Better formatting of Pexp_lazy

formatTest/typeCheckedTests/expected_output/lazy.re

@@ -1,9 +1,9 @@
 let myComputation =
-  lazy {
+  lazy({
     let tmp = 10;
     let tmp2 = 20;
     tmp + tmp2;
-  };
+  });
 
 type myRecord = {myRecordField: int};
 
@@ -14,18 +14,25 @@ let operateOnLazyValue = (lazy {myRecordField}) => {
 
 let result =
   operateOnLazyValue(
-    lazy {myRecordField: 100},
+    lazy({myRecordField: 100}),
   );
 
 type box('a) =
   | Box('a);
 
-let lazy thisIsActuallyAPatternMatch = lazy 200;
+let lazy thisIsActuallyAPatternMatch = lazy(200);
 let tmp: int = thisIsActuallyAPatternMatch;
 let (lazy (Box(i)), x) = (
-  lazy (Box(200)),
+  lazy(Box(200)),
   100,
 );
 let tmp: int = i;
 
-let myComputation = lazy 200;
+let myComputation = lazy(200);
+
+let reallyLoooooooooooooongIdentifierThatSpansMoreThan50Cols = 200;
+
+let foo =
+  lazy(
+    reallyLoooooooooooooongIdentifierThatSpansMoreThan50Cols
+  );

formatTest/typeCheckedTests/input/lazy.re

@@ -21,3 +21,7 @@ let (lazy (Box(i)), x) = (lazy (Box(200)), 100);
 let tmp: int = i;
 
 let myComputation = lazy (200);
+
+let reallyLoooooooooooooongIdentifierThatSpansMoreThan50Cols = 200;
+
+let foo = lazy(reallyLoooooooooooooongIdentifierThatSpansMoreThan50Cols)

formatTest/unit_tests/expected_output/modules_no_semi.re

@@ -645,7 +645,7 @@ let test = b => {
 
   assert(true);
 
-  lazy true;
+  lazy(true);
 
   Fun.ignore();
 };

src/reason-parser/reason_pprint_ast.ml

@@ -1794,20 +1794,20 @@ let partitionFinalWrapping listTester wrapFinalItemSetting x =
 let semiTerminated term = makeList [term; atom ";"]
 
 (* postSpace is so that when comments are interleaved, we still use spacing rules. *)
-let makeLetSequence letItems =
+let makeLetSequence ?(wrap=("{", "}")) letItems =
   makeList
     ~break:Always_rec
     ~inline:(true, false)
-    ~wrap:("{", "}")
+    ~wrap
     ~postSpace:true
     ~sep:(SepFinal (";", ";"))
     letItems
 
-let makeLetSequenceSingleLine letItems =
+let makeLetSequenceSingleLine ?(wrap=("{", "}")) letItems =
   makeList
     ~break:IfNeed
     ~inline:(true, false)
-    ~wrap:("{", "}")
+    ~wrap
     ~preSpace:true
     ~postSpace:true
     ~sep:(Sep ";")
@@ -5796,7 +5796,16 @@ let printer = object(self:'self)
                 (makeTup [(self#unparseExpr e)]);
             )
           | Pexp_lazy e ->
-              Some (label ~space:true (atom "lazy") (self#simplifyUnparseExpr e))
+            let lazy_atom = atom "lazy" in
+            let layout_right = match e with
+            | {pexp_desc = Pexp_let _} ->
+              makeLetSequence ~wrap:("({", "})") (self#letList e)
+            | e when isSingleArgParenApplication [e] ->
+              self#singleArgParenApplication [e]
+            | _ ->
+              formatPrecedence (self#unparseExpr e)
+            in
+            Some (label lazy_atom layout_right)
           | Pexp_poly _ ->
             failwith (
               "This version of the pretty printer assumes it is impossible to " ^