Auto merge of rust-lang#89237 - BoxyUwU:trackersMcCaller, r=eddyb

make `#[track_caller]` actually do stuff in `Steal::borrow`

makes this ICE message useful:
``thread 'rustc' panicked at 'attempted to read from stolen value', /rustc/ac2d9fc509e36d1b32513744adf58c34bcc4f43c\compiler\rustc_data_structures\src\steal.rs:37:21``

Author: bors

compiler/rustc_data_structures/src/steal.rs

@@ -33,10 +33,11 @@ impl<T> Steal<T> {
 
     #[track_caller]
     pub fn borrow(&self) -> MappedReadGuard<'_, T> {
-        ReadGuard::map(self.value.borrow(), |opt| match *opt {
-            None => panic!("attempted to read from stolen value"),
-            Some(ref v) => v,
-        })
+        let borrow = self.value.borrow();
+        if let None = &*borrow {
+            panic!("attempted to read from stolen value: {}", std::any::type_name::<T>());
+        }
+        ReadGuard::map(borrow, |opt| opt.as_ref().unwrap())
     }
 
     #[track_caller]