Support setting alignment on globals

[sagudev]

Currently if one wants to set alignment on globals (either static or const) it needs to use a wrapper:

#[repr(align(8))]
struct Aligned(u8);

static X: Aligned = Aligned(0);
const Y: Aligned = Aligned(0);

instead it would be nice to support align on static/const directly:

#[repr(align(8))] // or maybe #[align(8)]
static X: u8 = 0;
#[repr(align(8))] // or maybe #[align(8)]
const Y: u8 = 0;

[Jules-Bertholet]

Pre-RFC: #[align] attribute

Summary Add an #[align] attribute to set the minimum alignment of struct and enum fields, statics, and local variables. Motivation Bindings to C and C++ C and C++ provide an alignas modifier to set the alignment of specific struct fields. To represent such structures in Rust, bindgen is sometimes forced to add explicit padding fields: // C code #include <stdint.h> struct foo { uint8_t x; _Alignas(128) uint8_t y; uint8_t z; }; // Rust bindings generated by `bindgen` pub struct foo …

[Neutron3529]

@sagudev

it needs to use a wrapper

Yes it needs a wrapper. The type contains its align. Calling a function that need align on a not-aligned struct is unsafe (and perhaps unsound)

if a function needs a u8, the function should not acquire the u8 is aligned, and if that function required an aligned item, it should not require u8 type directly in safe Rust.