this change change `const` to `constexpr`. because the string literal
defined here is not only immutable, but also initialized at
compile-time, and can be used by constexpr expressions and functions.
this change is introduced to reduce the size of the change when moving
to compile-time format string in future. so far, seastar::format() does
not use the compile-time format string, but we have patches pending on
review implementing this. and the author of this change has local
branches implementing the changes on scylla side to support compile-time
format string, which practically replaces most of the `format()` calls
with `seastar::format()`.
without this change, if we use compile-time format check, compiler fails
like:
```
/home/kefu/dev/scylladb/tools/scylla-nodetool.cc:276:44: error: call to consteval function 'fmt::basic_format_string<char, const char *const &, seastar::basic_sstring<char, unsigned int, 15>>::basic_format_string<const char *, 0>' is not a constant expression
.description = seastar::format(description_template, app_name, boost::algorithm::join(operations | boost::adaptors::transformed([] (const auto& op) {
^
/usr/include/fmt/core.h:3148:67: note: read of non-constexpr variable 'description_template' is not allowed in a constant expression
FMT_CONSTEVAL FMT_INLINE basic_format_string(const S& s) : str_(s) {
^
/home/kefu/dev/scylladb/tools/scylla-nodetool.cc:276:44: note: in call to 'basic_format_string(description_template)'
.description = seastar::format(description_template, app_name, boost::algorithm::join(operations | boost::adaptors::transformed([] (const auto& op) {
^
/home/kefu/dev/scylladb/tools/scylla-nodetool.cc:258:16: note: declared here
const auto description_template =
^
```
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#15432
1e6b2eb4c8