add first batch of feedback from review

Author: yoshuawuyts

library/core/src/mem/drop_guard.rs

@@ -1,3 +1,4 @@
+use crate::fmt::{self, Debug};
 use crate::mem::ManuallyDrop;
 use crate::ops::{Deref, DerefMut};
 use crate::ptr;
@@ -26,8 +27,10 @@ use crate::ptr;
 /// }
 /// ```
 #[unstable(feature = "drop_guard", issue = "none")]
-#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct DropGuard<T, F>
+#[derive(PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[doc(alias = "ScopeGuard")]
+#[doc(alias = "defer")]
+pub struct DropGuard<T, F = fn(T)>
 where
     F: FnOnce(T),
 {
@@ -51,7 +54,8 @@ where
     /// let guard = DropGuard::new(value, |s| println!("{s}"));
     /// ```
     #[unstable(feature = "drop_guard", issue = "none")]
-    pub fn new(inner: T, f: F) -> Self {
+    #[must_use]
+    pub const fn new(inner: T, f: F) -> Self {
         Self { inner: ManuallyDrop::new(inner), f: ManuallyDrop::new(f) }
     }
 
@@ -62,8 +66,8 @@ where
     /// `into_inner` from the `Deref` and `DerefMut` impls.
     ///
     /// It is typically preferred to call this function instead of `mem::forget`
-    /// because it will appropriately de-initialize the closure stored in the
-    /// `DropGuard` before returning the stored value.
+    /// because it will return the stored value and drop variables captured
+    /// by the closure instead of leaking their owned resources.
     ///
     /// # Example
     ///
@@ -78,8 +82,6 @@ where
     #[unstable(feature = "drop_guard", issue = "none")]
     #[inline]
     pub fn into_inner(guard: Self) -> T {
-        // Implementation note: this is the same approach that scopeguard takes.
-
         // First we ensure that dropping the guard will not trigger
         // its destructor
         let mut guard = ManuallyDrop::new(guard);
@@ -136,3 +138,14 @@ where
         f(inner);
     }
 }
+
+#[unstable(feature = "drop_guard", issue = "none")]
+impl<T, F> Debug for DropGuard<T, F>
+where
+    T: Debug,
+    F: FnOnce(T),
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}