Merging upstream version 1.75.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

2 files changed, 13 insertions, 11 deletions

diff --git a/library/std/src/thread/local.rs b/library/std/src/thread/local.rs
index 09994e47f..def94acd4 100644
--- a/library/std/src/thread/local.rs
+++ b/library/std/src/thread/local.rs
@@ -29,9 +29,9 @@ use crate::fmt;
 /// within a thread, and values that implement [`Drop`] get destructed when a
 /// thread exits. Some caveats apply, which are explained below.
 ///
-/// A `LocalKey`'s initializer cannot recursively depend on itself, and using
-/// a `LocalKey` in this way will cause the initializer to infinitely recurse
-/// on the first call to `with`.
+/// A `LocalKey`'s initializer cannot recursively depend on itself. Using a
+/// `LocalKey` in this way may cause panics, aborts or infinite recursion on
+/// the first call to `with`.
 ///
 /// # Examples
 ///
diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs
index 7b26068c2..4097eb554 100644
--- a/library/std/src/thread/mod.rs
+++ b/library/std/src/thread/mod.rs
@@ -545,6 +545,15 @@ impl Builder {
             scope_data.increment_num_running_threads();
         }
 
+        let main = Box::new(main);
+        // SAFETY: dynamic size and alignment of the Box remain the same. See below for why the
+        // lifetime change is justified.
+        #[cfg(bootstrap)]
+        let main =
+            unsafe { mem::transmute::<Box<dyn FnOnce() + 'a>, Box<dyn FnOnce() + 'static>>(main) };
+        #[cfg(not(bootstrap))]
+        let main = unsafe { Box::from_raw(Box::into_raw(main) as *mut (dyn FnOnce() + 'static)) };
+
         Ok(JoinInner {
             // SAFETY:
             //
@@ -559,14 +568,7 @@ impl Builder {
             // Similarly, the `sys` implementation must guarantee that no references to the closure
             // exist after the thread has terminated, which is signaled by `Thread::join`
             // returning.
-            native: unsafe {
-                imp::Thread::new(
-                    stack_size,
-                    mem::transmute::<Box<dyn FnOnce() + 'a>, Box<dyn FnOnce() + 'static>>(
-                        Box::new(main),
-                    ),
-                )?
-            },
+            native: unsafe { imp::Thread::new(stack_size, main)? },
             thread: my_thread,
             packet: my_packet,
         })