Rollup merge of #123168 - joshtriplett:size-of-prelude, r=Amanieu

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

(Note: need to update the PR to add `align_of` and `align_of_val`, and remove the second commit with the myriad changes to appease the lint.)

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.

18 files changed, 22 insertions, 23 deletions

diff --git a/compiler/rustc_middle/src/query/erase.rs b/compiler/rustc_middle/src/query/erase.rs
index f98dbf8a0bd..b29a86d58ed 100644
--- a/compiler/rustc_middle/src/query/erase.rs
+++ b/compiler/rustc_middle/src/query/erase.rs
@@ -4,7 +4,7 @@ use crate::traits;
 use crate::ty::adjustment::CoerceUnsizedInfo;
 use crate::ty::{self, Ty};
 use std::intrinsics::transmute_unchecked;
-use std::mem::{size_of, MaybeUninit};
+use std::mem::MaybeUninit;
 
 #[derive(Copy, Clone)]
 pub struct Erased<T: Copy> {
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index 875c24c28e4..f3a4803e0d4 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -257,8 +257,6 @@ use core::intrinsics::abort;
 #[cfg(not(no_global_oom_handling))]
 use core::iter;
 use core::marker::{PhantomData, Unsize};
-#[cfg(not(no_global_oom_handling))]
-use core::mem::size_of_val;
 use core::mem::{self, align_of_val_raw, forget, ManuallyDrop};
 use core::ops::{CoerceUnsized, Deref, DerefMut, DerefPure, DispatchFromDyn, Receiver};
 use core::panic::{RefUnwindSafe, UnwindSafe};
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 7dcaa59dcd1..5a4f9df614e 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -18,8 +18,6 @@ use core::intrinsics::abort;
 #[cfg(not(no_global_oom_handling))]
 use core::iter;
 use core::marker::{PhantomData, Unsize};
-#[cfg(not(no_global_oom_handling))]
-use core::mem::size_of_val;
 use core::mem::{self, align_of_val_raw};
 use core::ops::{CoerceUnsized, Deref, DerefPure, DispatchFromDyn, Receiver};
 use core::panic::{RefUnwindSafe, UnwindSafe};
diff --git a/library/core/src/cell.rs b/library/core/src/cell.rs
index 6cdc1e00f47..efa0fd7b56c 100644
--- a/library/core/src/cell.rs
+++ b/library/core/src/cell.rs
@@ -253,7 +253,7 @@
 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 89e0b670995..28397fe4619 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 8e3447d0b1b..6661f6ee78b 100644
--- a/library/core/src/ptr/mod.rs
+++ b/library/core/src/ptr/mod.rs
@@ -415,7 +415,7 @@ 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.
diff --git a/library/portable-simd/crates/core_simd/src/simd/ptr/const_ptr.rs b/library/portable-simd/crates/core_simd/src/simd/ptr/const_ptr.rs
index 0f1719206c9..cbffbc564cf 100644
--- a/library/portable-simd/crates/core_simd/src/simd/ptr/const_ptr.rs
+++ b/library/portable-simd/crates/core_simd/src/simd/ptr/const_ptr.rs
@@ -96,7 +96,7 @@ where
     fn cast<U>(self) -> Self::CastPtr<U> {
         // SimdElement currently requires zero-sized metadata, so this should never fail.
         // If this ever changes, `simd_cast_ptr` should produce a post-mono error.
-        use core::{mem::size_of, ptr::Pointee};
+        use core::ptr::Pointee;
         assert_eq!(size_of::<<T as Pointee>::Metadata>(), 0);
         assert_eq!(size_of::<<U as Pointee>::Metadata>(), 0);
 
diff --git a/library/portable-simd/crates/core_simd/src/simd/ptr/mut_ptr.rs b/library/portable-simd/crates/core_simd/src/simd/ptr/mut_ptr.rs
index 7ba996d149c..6bc6ca3ac42 100644
--- a/library/portable-simd/crates/core_simd/src/simd/ptr/mut_ptr.rs
+++ b/library/portable-simd/crates/core_simd/src/simd/ptr/mut_ptr.rs
@@ -93,7 +93,7 @@ where
     fn cast<U>(self) -> Self::CastPtr<U> {
         // SimdElement currently requires zero-sized metadata, so this should never fail.
         // If this ever changes, `simd_cast_ptr` should produce a post-mono error.
-        use core::{mem::size_of, ptr::Pointee};
+        use core::ptr::Pointee;
         assert_eq!(size_of::<<T as Pointee>::Metadata>(), 0);
         assert_eq!(size_of::<<U as Pointee>::Metadata>(), 0);
 
diff --git a/library/proc_macro/src/bridge/fxhash.rs b/library/proc_macro/src/bridge/fxhash.rs
index f9f74c63fc4..9fb79eabd05 100644
--- a/library/proc_macro/src/bridge/fxhash.rs
+++ b/library/proc_macro/src/bridge/fxhash.rs
@@ -7,7 +7,6 @@
 use std::collections::HashMap;
 use std::hash::BuildHasherDefault;
 use std::hash::Hasher;
-use std::mem::size_of;
 use std::ops::BitXor;
 
 /// Type alias for a hashmap using the `fx` hash algorithm.
diff --git a/library/std/src/io/error/repr_bitpacked.rs b/library/std/src/io/error/repr_bitpacked.rs
index 6f8d5e37775..c9d3934ad70 100644
--- a/library/std/src/io/error/repr_bitpacked.rs
+++ b/library/std/src/io/error/repr_bitpacked.rs
@@ -104,7 +104,6 @@
 
 use super::{Custom, ErrorData, ErrorKind, RawOsError, SimpleMessage};
 use core::marker::PhantomData;
-use core::mem::{align_of, size_of};
 use core::ptr::{self, NonNull};
 
 // The 2 least-significant bits are used as tag.
diff --git a/library/std/src/os/unix/net/ancillary.rs b/library/std/src/os/unix/net/ancillary.rs
index 0597fdcbd72..fe8e2be9372 100644
--- a/library/std/src/os/unix/net/ancillary.rs
+++ b/library/std/src/os/unix/net/ancillary.rs
@@ -3,7 +3,7 @@
 use super::{sockaddr_un, SocketAddr};
 use crate::io::{self, IoSlice, IoSliceMut};
 use crate::marker::PhantomData;
-use crate::mem::{size_of, zeroed};
+use crate::mem::zeroed;
 use crate::os::unix::io::RawFd;
 use crate::path::Path;
 use crate::ptr::{eq, read_unaligned};
diff --git a/library/std/src/prelude/common.rs b/library/std/src/prelude/common.rs
index 01936734d75..ceee3e33c3e 100644
--- a/library/std/src/prelude/common.rs
+++ b/library/std/src/prelude/common.rs
@@ -14,6 +14,9 @@ pub use crate::ops::{Drop, Fn, FnMut, FnOnce};
 #[stable(feature = "rust1", since = "1.0.0")]
 #[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 = "rust1", since = "1.0.0")]
diff --git a/library/std/src/prelude/mod.rs b/library/std/src/prelude/mod.rs
index 0bdbab716ad..2d4639342bf 100644
--- a/library/std/src/prelude/mod.rs
+++ b/library/std/src/prelude/mod.rs
@@ -36,6 +36,10 @@
 //!   operations for both destructors and overloading `()`.
 //! * <code>[std::mem]::[drop]</code>, a convenience function for explicitly
 //!   dropping a value.
+//! * <code>[std::mem]::{[size_of], [size_of_val]}</code>, to get the size of
+//!   a type or value.
+//! * <code>[std::mem]::{[align_of], [align_of_val]}</code>, to get the
+//!   alignment of a type or value.
 //! * <code>[std::boxed]::[Box]</code>, a way to allocate values on the heap.
 //! * <code>[std::borrow]::[ToOwned]</code>, the conversion trait that defines
 //!   [`to_owned`], the generic method for creating an owned type from a
diff --git a/tests/ui/resolve/filter-intrinsics.rs b/tests/ui/resolve/filter-intrinsics.rs
index c0956ef85af..8d6d22817dc 100644
--- a/tests/ui/resolve/filter-intrinsics.rs
+++ b/tests/ui/resolve/filter-intrinsics.rs
@@ -1,6 +1,6 @@
 fn main() {
-    // Should suggest only `std::mem::size_of`
-    let _ = size_of::<usize>();
+    // Should suggest only `std::mem::transmute`
+    let _ = transmute::<usize>();
     //~^ ERROR cannot find
 
     // Should suggest `std::intrinsics::fabsf64`,
diff --git a/tests/ui/resolve/filter-intrinsics.stderr b/tests/ui/resolve/filter-intrinsics.stderr
index cc1092dd0cf..9c9e92f6d4f 100644
--- a/tests/ui/resolve/filter-intrinsics.stderr
+++ b/tests/ui/resolve/filter-intrinsics.stderr
@@ -1,12 +1,12 @@
-error[E0425]: cannot find function `size_of` in this scope
+error[E0425]: cannot find function `transmute` in this scope
   --> $DIR/filter-intrinsics.rs:3:13
    |
-LL |     let _ = size_of::<usize>();
-   |             ^^^^^^^ not found in this scope
+LL |     let _ = transmute::<usize>();
+   |             ^^^^^^^^^ not found in this scope
    |
 help: consider importing this function
    |
-LL + use std::mem::size_of;
+LL + use std::mem::transmute;
    |
 
 error[E0425]: cannot find function `fabsf64` in this scope