Add `size_of`, `size_of_val`, `align_of`, and `align_of_val` to the prelude

Many, many projects use `size_of` to get the size of a type. However,
it's also often equally easy to hardcode a size (e.g. `8` instead of
`size_of::<u64>()`). Minimizing friction in the use of `size_of` helps
ensure that people use it and make code more self-documenting.

The name `size_of` is unambiguous: the name alone, without any prefix or
path, is self-explanatory and unmistakeable for any other functionality.
Adding it to the prelude cannot produce any name conflicts, as any local
definition will silently shadow the one from the prelude. Thus, we don't
need to wait for a new edition prelude to add it.

Add `size_of_val`, `align_of`, and `align_of_val` as well, with similar
justification: widely useful, self-explanatory, unmistakeable for
anything else, won't produce conflicts.

6 files changed, 5 insertions, 7 deletions

diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs
index 4b491ffdafa..dd6466d6285 100644
--- a/library/core/src/cell.rs
+++ b/library/core/src/cell.rs
@@ -238,7 +238,7 @@
 use crate::cmp::Ordering;
 use crate::fmt::{self, Debug, Display};
 use crate::marker::{PhantomData, Unsize};
-use crate::mem::{self, size_of};
+use crate::mem;
 use crate::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn};
 use crate::ptr::{self, NonNull};
 
diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs
index d1450bf12ce..56c998d99f2 100644
--- a/library/core/src/intrinsics.rs
+++ b/library/core/src/intrinsics.rs
@@ -65,7 +65,6 @@
 
 use crate::marker::DiscriminantKind;
 use crate::marker::Tuple;
-use crate::mem::align_of;
 use crate::ptr;
 use crate::ub_checks;
 
diff --git a/library/core/src/prelude/common.rs b/library/core/src/prelude/common.rs
index afc6817aa1d..2a0331ef7b2 100644
--- a/library/core/src/prelude/common.rs
+++ b/library/core/src/prelude/common.rs
@@ -14,6 +14,9 @@ pub use crate::ops::{Drop, Fn, FnMut, FnOnce};
 #[stable(feature = "core_prelude", since = "1.4.0")]
 #[doc(no_inline)]
 pub use crate::mem::drop;
+#[stable(feature = "size_of_prelude", since = "CURRENT_RUSTC_VERSION")]
+#[doc(no_inline)]
+pub use crate::mem::{align_of, align_of_val, size_of, size_of_val};
 
 // Re-exported types and traits
 #[stable(feature = "core_prelude", since = "1.4.0")]
diff --git a/library/core/src/ptr/mod.rs b/library/core/src/ptr/mod.rs
index 8d7192c1b0f..3258e338e83 100644
--- a/library/core/src/ptr/mod.rs
+++ b/library/core/src/ptr/mod.rs
@@ -392,7 +392,7 @@ use crate::intrinsics;
 use crate::marker::FnPtr;
 use crate::ub_checks;
 
-use crate::mem::{self, align_of, size_of, MaybeUninit};
+use crate::mem::{self, MaybeUninit};
 
 mod alignment;
 #[unstable(feature = "ptr_alignment_type", issue = "102070")]
diff --git a/library/core/src/slice/raw.rs b/library/core/src/slice/raw.rs
index 29a12f106c5..3f4305866e6 100644
--- a/library/core/src/slice/raw.rs
+++ b/library/core/src/slice/raw.rs
@@ -1,7 +1,6 @@
 //! Free functions to create `&[T]` and `&mut [T]`.
 
 use crate::array;
-use crate::mem::{align_of, size_of};
 use crate::ops::Range;
 use crate::ptr;
 use crate::ub_checks;
diff --git a/library/core/src/sync/atomic.rs b/library/core/src/sync/atomic.rs
index 232ec589093..482bd19705c 100644
--- a/library/core/src/sync/atomic.rs
+++ b/library/core/src/sync/atomic.rs
@@ -1296,7 +1296,6 @@ impl<T> AtomicPtr<T> {
     #[cfg(target_has_atomic_equal_alignment = "ptr")]
     #[unstable(feature = "atomic_from_mut", issue = "76314")]
     pub fn from_mut(v: &mut *mut T) -> &mut Self {
-        use crate::mem::align_of;
         let [] = [(); align_of::<AtomicPtr<()>>() - align_of::<*mut ()>()];
         // SAFETY:
         //  - the mutable reference guarantees unique ownership.
@@ -2286,7 +2285,6 @@ macro_rules! atomic_int {
             #[$cfg_align]
             #[unstable(feature = "atomic_from_mut", issue = "76314")]
             pub fn from_mut(v: &mut $int_type) -> &mut Self {
-                use crate::mem::align_of;
                 let [] = [(); align_of::<Self>() - align_of::<$int_type>()];
                 // SAFETY:
                 //  - the mutable reference guarantees unique ownership.
@@ -2354,7 +2352,6 @@ macro_rules! atomic_int {
             #[$cfg_align]
             #[unstable(feature = "atomic_from_mut", issue = "76314")]
             pub fn from_mut_slice(v: &mut [$int_type]) -> &mut [Self] {
-                use crate::mem::align_of;
                 let [] = [(); align_of::<Self>() - align_of::<$int_type>()];
                 // SAFETY:
                 //  - the mutable reference guarantees unique ownership.