Improve error message, fix and add tests.

Changes the non-exhaustive match error message to generate more general
witnesses.

src/test/compile-fail/match-slice-patterns.rs

@@ -12,7 +12,7 @@
 
 fn check(list: &[Option<()>]) {
     match list {
-    //~^ ERROR `&[None, Some(_), None, _]` and `&[Some(_), Some(_), None, _]` not covered
+    //~^ ERROR `&[_, Some(_), None, _]` not covered
         &[] => {},
         &[_] => {},
         &[_, _] => {},

src/test/compile-fail/uninhabited-irrefutable.rs

@@ -0,0 +1,38 @@
+// Copyright 2012 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(never_type)]
+
+mod foo {
+    pub struct SecretlyEmpty {
+        _priv: !,
+    }
+
+    pub struct NotSoSecretlyEmpty {
+        pub _pub: !,
+    }
+}
+
+struct NotSoSecretlyEmpty {
+    _priv: !,
+}
+
+enum Foo {
+    A(foo::SecretlyEmpty),
+    B(foo::NotSoSecretlyEmpty),
+    C(NotSoSecretlyEmpty),
+    D(u32),
+}
+
+fn main() {
+    let x: Foo = Foo::D(123);
+    let Foo::D(_y) = x; //~ ERROR refutable pattern in local binding: `A(_)` not covered
+}
+

src/test/compile-fail/uninhabited-patterns.rs

@@ -0,0 +1,49 @@
+// Copyright 2012 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(box_patterns)]
+#![feature(slice_patterns)]
+#![feature(box_syntax)]
+#![feature(never_type)]
+#![deny(unreachable_patterns)]
+
+mod foo {
+    pub struct SecretlyEmpty {
+        _priv: !,
+    }
+}
+
+struct NotSoSecretlyEmpty {
+    _priv: !,
+}
+
+fn main() {
+    let x: &[!] = &[];
+
+    match x {
+        &[]   => (),
+        &[..] => (),    //~ ERROR unreachable pattern
+    };
+
+    let x: Result<Box<NotSoSecretlyEmpty>, &[Result<!, !>]> = Err(&[]);
+    match x {
+        Ok(box _) => (),    //~ ERROR unreachable pattern
+        Err(&[]) => (),
+        Err(&[..]) => (),   //~ ERROR unreachable pattern
+    }
+
+    let x: Result<foo::SecretlyEmpty, Result<NotSoSecretlyEmpty, u32>> = Err(Err(123));
+    match x {
+        Ok(_y) => (),
+        Err(Err(_y)) => (),
+        Err(Ok(_y)) => (),  //~ ERROR unreachable pattern
+    }
+}
+

src/test/ui/check_match/issue-35609.stderr

@@ -4,11 +4,11 @@ error[E0004]: non-exhaustive patterns: `(B, _)`, `(C, _)`, `(D, _)` and 2 more n
 20 |     match (A, ()) {
    |           ^^^^^^^ patterns `(B, _)`, `(C, _)`, `(D, _)` and 2 more not covered
 
-error[E0004]: non-exhaustive patterns: `(A, B)`, `(B, B)`, `(C, B)` and 27 more not covered
+error[E0004]: non-exhaustive patterns: `(_, B)`, `(_, C)`, `(_, D)` and 2 more not covered
   --> $DIR/issue-35609.rs:24:11
    |
 24 |     match (A, A) {
-   |           ^^^^^^ patterns `(A, B)`, `(B, B)`, `(C, B)` and 27 more not covered
+   |           ^^^^^^ patterns `(_, B)`, `(_, C)`, `(_, D)` and 2 more not covered
 
 error[E0004]: non-exhaustive patterns: `((B, _), _)`, `((C, _), _)`, `((D, _), _)` and 2 more not covered
   --> $DIR/issue-35609.rs:28:11