Auto merge of #35162 - canndrew:bang_type_coerced, r=nikomatsakis

Implement the `!` type

This implements the never type (`!`) and hides it behind the feature gate `#[feature(never_type)]`. With the feature gate off, things should build as normal (although some error messages may be different). With the gate on, `!` is usable as a type and diverging type variables (ie. types that are unconstrained by anything in the code) will default to `!` instead of `()`.

1 files changed, 3 insertions, 5 deletions

diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index e174f3ad08d..126e8816d05 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -1332,11 +1332,7 @@ impl<'a> Parser<'a> {
     /// Parse optional return type [ -> TY ] in function decl
     pub fn parse_ret_ty(&mut self) -> PResult<'a, FunctionRetTy> {
         if self.eat(&token::RArrow) {
-            if self.eat(&token::Not) {
-                Ok(FunctionRetTy::None(self.last_span))
-            } else {
-                Ok(FunctionRetTy::Ty(self.parse_ty()?))
-            }
+            Ok(FunctionRetTy::Ty(self.parse_ty()?))
         } else {
             let pos = self.span.lo;
             Ok(FunctionRetTy::Default(mk_sp(pos, pos)))
@@ -1399,6 +1395,8 @@ impl<'a> Parser<'a> {
             } else {
                 TyKind::Tup(ts)
             }
+        } else if self.eat(&token::Not) {
+            TyKind::Never
         } else if self.check(&token::BinOp(token::Star)) {
             // STAR POINTER (bare pointer?)
             self.bump();