Allow ! as the return type of proc/closure literals

Fixes #13490.

Author: ftxqxd

src/libsyntax/parse/parser.rs

@@ -4092,20 +4092,20 @@ impl<'a> Parser<'a> {
                 (optional_unboxed_closure_kind, args)
             }
         };
-        let output = if self.eat(&token::RARROW) {
-            self.parse_ty(true)
+        let (style, output) = if self.token == token::RARROW {
+            self.parse_ret_ty()
         } else {
-            P(Ty {
+            (Return, P(Ty {
                 id: ast::DUMMY_NODE_ID,
                 node: TyInfer,
                 span: self.span,
-            })
+            }))
         };
 
         (P(FnDecl {
             inputs: inputs_captures,
             output: output,
-            cf: Return,
+            cf: style,
             variadic: false
         }), optional_unboxed_closure_kind)
     }
@@ -4118,20 +4118,20 @@ impl<'a> Parser<'a> {
                                      seq_sep_trailing_allowed(token::COMMA),
                                      |p| p.parse_fn_block_arg());
 
-        let output = if self.eat(&token::RARROW) {
-            self.parse_ty(true)
+        let (style, output) = if self.token == token::RARROW {
+            self.parse_ret_ty()
         } else {
-            P(Ty {
+            (Return, P(Ty {
                 id: ast::DUMMY_NODE_ID,
                 node: TyInfer,
                 span: self.span,
-            })
+            }))
         };
 
         P(FnDecl {
             inputs: inputs,
             output: output,
-            cf: Return,
+            cf: style,
             variadic: false
         })
     }

src/test/run-pass/closure-syntax.rs

@@ -78,6 +78,10 @@ fn bar<'b>() {
 
     let a = A;
     a.foo::<<'a>||>();
+
+    // issue #13490
+    let _ = || -> ! loop {};
+    let _ = proc() -> ! loop {};
 }
 
 struct B<T>;