pyenv: add module

Adds a module for pyenv (https://github.com/pyenv/pyenv).

modules/programs/pyenv.nix

@@ -0,0 +1,79 @@
+{ config, pkgs, lib, ... }:
+
+let
+
+  cfg = config.programs.pyenv;
+
+  tomlFormat = pkgs.formats.toml { };
+
+in {
+  meta.maintainers = with lib.maintainers; [ tmarkus ];
+
+  options.programs.pyenv = {
+    enable = lib.mkEnableOption "pyenv";
+
+    package = lib.mkOption {
+      type = lib.types.package;
+      default = pkgs.pyenv;
+      defaultText = lib.literalExpression "pkgs.pyenv";
+      description = "The package to use for pyenv.";
+    };
+
+    enableBashIntegration = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = ''
+        Whether to enable pyenv's Bash integration.
+      '';
+    };
+
+    enableZshIntegration = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = ''
+        Whether to enable pyenv's Zsh integration.
+      '';
+    };
+
+    enableFishIntegration = lib.mkOption {
+      type = lib.types.bool;
+      default = true;
+      description = ''
+        Whether to enable pyenv's Fish integration.
+      '';
+    };
+
+    rootDirectory = lib.mkOption {
+      type = lib.types.path;
+      apply = toString;
+      default = "${config.xdg.dataHome}/pyenv";
+      defaultText = "\${config.xdg.dataHome}/pyenv";
+      description = ''
+        The pyenv root directory (PYENV_ROOT).
+        </para><para>
+        Note: Deviating from upstream which uses `$HOME/.pyenv`,
+        the default path is set according to the XDG base directory specification.
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    # Always add the configured `pyenv` package.
+    home.packages = [ cfg.package ];
+
+    programs.bash.initExtra = lib.mkIf cfg.enableBashIntegration ''
+      export PYENV_ROOT="${cfg.rootDirectory}"
+      eval "$(${lib.getExe cfg.package} init - bash)"
+    '';
+
+    programs.zsh.initExtra = lib.mkIf cfg.enableZshIntegration ''
+      export PYENV_ROOT="${cfg.rootDirectory}"
+      eval "$(${lib.getExe cfg.package} init - zsh)"
+    '';
+
+    programs.fish.interactiveShellInit = lib.mkIf cfg.enableFishIntegration ''
+      set -Ux PYENV_ROOT "${cfg.rootDirectory}"
+      ${lib.getExe cfg.package} init - fish | source
+    '';
+  };
+}