Remove RMM logger CMake targets and use forward declaration (#343)

Remove RMM logger CMake targets that are unused by UCXX, and thus prevent unnecessary linking to spdlog/fmt. Use a forward declaration for `rmm::device_buffer` to avoid symbols being added to the symbol table.

Authors:
  - Peter Andreas Entschev (https://github.com/pentschev)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)
  - Lawrence Mitchell (https://github.com/wence-)

URL: #343

cpp/CMakeLists.txt

@@ -188,8 +188,7 @@ target_compile_definitions(
 # Enable RMM if necessary
 if(UCXX_ENABLE_RMM)
     target_link_libraries(ucxx
-      PUBLIC rmm::rmm rmm::rmm_logger
-      PRIVATE rmm::rmm_logger_impl
+      PUBLIC rmm::rmm
     )
 
     # Define spdlog level

cpp/include/ucxx/buffer.h

@@ -9,9 +9,10 @@
 
 #include <ucxx/log.h>
 
-#if UCXX_ENABLE_RMM
-#include <rmm/device_buffer.hpp>
-#endif
+namespace rmm {
+// Forward declaration to prevent symbols from being added to symbol table unnecessarily.
+class device_buffer;
+}  // namespace rmm
 
 namespace ucxx {
 

cpp/tests/buffer.cpp

@@ -11,6 +11,10 @@
 
 #include <ucxx/api.h>
 
+#if UCXX_ENABLE_RMM
+#include <rmm/device_buffer.hpp>
+#endif
+
 namespace {
 
 class BufferAllocator : public ::testing::Test,

cpp/tests/request.cpp

@@ -20,6 +20,10 @@
 #include "ucxx/constructors.h"
 #include "ucxx/utils/ucx.h"
 
+#if UCXX_ENABLE_RMM
+#include <rmm/device_buffer.hpp>
+#endif
+
 namespace {
 
 using ::testing::Combine;