Reduce unsafe code in get_or

get_or() currently works as a wrapper around get_or_try(). It wraps the
result of the passed function into a Result<T, ()> and then calls
unreachable_unchecked, which is an unsafe function. However, as an Err
branch is never instantiated for this Result type, we can use the
uninhabited Infallible type instead of the unit type. At this point it
is 100% safe to unwrap the underlying result and match on the
uninhabited error type to eliminate that branch.

It turns out this was the only time that the "unreachable" module was
used in the library, so I've also taken the liberty of deleting that
file.

Signed-off-by: John Nunley <dev@notgull.net>

src/lib.rs

@@ -69,12 +69,12 @@
 
 mod cached;
 mod thread_id;
-mod unreachable;
 
 #[allow(deprecated)]
 pub use cached::{CachedIntoIter, CachedIterMut, CachedThreadLocal};
 
 use std::cell::UnsafeCell;
+use std::convert::Infallible;
 use std::fmt;
 use std::iter::FusedIterator;
 use std::mem;
@@ -83,7 +83,6 @@ use std::panic::UnwindSafe;
 use std::ptr;
 use std::sync::atomic::{AtomicBool, AtomicPtr, AtomicUsize, Ordering};
 use thread_id::Thread;
-use unreachable::UncheckedResultExt;
 
 // Use usize::BITS once it has stabilized and the MSRV has been bumped.
 #[cfg(target_pointer_width = "16")]
@@ -187,9 +186,9 @@ impl<T: Send> ThreadLocal<T> {
     where
         F: FnOnce() -> T,
     {
-        unsafe {
-            self.get_or_try(|| Ok::<T, ()>(create()))
-                .unchecked_unwrap_ok()
+        match self.get_or_try(|| Ok::<T, Infallible>(create())) {
+            Ok(val) => val,
+            Err(inf) => match inf {},
         }
     }