schema_tables: Add opaque context object

To allow carrying extensions and potentially more

db/schema_tables.cc

@@ -83,6 +83,23 @@ using namespace std::chrono_literals;
 
 /** system.schema_* tables used to store keyspace/table/type attributes prior to C* 3.0 */
 namespace db {
+
+schema_ctxt::schema_ctxt(const db::config& cfg)
+    : _extensions(cfg.extensions())
+{}
+
+schema_ctxt::schema_ctxt(const database& db)
+    : schema_ctxt(db.get_config())
+{}
+
+schema_ctxt::schema_ctxt(distributed<database>& db)
+    : schema_ctxt(db.local())
+{}
+
+schema_ctxt::schema_ctxt(distributed<service::storage_proxy>& proxy)
+    : schema_ctxt(proxy.local().get_db())
+{}
+
 namespace schema_tables {
 
 logging::logger slogger("schema_tables");

db/schema_tables.hh

@@ -54,6 +54,24 @@ class result_set;
 }
 
 namespace db {
+
+class extensions;
+class config;
+
+class schema_ctxt {
+public:
+    schema_ctxt(const config&);
+    schema_ctxt(const database&);
+    schema_ctxt(distributed<database>&);
+    schema_ctxt(distributed<service::storage_proxy>&);
+
+    const db::extensions& extensions() const {
+        return _extensions;
+    }
+private:
+    const db::extensions& _extensions;
+};
+
 namespace schema_tables {
 
 using schema_result = std::map<sstring, lw_shared_ptr<query::result_set>>;