Rollup merge of #45880 - arielb1:never-coerce, r=nikomatsakis

make coercions to `!` in unreachable code a hard error

This was added to cover up a lazy extra semicolon in #35849, but does
not actually make sense. This is removed as a part of the stabilization
of `never_type`.

src/test/ui/reachable/expr_unary.rs

@@ -12,11 +12,14 @@
 #![allow(unused_assignments)]
 #![allow(dead_code)]
 #![deny(unreachable_code)]
+#![deny(coerce_never)]
 #![feature(never_type)]
 
 fn foo() {
     let x: ! = ! { return; 22 }; //~ ERROR unreachable
-    //~^ ERROR cannot apply unary operator `!` to type `!`
+    //~^ ERROR cannot coerce
+    //~| hard error
+    //~| ERROR cannot apply unary operator `!` to type `!`
 }
 
 fn main() { }

src/test/ui/reachable/expr_unary.stderr

@@ -1,7 +1,7 @@
 error: unreachable expression
-  --> $DIR/expr_unary.rs:18:28
+  --> $DIR/expr_unary.rs:19:28
    |
-18 |     let x: ! = ! { return; 22 }; //~ ERROR unreachable
+19 |     let x: ! = ! { return; 22 }; //~ ERROR unreachable
    |                            ^^
    |
 note: lint level defined here
@@ -10,11 +10,25 @@ note: lint level defined here
 14 | #![deny(unreachable_code)]
    |         ^^^^^^^^^^^^^^^^
 
-error[E0600]: cannot apply unary operator `!` to type `!`
-  --> $DIR/expr_unary.rs:18:16
+error: cannot coerce `{integer}` to !
+  --> $DIR/expr_unary.rs:19:28
    |
-18 |     let x: ! = ! { return; 22 }; //~ ERROR unreachable
+19 |     let x: ! = ! { return; 22 }; //~ ERROR unreachable
+   |                            ^^
+   |
+note: lint level defined here
+  --> $DIR/expr_unary.rs:15:9
+   |
+15 | #![deny(coerce_never)]
+   |         ^^^^^^^^^^^^
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #46325 <https://github.com/rust-lang/rust/issues/46325>
+
+error[E0600]: cannot apply unary operator `!` to type `!`
+  --> $DIR/expr_unary.rs:19:16
+   |
+19 |     let x: ! = ! { return; 22 }; //~ ERROR unreachable
    |                ^^^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors