6917122: provide utility method to find the inner most type of a type tree

Reviewed-by: darcy, jjg
Contributed-by: mali@csail.mit.edu, mernst@cs.washington.edu

src/share/classes/com/sun/tools/javac/tree/Pretty.java

@@ -1152,20 +1152,7 @@ public class Pretty extends JCTree.Visitor {
 
     // Prints the inner element type of a nested array
     private void printBaseElementType(JCTree tree) throws IOException {
-        switch (tree.getTag()) {
-        case JCTree.TYPEARRAY:
-            printBaseElementType(((JCArrayTypeTree)tree).elemtype);
-            return;
-        case JCTree.WILDCARD:
-            printBaseElementType(((JCWildcard)tree).inner);
-            return;
-        case JCTree.ANNOTATED_TYPE:
-            printBaseElementType(((JCAnnotatedType)tree).underlyingType);
-            return;
-        default:
-            printExpr(tree);
-            return;
-        }
+        printExpr(TreeInfo.innermostType(tree));
     }
 
     // prints the brackets of a nested array in reverse order

src/share/classes/com/sun/tools/javac/tree/TreeInfo.java

@@ -891,4 +891,17 @@ public class TreeInfo {
             throw new AssertionError("Unexpected type tree: " + tree);
         }
     }
+
+    public static JCTree innermostType(JCTree type) {
+        switch (type.getTag()) {
+        case JCTree.TYPEARRAY:
+            return innermostType(((JCArrayTypeTree)type).elemtype);
+        case JCTree.WILDCARD:
+            return innermostType(((JCWildcard)type).inner);
+        case JCTree.ANNOTATED_TYPE:
+            return innermostType(((JCAnnotatedType)type).underlyingType);
+        default:
+            return type;
+        }
+    }
 }