rust: alloc: disable several new()s, pin()s, default()s, etc.

They are infallible, and could not be actually used because
they will trigger an error when monomorphized, but it is better
to just remove them.

Suggested-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

rust/alloc/rc.rs

@@ -264,6 +264,7 @@ use core::marker::{self, PhantomData, Unpin, Unsize};
 use core::mem::size_of_val;
 use core::mem::{self, align_of_val_raw, forget};
 use core::ops::{CoerceUnsized, Deref, DispatchFromDyn, Receiver};
+#[cfg(not(no_global_oom_handling))]
 use core::pin::Pin;
 use core::ptr::{self, NonNull};
 #[cfg(not(no_global_oom_handling))]
@@ -348,6 +349,7 @@ impl<T> Rc<T> {
     ///
     /// let five = Rc::new(5);
     /// ```
+    #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new(value: T) -> Rc<T> {
         // There is an implicit weak pointer owned by all the strong
@@ -383,6 +385,7 @@ impl<T> Rc<T> {
     ///     }
     /// }
     /// ```
+    #[cfg(not(no_global_oom_handling))]
     #[unstable(feature = "arc_new_cyclic", issue = "75861")]
     pub fn new_cyclic(data_fn: impl FnOnce(&Weak<T>) -> T) -> Rc<T> {
         // Construct the inner in the "uninitialized" state with a single
@@ -579,6 +582,7 @@ impl<T> Rc<T> {
     }
     /// Constructs a new `Pin<Rc<T>>`. If `T` does not implement `Unpin`, then
     /// `value` will be pinned in memory and unable to be moved.
+    #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "pin", since = "1.33.0")]
     pub fn pin(value: T) -> Pin<Rc<T>> {
         unsafe { Pin::new_unchecked(Rc::new(value)) }
@@ -1475,6 +1479,7 @@ impl<T: ?Sized> Clone for Rc<T> {
     }
 }
 
+#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Default> Default for Rc<T> {
     /// Creates a new `Rc<T>`, with the `Default` value for `T`.
@@ -1733,6 +1738,7 @@ impl<T: ?Sized> fmt::Pointer for Rc<T> {
     }
 }
 
+#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
 impl<T> From<T> for Rc<T> {
     /// Converts a generic type `T` into a `Rc<T>`

rust/alloc/sync.rs

@@ -21,6 +21,7 @@ use core::marker::{PhantomData, Unpin, Unsize};
 use core::mem::size_of_val;
 use core::mem::{self, align_of_val_raw};
 use core::ops::{CoerceUnsized, Deref, DispatchFromDyn, Receiver};
+#[cfg(not(no_global_oom_handling))]
 use core::pin::Pin;
 use core::ptr::{self, NonNull};
 #[cfg(not(no_global_oom_handling))]
@@ -334,6 +335,7 @@ impl<T> Arc<T> {
     ///
     /// let five = Arc::new(5);
     /// ```
+    #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new(data: T) -> Arc<T> {
@@ -367,6 +369,7 @@ impl<T> Arc<T> {
     ///     me: me.clone(),
     /// });
     /// ```
+    #[cfg(not(no_global_oom_handling))]
     #[inline]
     #[unstable(feature = "arc_new_cyclic", issue = "75861")]
     pub fn new_cyclic(data_fn: impl FnOnce(&Weak<T>) -> T) -> Arc<T> {
@@ -487,6 +490,7 @@ impl<T> Arc<T> {
 
     /// Constructs a new `Pin<Arc<T>>`. If `T` does not implement `Unpin`, then
     /// `data` will be pinned in memory and unable to be moved.
+    #[cfg(not(no_global_oom_handling))]
     #[stable(feature = "pin", since = "1.33.0")]
     pub fn pin(data: T) -> Pin<Arc<T>> {
         unsafe { Pin::new_unchecked(Arc::new(data)) }
@@ -2276,6 +2280,7 @@ impl<T: ?Sized> fmt::Pointer for Arc<T> {
     }
 }
 
+#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Default> Default for Arc<T> {
     /// Creates a new `Arc<T>`, with the `Default` value for `T`.
@@ -2300,6 +2305,7 @@ impl<T: ?Sized + Hash> Hash for Arc<T> {
     }
 }
 
+#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
 impl<T> From<T> for Arc<T> {
     fn from(t: T) -> Self {