Add an advanced option to skip any Gemfile updates

README.md

@@ -104,6 +104,7 @@ There may be times where feature detection plus flags just aren't enough.  As an
 
 * `--instructions=path` - a dockerfile fragment to be inserted into the final document.
 * `--migration=cmd` - a replacement (generally a script) for `db:prepare`/`db:migrate`.
+* `--no-gemfile-updates` - do not modify my gemfile.
 * `--procfile=path` - a [Procfile](https://github.com/ddollar/foreman#foreman) to use in place of launching Rails directly.
 
 Like with environment variables, packages, and build args, `--instructions` can be tailored to a specific build phase by adding `-base`, `-build`, or `-deploy` after the flag name, with the default being `-deploy`.

lib/generators/dockerfile_generator.rb

@@ -14,6 +14,7 @@ class DockerfileGenerator < Rails::Generators::Base
     "ci" => false,
     "compose" => false,
     "fullstaq" => false,
+    "gemfile-updates" => true,
     "jemalloc" => false,
     "label" => {},
     "link" => true,
@@ -219,6 +220,9 @@ class DockerfileGenerator < Rails::Generators::Base
   class_option "private-gemserver-domain", type: :string, default: OPTION_DEFAULTS["private-gemserver-domain"],
     desc: "domain name of a private gemserver used when installing application gems"
 
+  class_option "gemfile-updates", type: :boolean, default: OPTION_DEFAULTS["gemfile-updates"],
+    desc: "include gemfile updates"
+
 
   class_option "add-base", type: :array, default: [],
     desc: "additional packages to install for both build and deploy"
@@ -510,6 +514,8 @@ def keeps?
   end
 
   def install_gems
+    return unless options["gemfile-updates"]
+
     ENV["BUNDLE_IGNORE_MESSAGES"] = "1"
 
     gemfile = IO.read("Gemfile")