Auto merge of #30286 - oli-obk:const_error_span, r=nikomatsakis

previously the error was erased and a `non-const path` error was emitted at the location of the field access instead of at the overflow location (as can be seen in the playground: http://is.gd/EuAF5F )

src/librustc/middle/const_eval.rs

@@ -1182,46 +1182,40 @@ pub fn eval_const_expr_partial<'tcx>(tcx: &ty::ctxt<'tcx>,
       },
       hir::ExprTupField(ref base, index) => {
         let base_hint = ty_hint.erase_hint();
-        if let Ok(c) = eval_const_expr_partial(tcx, base, base_hint, fn_args) {
-            if let Tuple(tup_id) = c {
-                if let hir::ExprTup(ref fields) = tcx.map.expect_expr(tup_id).node {
-                    if index.node < fields.len() {
-                        return eval_const_expr_partial(tcx, &fields[index.node], base_hint, fn_args)
-                    } else {
-                        signal!(e, TupleIndexOutOfBounds);
-                    }
+        let c = try!(eval_const_expr_partial(tcx, base, base_hint, fn_args));
+        if let Tuple(tup_id) = c {
+            if let hir::ExprTup(ref fields) = tcx.map.expect_expr(tup_id).node {
+                if index.node < fields.len() {
+                    return eval_const_expr_partial(tcx, &fields[index.node], base_hint, fn_args)
                 } else {
-                    unreachable!()
+                    signal!(e, TupleIndexOutOfBounds);
                 }
             } else {
-                signal!(base, ExpectedConstTuple);
+                unreachable!()
             }
         } else {
-            signal!(base, NonConstPath)
+            signal!(base, ExpectedConstTuple);
         }
       }
       hir::ExprField(ref base, field_name) => {
         let base_hint = ty_hint.erase_hint();
         // Get the base expression if it is a struct and it is constant
-        if let Ok(c) = eval_const_expr_partial(tcx, base, base_hint, fn_args) {
-            if let Struct(struct_id) = c {
-                if let hir::ExprStruct(_, ref fields, _) = tcx.map.expect_expr(struct_id).node {
-                    // Check that the given field exists and evaluate it
-                    // if the idents are compared run-pass/issue-19244 fails
-                    if let Some(f) = fields.iter().find(|f| f.name.node
-                                                         == field_name.node) {
-                        return eval_const_expr_partial(tcx, &*f.expr, base_hint, fn_args)
-                    } else {
-                        signal!(e, MissingStructField);
-                    }
+        let c = try!(eval_const_expr_partial(tcx, base, base_hint, fn_args));
+        if let Struct(struct_id) = c {
+            if let hir::ExprStruct(_, ref fields, _) = tcx.map.expect_expr(struct_id).node {
+                // Check that the given field exists and evaluate it
+                // if the idents are compared run-pass/issue-19244 fails
+                if let Some(f) = fields.iter().find(|f| f.name.node
+                                                     == field_name.node) {
+                    return eval_const_expr_partial(tcx, &*f.expr, base_hint, fn_args)
                 } else {
-                    unreachable!()
+                    signal!(e, MissingStructField);
                 }
             } else {
-                signal!(base, ExpectedConstStruct);
+                unreachable!()
             }
         } else {
-            signal!(base, NonConstPath);
+            signal!(base, ExpectedConstStruct);
         }
       }
       _ => signal!(e, MiscCatchAll)

src/test/compile-fail/const-tup-index-span.rs

@@ -0,0 +1,18 @@
+// 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.
+
+// Test spans of errors
+
+const TUP: (usize,) = 5 << 64;
+//~^ ERROR: attempted left shift with overflow [E0250]
+const ARR: [i32; TUP.0] = [];
+
+fn main() {
+}