Merge pull request #4358 from jld/constenum-unit

Fix consts of nullary univariant enum type.

Author: catamorphism

src/librustc/middle/trans/consts.rs

@@ -398,7 +398,6 @@ fn const_expr(cx: @crate_ctxt, e: @ast::expr) -> ValueRef {
                 // forbids paths that don't map to C-like enum variants.
                 let ety = ty::expr_ty(cx.tcx, e);
                 let llty = type_of::type_of(cx, ety);
-                let llstructtys = lib::llvm::struct_element_types(llty);
 
                 // Can't use `discrims` from the crate context here because
                 // those discriminants have an extra level of indirection,
@@ -422,8 +421,14 @@ fn const_expr(cx: @crate_ctxt, e: @ast::expr) -> ValueRef {
                         lldiscrim = found_lldiscrim;
                     }
                 }
+                let fields = if ty::enum_is_univariant(cx.tcx, enum_did) {
+                    ~[lldiscrim]
+                } else {
+                    let llstructtys = lib::llvm::struct_element_types(llty);
+                    ~[lldiscrim, C_null(llstructtys[1])]
+                };
 
-                C_named_struct(llty, ~[ lldiscrim, C_null(llstructtys[1]) ])
+                C_named_struct(llty, fields)
             }
             Some(ast::def_struct(_)) => {
                 let ety = ty::expr_ty(cx.tcx, e);

src/test/run-pass/const-nullary-univariant-enum.rs

@@ -0,0 +1,19 @@
+// Copyright 2013 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.
+
+enum Foo {
+    Bar = 0xDEADBEE
+}
+
+const X: Foo = Bar;
+
+fn main() {
+    assert((X as uint) == 0xDEADBEE);
+}