1 // compile-flags: -Z print-type-sizes
4 // ^-- needed because `--pass check` does not emit the output needed.
5 // FIXME: consider using an attribute instead of side-effects.
7 // This file illustrates how niche-filling enums are handled,
8 // modelled after cases like `Option<&u32>`, `Option<bool>` and such.
10 // It uses NonZeroU32 rather than `&_` or `Unique<_>`, because
11 // the test is not set up to deal with target-dependent pointer width.
13 // It avoids using u64/i64 because on some targets that is only 4-byte
14 // aligned (while on most it is 8-byte aligned) and so the resulting
15 // padding and overall computed sizes can be quite different.
18 #![feature(rustc_attrs)]
21 use std::num::NonZeroU32;
23 pub enum MyOption<T> { None, Some(T) }
25 #[rustc_layout_scalar_valid_range_start(0)]
26 #[rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FE)]
27 pub struct MyNotNegativeOne {
31 impl<T> Default for MyOption<T> {
32 fn default() -> Self { MyOption::None }
35 pub enum EmbeddedDiscr {
37 Record { pre: u8, val: NonZeroU32, post: u16 },
40 impl Default for EmbeddedDiscr {
41 fn default() -> Self { EmbeddedDiscr::None }
45 pub struct IndirectNonZero {
47 nested: NestedNonZero,
51 pub struct NestedNonZero {
57 impl Default for NestedNonZero {
58 fn default() -> Self {
59 NestedNonZero { pre: 0, val: NonZeroU32::new(1).unwrap(), post: 0 }
63 pub enum Enum4<A, B, C, D> {
70 pub union Union1<A: Copy> {
74 pub union Union2<A: Copy, B: Copy> {
80 fn start(_: isize, _: *const *const u8) -> isize {
81 let _x: MyOption<NonZeroU32> = Default::default();
82 let _y: EmbeddedDiscr = Default::default();
83 let _z: MyOption<IndirectNonZero> = Default::default();
84 let _a: MyOption<bool> = Default::default();
85 let _b: MyOption<char> = Default::default();
86 let _c: MyOption<std::cmp::Ordering> = Default::default();
87 let _d: MyOption<MyOption<u8>> = Default::default();
88 let _e: Enum4<(), char, (), ()> = Enum4::One(());
89 let _f: Enum4<(), (), bool, ()> = Enum4::One(());
90 let _g: Enum4<(), (), (), MyOption<u8>> = Enum4::One(());
91 let _h: MyOption<MyNotNegativeOne> = Default::default();
93 // Unions do not currently participate in niche filling.
94 let _i: MyOption<Union2<NonZeroU32, u32>> = Default::default();
96 // ...even when theoretically possible.
97 let _j: MyOption<Union1<NonZeroU32>> = Default::default();
98 let _k: MyOption<Union2<NonZeroU32, NonZeroU32>> = Default::default();