Just use the gemspec file inside the Rakefile and don't completely recreate it

Author: myobie

.gitignore

@@ -8,3 +8,4 @@ Gemfile.lock
 .bundle
 *.gem
 *.patch
+vendor/bundle/*

Rakefile

@@ -1,57 +1,19 @@
-require 'rubygems'
-require 'rake/gempackagetask'
-require 'rubygems/specification'
-require 'date'
-require 'spec/rake/spectask'
+require 'rubygems/package_task'
+require 'rspec/core/rake_task'
 
-GEM = "htmldiff"
-GEM_VERSION = "0.0.1"
-AUTHOR = "Nathan Herald"
-EMAIL = "[email protected]"
-HOMEPAGE = "http://github.com/myobie/htmldiff"
-SUMMARY = "HTML diffs of text (borrowed from a wiki software I no longer remember)"
+spec = Gem::Specification.load(File.expand_path('htmldiff.gemspec', __dir__))
 
-spec = Gem::Specification.new do |s|
-  s.name = GEM
-  s.version = GEM_VERSION
-  s.platform = Gem::Platform::RUBY
-  s.has_rdoc = true
-  s.extra_rdoc_files = ["README", "LICENSE", 'TODO']
-  s.summary = SUMMARY
-  s.description = s.summary
-  s.author = AUTHOR
-  s.email = EMAIL
-  s.homepage = HOMEPAGE
-  
-  # Uncomment this to add a dependency
-  # s.add_dependency "foo"
-  
-  s.require_path = 'lib'
-  s.autorequire = GEM
-  s.files = %w(LICENSE README Rakefile TODO) + Dir.glob("{lib,spec}/**/*")
+RSpec::Core::RakeTask.new(:spec) do |t|
+  t.pattern = 'spec/**/*_spec.rb'
 end
 
 task :default => :spec
 
-desc "Run specs"
-Spec::Rake::SpecTask.new do |t|
-  t.spec_files = FileList['spec/**/*_spec.rb']
-  t.spec_opts = %w(-fs --color)
-end
-
-
-Rake::GemPackageTask.new(spec) do |pkg|
+Gem::PackageTask.new(spec) do |pkg|
   pkg.gem_spec = spec
 end
 
-desc "install the gem locally"
+desc "Install the gem locally"
 task :install => [:package] do
-  sh %{sudo gem install pkg/#{GEM}-#{GEM_VERSION}}
+  sh "gem install pkg/#{GEM}-#{GEM_VERSION}.gem"
 end
-
-desc "create a gemspec file"
-task :make_spec do
-  File.open("#{GEM}.gemspec", "w") do |file|
-    file.puts spec.to_ruby
-  end
-end