std::thread: add SAFETY comment

RalfJung · RalfJung · commit ccb36a688d2b · 2023-10-27T15:18:32.000+02:00
diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs
@@ -546,6 +546,8 @@ impl Builder {
         }
 
         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) };

Original file line number	Diff line number	Diff line change
`@@ -546,6 +546,8 @@ impl Builder {`
`546`	`546`	`}`
`547`	`547`
`548`	`548`	`let main = Box::new(main);`
	`549`	`+ // SAFETY: dynamic size and alignment of the Box remain the same. See below for why the`
	`550`	`+ // lifetime change is justified.`
`549`	`551`	`#[cfg(bootstrap)]`
`550`	`552`	`let main =`
`551`	`553`	`unsafe { mem::transmute::<Box<dyn FnOnce() + 'a>, Box<dyn FnOnce() + 'static>>(main) };`