TokenTree};
 use std::iter;
-use std::panic;
 use std::str::{self, FromStr};
 
 #[test]
@@ -90,24 +89,9 @@ fn lifetime_number() {
 }
 
 #[test]
+#[should_panic(expected = r#""'a#" is not a valid Ident"#)]
 fn lifetime_invalid() {
-    let result = panic::catch_unwind(|| Ident::new("'a#", Span::call_site()));
-    match result {
-        Err(box_any) => {
-            let message = box_any.downcast_ref::<String>().unwrap();
-            let expected1 = r#""\'a#" is not a valid Ident"#; // 1.31.0 .. 1.53.0
-            let expected2 = r#""'a#" is not a valid Ident"#; // 1.53.0 ..
-            assert!(
-                message == expected1 || message == expected2,
-                "panic message does not match expected string\n\
-                 \x20   panic message: `{:?}`\n\
-                 \x20expected message: `{:?}`",
-                message,
-                expected2,
-            );
-        }
-        Ok(_) => panic!("test did not panic as expected"),
-    }
+    Ident::new("'a#", Span::call_site());
 }
 
 #[test]
@@ -119,6 +103,9 @@ fn literal_string() {
         Literal::string("a\00b\07c\08d\0e\0").to_string(),
         "\"a\\x000b\\x007c\\08d\\0e\\0\"",
     );
+
+    "\"\\\r\n    x\"".parse::<TokenStream>().unwrap();
+    "\"\\\r\n  \rx\"".parse::<TokenStream>().unwrap_err();
 }
 
 #[test]
@@ -156,6 +143,47 @@ fn literal_byte_string() {
         Literal::byte_string(b"a\00b\07c\08d\0e\0").to_string(),
         "b\"a\\x000b\\x007c\\08d\\0e\\0\"",
     );
+
+    "b\"\\\r\n    x\"".parse::<TokenStream>().unwrap();
+    "b\"\\\r\n  \rx\"".parse::<TokenStream>().unwrap_err();
+    "b\"\\\r\n  \u{a0}x\"".parse::<TokenStream>().unwrap_err();
+    "br\"\u{a0}\"".parse::<TokenStream>().unwrap_err();
+}
+
+#[test]
+fn literal_c_string() {
+    let strings = r###"
+        c"hello\x80我叫\u{1F980}"  // from the RFC
+        cr"\"
+        cr##"Hello "world"!"##
+        c"\t\n\r\"\\"
+    "###;
+
+    let mut tokens = strings.parse::<TokenStream>().unwrap().into_iter();
+
+    for expected in &[
+        r#"c"hello\x80我叫\u{1F980}""#,
+        r#"cr"\""#,
+        r###"cr##"Hello "world"!"##"###,
+        r#"c"\t\n\r\"\\""#,
+    ] {
+        match tokens.next().unwrap() {
+            TokenTree::Literal(literal) => {
+                assert_eq!(literal.to_string(), *expected);
+            }
+            unexpected => panic!("unexpected token: {:?}", unexpected),
+        }
+    }
+
+    if let Some(unexpected) = tokens.next() {
+        panic!("unexpected token: {:?}", unexpected);
+    }
+
+    for invalid in &[r#"c"\0""#, r#"c"\x00""#, r#"c"\u{0}""#, "c\"\0\""] {
+        if let Ok(unexpected) = invalid.parse::<TokenStream>() {
+            panic!("unexpected token: {:?}", unexpected);
+        }
+    }
 }
 
 #[test]
@@ -636,8 +664,8 @@ fn non_ascii_tokens() {
     check_spans("/*** ábc */ x", &[(1, 12, 1, 13)]);
     check_spans(r#""abc""#, &[(1, 0, 1, 5)]);
     check_spans(r#""ábc""#, &[(1, 0, 1, 5)]);
-    check_spans(r###"r#"abc"#"###, &[(1, 0, 1, 8)]);
-    check_spans(r###"r#"ábc"#"###, &[(1, 0, 1, 8)]);
+    check_spans(r##"r#"abc"#"##, &[(1, 0, 1, 8)]);
+    check_spans(r##"r#"ábc"#"##, &[(1, 0, 1, 8)]);
     check_spans("r#\"a\nc\"#", &[(1, 0, 2, 3)]);
     check_spans("r#\"á\nc\"#", &[(1, 0, 2, 3)]);
     check_spans("'a'", &[(1, 0, 1, 3)]);
@@ -657,7 +685,6 @@ fn non_ascii_tokens() {
     check_spans("ábc// foo", &[(1, 0, 1, 3)]);
     check_spans("ábć// foo", &[(1, 0, 1, 3)]);
     check_spans("b\"a\\\n c\"", &[(1, 0, 2, 3)]);
-    check_spans("b\"a\\\n\u{00a0}c\"", &[(1, 0, 2, 3)]);
 }
 
 #[cfg(span_locations)]
@@ -689,6 +716,18 @@ fn check_spans_internal(ts: TokenStream, lines: &mut &[(usize, usize, usize, usi
 }
 
 #[test]
+fn whitespace() {
+    // space, horizontal tab, vertical tab, form feed, carriage return, line
+    // feed, non-breaking space, left-to-right mark, right-to-left mark
+    let various_spaces = " \t\u{b}\u{c}\r\n\u{a0}\u{200e}\u{200f}";
+    let tokens = various_spaces.parse::<TokenStream>().unwrap();
+    assert_eq!(tokens.into_iter().count(), 0);
+
+    let lone_carriage_returns = " \r \r\r\n ";
+    lone_carriage_returns.parse::<TokenStream>().unwrap();
+}
+
+#[test]
 fn byte_order_mark() {
     let string = "\u{feff}foo";
     let tokens = string.parse::<TokenStream>().unwrap();
diff --git a/tests/test_fmt.rs b/tests/test_fmt.rs
index 93dd19e..86a4c38 100644
--- a/tests/test_fmt.rs
+++ b/tests/test_fmt.rs
@@ -1,7 +1,7 @@
 #![allow(clippy::from_iter_instead_of_collect)]
 
 use proc_macro2::{Delimiter, Group, Ident, Span, TokenStream, TokenTree};
-use std::iter::{self, FromIterator};
+use std::iter;
 
 #[test]
 fn test_fmt_group() {