Restore old match behaviour

Author: varkor

src/librustc_mir/hair/pattern/check_match.rs

@@ -230,7 +230,11 @@ impl<'a, 'tcx> MatchVisitor<'a, 'tcx> {
                 let scrutinee_is_uninhabited = if self.tcx.features().exhaustive_patterns {
                     self.tcx.is_ty_uninhabited_from(module, pat_ty)
                 } else {
-                    pat_ty.is_never()
+                    match pat_ty.sty {
+                        ty::Never => true,
+                        ty::Adt(def, _) => def.variants.is_empty(),
+                        _ => false
+                    }
                 };
                 if !scrutinee_is_uninhabited {
                     // We know the type is inhabited, so this must be wrong

src/test/ui/uninhabited/uninhabited-matches-feature-gated.rs

@@ -20,10 +20,10 @@ fn main() {
     let _ = match x {}; //~ ERROR non-exhaustive
 
     let x: (Void,) = unsafe { std::mem::uninitialized() };
-    let _ = match x {}; // okay
+    let _ = match x {}; //~ ERROR non-exhaustive
 
     let x: [Void; 1] = unsafe { std::mem::uninitialized() };
-    let _ = match x {}; // okay
+    let _ = match x {}; //~ ERROR non-exhaustive
 
     let x: &[Void] = unsafe { std::mem::uninitialized() };
     let _ = match x {   //~ ERROR non-exhaustive

src/test/ui/uninhabited/uninhabited-matches-feature-gated.stderr

@@ -16,6 +16,30 @@ help: ensure that all possible cases are being handled, possibly by adding wildc
 LL |     let _ = match x {}; //~ ERROR non-exhaustive
    |                   ^
 
+error[E0004]: non-exhaustive patterns: type (Void,) is non-empty
+  --> $DIR/uninhabited-matches-feature-gated.rs:23:19
+   |
+LL |     let _ = match x {}; //~ ERROR non-exhaustive
+   |                   ^
+   |
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+  --> $DIR/uninhabited-matches-feature-gated.rs:23:19
+   |
+LL |     let _ = match x {}; //~ ERROR non-exhaustive
+   |                   ^
+
+error[E0004]: non-exhaustive patterns: type [Void; 1] is non-empty
+  --> $DIR/uninhabited-matches-feature-gated.rs:26:19
+   |
+LL |     let _ = match x {}; //~ ERROR non-exhaustive
+   |                   ^
+   |
+help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+  --> $DIR/uninhabited-matches-feature-gated.rs:26:19
+   |
+LL |     let _ = match x {}; //~ ERROR non-exhaustive
+   |                   ^
+
 error[E0004]: non-exhaustive patterns: `&[_]` not covered
   --> $DIR/uninhabited-matches-feature-gated.rs:29:19
    |
@@ -34,7 +58,7 @@ error[E0005]: refutable pattern in local binding: `Err(_)` not covered
 LL |     let Ok(x) = x;
    |         ^^^^^ pattern `Err(_)` not covered
 
-error: aborting due to 5 previous errors
+error: aborting due to 7 previous errors
 
 Some errors occurred: E0004, E0005.
 For more information about an error, try `rustc --explain E0004`.