JCBC-960: Expression method to wrap in parenthesis

Motivation
----------
Often, N1QL statements will need to explicitly define evaluation order
by using parenthesis. There is currently no method to do that and one
as to fallback to string concatenation inside of an x() call.

Modifications
-------------
Added the `par()` method that infixes an Expression inside parenthesis.

Result
------
Better looking wrapping of Expression in parenthesis.

Change-Id: Ia35ac8266e54a3ecc4e439c2f0a809a83312283d
Reviewed-on: http://review.couchbase.org/64210
Tested-by: Simon Baslé <simon@couchbase.com>
Reviewed-by: Michael Nitschinger <michael@nitschinger.at>

src/main/java/com/couchbase/client/java/query/dsl/Expression.java

@@ -173,6 +173,16 @@ public static Expression sub(final Statement statement) {
         return x("(" + statement.toString() + ")");
     }
 
+    /**
+     * Puts an {@link Expression} in parenthesis.
+     *
+     * @param expression the expression to wrap in parenthesis.
+     * @return the expression, wrapped in parenthesis.
+     */
+    public static Expression par(final Expression expression) {
+        return infix(expression.toString(), "(", ")");
+    }
+
     /**
      * Construct a path ("a.b.c") from Expressions or values. Strings are considered identifiers
      * (so they won't be quoted).

src/test/java/com/couchbase/client/java/query/dsl/ExpressionTest.java

@@ -22,6 +22,7 @@
 import org.junit.Test;
 
 import static com.couchbase.client.java.query.dsl.Expression.i;
+import static com.couchbase.client.java.query.dsl.Expression.par;
 import static com.couchbase.client.java.query.dsl.Expression.s;
 import static com.couchbase.client.java.query.dsl.Expression.x;
 import static org.junit.Assert.assertEquals;
@@ -197,4 +198,11 @@ public void shouldAcceptArithmeticOperationsForAllKindOfNumbers() {
         assertEquals("1 / user.id / user.age / 1 / 100 / 2.3 / 4.5", divide.toString());
     }
 
+    @Test
+    public void shouldWrapExpressionInParenthesis() {
+        Expression base = x("foo").eq(x("bar"));
+
+        assertEquals("( foo = bar )", par(base).toString());
+    }
+
 }