neovim + clangd Unknown argument: '-fno-reorder-functions'

[cbrake]

I'm using Neovim with clangd language server -- it is generally working great. The build process generates compile_commands.json and .clang-format is provided -- very well done!

I am seeing one issue where -fno-reorder-functions is is passed as an argument to GCC. This causes the following error in Neovim, generated by the clangd language server:

Unknown argument: '-fno-reorder-functions'

This is enabled in CMakeLists.txt:

if(NOT CMAKE_C_COMPILER_ID STREQUAL "Clang" AND
   NOT CMAKE_C_COMPILER_ID STREQUAL "IntelLLVM" AND
   NOT CMAKE_C_COMPILER_ID STREQUAL "ARMClang")
  # GCC assumed
  zephyr_cc_option(-fno-reorder-functions)

  # GCC 11 and above may generate a warning when dereferencing a constant
  # address pointer whose address is below the value specified by the
  # `min-pagesize` parameter (defaults to 0x1000). The `min-pagesize` parameter
  # is set to 0 such that GCC never generates any warnings for the constant
  # address pointers. For more details, refer to the GCC PR99578.
  zephyr_cc_option(--param=min-pagesize=0)

  if(NOT ${ZEPHYR_TOOLCHAIN_VARIANT} STREQUAL "xcc")
    zephyr_cc_option(-fno-defer-pop)
  endif()
else()
  # Clang produces false positive vla warnings
  zephyr_cc_option(-Wno-vla)
endif()

So we are using GCC to build and Clangd for the language server, and it appears not all arguments are compatible. What is the best solution to this?

[cbrake]

From clangd/clangd#662

adding the following to a .clangd config file removed this error.

CompileFlags:
  Add: -Wno-unknown-warning-option
  Remove: [-m*, -f*]

Would it make sense to add this .clangd file to the zephyr repo?

[cbrake]

I see this is already ignored by in .gitignore so I guess it is up to users to find solutions like this -- perhaps because .clangd is needed for user-specific settings. Maybe it would make more sense to document things like this or provide a sample .clangd file with common fixes.

[kraj]

From clangd/clangd#662

adding the following to a .clangd config file removed this error.

CompileFlags:
  Add: -Wno-unknown-warning-option
  Remove: [-m*, -f*]

Would it make sense to add this .clangd file to the zephyr repo?
-fno-reorder-functions is gcc specific option which is not available in llvm/clang and thats what its complaining about.
I think it would be good to support clangd language server but unless thats supported adding a .clangd file maybe not a good thing to do as it wont be tested regularly, so maybe adding a CI step to test use of clangd and then appropriate .clangd file might be a long term maintainable solution.

[szczys]

Thanks for the clangd pointers! Since this is an issue for every Zephyr project I open, I solved this at the system-wide level:

1. Create directory in the Linux config home

   $ mkdir -p ~/.config/clangd
   

2. Add ~/.config/clangd/config.yml file and populate it with the workaround for the error

   CompileFlags:
     Add: -Wno-unknown-warning-option
     Remove: [-m*, -f*]