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https://github.com/danielbarter/mini_compile_commands


https://github.com/danielbarter/mini_compile_commands

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README 

        
# Mini Compile Commands



Mini compile commands instruments the compiler wrappers in nixpkgs to generate `compile_commands.json` files. Using a version of nixpkgs after [this PR](https://github.com/NixOS/nixpkgs/pull/197937), it can be used in a `shell.nix` as follows:



```

with import  {};

let mcc-env = (callPackage  {}).wrap stdenv;

in (mkShell.override {stdenv = mcc-env;}) {

   buildInputs = [ cmake gtest ];

}

```



When the compiler is invoked, it will send a message to `mini_compile_commands_server.py`:



https://user-images.githubusercontent.com/8081722/192353380-5c417134-1cf5-4f60-97c1-386f24b0d4f7.mp4



## Mini Compile Commands and flakes



If your project is flake based, add `mini-compile-commands = { url = github:danielbarter/mini_compile_commands; flake = false;};` to your inputs and `mini-compile-commands` as an argument to your outputs. Then the above development shell output would be specified as



```

devShell.x86_64-linux =

  with import nixpkgs { system = "x86_64-linux"; };

  let mcc-env = (callPackage mini-compile-commands {}).wrap stdenv;

  in (mkShell.override {stdenv = mcc-env;}) {

    buildInputs = [ cmake gtest ];

  };

```



## Examples



Mini compile commands can be used to generate a `compile_commands.json` for the linux kernel:



```

nix-shell -E 'with import  {}; let mcc-env = (callPackage  {}).wrap stdenv; in linux.override { stdenv = mcc-env; }'

```



As demonstrated in the above video, create two shells. In one, run `mini_compile_commands_server.py compile_commands.json` and in the other, run `genericBuild`.



For certain packages (like those included in `python3Packages`), there is currently no easy way to override the standard environment. To use mini compile commands for these packages, we can override the standard environment for all nixpkgs as follows:



```

nix-build -E 'with import  { config.replaceStdenv = ({ pkgs }: (pkgs.callPackage  {}).wrap pkgs.stdenv);}; python3Packages.pybind11'

```



Warning: This requires a huge amount of rebuilding.



## Testing



There are tests for `gcc` and `clang` in `tests/gcc` and `tests/clang` respectively. In either of these directories, running `nix-shell` will generate a `compile_commands.json`. To test if things are working, open `test.cc` (make sure your editor can locate clangd) and try and jump into the `iostream` header.



## Build input hook



It is possible to use mini compile commands to generate a `compile_commands.json` while building a derivation. This involves using a wrapped standard standard environment and adding a hook to the `buildInputs`:

```

with import  {};

let mcc-env = (callPackage  {}).wrap stdenv;

    mcc-hook = (callPackage  {}).hook;

in (hello.override { stdenv = mcc-env; }).overrideAttrs

  (finalAttrs: previousAttrs: {

    buildInputs = (previousAttrs.buildInputs or []) ++ [ mcc-hook ];

  })

```

Running `nix-build` on this derivation will generate a `compile_commands.json` and move it into `$out`. As explained in [the compile commands specification](https://clang.llvm.org/docs/JSONCompilationDatabase.html), each entry contains a `directory` attribute which is the absolute path of the directory from which the compiler invocation occurred. To use this generated json with `clangd`, the source code needs to be located in the same place as during the nix build (typically `/build`). Since this is inconvenient, we recommend using mini compile commands interactively.