refactor: FDv2Builder starts empty; add Default() for spec config

Author: beekld

libs/server-sdk/include/launchdarkly/server_side/config/builders/data_system/fdv2_builder.hpp

@@ -38,12 +38,22 @@ class FDv2Builder {
         std::optional<std::string> base_url_override_;
     };
 
+    /**
+     * Constructs a builder with no initializers, no synchronizers, and no
+     * FDv1 fallback. Use Default() for the spec-recommended configuration.
+     */
     FDv2Builder();
 
     /**
-     * @brief Appends a polling initializer to the initializers list. The
-     * first call to this method on a default-constructed builder replaces
-     * the spec-default initializer list; subsequent calls append.
+     * @return A builder pre-populated with the spec-recommended initializers,
+     *     synchronizers, and FDv1 fallback. Equivalent to calling
+     *     Initializer(), Synchronizer(), and FDv1Fallback() with the
+     *     standard sources.
+     */
+    static FDv2Builder Default();
+
+    /**
+     * @brief Appends a polling initializer to the initializers list.
      * @param source Polling source configuration for the initializer.
      * @return Reference to this.
      */
@@ -52,18 +62,15 @@ class FDv2Builder {
     /**
      * @brief Appends a streaming synchronizer to the synchronizers list.
      * Order in the list determines preference: the first entry is the
-     * primary synchronizer, subsequent entries are fallbacks. The first
-     * call to a Synchronizer overload on a default-constructed builder
-     * replaces the spec-default synchronizer list; subsequent calls append.
+     * primary synchronizer, subsequent entries are fallbacks.
      * @param source Streaming source configuration.
      * @return Reference to this.
      */
     FDv2Builder& Synchronizer(Streaming source);
 
     /**
      * @brief Appends a polling synchronizer to the synchronizers list. See
-     * Synchronizer(Streaming) for ordering and default-replacement
-     * semantics.
+     * Synchronizer(Streaming) for ordering semantics.
      * @param source Polling source configuration.
      * @return Reference to this.
      */
@@ -130,8 +137,6 @@ class FDv2Builder {
 
    private:
     built::FDv2Config config_;
-    bool initializers_explicit_;
-    bool synchronizers_explicit_;
 };
 
 }  // namespace launchdarkly::server_side::config::builders

libs/server-sdk/src/config/builders/data_system/fdv2_builder.cpp

@@ -45,33 +45,31 @@ built::FDv2Config::PollingConfig FDv2Builder::Polling::Build() const {
 }
 
 FDv2Builder::FDv2Builder()
-    : config_(Defaults::FDv2Config()),
-      initializers_explicit_(false),
-      synchronizers_explicit_(false) {}
+    : config_{{},
+              {},
+              std::nullopt,
+              std::chrono::minutes{2},
+              std::chrono::minutes{5}} {}
+
+FDv2Builder FDv2Builder::Default() {
+    return FDv2Builder()
+        .Initializer(Polling{})
+        .Synchronizer(Streaming{})
+        .Synchronizer(Polling{})
+        .FDv1Fallback(FDv1Streaming{});
+}
 
 FDv2Builder& FDv2Builder::Initializer(Polling source) {
-    if (!initializers_explicit_) {
-        config_.initializers.clear();
-        initializers_explicit_ = true;
-    }
     config_.initializers.push_back(source.Build());
     return *this;
 }
 
 FDv2Builder& FDv2Builder::Synchronizer(Streaming source) {
-    if (!synchronizers_explicit_) {
-        config_.synchronizers.clear();
-        synchronizers_explicit_ = true;
-    }
     config_.synchronizers.push_back(source.Build());
     return *this;
 }
 
 FDv2Builder& FDv2Builder::Synchronizer(Polling source) {
-    if (!synchronizers_explicit_) {
-        config_.synchronizers.clear();
-        synchronizers_explicit_ = true;
-    }
     config_.synchronizers.push_back(source.Build());
     return *this;
 }

libs/server-sdk/tests/config_builder_test.cpp

@@ -104,7 +104,7 @@ TEST_F(ConfigBuilderTest, CanSetPollingPayloadFilterKey) {
 
 TEST_F(ConfigBuilderTest, FDv2_DefaultsAreUsed) {
     ConfigBuilder builder("sdk-123");
-    builder.DataSystem().Method(builders::DataSystemBuilder::FDv2());
+    builder.DataSystem().Method(builders::DataSystemBuilder::FDv2::Default());
 
     auto cfg = builder.Build();