fix(config-inversion): preserve implementation versions from existing JSON

Author: genesor

supported-configurations.json

@@ -59,14 +59,14 @@
     "DD_PROPAGATION_STYLE_EXTRACT": [
       {
         "default": "datadog,tracecontext,baggage",
-        "implementation": "A",
+        "implementation": "C",
         "type": "array"
       }
     ],
     "DD_PROPAGATION_STYLE_INJECT": [
       {
         "default": "datadog,tracecontext,baggage",
-        "implementation": "A",
+        "implementation": "C",
         "type": "array"
       }
     ],
@@ -87,7 +87,7 @@
     "DD_SERVICE": [
       {
         "default": "",
-        "implementation": "A",
+        "implementation": "F",
         "type": "string"
       }
     ],
@@ -101,7 +101,7 @@
     "DD_SPAN_SAMPLING_RULES_FILE": [
       {
         "default": "",
-        "implementation": "A",
+        "implementation": "B",
         "type": "string"
       }
     ],
@@ -129,7 +129,7 @@
     "DD_TELEMETRY_HEARTBEAT_INTERVAL": [
       {
         "default": "10",
-        "implementation": "A",
+        "implementation": "D",
         "type": "decimal"
       }
     ],
@@ -206,21 +206,21 @@
     "DD_TRACE_PROPAGATION_STYLE": [
       {
         "default": "datadog,tracecontext,baggage",
-        "implementation": "A",
+        "implementation": "D",
         "type": "array"
       }
     ],
     "DD_TRACE_PROPAGATION_STYLE_EXTRACT": [
       {
         "default": "datadog,tracecontext,baggage",
-        "implementation": "A",
+        "implementation": "D",
         "type": "array"
       }
     ],
     "DD_TRACE_PROPAGATION_STYLE_INJECT": [
       {
         "default": "datadog,tracecontext,baggage",
-        "implementation": "A",
+        "implementation": "D",
         "type": "array"
       }
     ],
@@ -255,14 +255,14 @@
     "DD_TRACE_SAMPLE_RATE": [
       {
         "default": "1",
-        "implementation": "A",
+        "implementation": "C",
         "type": "decimal"
       }
     ],
     "DD_TRACE_SAMPLING_RULES": [
       {
         "default": "[]",
-        "implementation": "A",
+        "implementation": "D",
         "type": "array"
       }
     ],

tools/config-inversion/main.cpp

@@ -18,7 +18,23 @@ std::string to_string_any(const T& value) {
   return oss.str();
 }
 
-nlohmann::json build_configuration() {
+// Look up the existing implementation version for a config name from a
+// previously generated JSON. Returns "A" if not found.
+std::string existing_version(const nlohmann::json& existing,
+                             const std::string& name) {
+  if (existing.contains("supportedConfigurations")) {
+    const auto& sc = existing["supportedConfigurations"];
+    if (sc.contains(name) && sc[name].is_array() && !sc[name].empty()) {
+      const auto& first = sc[name][0];
+      if (first.contains("implementation")) {
+        return first["implementation"].get<std::string>();
+      }
+    }
+  }
+  return "A";
+}
+
+nlohmann::json build_configuration(const nlohmann::json& existing) {
   nlohmann::json j;
   j["version"] = "2";
 
@@ -33,7 +49,7 @@ nlohmann::json build_configuration() {
   do {                                                                     \
     auto obj = nlohmann::json::object();                                   \
     obj["default"] = to_string_any(DEFAULT_VALUE);                         \
-    obj["implementation"] = "A";                                           \
+    obj["implementation"] = existing_version(existing, QUOTED(NAME));      \
     {                                                                      \
       std::string type_str = QUOTED(TYPE);                                 \
       std::transform(type_str.begin(), type_str.end(), type_str.begin(),   \
@@ -70,7 +86,17 @@ int main(int argc, char** argv) {
 
   const fs::path output_file = result["output-file"].as<std::string>();
 
-  const auto j = build_configuration();
+  // Read existing file to preserve implementation versions.
+  nlohmann::json existing;
+  {
+    std::ifstream in(output_file);
+    if (in) {
+      existing = nlohmann::json::parse(in, nullptr, false);
+      if (existing.is_discarded()) existing = nlohmann::json::object();
+    }
+  }
+
+  const auto j = build_configuration(existing);
   std::ofstream file(output_file, std::ios::binary);
   if (!file) {
     std::cerr << "Unable to write configuration file";