From a4bff741d0bd128dc92a7e36c96af91461bd3611 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sun, 21 Nov 2021 19:09:14 -0800
Subject: [PATCH 1/4] Test not never

Currently fails to build:

    error[E0600]: cannot apply unary operator `!` to type `!`
       --> library/core/tests/ops.rs:239:8
        |
    239 |     if !return () {}
        |        ^^^^^^^^^^ cannot apply unary operator `!`
---
 library/core/tests/ops.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/library/core/tests/ops.rs b/library/core/tests/ops.rs
index aa79dbac8f3..0c81cba35b3 100644
--- a/library/core/tests/ops.rs
+++ b/library/core/tests/ops.rs
@@ -232,3 +232,9 @@ fn deref_on_ref() {
     let y = deref(&mut x);
     assert_eq!(y, 4);
 }
+
+#[test]
+#[allow(unreachable_code)]
+fn test_not_never() {
+    if !return () {}
+}

From 9e834785787961646fd3951757b48d87f1afe6ef Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sun, 21 Nov 2021 19:06:35 -0800
Subject: [PATCH 2/4] impl Not for !

---
 library/core/src/ops/bit.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/library/core/src/ops/bit.rs b/library/core/src/ops/bit.rs
index 255f6cb7933..d9ce84541cf 100644
--- a/library/core/src/ops/bit.rs
+++ b/library/core/src/ops/bit.rs
@@ -68,6 +68,17 @@ macro_rules! not_impl {
 
 not_impl! { bool usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
 
+#[stable(feature = "not_never", since = "1.58.0")]
+#[rustc_const_unstable(feature = "const_ops", issue = "90080")]
+impl const Not for ! {
+    type Output = !;
+
+    #[inline]
+    fn not(self) -> ! {
+        match self {}
+    }
+}
+
 /// The bitwise AND operator `&`.
 ///
 /// Note that `Rhs` is `Self` by default, but this is not mandatory.

From 881e093f6d3c68caaad64fa28a5def6d308c52cd Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sun, 21 Nov 2021 19:30:17 -0800
Subject: [PATCH 3/4] Replace ! with * in ui test of unary expr reachability

---
 src/test/ui/reachable/expr_unary.rs     |  4 ++--
 src/test/ui/reachable/expr_unary.stderr | 10 +++++-----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/test/ui/reachable/expr_unary.rs b/src/test/ui/reachable/expr_unary.rs
index e229d22ebc7..190c7447dcc 100644
--- a/src/test/ui/reachable/expr_unary.rs
+++ b/src/test/ui/reachable/expr_unary.rs
@@ -5,8 +5,8 @@
 #![deny(unreachable_code)]
 
 fn foo() {
-    let x: ! = ! { return; }; //~ ERROR unreachable
-    //~| ERROR cannot apply unary operator `!` to type `!`
+    let x: ! = * { return; }; //~ ERROR unreachable
+    //~| ERROR type `!` cannot be dereferenced
 }
 
 fn main() { }
diff --git a/src/test/ui/reachable/expr_unary.stderr b/src/test/ui/reachable/expr_unary.stderr
index 063d841c25e..0a763087c6f 100644
--- a/src/test/ui/reachable/expr_unary.stderr
+++ b/src/test/ui/reachable/expr_unary.stderr
@@ -1,13 +1,13 @@
-error[E0600]: cannot apply unary operator `!` to type `!`
+error[E0614]: type `!` cannot be dereferenced
   --> $DIR/expr_unary.rs:8:16
    |
-LL |     let x: ! = ! { return; };
-   |                ^^^^^^^^^^^^^ cannot apply unary operator `!`
+LL |     let x: ! = * { return; };
+   |                ^^^^^^^^^^^^^
 
 error: unreachable expression
   --> $DIR/expr_unary.rs:8:16
    |
-LL |     let x: ! = ! { return; };
+LL |     let x: ! = * { return; };
    |                ^^^^------^^^
    |                |   |
    |                |   any code following this expression is unreachable
@@ -21,4 +21,4 @@ LL | #![deny(unreachable_code)]
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0600`.
+For more information about this error, try `rustc --explain E0614`.

From 3136c5f752837ce48d2e6cf1cc643929d294cfe0 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Wed, 19 Jan 2022 23:30:42 -0800
Subject: [PATCH 4/4] Update stabilization version of impl Not for !

---
 library/core/src/ops/bit.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/library/core/src/ops/bit.rs b/library/core/src/ops/bit.rs
index d9ce84541cf..7c664226fc2 100644
--- a/library/core/src/ops/bit.rs
+++ b/library/core/src/ops/bit.rs
@@ -68,7 +68,7 @@ macro_rules! not_impl {
 
 not_impl! { bool usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
 
-#[stable(feature = "not_never", since = "1.58.0")]
+#[stable(feature = "not_never", since = "1.60.0")]
 #[rustc_const_unstable(feature = "const_ops", issue = "90080")]
 impl const Not for ! {
     type Output = !;