cop for gem fetched from a git source

rubocop/cop/gem_fetcher.rb

+module RuboCop
+  module Cop
+    # Cop that checks for all gems specified in the Gemfile, and will
+    # alert if any gem is to be fetched not from the RubyGems index.
+    # This enforcement is done so as to minimize external build
+    # dependencies and build times.
+    class GemFetcher < RuboCop::Cop::Cop
+      MSG = 'Do not use gems from git repositories, only use gems from RubyGems.'
+
+      GIT_KEYS = [:git, :github]
+
+      def on_send(node)
+        file_path = node.location.expression.source_buffer.name
+        return unless file_path.end_with?("Gemfile")
+
+        func_name = node.children[1]
+        return unless func_name == :gem
+
+        node.children.last.each_node(:pair) do |pair|
+          key_name = pair.children[0].children[0].to_sym
+          if GIT_KEYS.include?(key_name)
+            add_offense(node, :selector)
+          end
+        end
+      end
+    end
+  end
+end

rubocop/rubocop.rb

 require_relative 'migration_helpers'
 require_relative 'cop/migration/add_index'
 require_relative 'cop/migration/column_with_default'
+require_relative 'cop/gem_fetcher'