src: migrate to fmt::formattable for format support

Replace custom has_formatter concept with fmtlib's fmt::formattable

- Deprecate usage of fmt::has_formatter
- Resolve compiler warnings with recent fmtlib versions

The custom concept of has_formatter is no longer necessary with
recent updates to the fmtlib library, as fmt::formattable was introduced
in fmtlib v11.0.0. By switching to fmt::formattable, we simplify our
code and stop using the deprecated `fmt::has_formatter` template.

Signed-off-by: Kefu Chai <[email protected]>

Author: tchaikov

src/common/bitset_set.h

@@ -412,7 +412,7 @@ class bitset_set {
   }
 
   std::string fmt_print() const
-  requires has_formatter<KeyT> {
+  requires fmt::formattable<KeyT> {
     std::string s = "{";
     int c = (int)size();
     for (auto k : *this) {

src/common/fmt_common.h

@@ -2,7 +2,9 @@
 // vim: ts=8 sw=2 smarttab
 #pragma once
 
+#include <fmt/base.h>
 #include <optional>
+#include <type_traits>
 
 /**
  * \file default fmtlib formatters for specifically-tagged types
@@ -17,8 +19,13 @@
  * such classes in Crimson.
  */
 
-template <typename T>
-concept has_formatter = fmt::has_formatter<T, fmt::format_context>::value;
+#if FMT_VERSION < 110000
+// TODO: drop me once fmt v11 is required
+namespace fmt {
+  template <typename T, typename Char = char>
+  concept formattable = is_formattable<std::remove_reference_t<T>, Char>::value>;
+}
+#endif
 
 /**
  * Tagging classes that provide support for default fmtlib formatting,

src/common/interval_map.h

@@ -324,7 +324,7 @@ class interval_map {
   }
 
   std::string fmt_print() const
-  requires has_formatter<K> {
+  requires fmt::formattable<K> {
     std::string str = "{";
     bool first = true;
     for (auto &&i: *this) {

src/common/mini_flat_map.h

@@ -495,7 +495,7 @@ class mini_flat_map {
   }
 
   std::string fmt_print() const
-  requires has_formatter<KeyT> && has_formatter<ValueT> {
+  requires fmt::formattable<KeyT> && fmt::formattable<ValueT> {
     int c = (int)_size;
     std::string s = "{";
     for (auto&& [k, v] : *this) {

src/crimson/osd/scrub/scrub_machine.h

@@ -49,7 +49,7 @@ struct simple_event_t : sc::event<T> {
   }
 };
 
-template <typename T, has_formatter V>
+template <typename T, fmt::formattable V>
 struct value_event_t : sc::event<T> {
   const V value;
 

src/include/interval_set.h

@@ -263,7 +263,7 @@ class interval_set {
   }
 
   std::string fmt_print() const
-  requires has_formatter<T> {
+  requires fmt::formattable<T> {
     std::string s = "[";
     bool first = true;
     for (const auto& [start, len] : *this) {

src/osd/scrubber/scrub_machine.h

@@ -105,7 +105,7 @@ OP_EV(ReplicaReserveReq);
 /// explicit release request from the Primary
 OP_EV(ReplicaRelease);
 
-template <typename T, has_formatter V>
+template <typename T, fmt::formattable V>
 struct value_event_t : sc::event<T> {
   const V value;