Add #[must_use] to remaining core functions

library/core/src/alloc/layout.rs

@@ -104,6 +104,7 @@ impl Layout {
     /// The minimum size in bytes for a memory block of this layout.
     #[stable(feature = "alloc_layout", since = "1.28.0")]
     #[rustc_const_stable(feature = "const_alloc_layout", since = "1.50.0")]
+    #[must_use]
     #[inline]
     pub const fn size(&self) -> usize {
         self.size_
@@ -137,6 +138,7 @@ impl Layout {
     /// allocate backing structure for `T` (which could be a trait
     /// or other unsized type like a slice).
     #[stable(feature = "alloc_layout", since = "1.28.0")]
+    #[must_use]
     #[inline]
     pub fn for_value<T: ?Sized>(t: &T) -> Self {
         let (size, align) = (mem::size_of_val(t), mem::align_of_val(t));
@@ -171,6 +173,7 @@ impl Layout {
     /// [trait object]: ../../book/ch17-02-trait-objects.html
     /// [extern type]: ../../unstable-book/language-features/extern-types.html
     #[unstable(feature = "layout_for_ptr", issue = "69835")]
+    #[must_use]
     pub unsafe fn for_value_raw<T: ?Sized>(t: *const T) -> Self {
         // SAFETY: we pass along the prerequisites of these functions to the caller
         let (size, align) = unsafe { (mem::size_of_val_raw(t), mem::align_of_val_raw(t)) };
@@ -187,6 +190,7 @@ impl Layout {
     /// some other means.
     #[unstable(feature = "alloc_layout_extra", issue = "55724")]
     #[rustc_const_unstable(feature = "alloc_layout_extra", issue = "55724")]
+    #[must_use]
     #[inline]
     pub const fn dangling(&self) -> NonNull<u8> {
         // SAFETY: align is guaranteed to be non-zero