streaming: specialize fmt::formatter<stream_reason>

this is a part of a series to migrating from `operator<<(ostream&, ..)`
based formatting to fmtlib based formatting. the goal here is to enable
fmtlib to print `stream_reason` without the help of `operator<<`.

please note, because we still cannot use the generic formatter for
std::unordered_map provided by fmtlib, so in order to drop `operator<<`
for `stream_reason`, and to print `unordered_map<stream_reason>`,
`fmt::join()` is used as a temporary solution. we will audit all
`fmt::join()` calls, after removing the homebrew formatter of
`std::unordered_map`.

the corresponding `operator<<()` are dropped dropped in this change,
as all its callers are now using fmtlib for formatting now.

Refs #13245

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

Closes #13609

configure.py

@@ -969,7 +969,6 @@ scylla_core = (['message/messaging_service.cc',
                 'streaming/stream_manager.cc',
                 'streaming/stream_result_future.cc',
                 'streaming/stream_session_state.cc',
-                'streaming/stream_reason.cc',
                 'streaming/consumer.cc',
                 'clocks-impl.cc',
                 'partition_slice_builder.cc',

service/storage_service.cc

@@ -5016,7 +5016,7 @@ bool storage_service::is_repair_based_node_ops_enabled(streaming::stream_reason
         }
     }
     bool global_enabled = _db.local().get_config().enable_repair_based_node_ops();
-    slogger.info("enable_repair_based_node_ops={}, allowed_repair_based_node_ops={}", global_enabled, enabled_set);
+    slogger.info("enable_repair_based_node_ops={}, allowed_repair_based_node_ops={{{}}}", global_enabled, fmt::join(enabled_set, " ,"));
     return global_enabled && enabled_set.contains(reason);
 }
 

streaming/CMakeLists.txt

@@ -7,7 +7,6 @@ target_sources(streaming
     stream_coordinator.cc
     stream_manager.cc
     stream_plan.cc
-    stream_reason.cc
     stream_receive_task.cc
     stream_request.cc
     stream_result_future.cc

streaming/stream_reason.cc

@@ -1,27 +0,0 @@
-/*
- * Copyright (C) 2020-present ScyllaDB
- */
-
-/*
- * SPDX-License-Identifier: AGPL-3.0-or-later
- */
-
-#include "streaming/stream_reason.hh"
-#include <ostream>
-
-namespace streaming {
-
-std::ostream& operator<<(std::ostream& out, stream_reason r) {
-    switch (r) {
-	case stream_reason::unspecified: out << "unspecified"; break;
-	case stream_reason::bootstrap: out << "bootstrap"; break;
-	case stream_reason::decommission: out << "decommission"; break;
-	case stream_reason::removenode: out << "removenode"; break;
-	case stream_reason::rebuild: out << "rebuild"; break;
-	case stream_reason::repair: out << "repair"; break;
-	case stream_reason::replace: out << "replace"; break;
-    }
-    return out;
-}
-
-}

streaming/stream_reason.hh

@@ -9,7 +9,8 @@
 #pragma once
 
 #include <cstdint>
-#include <ostream>
+#include <string_view>
+#include <fmt/format.h>
 
 namespace streaming {
 
@@ -23,6 +24,29 @@ enum class stream_reason : uint8_t {
     replace,
 };
 
-std::ostream& operator<<(std::ostream& out, stream_reason r);
-
 }
+
+template <>
+struct fmt::formatter<streaming::stream_reason> : fmt::formatter<std::string_view> {
+    template <typename FormatContext>
+    auto format(const streaming::stream_reason& r, FormatContext& ctx) const {
+        using enum streaming::stream_reason;
+        switch (r) {
+        case unspecified:
+            return formatter<std::string_view>::format("unspecified", ctx);
+        case bootstrap:
+            return formatter<std::string_view>::format("bootstrap", ctx);
+        case decommission:
+            return formatter<std::string_view>::format("decommission", ctx);
+        case removenode:
+            return formatter<std::string_view>::format("removenode", ctx);
+        case rebuild:
+            return formatter<std::string_view>::format("rebuild", ctx);
+        case repair:
+            return formatter<std::string_view>::format("repair", ctx);
+        case replace:
+            return formatter<std::string_view>::format("replace", ctx);
+        }
+        std::abort();
+    }
+};