How can I configure nvim-lspconfig & clangd to continue using my compile_commands.json after jumping to external definition?

[tomasgareau]

Background

Say I have a root directory containing a C project called my_project which depends on some external dependency foo outside the root directory. I've built my_project and generated a compile_commands.json file.

.
├── external/
│   └── foo/...
│
└── my_project/  # root dir
    ├── compile_commands.json
    └── src/
        └── main.c

Within my_project, LSP commands work great. The clangd instance picks up my compile_commands.json compilation database and is able to resolve any foo symbols. I can, for example, hover over functions from the external dependency foo and see their documentation. Great!

#include "foo.h"

int main(int argc, char** argv)
{
    int rc = foo_init();
    if (rc !=╭────────────────────────────────────────────────────────────────────────────────────────────╮
    {        │### function foo_init                                                                       │
        print│provided by "foo.h"                                                                         │
             │────────────────────────────────────────────────────────────────────────────────────────────│
    }        │→ uint32_t (aka unsigned int)                                                               │
}            │@brief Initialize foo client.                                                               │
             │@returns 0 if init successful. Otherwise an error code indicating problem.                  │
             │────────────────────────────────────────────────────────────────────────────────────────────│
             │uint32_t foo_init()                                                                         │
             ╰────────────────────────────────────────────────────────────────────────────────────────────╯

If I go-to-definition on foo_init, Neovim will jump to (for example) external/foo/include/foo.h. This will spawn a new LSP client with a root dir somewhere in my external dependency tree...

.
├── external/
│   └── foo/...  # LSP client 2 root dir: no compile_commands.json :(
│
└── my_project/  # LSP client 1 root dir
    ├── compile_commands.json
    └── src/
        └── main.c

...and this LSP client doesn't find any compile_commands.json (which makes sense -- the external dependency is just source code, no build artifacts). But this means I can't use LSP features to navigate this external dependency: all the compilation information that clangd requires for this is in my original my_project/compile_commands.json.

If I manually symlink my_project/compile_commands.json to external/compile_commands.json, then the second LSP instance does pick it up and I can navigate the external dependency using the compilation info from my_project.

Question

Is there a recommended approach to using compilation info in external dependencies? I'm not sure whether I'm supposed to:

• force nvim to only spawn a single client using my_project as a root, even for external code
• inform the second client that it should use the same compile_commands.json as my first client
• feed the external dependency into some LLM and ask it my questions instead haha

Related issues

This seems related to neovim/nvim-lspconfig#2287, which allowed using the same LSP server for a filetype if it exists, and neovim/nvim-lspconfig#2330, which disabled re-using the same server for multiple instances if the LSP server does not have the workspaceFolders server capability (which AFAIK clangd does not).