Auto merge of #138996 - CAD97:use_cfg_match, r=joboet

Use `cfg_match!` in core

All of these uses of `cfg_if!` do not utilize that `cfg_if!` works with auto-`doc(cfg)`, so no functionality is lost from switching to use `cfg_match!` instead. We *do* lose what rustfmt special support exists for `cfg_if!`, though.

Tracking issue: #115585

library/core/src/ffi/primitives.rs

@@ -35,7 +35,7 @@ type_alias! { "c_float.md", c_float = f32; }
 type_alias! { "c_double.md", c_double = f64; }
 
 mod c_char_definition {
-    cfg_if! {
+    crate::cfg_match! {
         // These are the targets on which c_char is unsigned. Usually the
         // signedness is the same for all target_os values on a given architecture
         // but there are some exceptions (see isSignedCharDefault() in clang).
@@ -105,7 +105,7 @@ mod c_char_definition {
         //   architecture defaults). As we only have a target for userspace apps so there are no
         //   special cases for L4Re below.
         //   https://github.com/rust-lang/rust/pull/132975#issuecomment-2484645240
-        if #[cfg(all(
+        all(
             not(windows),
             not(target_vendor = "apple"),
             not(target_os = "vita"),
@@ -122,24 +122,27 @@ mod c_char_definition {
                 target_arch = "s390x",
                 target_arch = "xtensa",
             )
-        ))] {
+        ) => {
             pub(super) type c_char = u8;
-        } else {
+        }
-            // On every other target, c_char is signed.
+        // On every other target, c_char is signed.
+        _ => {
             pub(super) type c_char = i8;
         }
     }
 }
 
 mod c_long_definition {
-    cfg_if! {
+    crate::cfg_match! {
-        if #[cfg(any(
+        any(
             all(target_pointer_width = "64", not(windows)),
             // wasm32 Linux ABI uses 64-bit long
-            all(target_arch = "wasm32", target_os = "linux")))] {
+            all(target_arch = "wasm32", target_os = "linux")
+        ) => {
             pub(super) type c_long = i64;
             pub(super) type c_ulong = u64;
-        } else {
+        }
+        _ => {
             // The minimal size of `long` in the C standard is 32 bits
             pub(super) type c_long = i32;
             pub(super) type c_ulong = u32;
@@ -169,11 +172,12 @@ pub type c_ptrdiff_t = isize;
 pub type c_ssize_t = isize;
 
 mod c_int_definition {
-    cfg_if! {
+    crate::cfg_match! {
-        if #[cfg(any(target_arch = "avr", target_arch = "msp430"))] {
+        any(target_arch = "avr", target_arch = "msp430") => {
             pub(super) type c_int = i16;
             pub(super) type c_uint = u16;
-        } else {
+        }
+        _ => {
             pub(super) type c_int = i32;
             pub(super) type c_uint = u32;
         }

library/core/src/internal_macros.rs

@@ -120,80 +120,3 @@ macro_rules! impl_fn_for_zst {
         )+
     }
 }
-
-/// A macro for defining `#[cfg]` if-else statements.
-///
-/// `cfg_if` is similar to the `if/elif` C preprocessor macro by allowing definition of a cascade
-/// of `#[cfg]` cases, emitting the implementation which matches first.
-///
-/// This allows you to conveniently provide a long list `#[cfg]`'d blocks of code without having to
-/// rewrite each clause multiple times.
-///
-/// # Example
-///
-/// ```ignore(cannot-test-this-because-non-exported-macro)
-/// cfg_if! {
-///     if #[cfg(unix)] {
-///         fn foo() { /* unix specific functionality */ }
-///     } else if #[cfg(target_pointer_width = "32")] {
-///         fn foo() { /* non-unix, 32-bit functionality */ }
-///     } else {
-///         fn foo() { /* fallback implementation */ }
-///     }
-/// }
-///
-/// # fn main() {}
-/// ```
-// This is a copy of `cfg_if!` from the `cfg_if` crate.
-// The recursive invocations should use $crate if this is ever exported.
-macro_rules! cfg_if {
-    // match if/else chains with a final `else`
-    (
-        $(
-            if #[cfg( $i_meta:meta )] { $( $i_tokens:tt )* }
-        ) else+
-        else { $( $e_tokens:tt )* }
-    ) => {
-        cfg_if! {
-            @__items () ;
-            $(
-                (( $i_meta ) ( $( $i_tokens )* )) ,
-            )+
-            (() ( $( $e_tokens )* )) ,
-        }
-    };
-
-    // Internal and recursive macro to emit all the items
-    //
-    // Collects all the previous cfgs in a list at the beginning, so they can be
-    // negated. After the semicolon is all the remaining items.
-    (@__items ( $( $_:meta , )* ) ; ) => {};
-    (
-        @__items ( $( $no:meta , )* ) ;
-        (( $( $yes:meta )? ) ( $( $tokens:tt )* )) ,
-        $( $rest:tt , )*
-    ) => {
-        // Emit all items within one block, applying an appropriate #[cfg]. The
-        // #[cfg] will require all `$yes` matchers specified and must also negate
-        // all previous matchers.
-        #[cfg(all(
-            $( $yes , )?
-            not(any( $( $no ),* ))
-        ))]
-        cfg_if! { @__identity $( $tokens )* }
-
-        // Recurse to emit all other items in `$rest`, and when we do so add all
-        // our `$yes` matchers to the list of `$no` matchers as future emissions
-        // will have to negate everything we just matched as well.
-        cfg_if! {
-            @__items ( $( $no , )* $( $yes , )? ) ;
-            $( $rest , )*
-        }
-    };
-
-    // Internal macro to make __apply work out right for different match types,
-    // because of how macros match/expand stuff.
-    (@__identity $( $tokens:tt )* ) => {
-        $( $tokens )*
-    };
-}

library/core/src/lib.rs

@@ -100,6 +100,7 @@
 #![feature(bigint_helper_methods)]
 #![feature(bstr)]
 #![feature(bstr_internals)]
+#![feature(cfg_match)]
 #![feature(closure_track_caller)]
 #![feature(const_carrying_mul_add)]
 #![feature(const_eval_select)]

library/core/src/num/f32.rs

@@ -14,7 +14,7 @@
 use crate::convert::FloatToInt;
 use crate::num::FpCategory;
 use crate::panic::const_assert;
-use crate::{intrinsics, mem};
+use crate::{cfg_match, intrinsics, mem};
 
 /// The radix or base of the internal representation of `f32`.
 /// Use [`f32::RADIX`] instead.
@@ -996,21 +996,22 @@ impl f32 {
     #[stable(feature = "num_midpoint", since = "1.85.0")]
     #[rustc_const_stable(feature = "num_midpoint", since = "1.85.0")]
     pub const fn midpoint(self, other: f32) -> f32 {
-        cfg_if! {
+        cfg_match! {
             // Allow faster implementation that have known good 64-bit float
             // implementations. Falling back to the branchy code on targets that don't
             // have 64-bit hardware floats or buggy implementations.
             // https://github.com/rust-lang/rust/pull/121062#issuecomment-2123408114
-            if #[cfg(any(
+            any(
-                    target_arch = "x86_64",
+                target_arch = "x86_64",
-                    target_arch = "aarch64",
+                target_arch = "aarch64",
-                    all(any(target_arch = "riscv32", target_arch = "riscv64"), target_feature = "d"),
+                all(any(target_arch = "riscv32", target_arch = "riscv64"), target_feature = "d"),
-                    all(target_arch = "arm", target_feature = "vfp2"),
+                all(target_arch = "arm", target_feature = "vfp2"),
-                    target_arch = "wasm32",
+                target_arch = "wasm32",
-                    target_arch = "wasm64",
+                target_arch = "wasm64",
-                ))] {
+            ) => {
                 ((self as f64 + other as f64) / 2.0) as f32
-            } else {
+            }
+            _ => {
                 const LO: f32 = f32::MIN_POSITIVE * 2.;
                 const HI: f32 = f32::MAX / 2.;
 

library/core/src/slice/sort/select.rs

@@ -6,6 +6,7 @@
 //! for pivot selection. Using this as a fallback ensures O(n) worst case running time with
 //! better performance than one would get using heapsort as fallback.
 
+use crate::cfg_match;
 use crate::mem::{self, SizedTypeProperties};
 #[cfg(not(feature = "optimize_for_size"))]
 use crate::slice::sort::shared::pivot::choose_pivot;
@@ -41,10 +42,11 @@ where
         let min_idx = min_index(v, &mut is_less).unwrap();
         v.swap(min_idx, index);
     } else {
-        cfg_if! {
+        cfg_match! {
-            if #[cfg(feature = "optimize_for_size")] {
+            feature = "optimize_for_size" => {
                 median_of_medians(v, &mut is_less, index);
-            } else {
+            }
+            _ => {
                 partition_at_index_loop(v, index, None, &mut is_less);
             }
         }

library/core/src/slice/sort/stable/mod.rs

@@ -2,12 +2,12 @@
 
 #[cfg(not(any(feature = "optimize_for_size", target_pointer_width = "16")))]
 use crate::cmp;
-use crate::intrinsics;
 use crate::mem::{MaybeUninit, SizedTypeProperties};
 #[cfg(not(any(feature = "optimize_for_size", target_pointer_width = "16")))]
 use crate::slice::sort::shared::smallsort::{
     SMALL_SORT_GENERAL_SCRATCH_LEN, StableSmallSortTypeImpl, insertion_sort_shift_left,
 };
+use crate::{cfg_match, intrinsics};
 
 pub(crate) mod merge;
 
@@ -39,17 +39,18 @@ pub fn sort<T, F: FnMut(&T, &T) -> bool, BufT: BufGuard<T>>(v: &mut [T], is_less
         return;
     }
 
-    cfg_if! {
+    cfg_match! {
-        if #[cfg(any(feature = "optimize_for_size", target_pointer_width = "16"))] {
+        any(feature = "optimize_for_size", target_pointer_width = "16") => {
             // Unlike driftsort, mergesort only requires len / 2,
             // not len - len / 2.
             let alloc_len = len / 2;
 
-            cfg_if! {
+            cfg_match! {
-                if #[cfg(target_pointer_width = "16")] {
+                target_pointer_width = "16" => {
                     let mut heap_buf = BufT::with_capacity(alloc_len);
                     let scratch = heap_buf.as_uninit_slice_mut();
-                } else {
+                }
+                _ => {
                     // For small inputs 4KiB of stack storage suffices, which allows us to avoid
                     // calling the (de-)allocator. Benchmarks showed this was quite beneficial.
                     let mut stack_buf = AlignedStorage::<T, 4096>::new();
@@ -65,7 +66,8 @@ pub fn sort<T, F: FnMut(&T, &T) -> bool, BufT: BufGuard<T>>(v: &mut [T], is_less
             }
 
             tiny::mergesort(v, scratch, is_less);
-        } else {
+        }
+        _ => {
             // More advanced sorting methods than insertion sort are faster if called in
             // a hot loop for small inputs, but for general-purpose code the small
             // binary size of insertion sort is more important. The instruction cache in

library/core/src/slice/sort/unstable/mod.rs

@@ -1,11 +1,11 @@
 //! This module contains the entry points for `slice::sort_unstable`.
 
-use crate::intrinsics;
 use crate::mem::SizedTypeProperties;
 #[cfg(not(any(feature = "optimize_for_size", target_pointer_width = "16")))]
 use crate::slice::sort::shared::find_existing_run;
 #[cfg(not(any(feature = "optimize_for_size", target_pointer_width = "16")))]
 use crate::slice::sort::shared::smallsort::insertion_sort_shift_left;
+use crate::{cfg_match, intrinsics};
 
 pub(crate) mod heapsort;
 pub(crate) mod quicksort;
@@ -30,10 +30,11 @@ pub fn sort<T, F: FnMut(&T, &T) -> bool>(v: &mut [T], is_less: &mut F) {
         return;
     }
 
-    cfg_if! {
+    cfg_match! {
-        if #[cfg(any(feature = "optimize_for_size", target_pointer_width = "16"))] {
+        any(feature = "optimize_for_size", target_pointer_width = "16") => {
             heapsort::heapsort(v, is_less);
-        } else {
+        }
+        _ => {
             // More advanced sorting methods than insertion sort are faster if called in
             // a hot loop for small inputs, but for general-purpose code the small
             // binary size of insertion sort is more important. The instruction cache in

library/core/src/slice/sort/unstable/quicksort.rs

@@ -9,7 +9,7 @@ use crate::slice::sort::shared::pivot::choose_pivot;
 use crate::slice::sort::shared::smallsort::UnstableSmallSortTypeImpl;
 #[cfg(not(feature = "optimize_for_size"))]
 use crate::slice::sort::unstable::heapsort;
-use crate::{intrinsics, ptr};
+use crate::{cfg_match, intrinsics, ptr};
 
 /// Sorts `v` recursively.
 ///
@@ -142,10 +142,11 @@ const fn inst_partition<T, F: FnMut(&T, &T) -> bool>() -> fn(&mut [T], &T, &mut
     if size_of::<T>() <= MAX_BRANCHLESS_PARTITION_SIZE {
         // Specialize for types that are relatively cheap to copy, where branchless optimizations
         // have large leverage e.g. `u64` and `String`.
-        cfg_if! {
+        cfg_match! {
-            if #[cfg(feature = "optimize_for_size")] {
+            feature = "optimize_for_size" => {
                 partition_lomuto_branchless_simple::<T, F>
-            } else {
+            }
+            _ => {
                 partition_lomuto_branchless_cyclic::<T, F>
             }
         }