Two-body Interactions (QED)

.gitignore

@@ -64,4 +64,9 @@ action-token
 ignore-*
 tombi/
 tidy/
-.claude
+.claude
+.understand-anything
+
+# devenv
+.devenv*
+devenv.local.nix

CODEGUIDE.md

@@ -16,7 +16,7 @@ entity
 │   ├── styling.cmake            #   styling functions
 │   └── tests.cmake              #   root cmake for tests
 ├── dev                          # developer-specific tools
-│   ├── nix                      #   nix-shells
+│   ├── nix                      #   nix-shell & devenv environments
 │   ├── runners                  #   dockerfiles for github runners on different architectures
 │   ├── scripts                  #   developer-specific scripts
 │   ├── Dockerfile.common        #   parent docker environment for development

dev/nix/adios2.nix

@@ -39,6 +39,7 @@ stdenv.mkDerivation {
   ];
 
   propagatedBuildInputs = [
+    pkgs.libgcc
     pkgs.gcc15
   ]
   ++ (

dev/nix/devenv.lock

@@ -0,0 +1,45 @@
+{
+  "nodes": {
+    "devenv": {
+      "locked": {
+        "dir": "src/modules",
+        "lastModified": 1789340509,
+        "narHash": "sha256-It2AD16uFwiAe9GvuLbk+j+qTDrQxT3XPclL71ZnJ3I=",
+        "owner": "cachix",
+        "repo": "devenv",
+        "rev": "6e830506b517d6a373f2dec6ee8c7f4683908856",
+        "type": "github"
+      },
+      "original": {
+        "dir": "src/modules",
+        "owner": "cachix",
+        "repo": "devenv",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1789286504,
+        "narHash": "sha256-eiEK7cKZORNEvX0GeF3RtNEF/JXhgf2RqSp3230q13E=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "ef34387ddd751e1ab8857adf4676492d32eb24ec",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "devenv": "devenv",
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

dev/nix/devenv.nix

@@ -0,0 +1,173 @@
+# devenv counterpart of `shell.nix`; run from this directory:
+#   devenv shell                                            # cpu-only
+#   devenv shell -P cuda -O entity.arch:string AMPERE80      # cuda
+#   devenv shell -P hip -O entity.arch:string AMD_GFX90A     # hip
+#   devenv shell -P mpi -P hdf5                              # adios2 with mpi + hdf5
+# persistent settings can be put into `devenv.local.nix` (gitignored).
+{
+  pkgs,
+  lib,
+  config,
+  inputs,
+  ...
+}:
+
+let
+  cfg = config.entity;
+
+  gpu = lib.toUpper cfg.gpu;
+  arch = lib.toUpper cfg.arch;
+
+  # `shell.nix` imports nixpkgs with `allowUnfree`/`cudaSupport` decided by the
+  # requested backend. devenv instantiates its own `pkgs` before this module is
+  # evaluated, so it cannot be reconfigured from here -- import the same input
+  # ourselves and build everything from that instance.
+  nixpkgs = import inputs.nixpkgs {
+    inherit (pkgs.stdenv.hostPlatform) system;
+    config = {
+      allowUnfree = true;
+      cudaSupport = gpu == "CUDA";
+    };
+  };
+
+  adios2Pkg = nixpkgs.callPackage ./adios2.nix {
+    pkgs = nixpkgs;
+    inherit (cfg) hdf5 mpi;
+  };
+
+  kokkosPkg = nixpkgs.callPackage ./kokkos.nix {
+    pkgs = nixpkgs;
+    stdenv = nixpkgs.stdenv;
+    inherit arch gpu;
+  };
+
+  extraPkgs = map (name: nixpkgs.${name}) (lib.filter (s: s != "") (lib.splitString "," cfg.extra));
+
+  # compilers are picked by the backend; CUDA goes through kokkos' nvcc_wrapper
+  compilerEnv =
+    {
+      NONE = {
+        CXX = "g++";
+        CC = "gcc";
+      };
+      HIP = {
+        CXX = "clang++";
+        CC = "clang";
+      };
+      CUDA = { };
+    }
+    .${gpu};
+in
+{
+  options.entity = {
+    gpu = lib.mkOption {
+      # case-insensitive, as in `shell.nix`
+      type = lib.types.enum [
+        "NONE"
+        "none"
+        "CUDA"
+        "cuda"
+        "HIP"
+        "hip"
+      ];
+      default = "NONE";
+      description = "GPU backend to build Kokkos with.";
+    };
+
+    arch = lib.mkOption {
+      type = lib.types.str;
+      default = "NATIVE";
+      example = "AMPERE80";
+      description = ''
+        Kokkos architecture; mandatory when `gpu` is not `NONE`. See
+        https://kokkos.org/kokkos-core-wiki/get-started/configuration-guide.html#gpu-architectures
+      '';
+    };
+
+    hdf5 = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = "Build ADIOS2 with HDF5 support.";
+    };
+
+    mpi = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = "Build ADIOS2 with MPI support.";
+    };
+
+    extra = lib.mkOption {
+      type = lib.types.str;
+      default = "";
+      example = "gdb,valgrind";
+      description = ''
+        Comma-separated nixpkgs attributes to add to the environment, kept for
+        parity with `shell.nix`. `-O packages:pkgs "gdb valgrind"` does the same
+        without going through this option.
+      '';
+    };
+  };
+
+  config = {
+    name =
+      "nt2" + (if gpu != "NONE" then "-${lib.toLower gpu}" else "") + (if cfg.mpi then "-mpi" else "");
+
+    profiles = {
+      cuda.module = {
+        entity.gpu = "CUDA";
+      };
+      hip.module = {
+        entity.gpu = "HIP";
+      };
+      mpi.module = {
+        entity.mpi = true;
+      };
+      hdf5.module = {
+        entity.hdf5 = true;
+      };
+    };
+
+    packages =
+      (with nixpkgs; [
+        zlib
+        cmake
+
+        adios2Pkg
+        kokkosPkg
+
+        python314
+
+        cmake-format
+        cmake-lint
+        neocmakelsp
+        black
+        pyright
+        taplo
+        vscode-langservers-extracted
+      ])
+      ++ extraPkgs;
+
+    env = compilerEnv // {
+      LD_LIBRARY_PATH = lib.makeLibraryPath [
+        nixpkgs.stdenv.cc.cc
+        nixpkgs.zlib
+      ];
+    };
+
+    enterShell = ''
+      BLUE='\033[0;34m'
+      NC='\033[0m'
+
+      echo "following environment variables are set:"
+    ''
+    + lib.concatStringsSep "" (
+      lib.mapAttrsToList (name: value: ''
+        echo -e "  ''${BLUE}${name}''${NC}=${value}"
+      '') compilerEnv
+    )
+    + ''
+      echo ""
+      echo -e "${config.name} devenv activated"
+    '';
+  };
+}

dev/nix/devenv.yaml

@@ -0,0 +1,4 @@
+# devenv inputs; update the lock with `devenv update --from path:./dev/nix`
+inputs:
+  nixpkgs:
+    url: github:NixOS/nixpkgs/nixos-unstable

dev/nix/kokkos.nix

@@ -27,6 +27,7 @@ let
     ];
     "NONE" = [
       pkgs.clang-tools
+      pkgs.libgcc
       pkgs.gcc15
     ];
   };

dev/nix/shell.nix

@@ -7,6 +7,7 @@
   arch ? "NATIVE",
   hdf5 ? false,
   mpi ? false,
+  extra ? "",
 }:
 
 let
@@ -22,6 +23,9 @@ let
       gpu = gpuUpper;
     }
   );
+  extraPkgs = map (name: pkgs.${name}) (
+    pkgs.lib.filter (s: s != "") (pkgs.lib.splitString "," extra)
+  );
   envVars = {
     compiler = {
       NONE = {
@@ -41,28 +45,31 @@ pkgs.mkShell {
     "${name}"
     + (if gpu != "NONE" then "-${pkgs.lib.toLower gpu}" else "")
     + (if mpi then "-mpi" else "");
-  nativeBuildInputs = with pkgs; [
-    zlib
-    cmake
+  nativeBuildInputs =
+    with pkgs;
+    [
+      zlib
+      cmake
 
-    adios2Pkg
-    kokkosPkg
+      adios2Pkg
+      kokkosPkg
 
-    python314
+      python314
 
-    cmake-format
-    cmake-lint
-    neocmakelsp
-    black
-    pyright
-    taplo
-    vscode-langservers-extracted
-  ];
+      cmake-format
+      cmake-lint
+      neocmakelsp
+      black
+      pyright
+      taplo
+      vscode-langservers-extracted
+    ]
+    ++ extraPkgs;
 
-  LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath ([
+  LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath [
     pkgs.stdenv.cc.cc
     pkgs.zlib
-  ]);
+  ];
 
   shellHook = ''
     BLUE='\033[0;34m'