From f344e1306618f388056056e5cc61e4bb2a796137 Mon Sep 17 00:00:00 2001
From: Kefu Chai <kefu.chai@scylladb.com>
Date: Sun, 14 Jan 2024 12:32:11 +0800
Subject: [PATCH] types: add formatter for data_value

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 a formatter for data_value, but its
its operator<<() is preserved as we are still using the generic
homebrew formatter for formatting std::vector, which in turn uses
operator<< of the element type.

Refs #13245

Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

Closes scylladb/scylladb#16767
---
 types/types.cc | 12 +++++++++---
 types/types.hh |  9 ++++++++-
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/types/types.cc b/types/types.cc
index edad9a623b..dad399f904 100644
--- a/types/types.cc
+++ b/types/types.cc
@@ -3679,11 +3679,17 @@ make_user_value(data_type type, user_type_impl::native_type value) {
     return data_value::make_new(std::move(type), std::move(value));
 }
 
-std::ostream& operator<<(std::ostream& out, const data_value& v) {
+ auto fmt::formatter<data_value>::format(const data_value& v,
+                                         fmt::format_context& ctx) const -> decltype(ctx.out()) {
     if (v.is_null()) {
-        return out << "null";
+        return fmt::format_to(ctx.out(), "null");
     }
-    return out << v.type()->to_string_impl(v);
+    return fmt::format_to(ctx.out(), "{}", v.type()->to_string_impl(v));
+}
+
+std::ostream& operator<<(std::ostream& out, const data_value& v) {
+    fmt::print(out, "{}", v);
+    return out;
 }
 
 shared_ptr<const reversed_type_impl> reversed_type_impl::get_instance(data_type type) {
diff --git a/types/types.hh b/types/types.hh
index 5336151876..a80997507e 100644
--- a/types/types.hh
+++ b/types/types.hh
@@ -269,7 +269,6 @@ public:
     friend class empty_type_impl;
     template <typename T> friend const T& value_cast(const data_value&);
     template <typename T> friend T&& value_cast(data_value&&);
-    friend std::ostream& operator<<(std::ostream&, const data_value&);
     friend data_value make_tuple_value(data_type, maybe_empty<std::vector<data_value>>);
     friend data_value make_set_value(data_type, maybe_empty<std::vector<data_value>>);
     friend data_value make_list_value(data_type, maybe_empty<std::vector<data_value>>);
@@ -1034,4 +1033,12 @@ struct fmt::formatter<data_value_or_unset> : fmt::formatter<std::string_view> {
     }
 };
 
+template <> struct fmt::formatter<data_value> {
+    constexpr auto parse(format_parse_context& ctx) { return ctx.begin(); }
+    auto format(const data_value&, fmt::format_context& ctx) const -> decltype(ctx.out());
+};
+
+std::ostream& operator<<(std::ostream& out, const data_value& v);
+
 using data_value_list = std::initializer_list<data_value_or_unset>;
+