Stabilize the `never_type`, written `!`.

src/libcore/clone.rs

@@ -185,7 +185,7 @@ mod impls {
         bool char
     }
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[stable(feature = "never_type", since = "1.41.0")]
     impl Clone for ! {
         #[inline]
         fn clone(&self) -> Self {

src/libcore/cmp.rs

@@ -1128,24 +1128,24 @@ mod impls {
 
     ord_impl! { char usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 }
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[stable(feature = "never_type", since = "1.41.0")]
     impl PartialEq for ! {
         fn eq(&self, _: &!) -> bool {
             *self
         }
     }
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[stable(feature = "never_type", since = "1.41.0")]
     impl Eq for ! {}
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[stable(feature = "never_type", since = "1.41.0")]
     impl PartialOrd for ! {
         fn partial_cmp(&self, _: &!) -> Option<Ordering> {
             *self
         }
     }
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[stable(feature = "never_type", since = "1.41.0")]
     impl Ord for ! {
         fn cmp(&self, _: &!) -> Ordering {
             *self

src/libcore/fmt/mod.rs

@@ -1935,14 +1935,14 @@ macro_rules! fmt_refs {
 
 fmt_refs! { Debug, Display, Octal, Binary, LowerHex, UpperHex, LowerExp, UpperExp }
 
-#[unstable(feature = "never_type", issue = "35121")]
+#[stable(feature = "never_type", since = "1.41.0")]
 impl Debug for ! {
     fn fmt(&self, _: &mut Formatter<'_>) -> Result {
         *self
     }
 }
 
-#[unstable(feature = "never_type", issue = "35121")]
+#[stable(feature = "never_type", since = "1.41.0")]
 impl Display for ! {
     fn fmt(&self, _: &mut Formatter<'_>) -> Result {
         *self

src/libcore/lib.rs

@@ -85,7 +85,7 @@
 #![feature(iter_once_with)]
 #![feature(lang_items)]
 #![feature(link_llvm_intrinsics)]
-#![feature(never_type)]
+#![cfg_attr(bootstrap, feature(never_type))]
 #![feature(nll)]
 #![feature(exhaustive_patterns)]
 #![feature(no_core)]

src/libcore/marker.rs

@@ -774,7 +774,7 @@ mod copy_impls {
         bool char
     }
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[stable(feature = "never_type", since = "1.41.0")]
     impl Copy for ! {}
 
     #[stable(feature = "rust1", since = "1.0.0")]

src/libcore/num/mod.rs

@@ -4728,7 +4728,7 @@ impl From<Infallible> for TryFromIntError {
     }
 }
 
-#[unstable(feature = "never_type", issue = "35121")]
+#[stable(feature = "never_type", since = "1.41.0")]
 impl From<!> for TryFromIntError {
     fn from(never: !) -> TryFromIntError {
         // Match rather than coerce to make sure that code like

src/librustc/lib.rs

@@ -36,7 +36,7 @@
 #![feature(core_intrinsics)]
 #![feature(drain_filter)]
 #![cfg_attr(windows, feature(libc))]
-#![feature(never_type)]
+#![cfg_attr(bootstrap, feature(never_type))]
 #![feature(exhaustive_patterns)]
 #![feature(overlapping_marker_traits)]
 #![feature(extern_types)]

src/librustc/ty/context.rs

@@ -2440,11 +2440,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
     #[inline]
     pub fn mk_diverging_default(self) -> Ty<'tcx> {
-        if self.features().never_type {
-            self.types.never
-        } else {
-            self.intern_tup(&[])
-        }
+        self.types.never
     }
 
     #[inline]

src/librustc_codegen_utils/lib.rs

@@ -8,7 +8,7 @@
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(core_intrinsics)]
-#![feature(never_type)]
+#![cfg_attr(bootstrap, feature(never_type))]
 #![feature(nll)]
 #![feature(in_band_lifetimes)]
 

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(never_type)] // error: the feature `never_type` is not in
-                        // the list of allowed features
+#![feature(specialization)] // error: the feature `specialization` is not in
+                            // the list of allowed features
 ```
 
 Delete the offending feature attribute, or add it to the list of allowed

src/librustc_mir/lib.rs

@@ -16,7 +16,7 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 #![feature(decl_macro)]
 #![feature(drain_filter)]
 #![feature(exhaustive_patterns)]
-#![feature(never_type)]
+#![cfg_attr(bootstrap, feature(never_type))]
 #![feature(specialization)]
 #![feature(try_trait)]
 #![feature(unicode_internals)]

src/librustc_typeck/check/mod.rs

@@ -3129,9 +3129,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     }
 
     // Tries to apply a fallback to `ty` if it is an unsolved variable.
-    // Non-numerics get replaced with ! or () (depending on whether
-    // feature(never_type) is enabled, unconstrained ints with i32,
-    // unconstrained floats with f64.
+    // Non-numerics get replaced with `!`, unconstrained ints with `i32`,
+    // unconstrained floats with `f64`.
     // Fallback becomes very dubious if we have encountered type-checking errors.
     // In that case, fallback to Error.
     // The return value indicates whether fallback has occurred.

src/librustc_typeck/lib.rs

@@ -66,7 +66,7 @@ This API is completely unstable and subject to change.
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
 #![feature(slice_patterns)]
-#![feature(never_type)]
+#![cfg_attr(bootstrap, feature(never_type))]
 
 #![recursion_limit="256"]
 

src/librustdoc/lib.rs

@@ -14,7 +14,7 @@
 #![feature(crate_visibility_modifier)]
 #![feature(const_fn)]
 #![feature(drain_filter)]
-#![feature(never_type)]
+#![cfg_attr(bootstrap, feature(never_type))]
 #![feature(unicode_internals)]
 
 #![recursion_limit="256"]

src/libserialize/lib.rs

@@ -11,7 +11,7 @@ Core encoding and decoding interfaces.
 #![feature(box_syntax)]
 #![feature(core_intrinsics)]
 #![feature(specialization)]
-#![feature(never_type)]
+#![cfg_attr(bootstrap, feature(never_type))]
 #![feature(nll)]
 #![feature(associated_type_bounds)]
 #![cfg_attr(test, feature(test))]

src/libstd/error.rs

@@ -465,7 +465,7 @@ impl<'a> From<Cow<'a, str>> for Box<dyn Error> {
     }
 }
 
-#[unstable(feature = "never_type", issue = "35121")]
+#[stable(feature = "never_type", since = "1.41.0")]
 impl Error for ! {
     fn description(&self) -> &str { *self }
 }

src/libstd/lib.rs

@@ -280,7 +280,7 @@
 #![feature(maybe_uninit_ref)]
 #![feature(maybe_uninit_slice)]
 #![feature(needs_panic_runtime)]
-#![feature(never_type)]
+#![cfg_attr(bootstrap, feature(never_type))]
 #![feature(nll)]
 #![cfg_attr(bootstrap, feature(on_unimplemented))]
 #![feature(optin_builtin_traits)]

src/libstd/primitive_docs.rs

@@ -71,7 +71,6 @@ mod prim_bool { }
 /// write:
 ///
 /// ```
-/// #![feature(never_type)]
 /// # fn foo() -> u32 {
 /// let x: ! = {
 ///     return 123
@@ -201,7 +200,6 @@ mod prim_bool { }
 /// for example:
 ///
 /// ```
-/// #![feature(never_type)]
 /// # use std::fmt;
 /// # trait Debug {
 /// # fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result;
@@ -239,7 +237,7 @@ mod prim_bool { }
 /// [`Default`]: default/trait.Default.html
 /// [`default()`]: default/trait.Default.html#tymethod.default
 ///
-#[unstable(feature = "never_type", issue = "35121")]
+#[stable(feature = "never_type", since = "1.41.0")]
 mod prim_never { }
 
 #[doc(primitive = "char")]

src/libsyntax/feature_gate/accepted.rs

@@ -253,6 +253,8 @@ 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),

src/libsyntax/feature_gate/active.rs

@@ -318,9 +318,6 @@ 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),
 

src/libsyntax/feature_gate/check.rs

@@ -521,25 +521,11 @@ 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(_) => {
@@ -567,10 +553,6 @@ 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) => {