The system.config virtual tables prints each configuration variable of
type T based on the JSON printer specified in the config_type_for<T>
in db/config.cc.
For two variable types - experimental_features and tri_mode_restriction,
the specified converter was wrong: We used value_to_json<string> or
value_to_json<vector<string>> on something which was *not* a string.
Unfortunately, value_to_json silently casted the given objects into
strings, and the result was garbage: For example as noted in #10047,
for experimental_features instead of printing a list of features *names*,
e.g., "raft", we got a bizarre list of one-byte strings with each feature's
number (which isn't documented or even guaranteed to not change) as well
as carriage-return characters (!?).
So solution is a new printable_to_json<T> which works on a type T that
can be printed with operator<< - as in fact the above two types can -
and the type is converted into a string or vector of strings using this
operator<<, not a cast.
Also added a cql-pytest test for reading system.config and in particular
options of the above two types - checking that they contain sensible
strings and not "garbage" like before this patch.
Fixes#10047.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20220209090421.298849-1-nyh@scylladb.com>
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