.github/workflows/ci.yml

@@ -40,6 +40,7 @@ jobs:
       - 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

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "proc-macro2"
-version = "1.0.20" # remember to update html_root_url
+version = "1.0.21" # remember to update html_root_url
 authors = ["Alex Crichton <alex@alexcrichton.com>", "David Tolnay <dtolnay@gmail.com>"]
 license = "MIT OR Apache-2.0"
 readme = "README.md"
@@ -40,7 +40,7 @@ span-locations = []
 nightly = []
 
 [workspace]
-members = ["benches/bench-libproc-macro"]
+members = ["benches/bench-libproc-macro", "tests/ui"]
 
 [patch.crates-io]
 # Our doc tests depend on quote which depends on proc-macro2. Without this line,

build.rs

@@ -61,6 +61,10 @@ fn main() {
         println!("cargo:rustc-cfg=span_locations");
     }
 
+    if version.minor < 32 {
+        println!("cargo:rustc-cfg=no_libprocmacro_unwind_safe");
+    }
+
     if version.minor < 39 {
         println!("cargo:rustc-cfg=no_bind_by_move_pattern_guard");
     }

src/lib.rs

@@ -78,25 +78,15 @@
 //! a different thread.
 
 // Proc-macro2 types in rustdoc of other crates get linked to here.
-#![doc(html_root_url = "https://docs.rs/proc-macro2/1.0.20")]
+#![doc(html_root_url = "https://docs.rs/proc-macro2/1.0.21")]
 #![cfg_attr(any(proc_macro_span, super_unstable), feature(proc_macro_span))]
 #![cfg_attr(super_unstable, feature(proc_macro_raw_ident, proc_macro_def_site))]
 #![allow(clippy::needless_doctest_main)]
 
 #[cfg(use_proc_macro)]
 extern crate proc_macro;
 
-use std::cmp::Ordering;
-use std::fmt::{self, Debug, Display};
-use std::hash::{Hash, Hasher};
-use std::iter::FromIterator;
-use std::marker;
-use std::ops::RangeBounds;
-#[cfg(procmacro2_semver_exempt)]
-use std::path::PathBuf;
-use std::rc::Rc;
-use std::str::FromStr;
-
+mod marker;
 mod parse;
 
 #[cfg(wrap_proc_macro)]
@@ -113,6 +103,16 @@ use crate::fallback as imp;
 #[cfg(wrap_proc_macro)]
 mod imp;
 
+use crate::marker::Marker;
+use std::cmp::Ordering;
+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.
 ///
 /// This type provides interfaces for iterating over token trees and for
@@ -123,27 +123,27 @@ mod imp;
 #[derive(Clone)]
 pub struct TokenStream {
     inner: imp::TokenStream,
-    _marker: marker::PhantomData<Rc<()>>,
+    _marker: Marker,
 }
 
 /// Error returned from `TokenStream::from_str`.
 pub struct LexError {
     inner: imp::LexError,
-    _marker: marker::PhantomData<Rc<()>>,
+    _marker: Marker,
 }
 
 impl TokenStream {
     fn _new(inner: imp::TokenStream) -> TokenStream {
         TokenStream {
             inner,
-            _marker: marker::PhantomData,
+            _marker: Marker,
         }
     }
 
     fn _new_stable(inner: fallback::TokenStream) -> TokenStream {
         TokenStream {
             inner: inner.into(),
-            _marker: marker::PhantomData,
+            _marker: Marker,
         }
     }
 
@@ -180,7 +180,7 @@ impl FromStr for TokenStream {
     fn from_str(src: &str) -> Result<TokenStream, LexError> {
         let e = src.parse().map_err(|e| LexError {
             inner: e,
-            _marker: marker::PhantomData,
+            _marker: Marker,
         })?;
         Ok(TokenStream::_new(e))
     }
@@ -261,15 +261,15 @@ impl Debug for LexError {
 #[derive(Clone, PartialEq, Eq)]
 pub struct SourceFile {
     inner: imp::SourceFile,
-    _marker: marker::PhantomData<Rc<()>>,
+    _marker: Marker,
 }
 
 #[cfg(procmacro2_semver_exempt)]
 impl SourceFile {
     fn _new(inner: imp::SourceFile) -> Self {
         SourceFile {
             inner,
-            _marker: marker::PhantomData,
+            _marker: Marker,
         }
     }
 
@@ -338,21 +338,21 @@ impl PartialOrd for LineColumn {
 #[derive(Copy, Clone)]
 pub struct Span {
     inner: imp::Span,
-    _marker: marker::PhantomData<Rc<()>>,
+    _marker: Marker,
 }
 
 impl Span {
     fn _new(inner: imp::Span) -> Span {
         Span {
             inner,
-            _marker: marker::PhantomData,
+            _marker: Marker,
         }
     }
 
     fn _new_stable(inner: fallback::Span) -> Span {
         Span {
             inner: inner.into(),
-            _marker: marker::PhantomData,
+            _marker: Marker,
         }
     }
 
@@ -840,14 +840,14 @@ impl Debug for Punct {
 #[derive(Clone)]
 pub struct Ident {
     inner: imp::Ident,
-    _marker: marker::PhantomData<Rc<()>>,
+    _marker: Marker,
 }
 
 impl Ident {
     fn _new(inner: imp::Ident) -> Ident {
         Ident {
             inner,
-            _marker: marker::PhantomData,
+            _marker: Marker,
         }
     }
 
@@ -968,7 +968,7 @@ impl Debug for Ident {
 #[derive(Clone)]
 pub struct Literal {
     inner: imp::Literal,
-    _marker: marker::PhantomData<Rc<()>>,
+    _marker: Marker,
 }
 
 macro_rules! suffixed_int_literals {
@@ -1015,14 +1015,14 @@ impl Literal {
     fn _new(inner: imp::Literal) -> Literal {
         Literal {
             inner,
-            _marker: marker::PhantomData,
+            _marker: Marker,
         }
     }
 
     fn _new_stable(inner: fallback::Literal) -> Literal {
         Literal {
             inner: inner.into(),
-            _marker: marker::PhantomData,
+            _marker: Marker,
         }
     }
 
@@ -1181,10 +1181,9 @@ impl Display for Literal {
 
 /// Public implementation details for the `TokenStream` type, such as iterators.
 pub mod token_stream {
+    use crate::marker::Marker;
     use crate::{imp, TokenTree};
     use std::fmt::{self, Debug};
-    use std::marker;
-    use std::rc::Rc;
 
     pub use crate::TokenStream;
 
@@ -1195,7 +1194,7 @@ pub mod token_stream {
     #[derive(Clone)]
     pub struct IntoIter {
         inner: imp::TokenTreeIter,
-        _marker: marker::PhantomData<Rc<()>>,
+        _marker: Marker,
     }
 
     impl Iterator for IntoIter {
@@ -1219,7 +1218,7 @@ pub mod token_stream {
         fn into_iter(self) -> IntoIter {
             IntoIter {
                 inner: self.inner.into_iter(),
-                _marker: marker::PhantomData,
+                _marker: Marker,
             }
         }
     }

src/marker.rs

@@ -0,0 +1,18 @@
+use std::marker::PhantomData;
+use std::panic::{RefUnwindSafe, UnwindSafe};
+use std::rc::Rc;
+
+// Zero sized marker with the correct set of autotrait impls we want all proc
+// macro types to have.
+pub(crate) type Marker = PhantomData<ProcMacroAutoTraits>;
+
+pub(crate) use self::value::*;
+
+mod value {
+    pub(crate) use std::marker::PhantomData as Marker;
+}
+
+pub(crate) struct ProcMacroAutoTraits(Rc<()>);
+
+impl UnwindSafe for ProcMacroAutoTraits {}
+impl RefUnwindSafe for ProcMacroAutoTraits {}

tests/marker.rs

@@ -57,3 +57,36 @@ mod semver_exempt {
 
     assert_impl!(SourceFile is not Send or Sync);
 }
+
+#[cfg(not(no_libprocmacro_unwind_safe))]
+mod unwind_safe {
+    use super::*;
+    use std::panic::{RefUnwindSafe, UnwindSafe};
+
+    macro_rules! assert_unwind_safe {
+        ($($types:ident)*) => {
+            $(
+                assert_impl!($types is UnwindSafe and RefUnwindSafe);
+            )*
+        };
+    }
+
+    assert_unwind_safe! {
+        Delimiter
+        Group
+        Ident
+        LexError
+        Literal
+        Punct
+        Spacing
+        Span
+        TokenStream
+        TokenTree
+    }
+
+    #[cfg(procmacro2_semver_exempt)]
+    assert_unwind_safe! {
+        LineColumn
+        SourceFile
+    }
+}

tests/ui/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "proc-macro2-ui-test"
+version = "0.0.0"
+edition = "2018"
+publish = false
+
+[[test]]
+name = "compiletest"
+path = "compiletest.rs"
+
+[dev-dependencies]
+proc-macro2 = { path = "../.." }
+trybuild = { version = "1.0", features = ["diff"] }

tests/ui/compiletest.rs

@@ -0,0 +1,5 @@
+#[test]
+fn ui() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("test-*.rs");
+}

tests/ui/test-not-send.rs

@@ -0,0 +1,6 @@
+use proc_macro2::Span;
+
+fn main() {
+    fn requires_send<T: Send>() {}
+    requires_send::<Span>();
+}

tests/ui/test-not-send.stderr

@@ -0,0 +1,24 @@
+error[E0277]: `proc_macro::Span` cannot be sent between threads safely
+ --> $DIR/test-not-send.rs:5:5
+  |
+4 |     fn requires_send<T: Send>() {}
+  |                         ---- required by this bound in `requires_send`
+5 |     requires_send::<Span>();
+  |     ^^^^^^^^^^^^^^^^^^^^^ `proc_macro::Span` cannot be sent between threads safely
+  |
+  = help: within `Span`, the trait `Send` is not implemented for `proc_macro::Span`
+  = note: required because it appears within the type `proc_macro2::imp::Span`
+  = note: required because it appears within the type `Span`
+
+error[E0277]: `Rc<()>` cannot be sent between threads safely
+ --> $DIR/test-not-send.rs:5:5
+  |
+4 |     fn requires_send<T: Send>() {}
+  |                         ---- required by this bound in `requires_send`
+5 |     requires_send::<Span>();
+  |     ^^^^^^^^^^^^^^^^^^^^^ `Rc<()>` cannot be sent between threads safely
+  |
+  = help: within `Span`, the trait `Send` is not implemented for `Rc<()>`
+  = note: required because it appears within the type `proc_macro2::marker::ProcMacroAutoTraits`
+  = note: required because it appears within the type `PhantomData<proc_macro2::marker::ProcMacroAutoTraits>`
+  = note: required because it appears within the type `Span`