utils/managed_bytes: add fmt::formatters for managed_bytes and friends

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

* managed_bytes
* managed_bytes_view
* managed_bytes_opt

Refs #13245

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

clustering_bounds_comparator.hh

@@ -153,6 +153,7 @@ public:
         return {typename R<clustering_key_prefix_view>::bound(bv._prefix.get().view(), inclusive)};
     }
     friend std::ostream& operator<<(std::ostream& out, const bound_view& b) {
-        return out << "{bound: prefix=" << b._prefix.get() << ", kind=" << b._kind << "}";
+        fmt::print(out, "{{bound: prefix={}, kind={}}}", b._prefix.get(), b._kind);
+        return out;
     }
 };

utils/managed_bytes.cc

@@ -28,16 +28,9 @@ managed_bytes_opt to_managed_bytes_opt(const bytes_opt& bo) {
 }
 
 sstring to_hex(const managed_bytes& b) {
-    return fmt::to_string(managed_bytes_view(b));
+    return seastar::format("{}", managed_bytes_view(b));
 }
 
 sstring to_hex(const managed_bytes_opt& b) {
     return !b ? "null" : to_hex(*b);
 }
-
-std::ostream& operator<<(std::ostream& os, const managed_bytes_opt& b) {
-    if (b) {
-        return os << *b;
-    }
-    return os << "null";
-}

utils/managed_bytes.hh

@@ -591,15 +591,36 @@ struct hash<managed_bytes> {
 sstring to_hex(const managed_bytes& b);
 sstring to_hex(const managed_bytes_opt& b);
 
-// The operators below are used only by tests.
-
-inline std::ostream& operator<<(std::ostream& os, const managed_bytes_view& v) {
-    for (bytes_view frag : fragment_range(v)) {
-        os << to_hex(frag);
+// The formatters below are used only by tests.
+template <> struct fmt::formatter<managed_bytes_view> : fmt::formatter<std::string_view> {
+    auto format(const managed_bytes_view& v, fmt::format_context& ctx) const {
+        auto out = ctx.out();
+        for (bytes_view frag : fragment_range(v)) {
+            out = fmt::format_to(out, "{}", fmt_hex(frag));
+        }
+        return out;
     }
+};
+inline std::ostream& operator<<(std::ostream& os, const managed_bytes_view& v) {
+    fmt::print(os, "{}", v);
     return os;
 }
+
+template <> struct fmt::formatter<managed_bytes> : fmt::formatter<std::string_view> {
+    auto format(const managed_bytes& b, fmt::format_context& ctx) const {
+        return fmt::format_to(ctx.out(), "{}", managed_bytes_view(b));
+    }
+};
 inline std::ostream& operator<<(std::ostream& os, const managed_bytes& b) {
-    return (os << managed_bytes_view(b));
+    fmt::print(os, "{}", b);
+    return os;
 }
-std::ostream& operator<<(std::ostream& os, const managed_bytes_opt& b);
+
+template <> struct fmt::formatter<managed_bytes_opt> : fmt::formatter<std::string_view> {
+    auto format(const managed_bytes_opt& opt, fmt::format_context& ctx) const {
+        if (opt) {
+            return fmt::format_to(ctx.out(), "{}", *opt);
+        }
+        return fmt::format_to(ctx.out(), "null");
+    }
+};