eval_const_expr_partial now returns ConstVal::Struct instead of None for unit-struct path expressions. Fixes #27008

Author: Detegr

src/librustc/middle/const_eval.rs

@@ -967,6 +967,9 @@ pub fn eval_const_expr_partial<'tcx>(tcx: &ty::ctxt<'tcx>,
               Some(def::DefVariant(enum_def, variant_def, _)) => {
                   (lookup_variant_by_id(tcx, enum_def, variant_def), None)
               }
+              Some(def::DefStruct(_)) => {
+                  return Ok(ConstVal::Struct(e.id))
+              }
               _ => (None, None)
           };
           let const_expr = match const_expr {

src/test/compile-fail/issue-27008.rs

@@ -0,0 +1,21 @@
+// Copyright 2015 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.
+
+struct S;
+
+fn main() {
+    let b = [0; S];
+    //~^ ERROR mismatched types
+    //~| expected `usize`
+    //~| found `S`
+    //~| expected usize
+    //~| found struct `S`
+    //~| ERROR expected positive integer for repeat count, found struct
+}