Rollup merge of #129555 - RalfJung:const_float_bits_conv, r=dtolnay

stabilize const_float_bits_conv

This stabilizes `const_float_bits_conv`, and thus fixes rust-lang/rust#72447. With rust-lang/rust#128596 having landed, this is entirely a libs-only question now.

```rust
impl f32 {
    pub const fn to_bits(self) -> u32;
    pub const fn from_bits(v: u32) -> Self;
    pub const fn to_be_bytes(self) -> [u8; 4];
    pub const fn to_le_bytes(self) -> [u8; 4]
    pub const fn to_ne_bytes(self) -> [u8; 4];
    pub const fn from_be_bytes(bytes: [u8; 4]) -> Self;
    pub const fn from_le_bytes(bytes: [u8; 4]) -> Self;
    pub const fn from_ne_bytes(bytes: [u8; 4]) -> Self;
}

impl f64 {
    pub const fn to_bits(self) -> u64;
    pub const fn from_bits(v: u64) -> Self;
    pub const fn to_be_bytes(self) -> [u8; 8];
    pub const fn to_le_bytes(self) -> [u8; 8]
    pub const fn to_ne_bytes(self) -> [u8; 8];
    pub const fn from_be_bytes(bytes: [u8; 8]) -> Self;
    pub const fn from_le_bytes(bytes: [u8; 8]) -> Self;
    pub const fn from_ne_bytes(bytes: [u8; 8]) -> Self;
}
````

Cc `@rust-lang/wg-const-eval` `@rust-lang/libs-api`

clippy_lints/src/transmute/mod.rs

@@ -619,10 +619,10 @@ impl<'tcx> LateLintPass<'tcx> for Transmute {
                 | transmute_ref_to_ref::check(cx, e, from_ty, to_ty, arg, const_context)
                 | transmute_ptr_to_ptr::check(cx, e, from_ty, to_ty, arg, &self.msrv)
                 | transmute_int_to_bool::check(cx, e, from_ty, to_ty, arg)
-                | transmute_int_to_float::check(cx, e, from_ty, to_ty, arg, const_context)
+                | transmute_int_to_float::check(cx, e, from_ty, to_ty, arg)
                 | transmute_int_to_non_zero::check(cx, e, from_ty, to_ty, arg)
-                | transmute_float_to_int::check(cx, e, from_ty, to_ty, arg, const_context)
-                | transmute_num_to_bytes::check(cx, e, from_ty, to_ty, arg, const_context)
+                | transmute_float_to_int::check(cx, e, from_ty, to_ty, arg)
+                | transmute_num_to_bytes::check(cx, e, from_ty, to_ty, arg)
                 | (unsound_collection_transmute::check(cx, e, from_ty, to_ty)
                     || transmute_undefined_repr::check(cx, e, from_ty, to_ty))
                 | (eager_transmute::check(cx, e, arg, from_ty, to_ty));

clippy_lints/src/transmute/transmute_float_to_int.rs

@@ -15,10 +15,9 @@ pub(super) fn check<'tcx>(
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
     mut arg: &'tcx Expr<'_>,
-    const_context: bool,
 ) -> bool {
     match (&from_ty.kind(), &to_ty.kind()) {
-        (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) if !const_context => {
+        (ty::Float(float_ty), ty::Int(_) | ty::Uint(_)) => {
             span_lint_and_then(
                 cx,
                 TRANSMUTE_FLOAT_TO_INT,

clippy_lints/src/transmute/transmute_int_to_float.rs

@@ -14,10 +14,9 @@ pub(super) fn check<'tcx>(
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
     arg: &'tcx Expr<'_>,
-    const_context: bool,
 ) -> bool {
     match (&from_ty.kind(), &to_ty.kind()) {
-        (ty::Int(_) | ty::Uint(_), ty::Float(_)) if !const_context => {
+        (ty::Int(_) | ty::Uint(_), ty::Float(_)) => {
             span_lint_and_then(
                 cx,
                 TRANSMUTE_INT_TO_FLOAT,

clippy_lints/src/transmute/transmute_num_to_bytes.rs

@@ -14,18 +14,12 @@ pub(super) fn check<'tcx>(
     from_ty: Ty<'tcx>,
     to_ty: Ty<'tcx>,
     arg: &'tcx Expr<'_>,
-    const_context: bool,
 ) -> bool {
     match (&from_ty.kind(), &to_ty.kind()) {
         (ty::Int(_) | ty::Uint(_) | ty::Float(_), ty::Array(arr_ty, _)) => {
             if !matches!(arr_ty.kind(), ty::Uint(UintTy::U8)) {
                 return false;
             }
-            if matches!(from_ty.kind(), ty::Float(_)) && const_context {
-                // TODO: Remove when const_float_bits_conv is stabilized
-                // rust#72447
-                return false;
-            }
 
             span_lint_and_then(
                 cx,

tests/ui/transmute.rs

@@ -140,24 +140,32 @@ mod int_to_float {
 
     mod issue_5747 {
         const VALUE16: f16 = unsafe { std::mem::transmute(0_u16) };
+        //~^ ERROR: transmute from a `u16` to a `f16`
         const VALUE32: f32 = unsafe { std::mem::transmute(0_u32) };
+        //~^ ERROR: transmute from a `u32` to a `f32`
         const VALUE64: f64 = unsafe { std::mem::transmute(0_i64) };
+        //~^ ERROR: transmute from a `i64` to a `f64`
         const VALUE128: f128 = unsafe { std::mem::transmute(0_i128) };
+        //~^ ERROR: transmute from a `i128` to a `f128`
 
         const fn from_bits_16(v: i16) -> f16 {
             unsafe { std::mem::transmute(v) }
+            //~^ ERROR: transmute from a `i16` to a `f16`
         }
 
         const fn from_bits_32(v: i32) -> f32 {
             unsafe { std::mem::transmute(v) }
+            //~^ ERROR: transmute from a `i32` to a `f32`
         }
 
         const fn from_bits_64(v: u64) -> f64 {
             unsafe { std::mem::transmute(v) }
+            //~^ ERROR: transmute from a `u64` to a `f64`
         }
 
         const fn from_bits_128(v: u128) -> f128 {
             unsafe { std::mem::transmute(v) }
+            //~^ ERROR: transmute from a `u128` to a `f128`
         }
     }
 }
@@ -205,9 +213,13 @@ mod num_to_bytes {
             //~^ ERROR: transmute from a `i128` to a `[u8; 16]`
 
             let _: [u8; 2] = std::mem::transmute(0.0f16);
+            //~^ ERROR: transmute from a `f16` to a `[u8; 2]`
             let _: [u8; 4] = std::mem::transmute(0.0f32);
+            //~^ ERROR: transmute from a `f32` to a `[u8; 4]`
             let _: [u8; 8] = std::mem::transmute(0.0f64);
+            //~^ ERROR: transmute from a `f64` to a `[u8; 8]`
             let _: [u8; 16] = std::mem::transmute(0.0f128);
+            //~^ ERROR: transmute from a `f128` to a `[u8; 16]`
         }
     }
 }

tests/ui/transmute.stderr

@@ -148,8 +148,56 @@ error: transmute from a `i128` to a `f128`
 LL |         let _: f128 = unsafe { std::mem::transmute(0_i128) };
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f128::from_bits(0_i128 as u128)`
 
+error: transmute from a `u16` to a `f16`
+  --> tests/ui/transmute.rs:142:39
+   |
+LL |         const VALUE16: f16 = unsafe { std::mem::transmute(0_u16) };
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f16::from_bits(0_u16)`
+
+error: transmute from a `u32` to a `f32`
+  --> tests/ui/transmute.rs:144:39
+   |
+LL |         const VALUE32: f32 = unsafe { std::mem::transmute(0_u32) };
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f32::from_bits(0_u32)`
+
+error: transmute from a `i64` to a `f64`
+  --> tests/ui/transmute.rs:146:39
+   |
+LL |         const VALUE64: f64 = unsafe { std::mem::transmute(0_i64) };
+   |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f64::from_bits(0_i64 as u64)`
+
+error: transmute from a `i128` to a `f128`
+  --> tests/ui/transmute.rs:148:41
+   |
+LL |         const VALUE128: f128 = unsafe { std::mem::transmute(0_i128) };
+   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f128::from_bits(0_i128 as u128)`
+
+error: transmute from a `i16` to a `f16`
+  --> tests/ui/transmute.rs:152:22
+   |
+LL |             unsafe { std::mem::transmute(v) }
+   |                      ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f16::from_bits(v as u16)`
+
+error: transmute from a `i32` to a `f32`
+  --> tests/ui/transmute.rs:157:22
+   |
+LL |             unsafe { std::mem::transmute(v) }
+   |                      ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f32::from_bits(v as u32)`
+
+error: transmute from a `u64` to a `f64`
+  --> tests/ui/transmute.rs:162:22
+   |
+LL |             unsafe { std::mem::transmute(v) }
+   |                      ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f64::from_bits(v)`
+
+error: transmute from a `u128` to a `f128`
+  --> tests/ui/transmute.rs:167:22
+   |
+LL |             unsafe { std::mem::transmute(v) }
+   |                      ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `f128::from_bits(v)`
+
 error: transmute from a `u8` to a `[u8; 1]`
-  --> tests/ui/transmute.rs:168:30
+  --> tests/ui/transmute.rs:176:30
    |
 LL |             let _: [u8; 1] = std::mem::transmute(0u8);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u8.to_ne_bytes()`
@@ -158,97 +206,121 @@ LL |             let _: [u8; 1] = std::mem::transmute(0u8);
    = help: to override `-D warnings` add `#[allow(clippy::transmute_num_to_bytes)]`
 
 error: transmute from a `u32` to a `[u8; 4]`
-  --> tests/ui/transmute.rs:171:30
+  --> tests/ui/transmute.rs:179:30
    |
 LL |             let _: [u8; 4] = std::mem::transmute(0u32);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u32.to_ne_bytes()`
 
 error: transmute from a `u128` to a `[u8; 16]`
-  --> tests/ui/transmute.rs:173:31
+  --> tests/ui/transmute.rs:181:31
    |
 LL |             let _: [u8; 16] = std::mem::transmute(0u128);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u128.to_ne_bytes()`
 
 error: transmute from a `i8` to a `[u8; 1]`
-  --> tests/ui/transmute.rs:175:30
+  --> tests/ui/transmute.rs:183:30
    |
 LL |             let _: [u8; 1] = std::mem::transmute(0i8);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i8.to_ne_bytes()`
 
 error: transmute from a `i32` to a `[u8; 4]`
-  --> tests/ui/transmute.rs:177:30
+  --> tests/ui/transmute.rs:185:30
    |
 LL |             let _: [u8; 4] = std::mem::transmute(0i32);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i32.to_ne_bytes()`
 
 error: transmute from a `i128` to a `[u8; 16]`
-  --> tests/ui/transmute.rs:179:31
+  --> tests/ui/transmute.rs:187:31
    |
 LL |             let _: [u8; 16] = std::mem::transmute(0i128);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i128.to_ne_bytes()`
 
 error: transmute from a `f16` to a `[u8; 2]`
-  --> tests/ui/transmute.rs:182:30
+  --> tests/ui/transmute.rs:190:30
    |
 LL |             let _: [u8; 2] = std::mem::transmute(0.0f16);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0.0f16.to_ne_bytes()`
 
 error: transmute from a `f32` to a `[u8; 4]`
-  --> tests/ui/transmute.rs:184:30
+  --> tests/ui/transmute.rs:192:30
    |
 LL |             let _: [u8; 4] = std::mem::transmute(0.0f32);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0.0f32.to_ne_bytes()`
 
 error: transmute from a `f64` to a `[u8; 8]`
-  --> tests/ui/transmute.rs:186:30
+  --> tests/ui/transmute.rs:194:30
    |
 LL |             let _: [u8; 8] = std::mem::transmute(0.0f64);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0.0f64.to_ne_bytes()`
 
 error: transmute from a `f128` to a `[u8; 16]`
-  --> tests/ui/transmute.rs:188:31
+  --> tests/ui/transmute.rs:196:31
    |
 LL |             let _: [u8; 16] = std::mem::transmute(0.0f128);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0.0f128.to_ne_bytes()`
 
 error: transmute from a `u8` to a `[u8; 1]`
-  --> tests/ui/transmute.rs:194:30
+  --> tests/ui/transmute.rs:202:30
    |
 LL |             let _: [u8; 1] = std::mem::transmute(0u8);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u8.to_ne_bytes()`
 
 error: transmute from a `u32` to a `[u8; 4]`
-  --> tests/ui/transmute.rs:196:30
+  --> tests/ui/transmute.rs:204:30
    |
 LL |             let _: [u8; 4] = std::mem::transmute(0u32);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u32.to_ne_bytes()`
 
 error: transmute from a `u128` to a `[u8; 16]`
-  --> tests/ui/transmute.rs:198:31
+  --> tests/ui/transmute.rs:206:31
    |
 LL |             let _: [u8; 16] = std::mem::transmute(0u128);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0u128.to_ne_bytes()`
 
 error: transmute from a `i8` to a `[u8; 1]`
-  --> tests/ui/transmute.rs:200:30
+  --> tests/ui/transmute.rs:208:30
    |
 LL |             let _: [u8; 1] = std::mem::transmute(0i8);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i8.to_ne_bytes()`
 
 error: transmute from a `i32` to a `[u8; 4]`
-  --> tests/ui/transmute.rs:202:30
+  --> tests/ui/transmute.rs:210:30
    |
 LL |             let _: [u8; 4] = std::mem::transmute(0i32);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i32.to_ne_bytes()`
 
 error: transmute from a `i128` to a `[u8; 16]`
-  --> tests/ui/transmute.rs:204:31
+  --> tests/ui/transmute.rs:212:31
    |
 LL |             let _: [u8; 16] = std::mem::transmute(0i128);
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0i128.to_ne_bytes()`
 
+error: transmute from a `f16` to a `[u8; 2]`
+  --> tests/ui/transmute.rs:215:30
+   |
+LL |             let _: [u8; 2] = std::mem::transmute(0.0f16);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0.0f16.to_ne_bytes()`
+
+error: transmute from a `f32` to a `[u8; 4]`
+  --> tests/ui/transmute.rs:217:30
+   |
+LL |             let _: [u8; 4] = std::mem::transmute(0.0f32);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0.0f32.to_ne_bytes()`
+
+error: transmute from a `f64` to a `[u8; 8]`
+  --> tests/ui/transmute.rs:219:30
+   |
+LL |             let _: [u8; 8] = std::mem::transmute(0.0f64);
+   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0.0f64.to_ne_bytes()`
+
+error: transmute from a `f128` to a `[u8; 16]`
+  --> tests/ui/transmute.rs:221:31
+   |
+LL |             let _: [u8; 16] = std::mem::transmute(0.0f128);
+   |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using `to_ne_bytes()`: `0.0f128.to_ne_bytes()`
+
 error: transmute from a `&[u8]` to a `&str`
-  --> tests/ui/transmute.rs:218:28
+  --> tests/ui/transmute.rs:230:28
    |
 LL |     let _: &str = unsafe { std::mem::transmute(B) };
    |                            ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::str::from_utf8(B).unwrap()`
@@ -257,16 +329,16 @@ LL |     let _: &str = unsafe { std::mem::transmute(B) };
    = help: to override `-D warnings` add `#[allow(clippy::transmute_bytes_to_str)]`
 
 error: transmute from a `&mut [u8]` to a `&mut str`
-  --> tests/ui/transmute.rs:221:32
+  --> tests/ui/transmute.rs:233:32
    |
 LL |     let _: &mut str = unsafe { std::mem::transmute(mb) };
    |                                ^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::str::from_utf8_mut(mb).unwrap()`
 
 error: transmute from a `&[u8]` to a `&str`
-  --> tests/ui/transmute.rs:223:30
+  --> tests/ui/transmute.rs:235:30
    |
 LL |     const _: &str = unsafe { std::mem::transmute(B) };
    |                              ^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::str::from_utf8_unchecked(B)`
 
-error: aborting due to 42 previous errors
+error: aborting due to 54 previous errors
 

tests/ui/transmute_float_to_int.fixed

@@ -1,7 +1,7 @@
 #![warn(clippy::transmute_float_to_int)]
 #![allow(clippy::missing_transmute_annotations)]
-#![feature(f128)]
-#![feature(f16)]
+#![feature(f128, f128_const)]
+#![feature(f16, f16_const)]
 
 fn float_to_int() {
     let _: u32 = unsafe { 1f32.to_bits() };
@@ -20,25 +20,33 @@ fn float_to_int() {
 }
 
 mod issue_5747 {
-    const VALUE16: i16 = unsafe { std::mem::transmute(1f16) };
-    const VALUE32: i32 = unsafe { std::mem::transmute(1f32) };
-    const VALUE64: u64 = unsafe { std::mem::transmute(1f64) };
-    const VALUE128: u128 = unsafe { std::mem::transmute(1f128) };
+    const VALUE16: i16 = unsafe { 1f16.to_bits() as i16 };
+    //~^ ERROR: transmute from a `f16` to a `i16`
+    const VALUE32: i32 = unsafe { 1f32.to_bits() as i32 };
+    //~^ ERROR: transmute from a `f32` to a `i32`
+    const VALUE64: u64 = unsafe { 1f64.to_bits() };
+    //~^ ERROR: transmute from a `f64` to a `u64`
+    const VALUE128: u128 = unsafe { 1f128.to_bits() };
+    //~^ ERROR: transmute from a `f128` to a `u128`
 
     const fn to_bits_16(v: f16) -> u16 {
-        unsafe { std::mem::transmute(v) }
+        unsafe { v.to_bits() }
+        //~^ ERROR: transmute from a `f16` to a `u16`
     }
 
     const fn to_bits_32(v: f32) -> u32 {
-        unsafe { std::mem::transmute(v) }
+        unsafe { v.to_bits() }
+        //~^ ERROR: transmute from a `f32` to a `u32`
     }
 
     const fn to_bits_64(v: f64) -> i64 {
-        unsafe { std::mem::transmute(v) }
+        unsafe { v.to_bits() as i64 }
+        //~^ ERROR: transmute from a `f64` to a `i64`
     }
 
     const fn to_bits_128(v: f128) -> i128 {
-        unsafe { std::mem::transmute(v) }
+        unsafe { v.to_bits() as i128 }
+        //~^ ERROR: transmute from a `f128` to a `i128`
     }
 }