Rstudio does not display correct C++ diagnostics; libclang error

Sure, here's the output of .rs.setClangDiagnostics(2)

.rs.setClangDiagnostics(2)
Attemping to load libclang for x86_64-w64-mingw32 
C:/Program Files/RStudio/bin/rsclang/x86_64/libclang.dll
   LOADED: 5.0.2
> 

Restarting R session...

CLANG INDEXING: C:/Users/Josh/Documents/test.cpp
C:/Program Files/RStudio/resources/libclang/builtin-headers/libc++/5.0.2\math.h:301:15: fatal error: 'math.h' file not found
  (Creating new index)
clang version 5.0.2 (tags/RELEASE_502/final)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: 
ignoring nonexistent directory "lib\clang\5.0.2\include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 10.0/VC/include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 9.0/VC/include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 9.0/VC/PlatformSDK/Include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 8/VC/include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 8/VC/PlatformSDK/Include"
#include "..." search starts here:
#include <...> search starts here:
 C:/Program Files/RStudio/resources/libclang/builtin-headers/5.0.2
 C:/Program Files/RStudio/resources/libclang/builtin-headers/libc++/5.0.2
 C:/PROGRA~1/R/R-35~1.1/include
 C:/Users/Josh/Documents/R/win-library/3.5/Rcpp/include
 C:/Users/Josh/Documents
End of search list.
C:/Users/Josh/Documents/test.cpp:6:12: error: member reference base type 'Rcpp::NumericVector' (aka 'int') is not a structure or union
TOTAL MEMORY: 22 mb (test.cpp)
PERFORMANCE 4415 ms (test.cpp)
CLANG INDEXING: C:/Users/Josh/Documents/test.cpp
CLANG REMOVE INDEX: C:/Users/Josh/Documents/test.cpp
  (Creating new index)
clang version 5.0.2 (tags/RELEASE_502/final)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: 
ignoring nonexistent directory "lib\clang\5.0.2\include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 10.0/VC/include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 9.0/VC/include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 9.0/VC/PlatformSDK/Include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 8/VC/include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 8/VC/PlatformSDK/Include"
#include "..." search starts here:
#include <...> search starts here:
 C:/Program Files/RStudio/resources/libclang/builtin-headers/5.0.2
 C:/Program Files/RStudio/resources/libclang/builtin-headers/libc++/5.0.2
 C:/PROGRA~1/R/R-35~1.1/include
 C:/Users/Josh/Documents/R/win-library/3.5/Rcpp/include
 C:/Users/Josh/Documents
End of search list.
C:/Users/Josh/Documents/test.cpp:6:12: error: member reference base type 'Rcpp::NumericVector' (aka 'int') is not a structure or union
TOTAL MEMORY: 22 mb (test.cpp)
PERFORMANCE 188 ms (test.cpp)
CLANG INDEXING: C:/Users/Josh/Documents/test.cpp
CLANG REMOVE INDEX: C:/Users/Josh/Documents/test.cpp
  (Creating new index)
clang version 5.0.2 (tags/RELEASE_502/final)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: 
ignoring nonexistent directory "lib\clang\5.0.2\include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 10.0/VC/include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 9.0/VC/include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 9.0/VC/PlatformSDK/Include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 8/VC/include"
ignoring nonexistent directory "C:/Program Files/Microsoft Visual Studio 8/VC/PlatformSDK/Include"
#include "..." search starts here:
#include <...> search starts here:
 C:/Program Files/RStudio/resources/libclang/builtin-headers/5.0.2
 C:/Program Files/RStudio/resources/libclang/builtin-headers/libc++/5.0.2
 C:/PROGRA~1/R/R-35~1.1/include
 C:/Users/Josh/Documents/R/win-library/3.5/Rcpp/include
 C:/Users/Josh/Documents
End of search list.
C:/Users/Josh/Documents/test.cpp:6:12: error: member reference base type 'Rcpp::NumericVector' (aka 'int') is not a structure or union
TOTAL MEMORY: 22 mb (test.cpp)
PERFORMANCE 179 ms (test.cpp)