feat: add refutation clause

CHANGES.md

@@ -7,6 +7,7 @@
 - Fix outcome printing of optional arguments on OCaml 5.2 (@anmonteiro, [#2753](https://github.com/reasonml/reason/pull/2753))
 - support parsing and printing of `external%extension` (@anmonteiro, [#2750](https://github.com/reasonml/reason/pull/2750))
 - install `refmt` manpage (@anmonteiro, [#2760](https://github.com/reasonml/reason/pull/2760))
+- add support for parsing / printing of refutation clause in `switch` (@anmonteiro, [#2765](https://github.com/reasonml/reason/pull/2765))
 
 ## 3.11.0
 

src/reason-parser/reason_parser.mly

@@ -3463,13 +3463,28 @@ letop_bindings:
 %inline match_cases(EXPR): lnonempty_list(match_case(EXPR)) { $1 };
 
 match_case(EXPR):
-  as_loc(BAR) pattern preceded(WHEN,expr)? EQUALGREATER EXPR
+  | as_loc(BAR) pattern EQUALGREATER EXPR
   { let pat = {$2 with ppat_loc =
       { $2.ppat_loc with
         loc_start = $1.loc.loc_start
       }
     } in
-    Ast_helper.Exp.case pat ?guard:$3 $5 }
+    Ast_helper.Exp.case pat $4 }
+  | as_loc(BAR) pattern preceded(WHEN,expr) EQUALGREATER EXPR
+  { let pat = {$2 with ppat_loc =
+      { $2.ppat_loc with
+        loc_start = $1.loc.loc_start
+      }
+    } in
+    Ast_helper.Exp.case pat ~guard:$3 $5 }
+  | as_loc(BAR) pattern EQUALGREATER as_loc(DOT)
+  {
+    let pat = {
+      $2 with ppat_loc =
+      { $2.ppat_loc with loc_start = $1.loc.loc_start }
+    } in
+    Ast_helper.Exp.(case pat (unreachable ~loc:$4.loc ()))
+  }
 ;
 
 fun_def(DELIM, typ):

src/reason-parser/reason_pprint_ast.ml

@@ -6483,6 +6483,7 @@ let printer = object(self:'self)
           let lhs = self#simple_enough_to_be_lhs_dot_send e in
           let lhs = if needparens then makeList ~wrap:("(",")") [lhs] else lhs in
           Some (label (makeList [lhs; atom "#";]) (atom s.txt))
+        | Pexp_unreachable -> Some (atom ".")
         | _ -> None
       in
       match item with

test/general-syntax-re.t/input.re

@@ -1282,3 +1282,5 @@ class y = {
 let x = 1G;
 let x = 1.123g;
 
+let x = switch () { | _ => .};
+

test/general-syntax-re.t/run.t

@@ -1467,3 +1467,8 @@ Format general implementation syntax
 
   let x = 1G;
   let x = 1.123g;
+
+  let x =
+    switch () {
+    | _ => .
+    };