Auto merge of #97522 - xfix:stabilize-slice-from-raw-parts, r=dtolnay

Partially stabilize const_slice_from_raw_parts

This doesn't stabilize methods working on mutable pointers.

This pull request continues from #94946.

Pinging `@rust-lang/wg-const-eval` this because I use `rustc_allow_const_fn_unstable`. I believe this is justifiable as it's already possible to use `slice::from_raw_parts` in stable by abusing `transmute`. The stable alternative to this would be to provide a stable const implementation of `std::ptr::from_raw_parts` (as it can already be implemented in stable).

```rust
use std::mem;

#[repr(C)]
struct Slice<T> {
    data: *const T,
    len: usize,
}

fn main() {
    let data: *const i32 = [1, 2, 3, 4].as_ptr();
    let len = 4;
    println!("{:?}", unsafe {
        mem::transmute::<Slice<i32>, &[i32]>(Slice { data, len })
    });
}
```

`@rustbot` modify labels: +T-libs-api

Author: bors

compiler/rustc_codegen_cranelift/example/issue-91827-extern-types.rs

@@ -6,7 +6,6 @@
 // Regression test for issue #91827.
 
 #![feature(const_ptr_offset_from)]
-#![feature(const_slice_from_raw_parts)]
 #![feature(extern_types)]
 
 use std::ptr::addr_of;

library/core/src/lib.rs

@@ -134,7 +134,7 @@
 #![feature(const_ptr_write)]
 #![feature(const_raw_ptr_comparison)]
 #![feature(const_size_of_val)]
-#![feature(const_slice_from_raw_parts)]
+#![feature(const_slice_from_raw_parts_mut)]
 #![feature(const_slice_ptr_len)]
 #![feature(const_str_from_utf8_unchecked_mut)]
 #![feature(const_swap)]

library/core/src/ptr/mod.rs

@@ -690,7 +690,8 @@ pub const fn null_mut<T: ?Sized + Thin>() -> *mut T {
 /// ```
 #[inline]
 #[stable(feature = "slice_from_raw_parts", since = "1.42.0")]
-#[rustc_const_unstable(feature = "const_slice_from_raw_parts", issue = "67456")]
+#[rustc_const_stable(feature = "const_slice_from_raw_parts", since = "1.64.0")]
+#[rustc_allow_const_fn_unstable(ptr_metadata)]
 pub const fn slice_from_raw_parts<T>(data: *const T, len: usize) -> *const [T] {
     from_raw_parts(data.cast(), len)
 }
@@ -722,7 +723,7 @@ pub const fn slice_from_raw_parts<T>(data: *const T, len: usize) -> *const [T] {
 /// ```
 #[inline]
 #[stable(feature = "slice_from_raw_parts", since = "1.42.0")]
-#[rustc_const_unstable(feature = "const_slice_from_raw_parts", issue = "67456")]
+#[rustc_const_unstable(feature = "const_slice_from_raw_parts_mut", issue = "67456")]
 pub const fn slice_from_raw_parts_mut<T>(data: *mut T, len: usize) -> *mut [T] {
     from_raw_parts_mut(data.cast(), len)
 }

library/core/src/slice/raw.rs

@@ -85,7 +85,7 @@ use crate::ptr;
 /// [`NonNull::dangling()`]: ptr::NonNull::dangling
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_slice_from_raw_parts", issue = "67456")]
+#[rustc_const_stable(feature = "const_slice_from_raw_parts", since = "1.64.0")]
 #[must_use]
 pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts`.
@@ -129,7 +129,7 @@ pub const unsafe fn from_raw_parts<'a, T>(data: *const T, len: usize) -> &'a [T]
 /// [`NonNull::dangling()`]: ptr::NonNull::dangling
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[rustc_const_unstable(feature = "const_slice_from_raw_parts", issue = "67456")]
+#[rustc_const_unstable(feature = "const_slice_from_raw_parts_mut", issue = "67456")]
 #[must_use]
 pub const unsafe fn from_raw_parts_mut<'a, T>(data: *mut T, len: usize) -> &'a mut [T] {
     // SAFETY: the caller must uphold the safety contract for `from_raw_parts_mut`.

library/core/tests/lib.rs

@@ -73,7 +73,6 @@
 #![feature(iterator_try_reduce)]
 #![feature(const_mut_refs)]
 #![feature(const_pin)]
-#![feature(const_slice_from_raw_parts)]
 #![feature(never_type)]
 #![feature(unwrap_infallible)]
 #![feature(result_into_ok_or_err)]

src/test/ui/const-ptr/allowed_slices.rs

@@ -1,6 +1,5 @@
 // run-pass
 #![feature(
-    const_slice_from_raw_parts,
     slice_from_ptr_range,
     const_slice_from_ptr_range,
     pointer_byte_offsets,

src/test/ui/const-ptr/forbidden_slices.32bit.stderr

@@ -7,10 +7,10 @@ LL |         &*ptr::slice_from_raw_parts(data, len)
    |         dereferencing pointer failed: null pointer is a dangling pointer (it has no provenance)
    |         inside `std::slice::from_raw_parts::<u32>` at $SRC_DIR/core/src/slice/raw.rs:LL:COL
    |
-  ::: $DIR/forbidden_slices.rs:19:34
+  ::: $DIR/forbidden_slices.rs:18:34
    |
 LL | pub static S0: &[u32] = unsafe { from_raw_parts(ptr::null(), 0) };
-   |                                  ------------------------------ inside `S0` at $DIR/forbidden_slices.rs:19:34
+   |                                  ------------------------------ inside `S0` at $DIR/forbidden_slices.rs:18:34
 
 error[E0080]: could not evaluate static initializer
   --> $SRC_DIR/core/src/slice/raw.rs:LL:COL
@@ -21,10 +21,10 @@ LL |         &*ptr::slice_from_raw_parts(data, len)
    |         dereferencing pointer failed: null pointer is a dangling pointer (it has no provenance)
    |         inside `std::slice::from_raw_parts::<()>` at $SRC_DIR/core/src/slice/raw.rs:LL:COL
    |
-  ::: $DIR/forbidden_slices.rs:20:33
+  ::: $DIR/forbidden_slices.rs:19:33
    |
 LL | pub static S1: &[()] = unsafe { from_raw_parts(ptr::null(), 0) };
-   |                                 ------------------------------ inside `S1` at $DIR/forbidden_slices.rs:20:33
+   |                                 ------------------------------ inside `S1` at $DIR/forbidden_slices.rs:19:33
 
 error[E0080]: could not evaluate static initializer
   --> $SRC_DIR/core/src/slice/raw.rs:LL:COL
@@ -35,13 +35,13 @@ LL |         &*ptr::slice_from_raw_parts(data, len)
    |         dereferencing pointer failed: ALLOC_ID has size 4, so pointer to 8 bytes starting at offset 0 is out-of-bounds
    |         inside `std::slice::from_raw_parts::<u32>` at $SRC_DIR/core/src/slice/raw.rs:LL:COL
    |
-  ::: $DIR/forbidden_slices.rs:23:34
+  ::: $DIR/forbidden_slices.rs:22:34
    |
 LL | pub static S2: &[u32] = unsafe { from_raw_parts(&D0, 2) };
-   |                                  ---------------------- inside `S2` at $DIR/forbidden_slices.rs:23:34
+   |                                  ---------------------- inside `S2` at $DIR/forbidden_slices.rs:22:34
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/forbidden_slices.rs:26:1
+  --> $DIR/forbidden_slices.rs:25:1
    |
 LL | pub static S4: &[u8] = unsafe { from_raw_parts((&D1) as *const _ as _, 1) };
    | ^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>[0]: encountered uninitialized bytes
@@ -52,7 +52,7 @@ LL | pub static S4: &[u8] = unsafe { from_raw_parts((&D1) as *const _ as _, 1) }
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/forbidden_slices.rs:28:1
+  --> $DIR/forbidden_slices.rs:27:1
    |
 LL | pub static S5: &[u8] = unsafe { from_raw_parts((&D3) as *const _ as _, size_of::<&u32>()) };
    | ^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>: encountered a pointer, but expected plain (non-pointer) bytes
@@ -63,7 +63,7 @@ LL | pub static S5: &[u8] = unsafe { from_raw_parts((&D3) as *const _ as _, size
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/forbidden_slices.rs:30:1
+  --> $DIR/forbidden_slices.rs:29:1
    |
 LL | pub static S6: &[bool] = unsafe { from_raw_parts((&D0) as *const _ as _, 4) };
    | ^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>[0]: encountered 0x11, but expected a boolean
@@ -74,7 +74,7 @@ LL | pub static S6: &[bool] = unsafe { from_raw_parts((&D0) as *const _ as _, 4)
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/forbidden_slices.rs:33:1
+  --> $DIR/forbidden_slices.rs:32:1
    |
 LL | pub static S7: &[u16] = unsafe {
    | ^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered an unaligned reference (required 2 byte alignment but found 1)
@@ -93,10 +93,10 @@ LL |         &*ptr::slice_from_raw_parts(data, len)
    |         dereferencing pointer failed: ALLOC_ID has size 8, so pointer to 8 bytes starting at offset 1 is out-of-bounds
    |         inside `std::slice::from_raw_parts::<u64>` at $SRC_DIR/core/src/slice/raw.rs:LL:COL
    |
-  ::: $DIR/forbidden_slices.rs:44:5
+  ::: $DIR/forbidden_slices.rs:43:5
    |
 LL |     from_raw_parts(ptr, 1)
-   |     ---------------------- inside `S8` at $DIR/forbidden_slices.rs:44:5
+   |     ---------------------- inside `S8` at $DIR/forbidden_slices.rs:43:5
 
 error[E0080]: could not evaluate static initializer
   --> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
@@ -112,10 +112,10 @@ LL |         unsafe { intrinsics::ptr_offset_from_unsigned(self, origin) }
 LL |     unsafe { from_raw_parts(range.start, range.end.sub_ptr(range.start)) }
    |                                          ------------------------------ inside `from_ptr_range::<u32>` at $SRC_DIR/core/src/slice/raw.rs:LL:COL
    |
-  ::: $DIR/forbidden_slices.rs:47:34
+  ::: $DIR/forbidden_slices.rs:46:34
    |
 LL | pub static R0: &[u32] = unsafe { from_ptr_range(ptr::null()..ptr::null()) };
-   |                                  ---------------------------------------- inside `R0` at $DIR/forbidden_slices.rs:47:34
+   |                                  ---------------------------------------- inside `R0` at $DIR/forbidden_slices.rs:46:34
 
 error[E0080]: could not evaluate static initializer
   --> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
@@ -131,10 +131,10 @@ LL |         assert!(0 < pointee_size && pointee_size <= isize::MAX as usize);
 LL |     unsafe { from_raw_parts(range.start, range.end.sub_ptr(range.start)) }
    |                                          ------------------------------ inside `from_ptr_range::<()>` at $SRC_DIR/core/src/slice/raw.rs:LL:COL
    |
-  ::: $DIR/forbidden_slices.rs:48:33
+  ::: $DIR/forbidden_slices.rs:47:33
    |
 LL | pub static R1: &[()] = unsafe { from_ptr_range(ptr::null()..ptr::null()) };
-   |                                 ---------------------------------------- inside `R1` at $DIR/forbidden_slices.rs:48:33
+   |                                 ---------------------------------------- inside `R1` at $DIR/forbidden_slices.rs:47:33
    |
    = note: this error originates in the macro `assert` (in Nightly builds, run with -Z macro-backtrace for more info)
 
@@ -150,13 +150,13 @@ LL |         unsafe { intrinsics::offset(self, count) }
 LL |         unsafe { self.offset(count as isize) }
    |                  --------------------------- inside `ptr::const_ptr::<impl *const u32>::add` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
    |
-  ::: $DIR/forbidden_slices.rs:51:25
+  ::: $DIR/forbidden_slices.rs:50:25
    |
 LL |     from_ptr_range(ptr..ptr.add(2))
-   |                         ---------- inside `R2` at $DIR/forbidden_slices.rs:51:25
+   |                         ---------- inside `R2` at $DIR/forbidden_slices.rs:50:25
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/forbidden_slices.rs:53:1
+  --> $DIR/forbidden_slices.rs:52:1
    |
 LL | pub static R4: &[u8] = unsafe {
    | ^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>[0]: encountered uninitialized bytes
@@ -167,7 +167,7 @@ LL | pub static R4: &[u8] = unsafe {
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/forbidden_slices.rs:58:1
+  --> $DIR/forbidden_slices.rs:57:1
    |
 LL | pub static R5: &[u8] = unsafe {
    | ^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>: encountered a pointer, but expected plain (non-pointer) bytes
@@ -178,7 +178,7 @@ LL | pub static R5: &[u8] = unsafe {
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/forbidden_slices.rs:63:1
+  --> $DIR/forbidden_slices.rs:62:1
    |
 LL | pub static R6: &[bool] = unsafe {
    | ^^^^^^^^^^^^^^^^^^^^^^ constructing invalid value at .<deref>[0]: encountered 0x11, but expected a boolean
@@ -189,7 +189,7 @@ LL | pub static R6: &[bool] = unsafe {
            }
 
 error[E0080]: it is undefined behavior to use this value
-  --> $DIR/forbidden_slices.rs:68:1
+  --> $DIR/forbidden_slices.rs:67:1
    |
 LL | pub static R7: &[u16] = unsafe {
    | ^^^^^^^^^^^^^^^^^^^^^ constructing invalid value: encountered an unaligned reference (required 2 byte alignment but found 1)
@@ -211,10 +211,10 @@ LL |         unsafe { intrinsics::offset(self, count) }
 LL |         unsafe { self.offset(count as isize) }
    |                  --------------------------- inside `ptr::const_ptr::<impl *const u64>::add` at $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
    |
-  ::: $DIR/forbidden_slices.rs:75:25
+  ::: $DIR/forbidden_slices.rs:74:25
    |
 LL |     from_ptr_range(ptr..ptr.add(1))
-   |                         ---------- inside `R8` at $DIR/forbidden_slices.rs:75:25
+   |                         ---------- inside `R8` at $DIR/forbidden_slices.rs:74:25
 
 error[E0080]: could not evaluate static initializer
   --> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
@@ -230,10 +230,10 @@ LL |         unsafe { intrinsics::ptr_offset_from_unsigned(self, origin) }
 LL |     unsafe { from_raw_parts(range.start, range.end.sub_ptr(range.start)) }
    |                                          ------------------------------ inside `from_ptr_range::<u32>` at $SRC_DIR/core/src/slice/raw.rs:LL:COL
    |
-  ::: $DIR/forbidden_slices.rs:80:34
+  ::: $DIR/forbidden_slices.rs:79:34
    |
 LL | pub static R9: &[u32] = unsafe { from_ptr_range(&D0..(&D0 as *const u32).add(1)) };
-   |                                  ----------------------------------------------- inside `R9` at $DIR/forbidden_slices.rs:80:34
+   |                                  ----------------------------------------------- inside `R9` at $DIR/forbidden_slices.rs:79:34
 
 error[E0080]: could not evaluate static initializer
   --> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
@@ -249,10 +249,10 @@ LL |         unsafe { intrinsics::ptr_offset_from_unsigned(self, origin) }
 LL |     unsafe { from_raw_parts(range.start, range.end.sub_ptr(range.start)) }
    |                                          ------------------------------ inside `from_ptr_range::<u32>` at $SRC_DIR/core/src/slice/raw.rs:LL:COL
    |
-  ::: $DIR/forbidden_slices.rs:81:35
+  ::: $DIR/forbidden_slices.rs:80:35
    |
 LL | pub static R10: &[u32] = unsafe { from_ptr_range(&D0..&D0) };
-   |                                   ------------------------ inside `R10` at $DIR/forbidden_slices.rs:81:35
+   |                                   ------------------------ inside `R10` at $DIR/forbidden_slices.rs:80:35
 
 error: aborting due to 18 previous errors