From cb6c7bb9bf89660d07704f7f0fe29a76ac6fc32e Mon Sep 17 00:00:00 2001
From: Kefu Chai <kefu.chai@scylladb.com>
Date: Fri, 8 Mar 2024 11:15:09 +0800
Subject: [PATCH] service/paxos: add fmt::formatter for paxos::proposal

before this change, we rely on the default-generated fmt::formatter
created from operator<<, but fmt v10 dropped the default-generated
formatter.

in this change, we define formatters for `service::paxos::proposal`,
but its operator<< is preserved, as it is still used by our generic
formatter for std::tuple<> which uses operator<< for printing the
elements in it, so operator<< of this class is indirectly used.

Refs #13245

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
---
 service/paxos/proposal.cc | 12 +++---------
 service/paxos/proposal.hh | 18 +++++++++++++++---
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/service/paxos/proposal.cc b/service/paxos/proposal.cc
index aacd7b9ef2..1382f5c36c 100644
--- a/service/paxos/proposal.cc
+++ b/service/paxos/proposal.cc
@@ -9,13 +9,7 @@
 
 #include "proposal.hh"
 
-namespace service {
-
-namespace paxos {
-
-std::ostream& operator<<(std::ostream& os, const proposal& proposal) {
-    return os << "proposal(" << proposal.ballot << ")";
+auto fmt::formatter<service::paxos::proposal>::format(const service::paxos::proposal& proposal,
+                                                      fmt::format_context& ctx) const -> decltype(ctx.out()) {
+    return fmt::format_to(ctx.out(), "proposal({})", proposal.ballot);
 }
-
-} // end of namespace "paxos"
-} // endf of namespace "service"
diff --git a/service/paxos/proposal.hh b/service/paxos/proposal.hh
index 98ae12cb4d..2444b9a793 100644
--- a/service/paxos/proposal.hh
+++ b/service/paxos/proposal.hh
@@ -9,6 +9,7 @@
 #pragma once
 
 #include "mutation/frozen_mutation.hh"
+#include <fmt/core.h>
 
 namespace service {
 
@@ -45,8 +46,19 @@ inline bool operator>(const proposal& lhs, const proposal& rhs) {
     return lhs.ballot.timestamp() > rhs.ballot.timestamp();
 }
 
-// Used for logging and debugging.
-std::ostream& operator<<(std::ostream& os, const proposal& proposal);
-
 } // end of namespace "paxos"
 } // end of namespace "service"
+
+// Used for logging and debugging.
+template <> struct fmt::formatter<service::paxos::proposal> : fmt::formatter<std::string_view> {
+    auto format(const service::paxos::proposal&, fmt::format_context& ctx) const -> decltype(ctx.out());
+};
+
+namespace service::paxos {
+
+static inline std::ostream& operator<<(std::ostream& os, const proposal& proposal) {
+    fmt::print(os, "{}", proposal);
+    return os;
+}
+
+}