Fix for #31267 and additional zero-width constant bug

src/librustc_trans/trans/expr.rs

@@ -149,6 +149,21 @@ pub fn trans_into<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
                     },
                 }
             }
+
+            // If we see a const here, that's because it evaluates to a type with zero size. We
+            // should be able to just discard it, since const expressions are guaranteed not to
+            // have side effects. This seems to be reached through tuple struct constructors being
+            // passed zero-size constants.
+            if let hir::ExprPath(..) = expr.node {
+                match bcx.def(expr.id) {
+                    Def::Const(_) | Def::AssociatedConst(_) => {
+                        assert!(type_is_zero_size(bcx.ccx(), bcx.tcx().node_id_to_type(expr.id)));
+                        return bcx;
+                    }
+                    _ => {}
+                }
+            }
+
             // Even if we don't have a value to emit, and the expression
             // doesn't have any side-effects, we still have to translate the
             // body of any closures.
@@ -160,7 +175,7 @@ pub fn trans_into<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
             match expr.node {
                 hir::ExprPath(..) => {
                     match bcx.def(expr.id) {
-                        Def::Const(did) => {
+                        Def::Const(did) | Def::AssociatedConst(did) => {
                             let empty_substs = bcx.tcx().mk_substs(Substs::trans_empty());
                             let const_expr = consts::get_const_expr(bcx.ccx(), did, expr,
                                                                     empty_substs);
@@ -896,7 +911,7 @@ fn trans_def<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
             let lval = Lvalue::new("expr::trans_def");
             DatumBlock::new(bcx, Datum::new(val, const_ty, LvalueExpr(lval)))
         }
-        Def::Const(_) => {
+        Def::Const(_) | Def::AssociatedConst(_) => {
             bcx.sess().span_bug(ref_expr.span,
                 "constant expression should not reach expr::trans_def")
         }

src/test/run-pass/issue-31267-additional.rs

@@ -0,0 +1,30 @@
+// 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.
+
+#![feature(associated_consts)]
+
+#[derive(Clone, Copy, Debug)]
+struct Bar;
+
+const BAZ: Bar = Bar;
+
+#[derive(Debug)]
+struct Foo([Bar; 1]);
+
+struct Biz;
+
+impl Biz {
+    const BAZ: Foo = Foo([BAZ; 1]);
+}
+
+fn main() {
+    let foo = Biz::BAZ;
+    println!("{:?}", foo);
+}

src/test/run-pass/issue-31267.rs

@@ -0,0 +1,24 @@
+// 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.
+
+// Regression test for issue #31267
+
+#![feature(associated_consts)]
+
+struct Foo;
+
+impl Foo {
+    const FOO: [i32; 3] = [0; 3];
+}
+
+pub fn main() {
+    let foo = Foo::FOO;
+    assert_eq!(foo, [0i32, 0, 0]);
+}