Fix range_covered_by_constructor for exclusive ranges.

This resolves rust-lang#43253

Author: feadoor

src/librustc_const_eval/_match.rs

@@ -845,14 +845,14 @@ fn range_covered_by_constructor(tcx: TyCtxt, span: Span,
     match *ctor {
         ConstantValue(ref value) => {
             let to = cmp_to(value)?;
-            let end = (to != Ordering::Greater) ||
-                      (end == RangeEnd::Excluded && to == Ordering::Equal);
+            let end = (to == Ordering::Less) ||
+                      (end == RangeEnd::Included && to == Ordering::Equal);
             Ok(cmp_from(value)? && end)
         },
         ConstantRange(ref from, ref to, RangeEnd::Included) => {
             let to = cmp_to(to)?;
-            let end = (to != Ordering::Greater) ||
-                      (end == RangeEnd::Excluded && to == Ordering::Equal);
+            let end = (to == Ordering::Less) ||
+                      (end == RangeEnd::Included && to == Ordering::Equal);
             Ok(cmp_from(from)? && end)
         },
         ConstantRange(ref from, ref to, RangeEnd::Excluded) => {

src/test/ui/check_match/issue-43253.rs

@@ -0,0 +1,51 @@
+// Copyright 2017 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(exclusive_range_pattern)]
+
+fn main() {
+    // These cases should generate no warning.
+    match 10 {
+        1..10 => {},
+        10 => {},
+        _ => {},
+    }
+
+    match 10 {
+        1..10 => {},
+        9...10 => {},
+        _ => {},
+    }
+
+    match 10 {
+        1..10 => {},
+        10...10 => {},
+        _ => {},
+    }
+
+    // These cases should generate an "unreachable pattern" warning.
+    match 10 {
+        1..10 => {},
+        9 => {},
+        _ => {},
+    }
+
+    match 10 {
+        1..10 => {},
+        8...9 => {},
+        _ => {},
+    }
+
+    match 10 {
+        1..10 => {},
+        9...9 => {},
+        _ => {},
+    }
+}

src/test/ui/check_match/issue-43253.stderr

@@ -0,0 +1,20 @@
+warning: unreachable pattern
+  --> $DIR/issue-43253.rs:36:9
+   |
+36 |         9 => {},
+   |         ^
+   |
+   = note: #[warn(unreachable_patterns)] on by default
+
+warning: unreachable pattern
+  --> $DIR/issue-43253.rs:42:9
+   |
+42 |         8...9 => {},
+   |         ^^^^^
+
+warning: unreachable pattern
+  --> $DIR/issue-43253.rs:48:9
+   |
+48 |         9...9 => {},
+   |         ^^^^^
+