Import cql3 package and sub-packages

Contains the cql3 grammer and supporting classes, which will be converted
one by one.

From commit bf599fb5b062cbcc652da78b7d699e7a01b949ad.

cql3/AssignmentTestable.java

@@ -0,0 +1,72 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.cassandra.cql3;
+
+import java.util.Collection;
+
+public interface AssignmentTestable
+{
+    /**
+     * @return whether this object can be assigned to the provided receiver. We distinguish
+     * between 3 values: 
+     *   - EXACT_MATCH if this object is exactly of the type expected by the receiver
+     *   - WEAKLY_ASSIGNABLE if this object is not exactly the expected type but is assignable nonetheless
+     *   - NOT_ASSIGNABLE if it's not assignable
+     * Most caller should just call the isAssignable() method on the result, though functions have a use for
+     * testing "strong" equality to decide the most precise overload to pick when multiple could match.
+     */
+    public TestResult testAssignment(String keyspace, ColumnSpecification receiver);
+
+    public enum TestResult
+    {
+        EXACT_MATCH, WEAKLY_ASSIGNABLE, NOT_ASSIGNABLE;
+
+        public boolean isAssignable()
+        {
+            return this != NOT_ASSIGNABLE;
+        }
+
+        public boolean isExactMatch()
+        {
+            return this == EXACT_MATCH;
+        }
+
+        // Test all elements of toTest for assignment. If all are exact match, return exact match. If any is not assignable,
+        // return not assignable. Otherwise, return weakly assignable.
+        public static TestResult testAll(String keyspace, ColumnSpecification receiver, Collection<? extends AssignmentTestable> toTest)
+        {
+            TestResult res = EXACT_MATCH;
+            for (AssignmentTestable rt : toTest)
+            {
+                if (rt == null)
+                {
+                    res = WEAKLY_ASSIGNABLE;
+                    continue;
+                }
+
+                TestResult t = rt.testAssignment(keyspace, receiver);
+                if (t == NOT_ASSIGNABLE)
+                    return NOT_ASSIGNABLE;
+
+                if (t == WEAKLY_ASSIGNABLE)
+                    res = WEAKLY_ASSIGNABLE;
+            }
+            return res;
+        }
+    }
+}