Configuring clangd for flipper zero development

This is a guide on how to configure clangd for code completion and definition lookup for flipper app development on linux. I used LSP-Zero for my basic LSP setup and installed the clangd language server via Mason. How to set this up will not be covered in the guide.

The micro Flipper Build Tool (ufbt) can generate a configuration for vscode, but doesn’t come with instructions for setting up with nvim. UFBT can be used to set up a project for VSCode by running ufbt vscode_dist create APPID=myapp.

When opening the generated myapp.c file at this state, a lot of errors appear. The clangd language server doesn’t know where to look for the included files.

To fix this, we need to create two files in our project root:

1. compile_commands.json
2. .clangd

Starting with the compile_commands.json file. This is generated automatically when the project is built by running ufbt. Unfortunately, the file ends up in the .vscode folder, where clangd isn’t looking for it.

We can simply copy it to the project root by running cp .vscode/compile_commands.json compile_commands.json in the project root. Alternatively we symlink to it by running ln -s .vscode/compile_commands.json compile_commands.json. That way the current version is used if the file should ever change.

Now that we set up compile_commands.json, we should already get less errors.

Next we need to set up the .clangd file to configure the language server. We need to write the following lines into .clangd in the project root.

CompileFlags:
    Add: -I/home/<username>/.ufbt/toolchain/x86_64-linux/arm-none-eabi/include
    Compiler: /home/<username>/.ufbt/toolchain/x86_64-linux/bin/arm-none-eabi-gcc
    Remove: -mword-relocations

You will need to replace <username> with your username.

The Add: instruction will add the include directory compiler flag. This is a directory, where some important header files are located. In general, if clangd produces errors for import statements, this can mostly be fixed by finding and adding the directory the file is in (e.g. by using VSCode to jump to definition). To add a second include flag use the syntax: Add: [-I<firstpath>, -I<secondpath>]

The Compiler: instruction is a link to the compiler that ufbt uses under the hood. It is run by clangd with special flags to figure out where other important files are.

The -mword-relocations flag is produced by the ufbt build tool in the compile_commands.json file, but causes an error in the LSP. Therefore it is removed here with Remove:. However, it could also be removed by deleting the flag in the compile_commands.json file if it was copied before.

Note that the setup is local only to your project, requiring the .clangd and compile_comands.json to be at the project root. That’s why, if you’re looking at the header files of the flipper firmware, you end up getting errors again. However, code completion and all other lsp features should now be working for developing your own flipper zero app.