nix flake: llvm 17 is retired

[ghuntley]

context

Onboarding for folks running NixOS is not smooth. Here's the default experience.

$ cd ~/work/boundaryml/baml
$ direnv allow .

direnv: loading ~/code/boundaryml/baml/.envrc
direnv: using flake
error:
       … while calling the 'derivationStrict' builtin
         at <nix/derivation-internal.nix>:37:12:
           36|
           37|   strict = derivationStrict drvAttrs;
             |            ^
           38|

       … while evaluating derivation 'nix-shell'
         whose name attribute is located at /nix/store/9v6qa656sq3xc58vkxslqy646p0ajj61-source/pkgs/stdenv/generic/make-derivation.nix:544:13

       … while evaluating attribute 'BINDGEN_EXTRA_CLANG_ARGS' of derivation 'nix-shell'
         at /nix/store/rgdhxcm6fzf2hjyc73cq3i6n1pd5rbka-source/flake.nix:777:13:
          776|             # UV_PYTHON = "${pythonEnv}/bin/python3"; // This doesn't work with maturin.
          777|             BINDGEN_EXTRA_CLANG_ARGS = if pkgs.stdenv.isDarwin then
             |             ^
          778|               "" # Rely on default includes provided by stdenv.cc + libclang

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: llvmPackages_17 has been removed, as it is unmaintained and obsolete
direnv: nix-direnv: Evaluating current devShell failed. Falling back to previous environment!

thoughts

• Is unpinned LLVM acceptable or should we move to 19 (or 19+)
• I note CONTRIBUTING.md references mise ala scripts/*.sh to bootstrap (bootstrapping rn so no feedback yet)

notes

• This is a simple version bump/unpin which hasn't been tested (raising and slapping CI with the change instead) generated via a low-effort Claude Code 'fix it' prompt.

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[entelligence-ai-pr-reviews]

correctness: pkgs.llvmPackages.libclang.version may not be defined or may not match the actual Clang version directory, causing incorrect include paths and build failures on non-Darwin systems.

🤖 AI Agent Prompt for Cursor/Windsurf

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In flake.nix, line 780, the code uses `${pkgs.llvmPackages.libclang.version}` to construct the Clang include path, but this attribute may not exist or may not match the actual Clang version directory, leading to build failures. Replace `${pkgs.llvmPackages.libclang.version}` with `${pkgs.llvmPackages.clang.version}` to ensure the include path matches the installed Clang version.

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Suggested change

	"-isystem ${pkgs.llvmPackages.libclang.lib}/lib/clang/${pkgs.llvmPackages.libclang.version}/include -isystem ${pkgs.llvmPackages.libclang.lib}/include -isystem ${pkgs.glibc.dev}/include";
	-isystem ${pkgs.llvmPackages.libclang.lib}/lib/clang/${pkgs.llvmPackages.clang.version}/include -isystem ${pkgs.llvmPackages.libclang.lib}/include -isystem ${pkgs.glibc.dev}/include";

[imalsogreg]

Thanks for this! I actually bumped dependencies in flake.nix and dropped the libclang_17 dep myself just a couple days ago. https://github.com/BoundaryML/baml/pull/2577/files

I'm curious if you are trying to use nix for your BAML apps? I just use this flake for local development of the BAML project, although I occasionally think about using nix to drive our packaging and deployment, as well as providing the baml-cli via nixpkgs.

[imalsogreg]

@ghuntley Are you having luck with canary:HEAD (our version of main)? If so I will close this PR.