ircd::db: Support future CanKeysWithDifferentByteContentsBeEqual feature.

include/ircd/db/comparator.h

@@ -35,6 +35,7 @@ struct ircd::db::comparator
 	std::function<bool (const string_view &, const string_view &)> equal;
 	std::function<void (std::string &, const string_view &)> separator;
 	std::function<void (std::string &)> successor;
+	bool hashable {true};
 };
 
 struct ircd::db::cmp_string_view

include/ircd/db/database/comparator.h

@@ -23,6 +23,7 @@ struct ircd::db::database::comparator final
 	database *d;
 	db::comparator user;
 
+	bool CanKeysWithDifferentByteContentsBeEqual() const noexcept; //TODO: override
 	bool IsSameLengthImmediateSuccessor(const Slice &s, const Slice &t) const noexcept override;
 	void FindShortestSeparator(std::string *start, const Slice &limit) const noexcept override;
 	void FindShortSuccessor(std::string *key) const noexcept override;

ircd/db.cc

@@ -1329,6 +1329,15 @@ const noexcept
 	return rocksdb::Comparator::IsSameLengthImmediateSuccessor(s, t);
 }
 
+bool
+ircd::db::database::comparator::CanKeysWithDifferentByteContentsBeEqual()
+const noexcept
+{
+	// When keys with different byte contents can be equal the keys are
+	// not hashable.
+	return !user.hashable;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 //
 // database::prefix_transform