std: Don't assume thread::current() works on panic

Inspecting the current thread's info may not always work due to the TLS value
having been destroyed (or is actively being destroyed). The code for printing
a panic message assumed, however, that it could acquire the thread's name
through this method.

Instead this commit propagates the `Option` outwards to allow the
`std::panicking` module to handle the case where the current thread isn't
present.

While it solves the immediate issue of #24313, there is still another underlying
issue of panicking destructors in thread locals will abort the process.

Closes #24313

1 files changed, 3 insertions, 1 deletions

diff --git a/src/libstd/thread/mod.rs b/src/libstd/thread/mod.rs
index 383726b3e83..ce531fb1381 100644
--- a/src/libstd/thread/mod.rs
+++ b/src/libstd/thread/mod.rs
@@ -407,7 +407,9 @@ pub fn scoped<'a, T, F>(f: F) -> JoinGuard<'a, T> where
 /// Gets a handle to the thread that invokes it.
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn current() -> Thread {
-    thread_info::current_thread()
+    thread_info::current_thread().expect("use of std::thread::current() is not \
+                                          possible after the thread's local \
+                                          data has been destroyed")
 }
 
 /// Cooperatively gives up a timeslice to the OS scheduler.