Auto merge of #23002 - pnkfelix:fsk-box-place-runway, r=nikomatsakis

Runway for RFC 809 (overloaded box/placement-in) by adding type annotations or explicit calls to `Box::new` where I found it necessary on PR #22086.

I have broken this up into more than one PR because the entire commit chain (see PR #22086) is long, widespread and unwieldy to rebase frequently.

To my knowledge this is not a breaking change.  Also, there is in principle nothing stopping someone from reverting some/all of these annotations, since without the rest of the commit chain in #22086, the associated code would continue to compile.

All I can do is ask: Try to discourage others from removing seemingly "unnecessary" uses of the `Box` type or the `Box::new()` function, until the rest of RFC 809 lands.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libstd/thread.rs b/src/libstd/thread.rs
index e8330820906..9be77e78ed1 100644
--- a/src/libstd/thread.rs
+++ b/src/libstd/thread.rs
@@ -804,7 +804,7 @@ mod test {
     fn avoid_copying_the_body<F>(spawnfn: F) where F: FnOnce(Thunk<'static>) {
         let (tx, rx) = channel();
 
-        let x = box 1;
+        let x: Box<_> = box 1;
         let x_in_parent = (&*x) as *const i32 as usize;
 
         spawnfn(Thunk::new(move|| {