[OCaml] Fix infix operator definition

Fixes sublimehq#1756

This commit partly applies the proposed change of the mentioned issue
to fix infix operator definitions as it seems safe enough not to break
something.

OCaml/OCaml.sublime-syntax

@@ -516,11 +516,14 @@ contexts:
     - include: variables
     - include: main
   module-signature:
-    - match: '(val)\s+([a-z_][a-zA-Z0-9_'']*)\s*(:)'
+    - match: '(val)\s+(?:([a-z_][a-zA-Z0-9_'']*)|(\()([^\s)]+)(\)))\s*(:)'
       captures:
         1: keyword.other.ocaml
         2: entity.name.type.value-signature.ocaml
-        3: punctuation.separator.type-constraint.ocaml
+        3: punctuation.section.parens.begin.ocaml
+        4: entity.name.type.value-signature.ocaml
+        5: punctuation.section.parens.end.ocaml
+        6: punctuation.separator.type-constraint.ocaml
       push:
         - meta_scope: meta.module.signature.val.ocaml
         - match: (?=\b(type|val|external|class|module|end)\b)|^\s*$

OCaml/syntax_test_ml.ml

@@ -25,6 +25,37 @@
 (*^^^ keyword.other.ocaml *)
 (*    ^^^^ variable.other.constant.ocaml *)
 
+(* Module Signatures *)
+
+  val foo   : 'a -> 'a
+(*^^^^^^^^^^^^^^^^^^^^^ meta.module.signature.val.ocaml *)
+(*^^^ keyword.other.ocaml *)
+(*    ^^^ entity.name.type.value-signature.ocaml *)
+(*          ^ punctuation.separator.type-constraint.ocaml *)
+(*            ^^ storage.type.ocaml *)
+(*               ^^ punctuation.separator.function-return.ocaml *)
+(*                  ^^ storage.type.ocaml *)
+
+  val (<*<) : 'a -> 'a
+(*^^^^^^^^^^^^^^^^^^^^^ meta.module.signature.val.ocaml *)
+(*^^^ keyword.other.ocaml *)
+(*    ^ punctuation.section.parens.begin.ocaml *)
+(*     ^^^ entity.name.type.value-signature.ocaml *)
+(*        ^ punctuation.section.parens.end.ocaml *)
+(*          ^ punctuation.separator.type-constraint.ocaml *)
+(*            ^^ storage.type.ocaml *)
+(*               ^^ punctuation.separator.function-return.ocaml *)
+(*                  ^^ storage.type.ocaml *)
+
+  val bar   : 'a -> 'a
+(*^^^^^^^^^^^^^^^^^^^^^ meta.module.signature.val.ocaml *)
+(*^^^ keyword.other.ocaml *)
+(*    ^^^ entity.name.type.value-signature.ocaml *)
+(*          ^ punctuation.separator.type-constraint.ocaml *)
+(*            ^^ storage.type.ocaml *)
+(*               ^^ punctuation.separator.function-return.ocaml *)
+(*                  ^^ storage.type.ocaml *)
+
 
 (* Integers *)