gig contains a rake task of the same name to check for consistency of files between git, gemspec, and the filesystem before building.

In your rakefile, require 'gig' and invoke Gig.make_task, passing gemspec_filename and ignore_files. Globs are useful for ignore_files, and File::FNM_DOTMATCH should be used when globs may contain dotfiles. For example:

require 'gig'

ignore_files = %w(
  .github/**/*
  .gitignore
  .gitmodules
  Gemfile
  Rakefile.rb
  test/**/*
).map { |glob| Dir.glob(glob, File::FNM_DOTMATCH) }.inject([], &:|)
Gig.make_task(gemspec_filename: 'my_gem.gemspec', ignore_files: ignore_files)

The gem is available under the terms of the MIT License.