Revert "Stabilize the never_type, written !."

Nicholas Matsakis · Nicholas Matsakis · commit 96511ce5379e · 2019-12-14T07:50:10.000-05:00
This reverts commit 15c30dd.
diff --git a/src/libcore/clone.rs b/src/libcore/clone.rs
@@ -195,7 +195,7 @@ mod impls {
         bool char
     }
 
-    #[stable(feature = "never_type", since = "1.41.0")]
+    #[unstable(feature = "never_type", issue = "35121")]
     impl Clone for ! {
         #[inline]
         fn clone(&self) -> Self {
diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs
@@ -1141,24 +1141,24 @@ mod impls {
 
     ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
 
-    #[stable(feature = "never_type", since = "1.41.0")]
+    #[unstable(feature = "never_type", issue = "35121")]
     impl PartialEq for ! {
         fn eq(&self, _: &!) -> bool {
             *self
         }
     }
 
-    #[stable(feature = "never_type", since = "1.41.0")]
+    #[unstable(feature = "never_type", issue = "35121")]
     impl Eq for ! {}
 
-    #[stable(feature = "never_type", since = "1.41.0")]
+    #[unstable(feature = "never_type", issue = "35121")]
     impl PartialOrd for ! {
         fn partial_cmp(&self, _: &!) -> Option<Ordering> {
             *self
         }
     }
 
-    #[stable(feature = "never_type", since = "1.41.0")]
+    #[unstable(feature = "never_type", issue = "35121")]
     impl Ord for ! {
         fn cmp(&self, _: &!) -> Ordering {
             *self
diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
@@ -1940,14 +1940,14 @@ macro_rules! fmt_refs {
 
 fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
 
-#[stable(feature = "never_type", since = "1.41.0")]
+#[unstable(feature = "never_type", issue = "35121")]
 impl Debug for ! {
     fn fmt(&self, _: &mut Formatter<'_>) -> Result {
         *self
     }
 }
 
-#[stable(feature = "never_type", since = "1.41.0")]
+#[unstable(feature = "never_type", issue = "35121")]
 impl Display for ! {
     fn fmt(&self, _: &mut Formatter<'_>) -> Result {
         *self
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
@@ -87,7 +87,7 @@
 #![feature(iter_once_with)]
 #![feature(lang_items)]
 #![feature(link_llvm_intrinsics)]
-#![cfg_attr(bootstrap, feature(never_type))]
+#![feature(never_type)]
 #![feature(nll)]
 #![feature(exhaustive_patterns)]
 #![feature(no_core)]
diff --git a/src/libcore/marker.rs b/src/libcore/marker.rs
@@ -776,7 +776,7 @@ mod copy_impls {
         bool char
     }
 
-    #[stable(feature = "never_type", since = "1.41.0")]
+    #[unstable(feature = "never_type", issue = "35121")]
     impl Copy for ! {}
 
     #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
@@ -4731,7 +4731,7 @@ impl From<Infallible> for TryFromIntError {
     }
 }
 
-#[stable(feature = "never_type", since = "1.41.0")]
+#[unstable(feature = "never_type", issue = "35121")]
 impl From<!> for TryFromIntError {
     fn from(never: !) -> TryFromIntError {
         // Match rather than coerce to make sure that code like
diff --git a/src/librustc/lib.rs b/src/librustc/lib.rs
@@ -37,7 +37,7 @@
 #![feature(core_intrinsics)]
 #![feature(drain_filter)]
 #![cfg_attr(windows, feature(libc))]
-#![cfg_attr(bootstrap, feature(never_type))]
+#![feature(never_type)]
 #![feature(exhaustive_patterns)]
 #![feature(overlapping_marker_traits)]
 #![feature(extern_types)]
diff --git a/src/librustc_codegen_utils/lib.rs b/src/librustc_codegen_utils/lib.rs
@@ -8,7 +8,7 @@
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(core_intrinsics)]
-#![cfg_attr(bootstrap, feature(never_type))]
+#![feature(never_type)]
 #![feature(nll)]
 #![feature(in_band_lifetimes)]
 
diff --git a/src/librustc_error_codes/error_codes/E0725.md b/src/librustc_error_codes/error_codes/E0725.md
@@ -4,8 +4,8 @@ command line flags.
 Erroneous code example:
 
 ```ignore (can't specify compiler flags from doctests)
-#![feature(specialization)] // error: the feature `specialization` is not in
-                            // the list of allowed features
+#![feature(never_type)] // error: the feature `never_type` is not in
+                        // the list of allowed features
 ```
 
 Delete the offending feature attribute, or add it to the list of allowed
diff --git a/src/librustc_feature/accepted.rs b/src/librustc_feature/accepted.rs
@@ -253,8 +253,6 @@ declare_features! (
     (accepted, const_constructor, "1.40.0", Some(61456), None),
     /// Allows the use of `#[cfg(doctest)]`, set when rustdoc is collecting doctests.
     (accepted, cfg_doctest, "1.40.0", Some(62210), None),
-    /// Allows the `!` type. Does not imply 'exhaustive_patterns' any more.
-    (accepted, never_type, "1.41.0", Some(35121), None),
     /// Allows relaxing the coherence rules such that
     /// `impl<T> ForeignTrait<LocalType> for ForeignType<T>` is permitted.
     (accepted, re_rebalance_coherence, "1.41.0", Some(55437), None),
diff --git a/src/librustc_feature/active.rs b/src/librustc_feature/active.rs
@@ -307,6 +307,9 @@ declare_features! (
     /// Allows `X..Y` patterns.
     (active, exclusive_range_pattern, "1.11.0", Some(37854), None),
 
+    /// Allows the `!` type. Does not imply 'exhaustive_patterns' (below) any more.
+    (active, never_type, "1.13.0", Some(35121), None),
+
     /// Allows exhaustive pattern matching on types that contain uninhabited types.
     (active, exhaustive_patterns, "1.13.0", Some(51085), None),
 
diff --git a/src/librustc_mir/lib.rs b/src/librustc_mir/lib.rs
@@ -18,7 +18,7 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 #![feature(drain_filter)]
 #![feature(exhaustive_patterns)]
 #![feature(iter_order_by)]
-#![cfg_attr(bootstrap, feature(never_type))]
+#![feature(never_type)]
 #![feature(specialization)]
 #![feature(try_trait)]
 #![feature(unicode_internals)]
diff --git a/src/librustc_typeck/lib.rs b/src/librustc_typeck/lib.rs
@@ -67,7 +67,7 @@ This API is completely unstable and subject to change.
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
 #![feature(slice_patterns)]
-#![cfg_attr(bootstrap, feature(never_type))]
+#![feature(never_type)]
 
 #![recursion_limit="256"]
 
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
@@ -14,7 +14,7 @@
 #![feature(crate_visibility_modifier)]
 #![feature(const_fn)]
 #![feature(drain_filter)]
-#![cfg_attr(bootstrap, feature(never_type))]
+#![feature(never_type)]
 #![feature(unicode_internals)]
 
 #![recursion_limit="256"]
diff --git a/src/libserialize/lib.rs b/src/libserialize/lib.rs
@@ -11,7 +11,7 @@ Core encoding and decoding interfaces.
 #![feature(box_syntax)]
 #![feature(core_intrinsics)]
 #![feature(specialization)]
-#![cfg_attr(bootstrap, feature(never_type))]
+#![feature(never_type)]
 #![feature(nll)]
 #![feature(associated_type_bounds)]
 #![cfg_attr(test, feature(test))]
diff --git a/src/libstd/error.rs b/src/libstd/error.rs
@@ -465,7 +465,7 @@ impl<'a> From<Cow<'a, str>> for Box<dyn Error> {
     }
 }
 
-#[stable(feature = "never_type", since = "1.41.0")]
+#[unstable(feature = "never_type", issue = "35121")]
 impl Error for ! {
     fn description(&self) -> &str { *self }
 }
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
@@ -281,7 +281,7 @@
 #![feature(maybe_uninit_ref)]
 #![feature(maybe_uninit_slice)]
 #![feature(needs_panic_runtime)]
-#![cfg_attr(bootstrap, feature(never_type))]
+#![feature(never_type)]
 #![feature(nll)]
 #![cfg_attr(bootstrap, feature(on_unimplemented))]
 #![feature(optin_builtin_traits)]
diff --git a/src/libstd/primitive_docs.rs b/src/libstd/primitive_docs.rs
@@ -71,6 +71,7 @@ mod prim_bool { }
 /// write:
 ///
 /// ```
+/// #![feature(never_type)]
 /// # fn foo() -> u32 {
 /// let x: ! = {
 ///     return 123
@@ -200,6 +201,7 @@ mod prim_bool { }
 /// for example:
 ///
 /// ```
+/// #![feature(never_type)]
 /// # use std::fmt;
 /// # trait Debug {
 /// # fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result;
@@ -237,7 +239,7 @@ mod prim_bool { }
 /// [`Default`]: default/trait.Default.html
 /// [`default()`]: default/trait.Default.html#tymethod.default
 ///
-#[stable(feature = "never_type", since = "1.41.0")]
+#[unstable(feature = "never_type", issue = "35121")]
 mod prim_never { }
 
 #[doc(primitive = "char")]
diff --git a/src/libsyntax/feature_gate/check.rs b/src/libsyntax/feature_gate/check.rs
@@ -464,11 +464,25 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
             ast::TyKind::BareFn(ref bare_fn_ty) => {
                 self.check_extern(bare_fn_ty.ext);
             }
+            ast::TyKind::Never => {
+                gate_feature_post!(&self, never_type, ty.span,
+                                   "The `!` type is experimental");
+            }
             _ => {}
         }
         visit::walk_ty(self, ty)
     }
 
+    fn visit_fn_ret_ty(&mut self, ret_ty: &'a ast::FunctionRetTy) {
+        if let ast::FunctionRetTy::Ty(ref output_ty) = *ret_ty {
+            if let ast::TyKind::Never = output_ty.kind {
+                // Do nothing.
+            } else {
+                self.visit_ty(output_ty)
+            }
+        }
+    }
+
     fn visit_expr(&mut self, e: &'a ast::Expr) {
         match e.kind {
             ast::ExprKind::Box(_) => {
@@ -499,6 +513,10 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         visit::walk_expr(self, e)
     }
 
+    fn visit_arm(&mut self, arm: &'a ast::Arm) {
+        visit::walk_arm(self, arm)
+    }
+
     fn visit_pat(&mut self, pattern: &'a ast::Pat) {
         match &pattern.kind {
             PatKind::Slice(pats) => {

Original file line number	Diff line number	Diff line change
`@@ -195,7 +195,7 @@ mod impls {`
`195`	`195`	`bool char`
`196`	`196`	`}`
`197`	`197`
`198`		`- #[stable(feature = "never_type", since = "1.41.0")]`
	`198`	`+ #[unstable(feature = "never_type", issue = "35121")]`
`199`	`199`	`impl Clone for ! {`
`200`	`200`	`#[inline]`
`201`	`201`	`fn clone(&self) -> Self {`
Original file line number	Diff line number	Diff line change
`@@ -1141,24 +1141,24 @@ mod impls {`
`1141`	`1141`
`1142`	`1142`	`ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }`
`1143`	`1143`
`1144`		`- #[stable(feature = "never_type", since = "1.41.0")]`
	`1144`	`+ #[unstable(feature = "never_type", issue = "35121")]`
`1145`	`1145`	`impl PartialEq for ! {`
`1146`	`1146`	`fn eq(&self, _: &!) -> bool {`
`1147`	`1147`	`*self`
`1148`	`1148`	`}`
`1149`	`1149`	`}`
`1150`	`1150`
`1151`		`- #[stable(feature = "never_type", since = "1.41.0")]`
	`1151`	`+ #[unstable(feature = "never_type", issue = "35121")]`
`1152`	`1152`	`impl Eq for ! {}`
`1153`	`1153`
`1154`		`- #[stable(feature = "never_type", since = "1.41.0")]`
	`1154`	`+ #[unstable(feature = "never_type", issue = "35121")]`
`1155`	`1155`	`impl PartialOrd for ! {`
`1156`	`1156`	`fn partial_cmp(&self, _: &!) -> Option<Ordering> {`
`1157`	`1157`	`*self`
`1158`	`1158`	`}`
`1159`	`1159`	`}`
`1160`	`1160`
`1161`		`- #[stable(feature = "never_type", since = "1.41.0")]`
	`1161`	`+ #[unstable(feature = "never_type", issue = "35121")]`
`1162`	`1162`	`impl Ord for ! {`
`1163`	`1163`	`fn cmp(&self, _: &!) -> Ordering {`
`1164`	`1164`	`*self`
Original file line number	Diff line number	Diff line change
`@@ -1940,14 +1940,14 @@ macro_rules! fmt_refs {`
`1940`	`1940`
`1941`	`1941`	`fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }`
`1942`	`1942`
`1943`		`-#[stable(feature = "never_type", since = "1.41.0")]`
	`1943`	`+#[unstable(feature = "never_type", issue = "35121")]`
`1944`	`1944`	`impl Debug for ! {`
`1945`	`1945`	`fn fmt(&self, _: &mut Formatter<'_>) -> Result {`
`1946`	`1946`	`*self`
`1947`	`1947`	`}`
`1948`	`1948`	`}`
`1949`	`1949`
`1950`		`-#[stable(feature = "never_type", since = "1.41.0")]`
	`1950`	`+#[unstable(feature = "never_type", issue = "35121")]`
`1951`	`1951`	`impl Display for ! {`
`1952`	`1952`	`fn fmt(&self, _: &mut Formatter<'_>) -> Result {`
`1953`	`1953`	`*self`
Original file line number	Diff line number	Diff line change
`@@ -776,7 +776,7 @@ mod copy_impls {`
`776`	`776`	`bool char`
`777`	`777`	`}`
`778`	`778`
`779`		`- #[stable(feature = "never_type", since = "1.41.0")]`
	`779`	`+ #[unstable(feature = "never_type", issue = "35121")]`
`780`	`780`	`impl Copy for ! {}`
`781`	`781`
`782`	`782`	`#[stable(feature = "rust1", since = "1.0.0")]`
Original file line number	Diff line number	Diff line change
`@@ -4731,7 +4731,7 @@ impl From<Infallible> for TryFromIntError {`
`4731`	`4731`	`}`
`4732`	`4732`	`}`
`4733`	`4733`
`4734`		`-#[stable(feature = "never_type", since = "1.41.0")]`
	`4734`	`+#[unstable(feature = "never_type", issue = "35121")]`
`4735`	`4735`	`impl From<!> for TryFromIntError {`
`4736`	`4736`	`fn from(never: !) -> TryFromIntError {`
`4737`	`4737`	`// Match rather than coerce to make sure that code like`