Nadav Har'El cc69177dcc config: fix printing of experimental feature list ...

Recently we noticed a regression where with certain versions of the fmt
library,

   SELECT value FROM system.config WHERE name = 'experimental_features'

returns string numbers, like "5", instead of feature names like "raft".

It turns out that the fmt library keep changing their overload resolution
order when there are several ways to print something. For enum_option<T> we
happen to have to conflicting ways to print it:
  1. We have an explicit operator<<.
  2. We have an *implicit* convertor to the type held by T.

We were hoping that the operator<< always wins. But in fmt 8.1, there is
special logic that if the type is convertable to an int, this is used
before operator<<()! For experimental_features_t, the type held in it was
an old-style enum, so it is indeed convertible to int.

The solution I used in this patch is to replace the old-style enum
in experimental_features_t by the newer and more recommended "enum class",
which does not have an implicit conversion to int.

I could have fixed it in other ways, but it wouldn't have been much
prettier. For example, dropping the implicit convertor would require
us to change a bunch of switch() statements over enum_option (and
not just experimental_features_t, but other types of enum_option).

Going forward, all uses of enum_option should use "enum class", not
"enum". tri_mode_restriction_t was already using an enum class, and
now so does experimental_features_t. I changed the examples in the
comments to also use "enum class" instead of enum.

This patch also adds to the existing experimental_features test a
check that the feature names are words that are not numbers.

Fixes #11003.

Signed-off-by: Nadav Har'El <nyh@scylladb.com>

Closes #11004

2022-07-11 09:17:30 +02:00

68 KiB

Raw Blame History

View Raw