Verify the presence of the private key before releasing. (#4899)

Rakefile

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "bundler"
+require "bundler/gem_tasks"
 Bundler.setup
 
 require "rake"
@@ -9,6 +10,9 @@ require "rspec/core/rake_task"
 $LOAD_PATH.unshift File.expand_path("../lib", __FILE__)
 require "mongoid/version"
 
+tasks = Rake.application.instance_variable_get('@tasks')
+tasks['release:do'] = tasks.delete('release')
+
 task :gem => :build
 task :build do
   system "gem build mongoid.gemspec"
@@ -54,3 +58,13 @@ namespace :docs do
     system "yardoc -o #{out} --title mongoid-#{Mongoid::VERSION}"
   end
 end
+
+namespace :release do
+  task :check_private_key do
+    unless File.exist?('gem-private_key.pem')
+      raise "No private key present, cannot release"
+    end
+  end
+end
+
+task :release => ['release:check_private_key', 'release:do']