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b4fc711903
Even before this patch, Scylla supported the "empty" type (a column with
no content) but only internally - i.e., in code but not in CQL syntax.
The "empty" type was used in dense tables without regular columns, and a
special optimization in db::cql_type_parser::parse() allowed this type
name to be parsed when reading the schema tables, without allowing the
"empty" type to be used by users in CQL statements.
However, parse() only supported "empty" itself, and more complex types
like list<empty> were not recognized by parse(). In the following patches,
we plan to add to virtual columns to materialized views, with types empty,
list<empty> or map<something, empty>. We need all these types to work, and
before this patch, they don't. But we want all of these types to only work
internally - when Scylla's code creates these hidden columns; we do not
want to add the "empty" type to CQL's syntax.
This is what we do in this patch: The CQL parser's comparator_type rule
now has a parameter, "internal", used to differenciate internal calls
via db::cql_type_parser::parse() from calls from CQL query parsing.
If a user tries something like:
CREATE TABLE e (pk empty PRIMARY KEY);
He will get the error:
Invalid (reserved) user type name empty
Note that here, as usual, unknown types are treated as "user types",
and "empty" is not allowed as a user type name - we "reserve" it in case
one day in the future we will want to allow users a direct syntax to
create empty columns. We already have, following Cassandra, a bunch of
other names reserved from being user type names, including "byte",
"complex", and others (see _reserved_type_names()), and using "empty"
as a type name will result in a similar error message.
Just like all other type names, the name "empty" is not a reserved
keyword in other senses: a user can create a table or a column with
the name "empty", just like he can create one with the name "int".
Refs #3362.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>