Improve functor printing.

HISTORY.md

@@ -1,5 +1,6 @@
 ## 3.9 (unreleased)
 
+- Reduce the amount of parentheses around functor usage. [#2683](https://github.com/reasonml/reason/pull/2683)
 - Print module type body on separate line (@SanderSpies) [#2709](https://github.com/reasonml/reason/pull/2709)
 - Fix missing patterns around contraint pattern (a pattern with a type annotation).
 - Fix top level extension printing

src/reason-parser/reason_pprint_ast.ml

@@ -1033,7 +1033,7 @@ let makeList
   let config =
     { Layout.
       listConfigIfCommentsInterleaved; listConfigIfEolCommentsInterleaved;
-      break; wrap; inline; sep; indent; sepLeft; preSpace; postSpace; pad;
+      break = if lst = [] then Layout.IfNeed else break; wrap; inline; sep; indent; sepLeft; preSpace; postSpace; pad;
     }
   in
   Layout.Sequence (config, lst)
@@ -2942,7 +2942,7 @@ let printer = object(self:'self)
       | (Ptype_variant lst, scope, None) -> [
           privatize scope
             [makeList
-              ~break:(if lst == [] then IfNeed else Always_rec)
+              ~break:Always_rec
               ~postSpace:true
               ~inline:(true, true)
               (self#type_variant_list lst)]
@@ -5060,7 +5060,7 @@ let printer = object(self:'self)
     | { pmod_desc = Pmod_functor(fp, me2) } ->
         let firstOne =
           match fp with
-            | Unit -> atom "()"
+            | Unit -> atom ""
             | Named (s, mt') ->
               let s = moduleIdent s in
               self#module_type (makeList [atom s; atom ":"]) mt'
@@ -7541,7 +7541,12 @@ let printer = object(self:'self)
         in
         formatPrecedence (self#module_type letPattern mt)
     | Pmod_structure s ->
-        let wrap = if hug then ("({", "})") else ("{", "}") in
+        let wrap = if hug then
+          if List.length s = 0 then 
+            ("(", ")") 
+          else 
+            ("({", "})")
+        else ("{", "}") in
         let items =
           groupAndPrint
             ~xf:self#structure_item
@@ -7558,7 +7563,7 @@ let printer = object(self:'self)
           items
     | _ ->
         (* For example, functor application will be wrapped. *)
-        formatPrecedence (self#module_expr x)
+        formatPrecedence ~wrap:("", "") (self#module_expr x)
 
   method module_expr x =
     match x.pmod_desc with

test/extensions.t/run.t

@@ -4,9 +4,7 @@ Format extensions
 
   [%extend open M];
 
-  [%extend
-    module M = {}
-  ];
+  [%extend module M = {}];
 
   [%extend module type M = {}];
 

test/modules.t/input.re

@@ -487,4 +487,16 @@ module type Event = (module type of {
 include (Version2: (module type of Version2));
 
 /* https://github.com/facebook/reason/issues/2608 */
-module Functor = (()): (module type of {}) => {};
+module Functor = (): (module type of {}) => {};
+
+module Lola1 = () => {
+  let a = 3;
+}
+
+module Lola2 = (C: Cat, D: Dog, L: Lion) => {
+  let a = 33;
+}
+
+module L = Lola1();
+
+module L2 = Lola2(Cat, Dog, Foo);

test/modules.t/run.t

@@ -324,12 +324,7 @@ Format modules
     );
 
   module ResultFromNonSimpleFunctorArg =
-    CurriedNoSugar(
-      (
-        MakeAModule({})
-      ),
-      BMod,
-    );
+    CurriedNoSugar(MakeAModule(), BMod);
 
   /* TODO: Functor type signatures should more resemble value signatures */
   let curriedFunc: (int, int) => int =
@@ -451,7 +446,7 @@ Format modules
            G: (Type) => Type,
            X: Type,
          ) =>
-    F((G(X)));
+    F(G(X));
   let l: Compose(List)(Maybe)(Char).t = [
     Some('a'),
   ];
@@ -657,7 +652,17 @@ Format modules
   include (Version2: (module type of Version2));
 
   /* https://github.com/facebook/reason/issues/2608 */
-  module Functor =
-         (())
-         : (module type of {}) => {};
+  module Functor = () : (module type of {}) => {};
+
+  module Lola1 = () => {
+    let a = 3;
+  };
+
+  module Lola2 = (C: Cat, D: Dog, L: Lion) => {
+    let a = 33;
+  };
+
+  module L = Lola1();
+
+  module L2 = Lola2(Cat, Dog, Foo);
 /* From http://stackoverflow.com/questions/1986374/  higher-order-type-constructors-and-functors-in-ocaml */

test/modules_no_semi.t/run.t

@@ -324,12 +324,7 @@ Format modules no semi
     );
 
   module ResultFromNonSimpleFunctorArg =
-    CurriedNoSugar(
-      (
-        MakeAModule({})
-      ),
-      BMod,
-    );
+    CurriedNoSugar(MakeAModule(), BMod);
 
   /* TODO: Functor type signatures should more resemble value signatures */
   let curriedFunc: (int, int) => int =
@@ -451,7 +446,7 @@ Format modules no semi
            G: (Type) => Type,
            X: Type,
          ) =>
-    F((G(X)));
+    F(G(X));
   let l: Compose(List)(Maybe)(Char).t = [
     Some('a'),
   ];