Auto merge of #47630 - canndrew:exhaustive-patterns, r=nikomatsakis

Stabilise feature(never_type). Introduce feature(exhaustive_patterns)

This stabilizes `!`, removing the feature gate as well as the old defaulting-to-`()` behavior. The pattern exhaustiveness checks which were covered by `feature(never_type)` have been moved behind a new `feature(exhaustive_patterns)` gate.

Author: bors

src/libcore/cmp.rs

@@ -882,24 +882,24 @@ 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 = "1.26.0")]
     impl PartialEq for ! {
         fn eq(&self, _: &!) -> bool {
             *self
         }
     }
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[stable(feature = "never_type", since = "1.26.0")]
     impl Eq for ! {}
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[stable(feature = "never_type", since = "1.26.0")]
     impl PartialOrd for ! {
         fn partial_cmp(&self, _: &!) -> Option<Ordering> {
             *self
         }
     }
 
-    #[unstable(feature = "never_type", issue = "35121")]
+    #[stable(feature = "never_type", since = "1.26.0")]
     impl Ord for ! {
         fn cmp(&self, _: &!) -> Ordering {
             *self

src/libcore/fmt/mod.rs

@@ -1711,14 +1711,14 @@ 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 = "1.26.0")]
 impl Debug for ! {
     fn fmt(&self, _: &mut Formatter) -> Result {
         *self
     }
 }
 
-#[unstable(feature = "never_type", issue = "35121")]
+#[stable(feature = "never_type", since = "1.26.0")]
 impl Display for ! {
     fn fmt(&self, _: &mut Formatter) -> Result {
         *self

src/libcore/lib.rs

@@ -85,7 +85,7 @@
 #![feature(iterator_repeat_with)]
 #![feature(lang_items)]
 #![feature(link_llvm_intrinsics)]
-#![feature(never_type)]
+#![feature(exhaustive_patterns)]
 #![feature(no_core)]
 #![feature(on_unimplemented)]
 #![feature(optin_builtin_traits)]
@@ -103,6 +103,7 @@
 #![feature(unwind_attributes)]
 
 #![cfg_attr(stage0, allow(unused_attributes))]
+#![cfg_attr(stage0, feature(never_type))]
 
 #[prelude_import]
 #[allow(unused)]

src/librustc/ich/impls_ty.rs

@@ -886,9 +886,8 @@ for ty::TypeVariants<'gcx>
             TyGeneratorWitness(types) => {
                 types.hash_stable(hcx, hasher)
             }
-            TyTuple(inner_tys, from_diverging_type_var) => {
+            TyTuple(inner_tys) => {
                 inner_tys.hash_stable(hcx, hasher);
-                from_diverging_type_var.hash_stable(hcx, hasher);
             }
             TyProjection(ref projection_ty) => {
                 projection_ty.hash_stable(hcx, hasher);

src/librustc/infer/canonical.rs

@@ -609,12 +609,6 @@ impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for Canonicalizer<'cx, 'gcx, 'tcx>
                 bug!("encountered a canonical type during canonicalization")
             }
 
-            // Replace a `()` that "would've fallen back" to `!` with just `()`.
-            ty::TyTuple(ref tys, true) => {
-                assert!(tys.is_empty());
-                self.tcx().mk_nil()
-            }
-
             ty::TyClosure(..)
             | ty::TyGenerator(..)
             | ty::TyGeneratorWitness(..)
@@ -634,7 +628,7 @@ impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for Canonicalizer<'cx, 'gcx, 'tcx>
             | ty::TyFnPtr(_)
             | ty::TyDynamic(..)
             | ty::TyNever
-            | ty::TyTuple(_, false)
+            | ty::TyTuple(..)
             | ty::TyProjection(..)
             | ty::TyForeign(..)
             | ty::TyParam(..)

src/librustc/infer/outlives/bounds.rs

@@ -151,7 +151,7 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
         // get solved *here*.
         match fulfill_cx.select_all_or_error(self) {
             Ok(()) => (),
-            Err(errors) => self.report_fulfillment_errors(&errors, None),
+            Err(errors) => self.report_fulfillment_errors(&errors, None, false),
         }
 
         implied_bounds

src/librustc/infer/resolve.rs

@@ -173,12 +173,6 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for FullTypeResolver<'a, 'gcx, 'tcx>
                 ty::TyInfer(_) => {
                     bug!("Unexpected type in full type resolver: {:?}", t);
                 }
-                ty::TyTuple(tys, true) => {
-                    // Un-default defaulted tuples - we are going to a
-                    // different infcx, and the default will just cause
-                    // pollution.
-                    self.tcx().intern_tup(tys, false)
-                }
                 _ => {
                     t.super_fold_with(self)
                 }

src/librustc/lib.rs

@@ -60,7 +60,7 @@
 #![feature(match_default_bindings)]
 #![feature(macro_lifetime_matcher)]
 #![feature(macro_vis_matcher)]
-#![feature(never_type)]
+#![feature(exhaustive_patterns)]
 #![feature(non_exhaustive)]
 #![feature(nonzero)]
 #![feature(proc_macro_internals)]

src/librustc/lint/builtin.rs

@@ -151,13 +151,6 @@ declare_lint! {
     "lints that have been renamed or removed"
 }
 
-declare_lint! {
-    pub RESOLVE_TRAIT_ON_DEFAULTED_UNIT,
-    Deny,
-    "attempt to resolve a trait on an expression whose type cannot be inferred but which \
-     currently defaults to ()"
-}
-
 declare_lint! {
     pub SAFE_EXTERN_STATICS,
     Deny,
@@ -237,12 +230,6 @@ declare_lint! {
     "detect mut variables which don't need to be mutable"
 }
 
-declare_lint! {
-    pub COERCE_NEVER,
-    Deny,
-    "detect coercion to !"
-}
-
 declare_lint! {
     pub SINGLE_USE_LIFETIME,
     Allow,
@@ -304,7 +291,6 @@ impl LintPass for HardwiredLints {
             INVALID_TYPE_PARAM_DEFAULT,
             CONST_ERR,
             RENAMED_AND_REMOVED_LINTS,
-            RESOLVE_TRAIT_ON_DEFAULTED_UNIT,
             SAFE_EXTERN_STATICS,
             SAFE_PACKED_BORROWS,
             PATTERNS_IN_FNS_WITHOUT_BODY,
@@ -318,7 +304,6 @@ impl LintPass for HardwiredLints {
             DEPRECATED,
             UNUSED_UNSAFE,
             UNUSED_MUT,
-            COERCE_NEVER,
             SINGLE_USE_LIFETIME,
             TYVAR_BEHIND_RAW_POINTER,
             ELIDED_LIFETIME_IN_PATH,

src/librustc/middle/mem_categorization.rs

@@ -1298,7 +1298,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
           PatKind::Tuple(ref subpats, ddpos) => {
             // (p1, ..., pN)
             let expected_len = match self.pat_ty(&pat)?.sty {
-                ty::TyTuple(ref tys, _) => tys.len(),
+                ty::TyTuple(ref tys) => tys.len(),
                 ref ty => span_bug!(pat.span, "tuple pattern unexpected type {:?}", ty),
             };
             for (i, subpat) in subpats.iter().enumerate_and_adjust(expected_len, ddpos) {