fix(grainfmt): Correct formatting of nested constraints (#2245)

Author: spotandjake

compiler/src/formatting/fmt.re

@@ -258,6 +258,13 @@ let needs_grouping = (~parent, ~side: infix_side, expr) => {
   | (PExpConstant(PConstNumber(PConstNumberRational(_))), _)
       when op_precedence('/') <= precedence(parent) =>
     ParenGrouping
+  | (PExpConstraint(_, _), _)
+      when
+        switch (parent.pexp_desc) {
+        | PExpConstraint(_, _) => true
+        | _ => false
+        } =>
+    ParenGrouping
   | _ => FormatterGrouping
   };
 };

compiler/test/grainfmt/constraints.expected.gr

@@ -8,3 +8,8 @@ let test = test => {
     print(i)
   }, test: List<Number>)
 }
+
+// Regression #2244
+(1: Number): Number
+
+((1: Number): Number): Number

compiler/test/grainfmt/constraints.input.gr

@@ -8,3 +8,8 @@ let test = test => {
     print(i)
   }, test: List<Number>)
 }
+
+// Regression #2244
+(1: Number): Number
+
+((1: Number): Number): Number