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Allow #[repr(i32)] for univariant enum
```
#[repr(i32)]
enum Univariant {
    X = 17
}
```

Fixes #10292
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stepancheg committed Jan 27, 2016
1 parent 4b61585 commit 641267e
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Showing 3 changed files with 50 additions and 15 deletions.
11 changes: 3 additions & 8 deletions src/librustc_typeck/check/mod.rs
Expand Up @@ -4250,14 +4250,9 @@ pub fn check_enum_variants<'a,'tcx>(ccx: &CrateCtxt<'a,'tcx>,
let def_id = ccx.tcx.map.local_def_id(id);
let hint = *ccx.tcx.lookup_repr_hints(def_id).get(0).unwrap_or(&attr::ReprAny);

if hint != attr::ReprAny && vs.len() <= 1 {
if vs.len() == 1 {
span_err!(ccx.tcx.sess, sp, E0083,
"unsupported representation for univariant enum");
} else {
span_err!(ccx.tcx.sess, sp, E0084,
"unsupported representation for zero-variant enum");
};
if hint != attr::ReprAny && vs.is_empty() {
span_err!(ccx.tcx.sess, sp, E0084,
"unsupported representation for zero-variant enum");
}

do_check(ccx, vs, id, hint);
Expand Down
7 changes: 0 additions & 7 deletions src/librustc_typeck/diagnostics.rs
Expand Up @@ -1062,13 +1062,6 @@ Note also that without a representation manually defined, the compiler will
optimize by using the smallest integer type possible.
"##,

E0083: r##"
At present, it's not possible to define a custom representation for an enum with
a single variant. As a workaround you can add a `Dummy` variant.
See: https://github.com/rust-lang/rust/issues/10292
"##,

E0084: r##"
It is impossible to define an integer type to be used to represent zero-variant
enum values because there are no zero-variant enum values. There is no way to
Expand Down
47 changes: 47 additions & 0 deletions src/test/run-pass/enum-univariant-repr.rs
@@ -0,0 +1,47 @@
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.


use std::mem;

// Univariant C-like enum
#[repr(i32)]
enum Univariant {
X = 17
}

#[repr(u16)]
enum UnivariantWithoutDescr {
Y
}

pub fn main() {
{
assert_eq!(4, mem::size_of::<Univariant>());
assert_eq!(17, Univariant::X as i32);

let enums: &[Univariant] =
&[Univariant::X, Univariant::X, Univariant::X];
let ints: &[i32] = unsafe { mem::transmute(enums) };
// check it has the same memory layout as i32
assert_eq!(&[17, 17, 17], ints);
}

{
assert_eq!(2, mem::size_of::<UnivariantWithoutDescr>());
let descr = UnivariantWithoutDescr::Y as u16;

let enums: &[UnivariantWithoutDescr] =
&[UnivariantWithoutDescr::Y, UnivariantWithoutDescr::Y, UnivariantWithoutDescr::Y];
let ints: &[u16] = unsafe { mem::transmute(enums) };
// check it has the same memory layout as u16
assert_eq!(&[descr, descr, descr], ints);
}
}

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