chore: initial commit

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));
+  };
+}