Rollup merge of #39980 - arielb1:privately-uninhabited, r=nikomatsakis

check_match: don't treat privately uninhabited types as uninhabited

Fixes #38972, which is a regression in 1.16 from @canndrew's patchset.

r? @nikomatsakis

beta-nominating because regression.

src/test/compile-fail/match-privately-empty.rs

@@ -0,0 +1,30 @@
+// 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(never_type)]
+
+mod private {
+    pub struct Private {
+        _bot: !,
+        pub misc: bool,
+    }
+    pub const DATA: Option<Private> = None;
+}
+
+fn main() {
+    match private::DATA {
+    //~^ ERROR non-exhaustive patterns: `Some(Private { misc: true, .. })` not covered
+        None => {}
+        Some(private::Private {
+            misc: false,
+            ..
+        }) => {}
+    }
+}

src/test/compile-fail/uninhabited-matches-feature-gated.rs

@@ -19,16 +19,13 @@ fn main() {
     };
 
     let x: &Void = unsafe { std::mem::uninitialized() };
-    let _ = match x {};
-    //~^ ERROR non-exhaustive
+    let _ = match x {}; //~ ERROR non-exhaustive
 
     let x: (Void,) = unsafe { std::mem::uninitialized() };
-    let _ = match x {};
-    //~^ ERROR non-exhaustive
+    let _ = match x {}; //~ ERROR non-exhaustive
 
     let x: [Void; 1] = unsafe { std::mem::uninitialized() };
-    let _ = match x {};
-    //~^ ERROR non-exhaustive
+    let _ = match x {}; //~ ERROR non-exhaustive
 
     let x: &[Void] = unsafe { std::mem::uninitialized() };
     let _ = match x {   //~ ERROR non-exhaustive
@@ -47,4 +44,3 @@ fn main() {
     let Ok(x) = x;
     //~^ ERROR refutable
 }
-

src/test/run-pass/issue-38972.rs

@@ -0,0 +1,25 @@
+// 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.
+
+// This issue tracks a regression (a new warning) without
+// feature(never_type). When we make that the default, please
+// remove this test.
+
+enum Foo { }
+
+fn make_foo() -> Option<Foo> { None }
+
+#[deny(warnings)]
+fn main() {
+    match make_foo() {
+        None => {},
+        Some(_) => {}
+    }
+}