option always exists

google/cloud/opentelemetry_options.h

@@ -15,7 +15,6 @@
 #ifndef GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_OPENTELEMETRY_OPTIONS_H
 #define GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_OPENTELEMETRY_OPTIONS_H
 
-#ifdef GOOGLE_CLOUD_CPP_HAVE_OPENTELEMETRY
 #include "google/cloud/version.h"
 
 namespace google {
@@ -26,20 +25,33 @@ namespace experimental {
 /**
  * Enables tracing with [OpenTelemetry]
  *
- * Setting this option enables the *generation* of [traces] by the client
- * library. Note that it does not enable the *export* of traces.
+ * Setting this option enables the generation of [traces] by the client
+ * library. The library uses the global [tracer provider] to generate traces.
  *
- * The library uses the global [tracer provider] to generate traces. In order to
- * export the traces, the application must set the global tracer provider. The
- * client library recommends using
+ * @par Prerequisites
+ * The library must be compiled with OpenTelemetry in order for this option to
+ * take effect.
+ *
+ * @see [The OpenTelemetry tracing quickstart][gc-quickstart] for instructions
+ * on how to compile google-cloud-cpp with opentelemetry-cpp.
+ *
+ * @par Effect
+ * Setting this option enables the generation of [traces] by the client
+ * library. The library uses the global [tracer provider] to generate traces.
+ *
+ * @par Exporting traces
+ * Providing this option to a client only enables the *generation* of traces. It
+ * does not enable the *export* of traces.
+ *
+ * In order to export the traces, the application must set the global tracer
+ * provider. The client library recommends using
  * `#google::cloud::otel::ConfigureBasicTracing()` to configure the global
  * tracer provider. This will send the traces generated by the client library to
  * [Cloud Trace], Google Cloud's visualizer for distributed traces.
  *
- * @see [The OpenTelemetry tracing quickstart][gc-quickstart].
- *
  * @see [Google Cloud C++ OpenTelemetry reference docs][gc-otel-docs].
  *
+ * @par Environment variable
  * This option is controlled by the `GOOGLE_CLOUD_CPP_OPENTELEMETRY_TRACING`
  * environment variable. If the environment variable is set, tracing with
  * OpenTelemetry is enabled.
@@ -67,6 +79,5 @@ struct OpenTelemetryTracingOption {
 GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
 }  // namespace cloud
 }  // namespace google
-#endif  // GOOGLE_CLOUD_CPP_HAVE_OPENTELEMETRY
 
 #endif  // GOOGLE_CLOUD_CPP_GOOGLE_CLOUD_OPENTELEMETRY_OPTIONS_H