Low Description
We do validate collection value types, but not collection key types, which allows counters to be used as map keys:
cqlsh> create keyspace test with replication = {'class': 'SimpleStrategy', 'replication_factor': 1};
cqlsh> use test;
cqlsh:test> create table test.test (id int primary key, amap map<counter, text>);
cqlsh:test> insert into test.test (id, amap) values (0, {1: '2'});
cqlsh:test> select * from test.test;
id | amap
----+----------
0 | {1: '2'}
(1 rows)
This should obviously not be allowed and must be rejected.
/cc slebresne