Merge 'auth: replace operator<<(..) with fmt formatter' from Kefu Chai

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 `auth::auth_authentication_options` and `auth::resource_kind`
without the help of fmt::ostream. and their `operator<<(ostream,..)` are
dropped, as there are no users of them anymore.

Refs #13245

Closes #13460

* github.com:scylladb/scylladb:
  auth: remove unused operator<<(.., resource_kind)
  auth: specialize fmt::formatter<resource_kind>
  auth: remove unused operator<<(.., authentication_option)
  auth: specialize fmt::formatter<authentication_option>

auth/CMakeLists.txt

@@ -6,7 +6,6 @@ target_sources(scylla_auth
     allow_all_authenticator.cc
     allow_all_authorizer.cc
     authenticated_user.cc
-    authentication_options.cc
     authenticator.cc
     common.cc
     default_authorizer.cc

auth/authentication_options.hh

@@ -26,8 +26,6 @@ enum class authentication_option {
     options
 };
 
-std::ostream& operator<<(std::ostream&, authentication_option);
-
 using authentication_option_set = std::unordered_set<authentication_option>;
 
 using custom_options = std::unordered_map<sstring, sstring>;
@@ -49,3 +47,18 @@ public:
 };
 
 }
+
+template <>
+struct fmt::formatter<auth::authentication_option> : fmt::formatter<std::string_view> {
+    template <typename FormatContext>
+    auto format(const auth::authentication_option a, FormatContext& ctx) const {
+        using enum auth::authentication_option;
+        switch (a) {
+        case password:
+            return formatter<std::string_view>::format("PASSWORD", ctx);
+        case options:
+            return formatter<std::string_view>::format("OPTIONS", ctx);
+        }
+        std::abort();
+    }
+};

auth/resource.cc

@@ -25,17 +25,6 @@
 
 namespace auth {
 
-std::ostream& operator<<(std::ostream& os, resource_kind kind) {
-    switch (kind) {
-        case resource_kind::data: os << "data"; break;
-        case resource_kind::role: os << "role"; break;
-        case resource_kind::service_level: os << "service_level"; break;
-        case resource_kind::functions: os << "functions"; break;
-    }
-
-    return os;
-}
-
 static const std::unordered_map<resource_kind, std::string_view> roots{
         {resource_kind::data, "data"},
         {resource_kind::role, "roles"},

auth/resource.hh

@@ -41,8 +41,6 @@ enum class resource_kind {
     data, role, service_level, functions
 };
 
-std::ostream& operator<<(std::ostream&, resource_kind);
-
 ///
 /// Type tag for constructing data resources.
 ///
@@ -266,6 +264,25 @@ std::pair<sstring, std::vector<data_type>> decode_signature(std::string_view enc
 
 }
 
+template <>
+struct fmt::formatter<auth::resource_kind> : fmt::formatter<std::string_view> {
+    template <typename FormatContext>
+    auto format(const auth::resource_kind kind, FormatContext& ctx) const {
+        using enum auth::resource_kind;
+        switch (kind) {
+        case data:
+            return formatter<std::string_view>::format("data", ctx);
+        case role:
+            return formatter<std::string_view>::format("role", ctx);
+        case service_level:
+            return formatter<std::string_view>::format("service_level", ctx);
+        case functions:
+            return formatter<std::string_view>::format("functions", ctx);
+        }
+        std::abort();
+    }
+};
+
 namespace std {
 
 template <>

configure.py

@@ -990,7 +990,6 @@ def find_headers(repodir, excluded_dirs):
                 'auth/service.cc',
                 'auth/standard_role_manager.cc',
                 'auth/transitional.cc',
-                'auth/authentication_options.cc',
                 'auth/role_or_anonymous.cc',
                 'auth/sasl_challenge.cc',
                 'tracing/tracing.cc',

test/boost/auth_resource_test.cc

@@ -16,6 +16,15 @@
 
 #include "utils/to_string.hh"
 
+namespace auth {
+
+std::ostream& operator<<(std::ostream& os, resource_kind kind) {
+    fmt::print(os, "{}", kind);
+    return os;
+}
+
+}
+
 BOOST_AUTO_TEST_CASE(root_of) {
     //
     // data