Added get_mut_unchecked for all feature selections

src/imp_cs.rs

@@ -66,6 +66,19 @@ impl<T> OnceCell<T> {
         crate::unwrap_unchecked(self.value.borrow(CriticalSection::new()).get())
     }
 
+    /// Gets the mutable reference to the underlying value, without checking if the cell
+    /// is initialized.
+    ///
+    /// # Safety
+    ///
+    /// Caller must ensure that the cell is in initialized state, and that
+    /// the contents are acquired by (synchronized to) this thread.
+    pub(crate) unsafe fn get_mut_unchecked(&mut self) -> &mut T {
+        debug_assert!(self.is_initialized());
+        // SAFETY: The caller ensures that the value is initialized and access synchronized.
+        self.get_mut().unwrap_unchecked()
+    }
+
     #[inline]
     pub(crate) fn get_mut(&mut self) -> Option<&mut T> {
         self.value.get_mut().get_mut()

src/imp_std.rs

@@ -119,7 +119,6 @@ impl<T> OnceCell<T> {
     ///
     /// Caller must ensure that the cell is in initialized state, and that
     /// the contents are acquired by (synchronized to) this thread.
-    #[cfg(not(feature = "critical_section"))]
     pub(crate) unsafe fn get_mut_unchecked(&mut self) -> &mut T {
         debug_assert!(self.is_initialized());
         let slot = &mut *self.value.get();

src/lib.rs

@@ -1039,7 +1039,6 @@ pub mod sync {
         /// Caller must ensure that the cell is in initialized state, and that
         /// the contents are acquired by (synchronized to) this thread.
         #[inline]
-        #[cfg(not(feature = "critical_section"))]
         pub unsafe fn get_mut_unchecked(&mut self) -> &mut T {
             self.0.get_mut_unchecked()
         }