Auto merge of #31232 - stepancheg:enum-univariant, r=nrc
``` enum Univariant { X = 17 } ``` Fixes #10292
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@ -4250,14 +4250,9 @@ pub fn check_enum_variants<'a,'tcx>(ccx: &CrateCtxt<'a,'tcx>,
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let def_id = ccx.tcx.map.local_def_id(id);
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let hint = *ccx.tcx.lookup_repr_hints(def_id).get(0).unwrap_or(&attr::ReprAny);
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if hint != attr::ReprAny && vs.len() <= 1 {
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if vs.len() == 1 {
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span_err!(ccx.tcx.sess, sp, E0083,
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"unsupported representation for univariant enum");
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} else {
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span_err!(ccx.tcx.sess, sp, E0084,
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"unsupported representation for zero-variant enum");
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};
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if hint != attr::ReprAny && vs.is_empty() {
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span_err!(ccx.tcx.sess, sp, E0084,
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"unsupported representation for zero-variant enum");
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}
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do_check(ccx, vs, id, hint);
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@ -1062,13 +1062,6 @@ Note also that without a representation manually defined, the compiler will
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optimize by using the smallest integer type possible.
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"##,
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E0083: r##"
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At present, it's not possible to define a custom representation for an enum with
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a single variant. As a workaround you can add a `Dummy` variant.
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See: https://github.com/rust-lang/rust/issues/10292
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"##,
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E0084: r##"
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It is impossible to define an integer type to be used to represent zero-variant
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enum values because there are no zero-variant enum values. There is no way to
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@ -0,0 +1,47 @@
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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use std::mem;
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// Univariant C-like enum
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#[repr(i32)]
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enum Univariant {
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X = 17
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}
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#[repr(u16)]
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enum UnivariantWithoutDescr {
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Y
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}
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pub fn main() {
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{
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assert_eq!(4, mem::size_of::<Univariant>());
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assert_eq!(17, Univariant::X as i32);
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let enums: &[Univariant] =
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&[Univariant::X, Univariant::X, Univariant::X];
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let ints: &[i32] = unsafe { mem::transmute(enums) };
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// check it has the same memory layout as i32
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assert_eq!(&[17, 17, 17], ints);
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}
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{
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assert_eq!(2, mem::size_of::<UnivariantWithoutDescr>());
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let descr = UnivariantWithoutDescr::Y as u16;
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let enums: &[UnivariantWithoutDescr] =
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&[UnivariantWithoutDescr::Y, UnivariantWithoutDescr::Y, UnivariantWithoutDescr::Y];
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let ints: &[u16] = unsafe { mem::transmute(enums) };
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// check it has the same memory layout as u16
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assert_eq!(&[descr, descr, descr], ints);
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}
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}
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