The schema module (everything in schema/) is supposed to be towards the
leafs in the ScyllaDB inter-module dependency graph. In other words, it
should not depend on many other modules. On the other hand, almost the
entire codebase depends on the schema module itself.
Currently there is a circular dependency between schema and
replica::database, as the latter is a required argument for
schema::describe(). This is bad, not just because of the dependency mess
it introduces, but also because now schema::describe() can only be used
by code which has a reference to the database handy.
This patch breaks this circular dependency, by introducing the
schema_describe_helper interface and providing an implementation for it
in database.hh.
There is another circular dependency: schema <-> replica::table. This is
not addressed by this patch.
Closesscylladb/scylladb#20893
86fd9ce8fd