1 files changed, 105 insertions, 0 deletions
diff --git a/tests/ui/const-ptr/allowed_slices.rs b/tests/ui/const-ptr/allowed_slices.rs
new file mode 100644
index 00000000000..3f19cd4d804
--- /dev/null
+++ b/tests/ui/const-ptr/allowed_slices.rs
@@ -0,0 +1,105 @@
+// run-pass
+#![feature(
+    slice_from_ptr_range,
+    const_slice_from_ptr_range,
+    pointer_byte_offsets,
+    const_pointer_byte_offsets
+)]
+use std::{
+    mem::MaybeUninit,
+    ptr,
+    slice::{from_ptr_range, from_raw_parts},
+};
+
+// Dangling is ok, as long as it's either for ZST reads or for no reads
+pub static S0: &[u32] = unsafe { from_raw_parts(dangling(), 0) };
+pub static S1: &[()] = unsafe { from_raw_parts(dangling(), 3) };
+
+// References are always valid of reads of a single element (basically `slice::from_ref`)
+pub static S2: &[u32] = unsafe { from_raw_parts(&D0, 1) };
+pub static S3: &[MaybeUninit<&u32>] = unsafe { from_raw_parts(&D1, 1) };
+
+// Reinterpreting data is fine, as long as layouts match
+pub static S4: &[u8] = unsafe { from_raw_parts((&D0) as *const _ as _, 3) };
+// This is only valid because D1 has uninitialized bytes, if it was an initialized pointer,
+// that would reinterpret pointers as integers which is UB in CTFE.
+pub static S5: &[MaybeUninit<u8>] = unsafe { from_raw_parts((&D1) as *const _ as _, 2) };
+// Even though u32 and [bool; 4] have different layouts, D0 has a value that
+// is valid as [bool; 4], so this is not UB (it's basically a transmute)
+pub static S6: &[bool] = unsafe { from_raw_parts((&D0) as *const _ as _, 4) };
+
+// Structs are considered single allocated objects,
+// as long as you don't reinterpret padding as initialized
+// data everything is ok.
+pub static S7: &[u16] = unsafe {
+    let ptr = (&D2 as *const Struct as *const u16).byte_add(4);
+
+    from_raw_parts(ptr, 3)
+};
+pub static S8: &[MaybeUninit<u16>] = unsafe {
+    let ptr = &D2 as *const Struct as *const MaybeUninit<u16>;
+
+    from_raw_parts(ptr, 6)
+};
+
+pub static R0: &[u32] = unsafe { from_ptr_range(dangling()..dangling()) };
+// from_ptr_range panics on zst
+//pub static R1: &[()] = unsafe { from_ptr_range(dangling(), dangling().byte_add(3)) };
+pub static R2: &[u32] = unsafe {
+    let ptr = &D0 as *const u32;
+    from_ptr_range(ptr..ptr.add(1))
+};
+pub static R3: &[MaybeUninit<&u32>] = unsafe {
+    let ptr = &D1 as *const MaybeUninit<&u32>;
+    from_ptr_range(ptr..ptr.add(1))
+};
+pub static R4: &[u8] = unsafe {
+    let ptr = &D0 as *const u32 as *const u8;
+    from_ptr_range(ptr..ptr.add(3))
+};
+pub static R5: &[MaybeUninit<u8>] = unsafe {
+    let ptr = &D1 as *const MaybeUninit<&u32> as *const MaybeUninit<u8>;
+    from_ptr_range(ptr..ptr.add(2))
+};
+pub static R6: &[bool] = unsafe {
+    let ptr = &D0 as *const u32 as *const bool;
+    from_ptr_range(ptr..ptr.add(4))
+};
+pub static R7: &[u16] = unsafe {
+    let d2 = &D2;
+    let l = &d2.b as *const u32 as *const u16;
+    let r = &d2.d as *const u8 as *const u16;
+
+    from_ptr_range(l..r)
+};
+pub static R8: &[MaybeUninit<u16>] = unsafe {
+    let d2 = &D2;
+    let l = d2 as *const Struct as *const MaybeUninit<u16>;
+    let r = &d2.d as *const u8 as *const MaybeUninit<u16>;
+
+    from_ptr_range(l..r)
+};
+
+// Using valid slice is always valid
+pub static R9: &[u32] = unsafe { from_ptr_range(R0.as_ptr_range()) };
+pub static R10: &[u32] = unsafe { from_ptr_range(R2.as_ptr_range()) };
+
+const D0: u32 = (1 << 16) | 1;
+const D1: MaybeUninit<&u32> = MaybeUninit::uninit();
+const D2: Struct = Struct { a: 1, b: 2, c: 3, d: 4 };
+
+const fn dangling<T>() -> *const T {
+    ptr::NonNull::dangling().as_ptr() as _
+}
+
+#[repr(C)]
+struct Struct {
+    a: u8,
+    // _pad: [MaybeUninit<u8>; 3]
+    b: u32,
+    c: u16,
+    d: u8,
+    // _pad: [MaybeUninit<u8>; 1]
+}
+
+fn main() {}