Types like A|function(B) don't have enough parens in resulting TS

[mtaran-google]

/** @param {string|function(string)} foo */ gets changed to foo: string|(p1: string) => AnyDuringMigration, but it actually needs an extra set of parens around the function type, to parse correctly.

[stringham]

I have a fix for this, and can submit a PR later, but don't have time to write tests right now. I'll post the diff here and you're welcome to use it or not.

+import static com.google.javascript.rhino.Token.FUNCTION_TYPE;
+
 /** Code generator for gents to add TypeScript specific code generation. */
 public class GentsCodeGenerator extends CodeGenerator {
   private final NodeComments nodeComments;
@@ -84,6 +86,22 @@ public class GentsCodeGenerator extends CodeGenerator {
     return prev != null && prev.isEmpty() && nodeComments.hasComment(prev);
   }
 
+  void addUnionType(Node firstInList) {
+    for (Node n = firstInList; n != null; n = n.getNext()) {
+      boolean isFirst = n == firstInList;
+      if (!isFirst) {
+        add("|");
+      }
+      if(n.getToken() == FUNCTION_TYPE) {
+        add("(");
+        add(n);
+        add(")");
+      } else {
+        add(n);
+      }
+    }
+  }
+
   /**
    * Attempts to seize control of code generation if necessary.
    *
@@ -150,6 +168,9 @@ public class GentsCodeGenerator extends CodeGenerator {
           return true;
         }
         return false;
+      case UNION_TYPE:
+          addUnionType(n.getFirstChild());
+        return true;