C / C++ — LSP setup

Builtin server: clangd — clangd --background-index --clang-tidy
Extensions: .c .cpp .cc .cxx .c++ .h .hpp .hh .hxx .h++
Install hint: https://clangd.llvm.org/installation

Install

macOS: brew install llvm (clangd ships in the LLVM keg; add its bin to PATH)
Linux: apt install clangd (Debian/Ubuntu); use your distro package elsewhere
Windows: install LLVM from https://releases.llvm.org or winget install LLVM.LLVM

See https://clangd.llvm.org/installation for other platforms.

Confirm it resolves:

bash

command -v clangd

Configure

Builtin — usually NO config needed (auto-resolved by extension). Configure only to set priority, init options, override extensions, or disable. Same JSON shape in .codex/lsp-client.json (Codex) AND .opencode/lsp.json (OpenCode/omo):

json

{ "lsp": { "clangd": { "priority": 100 } } }

For builtin ids in a PROJECT config, command is supplied automatically — only set priority/initialization/extensions/disabled/env. A fully custom (non-builtin) server with its own command must go in the USER config (~/.codex/lsp-client.json).

Initialization options (only if commonly needed)

None commonly required. clangd reads flags from a project .clangd file rather than initializationOptions. The builtin command already passes --background-index --clang-tidy.

Compile commands

clangd needs a compile_commands.json at the project root (or in build/) for accurate diagnostics and cross-file navigation. Generate it with:

CMake: cmake -B build -DCMAKE_EXPORT_COMPILE_COMMANDS=ON (symlink/copy build/compile_commands.json to the root)
Make / other: bear -- make

Without it, clangd falls back to heuristic flags and reports spurious errors.

Alternatives

None builtin. ccls exists as a third-party server but is not builtin — it would need a custom command in the USER config.

Troubleshooting

PATH: clangd must be on PATH; reopen shell after install. Homebrew LLVM is keg-only — add $(brew --prefix llvm)/bin to PATH.
Spurious "file not found" / unknown flags: missing or stale compile_commands.json — regenerate it after changing the build.
Header-only diagnostics wrong: ensure the header's translation unit appears in the compile database, or add a .clangd CompileFlags block.

Verify

bash

bun ../../scripts/verify-lsp.ts path/to/file.cpp