Auto merge of rust-lang#126829 - RalfJung:main-thread-tls, r=workingjubilee

add test for main thread thread-local destructors

Fixes rust-lang#28129

Author: bors

Diff for: tests/ui/thread-local/main-thread-dtor.rs

@@ -0,0 +1,29 @@
+//@ run-pass
+//@ check-run-results
+//@ needs-threads (really only needs TLS, not threads, but those seem to usually come together)
+//! Ensure that TLS destructors run on the main thread.
+
+struct Bar;
+
+impl Drop for Bar {
+    fn drop(&mut self) {
+        println!("Bar dtor");
+    }
+}
+
+struct Foo;
+
+impl Drop for Foo {
+    fn drop(&mut self) {
+        println!("Foo dtor");
+        // We initialize another thread-local inside the dtor, which is an interesting corner case.
+        thread_local!(static BAR: Bar = Bar);
+        BAR.with(|_| {});
+    }
+}
+
+thread_local!(static FOO: Foo = Foo);
+
+fn main() {
+    FOO.with(|_| {});
+}

Diff for: tests/ui/thread-local/main-thread-dtor.run.stdout

@@ -0,0 +1,2 @@
+Foo dtor
+Bar dtor