Remove argument from closure in thread::Scope::spawn.

library/std/src/thread/scoped.rs

@@ -9,23 +9,24 @@ use crate::sync::Arc;
 /// A scope to spawn scoped threads in.
 ///
 /// See [`scope`] for details.
-pub struct Scope<'env> {
+pub struct Scope<'scope, 'env: 'scope> {
     data: ScopeData,
-    /// Invariance over 'env, to make sure 'env cannot shrink,
+    /// Invariance over 'scope, to make sure 'scope cannot shrink,
     /// which is necessary for soundness.
     ///
     /// Without invariance, this would compile fine but be unsound:
     ///
-    /// ```compile_fail
+    /// ```compile_fail,E0373
     /// #![feature(scoped_threads)]
     ///
     /// std::thread::scope(|s| {
-    ///     s.spawn(|s| {
+    ///     s.spawn(|| {
     ///         let a = String::from("abcd");
-    ///         s.spawn(|_| println!("{:?}", a)); // might run after `a` is dropped
+    ///         s.spawn(|| println!("{:?}", a)); // might run after `a` is dropped
     ///     });
     /// });
     /// ```
+    scope: PhantomData<&'scope mut &'scope ()>,
     env: PhantomData<&'env mut &'env ()>,
 }
 
@@ -88,12 +89,12 @@ impl ScopeData {
 /// let mut x = 0;
 ///
 /// thread::scope(|s| {
-///     s.spawn(|_| {
+///     s.spawn(|| {
 ///         println!("hello from the first scoped thread");
 ///         // We can borrow `a` here.
 ///         dbg!(&a);
 ///     });
-///     s.spawn(|_| {
+///     s.spawn(|| {
 ///         println!("hello from the second scoped thread");
 ///         // We can even mutably borrow `x` here,
 ///         // because no other threads are using it.
@@ -109,7 +110,7 @@ impl ScopeData {
 #[track_caller]
 pub fn scope<'env, F, T>(f: F) -> T
 where
-    F: FnOnce(&Scope<'env>) -> T,
+    F: for<'scope> FnOnce(&'scope Scope<'scope, 'env>) -> T,
 {
     let scope = Scope {
         data: ScopeData {
@@ -118,6 +119,7 @@ where
             a_thread_panicked: AtomicBool::new(false),
         },
         env: PhantomData,
+        scope: PhantomData,
     };
 
     // Run `f`, but catch panics so we can make sure to wait for all the threads to join.
@@ -138,7 +140,7 @@ where
     }
 }
 
-impl<'env> Scope<'env> {
+impl<'scope, 'env> Scope<'scope, 'env> {
     /// Spawns a new thread within a scope, returning a [`ScopedJoinHandle`] for it.
     ///
     /// Unlike non-scoped threads, threads spawned with this function may
@@ -163,10 +165,10 @@ impl<'env> Scope<'env> {
     /// to recover from such errors.
     ///
     /// [`join`]: ScopedJoinHandle::join
-    pub fn spawn<'scope, F, T>(&'scope self, f: F) -> ScopedJoinHandle<'scope, T>
+    pub fn spawn<F, T>(&'scope self, f: F) -> ScopedJoinHandle<'scope, T>
     where
-        F: FnOnce(&Scope<'env>) -> T + Send + 'env,
-        T: Send + 'env,
+        F: FnOnce() -> T + Send + 'scope,
+        T: Send + 'scope,
     {
         Builder::new().spawn_scoped(self, f).expect("failed to spawn thread")
     }
@@ -196,7 +198,7 @@ impl Builder {
     /// thread::scope(|s| {
     ///     thread::Builder::new()
     ///         .name("first".to_string())
-    ///         .spawn_scoped(s, |_|
+    ///         .spawn_scoped(s, ||
     ///     {
     ///         println!("hello from the {:?} scoped thread", thread::current().name());
     ///         // We can borrow `a` here.
@@ -205,7 +207,7 @@ impl Builder {
     ///     .unwrap();
     ///     thread::Builder::new()
     ///         .name("second".to_string())
-    ///         .spawn_scoped(s, |_|
+    ///         .spawn_scoped(s, ||
     ///     {
     ///         println!("hello from the {:?} scoped thread", thread::current().name());
     ///         // We can even mutably borrow `x` here,
@@ -222,14 +224,14 @@ impl Builder {
     /// ```
     pub fn spawn_scoped<'scope, 'env, F, T>(
         self,
-        scope: &'scope Scope<'env>,
+        scope: &'scope Scope<'scope, 'env>,
         f: F,
     ) -> io::Result<ScopedJoinHandle<'scope, T>>
     where
-        F: FnOnce(&Scope<'env>) -> T + Send + 'env,
-        T: Send + 'env,
+        F: FnOnce() -> T + Send + 'scope,
+        T: Send + 'scope,
     {
-        Ok(ScopedJoinHandle(unsafe { self.spawn_unchecked_(|| f(scope), Some(&scope.data)) }?))
+        Ok(ScopedJoinHandle(unsafe { self.spawn_unchecked_(|| f(), Some(&scope.data)) }?))
     }
 }
 
@@ -245,7 +247,7 @@ impl<'scope, T> ScopedJoinHandle<'scope, T> {
     /// use std::thread;
     ///
     /// thread::scope(|s| {
-    ///     let t = s.spawn(|_| {
+    ///     let t = s.spawn(|| {
     ///         println!("hello");
     ///     });
     ///     println!("thread id: {:?}", t.thread().id());
@@ -279,7 +281,7 @@ impl<'scope, T> ScopedJoinHandle<'scope, T> {
     /// use std::thread;
     ///
     /// thread::scope(|s| {
-    ///     let t = s.spawn(|_| {
+    ///     let t = s.spawn(|| {
     ///         panic!("oh no");
     ///     });
     ///     assert!(t.join().is_err());
@@ -299,7 +301,7 @@ impl<'scope, T> ScopedJoinHandle<'scope, T> {
     }
 }
 
-impl<'env> fmt::Debug for Scope<'env> {
+impl<'scope, 'env> fmt::Debug for Scope<'scope, 'env> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("Scope")
             .field("num_running_threads", &self.data.num_running_threads.load(Ordering::Relaxed))