chore: initial commit

lib/modules/default.nix

@@ -0,0 +1,6 @@
+{
+  imports = [
+    ./main.nix
+    ./env.nix
+  ];
+}

lib/modules/env.nix

@@ -0,0 +1,99 @@
+{
+  lib,
+  pkgs,
+  config,
+  ...
+}: let
+  inherit (lib) filter assertMsg head length escapeShellArg types mkOption concatStringsSep;
+
+  envToBash = {
+    name,
+    value,
+    eval,
+    prefix,
+    ...
+  } @ args: let
+    vals = filter (key: args.${key} != null && args.${key} != false) [
+      "eval"
+      "prefix"
+      "unset"
+      "value"
+    ];
+    valType = head vals;
+  in
+    assert assertMsg (
+      (length vals) > 0
+    ) "[devshell/env]: ${name} expected one of (value|eval|prefix|unset) to be set.";
+    assert assertMsg ((length vals) < 2)
+    "[devshell/env]: ${name} expected only one of (value|eval|prefix|unset) to be set. Not ${toString vals}";
+    assert assertMsg (!(name == "PATH" && valType == "value")) "[devshell/env]: ${name} should not override the value. Use 'prefix' instead.";
+      if valType == "value"
+      then "export ${name}=${escapeShellArg (toString value)}"
+      else if valType == "eval"
+      then "export ${name}=${eval}"
+      else if valType == "prefix"
+      then ''export ${name}=$(${pkgs.coreutils}/bin/realpath --canonicalize-missing "${prefix}")''${${name}+:''${${name}}}''
+      else if valType == "unset"
+      then ''unset ${name}''
+      else throw "[devshell] BUG in the env module. This should never be reached.";
+
+  envType = types.submodule ({name, ...}: {
+    options = {
+      name = mkOption {
+        type = types.str;
+        default = name;
+      };
+      value = mkOption {
+        type = with types;
+          nullOr (oneOf [
+            str
+            int
+            bool
+            package
+          ]);
+        default = null;
+      };
+
+      eval = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+        description = ''
+          Like value but not evaluated by Bash. This allows to inject other
+          variable names or even commands using the `$()` notation.
+        '';
+        example = "$OTHER_VAR";
+      };
+
+      prefix = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+        description = ''
+          Prepend to PATH-like environment variables.
+
+          For example name = "PATH"; prefix = "bin"; will expand the path of
+          ./bin and prepend it to the PATH, separated by ':'.
+        '';
+        example = "bin";
+      };
+
+      unset = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''Unset the env variable'';
+      };
+    };
+  });
+in {
+  options.env = mkOption {
+    type = types.attrsOf envType;
+    default = {};
+    description = '''';
+  };
+
+  config = {
+    env = {
+      "XDG_DATA_DIRS".eval = "$DEVSHELL_DIR/share:\${XDG_DATA_DIRS-}";
+    };
+    enterShellCommands."env".text = concatStringsSep "\n" (map envToBash (builtins.attrValues config.env));
+  };
+}

lib/modules/main.nix

@@ -0,0 +1,113 @@
+{
+  pkgs,
+  lib ? pkgs.lib,
+  config,
+  ...
+}: let
+  inherit (lib) mapAttrs mkOption types textClosureMap id attrNames;
+  mkNakedShell = pkgs.callPackage ./../utils/mkNakedShell.nix {};
+
+  addAttributeName = prefix:
+    mapAttrs (
+      k: v:
+        v
+        // {
+          text = ''
+            #### ${prefix}.${k}
+            ${v.text}
+          '';
+        }
+    );
+
+  envBash =
+    pkgs.writeText "devshell-env.bash"
+    # sh
+    ''
+      export DEVSHELL_DIR=@DEVSHELL_DIR@
+      # nicely handle it at the front or between/end
+      PATH=''${PATH#/path-not-set:}
+      PATH=''${PATH#:/path-not-set}
+      export PATH=$DEVSHELL_DIR/bin:$PATH
+
+      ${textClosureMap
+        id
+        (addAttributeName "startup" config.enterShellCommands)
+        (attrNames config.enterShellCommands)}
+
+      # interactive session
+      if [[ $- == *i* ]]; then
+        true
+        ${textClosureMap
+        id
+        (addAttributeName "interactive" config.interactiveShellCommands)
+        (attrNames config.interactiveShellCommands)}
+      fi # interactive session
+
+      unset DEVSHELL_DIR
+    '';
+
+  entryType = types.submodule {
+    options = {
+      text = mkOption {
+        type = types.str;
+        description = ''
+          Script to run.
+        '';
+      };
+
+      deps = mkOption {
+        type = types.listOf types.str;
+        default = [];
+        description = ''
+          A list of other steps that this one depends on.
+        '';
+      };
+    };
+  };
+in {
+  options = {
+    shell = {
+      finalPackage = mkOption {
+        type = types.package;
+        internal = true;
+      };
+      finalProfile = mkOption {
+        type = types.package;
+        internal = true;
+      };
+    };
+
+    name = mkOption {
+      type = types.str;
+      default = "devshell";
+    };
+    packages = mkOption {
+      type = types.listOf types.package;
+      default = [];
+    };
+    enterShellCommands = mkOption {
+      type = types.attrsOf entryType;
+      default = {};
+    };
+    interactiveShellCommands = mkOption {
+      type = types.attrsOf entryType;
+      default = {};
+    };
+  };
+
+  config.shell = {
+    finalProfile = pkgs.buildEnv {
+      name = "${config.name}-profile";
+      paths = config.packages;
+      postBuild = ''
+        substitute ${envBash} $out/env.bash --subst-var-by DEVSHELL_DIR $out
+        # NOTE: maybe also add an entrypoint shell script at $out/bin/devshell-${config.name}?
+      '';
+      meta.mainProgram = "devshell-${config.name}";
+    };
+    finalPackage = mkNakedShell {
+      name = config.name;
+      profile = config.shell.finalProfile;
+    };
+  };
+}