zsh: fix double compinit slowdown with oh-my-zsh

Integrate oh-my-zsh into zsh module
to be able to control invocation order.

modules/default.nix

@@ -29,7 +29,6 @@ let
     ./programs/htop.nix
     ./programs/info.nix
     ./programs/lesspipe.nix
-    ./programs/oh-my-zsh.nix
     ./programs/ssh.nix
     ./programs/termite.nix
     ./programs/texlive.nix

modules/programs/oh-my-zsh.nix

@@ -1,66 +0,0 @@
-{ config, lib, pkgs, ... }:
-
-with lib;
-
-let
-
-  cfg = config.programs.zsh.oh-my-zsh;
-
-in
-
-{
-  options = {
-    programs.zsh.oh-my-zsh = {
-      enable = mkEnableOption "oh-my-zsh";
-
-      plugins = mkOption {
-        default = [];
-        example = [ "git" "sudo" ];
-        type = types.listOf types.str;
-        description = ''
-          List of oh-my-zsh plugins
-        '';
-      };
-
-      custom = mkOption {
-        default = "";
-        type = types.str;
-        example = "$HOME/my_customizations";
-        description = ''
-          Path to a custom oh-my-zsh package to override config of oh-my-zsh.
-          See: https://github.com/robbyrussell/oh-my-zsh/wiki/Customization
-        '';
-      };
-
-      theme = mkOption {
-        default = "";
-        example = "robbyrussell";
-        type = types.str;
-        description = ''
-          Name of the theme to be used by oh-my-zsh.
-        '';
-      };
-    };
-  };
-
-  config = mkIf cfg.enable {
-    home.packages = [ pkgs.oh-my-zsh ];
-
-    programs.zsh.initExtra = with pkgs; ''
-      # oh-my-zsh configuration generated by NixOS
-      export ZSH=${oh-my-zsh}/share/oh-my-zsh
-      export ZSH_CACHE_DIR=''${XDG_CACHE_HOME:-$HOME/.cache}/oh-my-zsh
-
-      ${optionalString (cfg.plugins != [])
-        "plugins=(${concatStringsSep " " cfg.plugins})"
-      }
-      ${optionalString (cfg.custom != "")
-        "ZSH_CUSTOM=\"${cfg.custom}\""
-      }
-      ${optionalString (cfg.theme != "")
-        "ZSH_THEME=\"${cfg.theme}\""
-      }
-      source $ZSH/oh-my-zsh.sh
-    '';
-  };
-}

modules/programs/zsh.nix

@@ -67,6 +67,40 @@ let
     config.file = mkDefault "${config.name}.plugin.zsh";
   });
 
+  ohMyZshModule = types.submodule {
+    options = {
+      enable = mkEnableOption "oh-my-zsh";
+
+      plugins = mkOption {
+        default = [];
+        example = [ "git" "sudo" ];
+        type = types.listOf types.str;
+        description = ''
+          List of oh-my-zsh plugins
+        '';
+      };
+
+      custom = mkOption {
+        default = "";
+        type = types.str;
+        example = "$HOME/my_customizations";
+        description = ''
+          Path to a custom oh-my-zsh package to override config of oh-my-zsh.
+          See: https://github.com/robbyrussell/oh-my-zsh/wiki/Customization
+        '';
+      };
+
+      theme = mkOption {
+        default = "";
+        example = "robbyrussell";
+        type = types.str;
+        description = ''
+          Name of the theme to be used by oh-my-zsh.
+        '';
+      };
+    };
+  };
+
 in
 
 {
@@ -136,6 +170,12 @@ in
         '';
         description = "Plugins to source in <filename>.zshrc</filename>.";
       };
+
+      oh-my-zsh = mkOption {
+        type = ohMyZshModule;
+        default = {};
+        description = "Options to configure oh-my-zsh.";
+      };
     };
   };
 
@@ -151,8 +191,9 @@ in
         mapAttrsToList export config.home.sessionVariables
       );
     in mkIf cfg.enable {
-      home.packages = [ pkgs.zsh ]
-        ++ optional cfg.enableCompletion pkgs.nix-zsh-completions;
+      home.packages = with pkgs; [ zsh ]
+        ++ optional cfg.enableCompletion nix-zsh-completions
+        ++ optional cfg.oh-my-zsh.enable oh-my-zsh;
 
       home.file.".zshenv".text = ''
         ${optionalString (config.home.sessionVariableSetter == "zsh")
@@ -179,6 +220,23 @@ in
           "source ${pkgs.zsh-autosuggestions}/share/zsh-autosuggestions/zsh-autosuggestions.zsh"
         }
 
+        ${optionalString cfg.oh-my-zsh.enable ''
+            # oh-my-zsh configuration generated by NixOS
+            export ZSH=${pkgs.oh-my-zsh}/share/oh-my-zsh
+            export ZSH_CACHE_DIR=''${XDG_CACHE_HOME:-$HOME/.cache}/oh-my-zsh
+
+            ${optionalString (cfg.oh-my-zsh.plugins != [])
+              "plugins=(${concatStringsSep " " cfg.oh-my-zsh.plugins})"
+            }
+            ${optionalString (cfg.oh-my-zsh.custom != "")
+              "ZSH_CUSTOM=\"${cfg.oh-my-zsh.custom}\""
+            }
+            ${optionalString (cfg.oh-my-zsh.theme != "")
+              "ZSH_THEME=\"${cfg.oh-my-zsh.theme}\""
+            }
+            source $ZSH/oh-my-zsh.sh
+        ''}
+
         ${concatStrings (map (plugin: ''
           source "$HOME/.zsh/plugins/${plugin.name}/${plugin.file}"
         '') cfg.plugins)}
@@ -188,6 +246,12 @@ in
         ${cfg.initExtra}
       '';
     })
+    (mkIf cfg.oh-my-zsh.enable {
+      # Oh-My-Zsh calls compinit during initialization,
+      # calling it twice causes sight start up slowdown
+      # as all $fpath entries will be traversed again.
+      programs.zsh.enableCompletion = mkForce false;
+    })
     (mkIf (cfg.plugins != []) {
       # Many plugins require compinit to be called
       # but allow the user to opt out.