Use forward declarations of prometheus-cpp types in telemetry::Manager

src/telemetry/Manager.cc

@@ -6,6 +6,8 @@
 
 // CivetServer is from the civetweb submodule in prometheus-cpp
 #include <CivetServer.h>
+#include <prometheus/exposer.h>
+#include <prometheus/registry.h>
 #include <rapidjson/document.h>
 #include <rapidjson/writer.h>
 #include <algorithm>
@@ -25,6 +27,10 @@ namespace zeek::telemetry {
 
 Manager::Manager() { prometheus_registry = std::make_shared<prometheus::Registry>(); }
 
+// This can't be defined as =default because of the use of unique_ptr with a forward-declared type
+// in Manager.h
+Manager::~Manager() {}
+
 void Manager::InitPostScript() {
     // Metrics port setting is used to calculate a URL for prometheus scraping
     std::string prometheus_url;

src/telemetry/Manager.h

@@ -2,8 +2,6 @@
 
 #pragma once
 
-#include <prometheus/exposer.h>
-#include <prometheus/registry.h>
 #include <condition_variable>
 #include <cstdint>
 #include <initializer_list>
@@ -24,6 +22,11 @@ class RecordVal;
 using RecordValPtr = IntrusivePtr<RecordVal>;
 } // namespace zeek
 
+namespace prometheus {
+class Exposer;
+class Registry;
+} // namespace prometheus
+
 namespace zeek::telemetry {
 
 /**
@@ -37,7 +40,7 @@ public:
 
     Manager& operator=(const Manager&) = delete;
 
-    ~Manager() = default;
+    ~Manager();
 
     /**
      * Initialization of the manager. This is called late during Zeek's