Clangd LSP shows unknown type name 'interface' in dsound.h

I just starting working on a Win32 application and I'm editing in Neovim. I'm running off WSL and using clangd as my LSP. To compile I'm using Microsoft cl and it's building the binary fine.

I was refactoring some code and I encountered a weird LSP error when moving my #include <dsound.h> from it's original main.cpp to a new header file (windows_sound.h). My LSP gave me the following complaint: clang: In included file: unknown type name 'interface'.

This error shows up even when it's the only thing in the file (without include guards). However, if I move the include into an empty .cpp (windows_sound.cpp) the LSP gives me no errors. Any idea what's going on?

My .clangd (which points to MingW64's windows header files):

CompileFlags:
    Add:
        - "--target=x86_64-w64-windows-gnu"
        - "-std=c++20"
        - "-fms-extensions"
        - "Wall"
        - "-isystem/usr/share/mingw-w64/include/"

My clangd version: 15.0.6

nvim version: 0.8.0-1210

The only additional thing I do in my config is I modified the clangd command to:

cmd =
{
    "clangd",
    "--header-insertion=never",
},

The error occuring in an .h but not in a .cpp file may indicate that clangd is treating the .h file as a C header rather than a C++ header.

One solution is to rename the header to .hpp which identifies it as a C++ header.

Another solution is to instruct clangd to parse .h files in your project as C++ headers by adding the following to a .clangd file in the project root:

If:
  PathMatch: .*\.h

CompileFlags:
  Add: [-xc++-header]

Clangd does have some heuristics to classify .h files as C++, e.g. if there is a file with the same name but a .cpp extension next to it, it will treat the .h file as C++. There are plans to expand this heuristic to consider actual inclusion relationships in the project (i.e. treat an .h file as C++ if any .cpp file in the project includes it), but until then one of the above two workarounds may be necessary.