Expand gemspec files within gem directory

Author: chriscz

railties/lib/rails/generators/rails/plugin/templates/%name%.gemspec.tt

@@ -20,7 +20,9 @@ Gem::Specification.new do |spec|
   spec.metadata["source_code_uri"] = "TODO: Put your gem's public repo URL here."
   spec.metadata["changelog_uri"] = "TODO: Put your gem's CHANGELOG.md URL here."
 
-  spec.files = Dir["{app,config,db,lib}/**/*", "MIT-LICENSE", "Rakefile", "README.md"]
+  spec.files = Dir.chdir(File.expand_path(__dir__)) do
+    Dir["{app,config,db,lib}/**/*", "MIT-LICENSE", "Rakefile", "README.md"]
+  end
 
   <%= '# ' if options.dev? || options.edge? || options.main? -%>spec.add_dependency "rails", "<%= Array(rails_version_specifier).join('", "') %>"
 end

railties/test/generators/plugin_generator_test.rb

@@ -535,7 +535,7 @@ def test_creating_mountable_engine_mode_adds_keeps
   def test_creating_gemspec
     run_generator
     assert_file "bukkits.gemspec", /spec\.name\s+= "bukkits"/
-    assert_file "bukkits.gemspec", /spec\.files = Dir\["\{app,config,db,lib\}\/\*\*\/\*", "MIT-LICENSE", "Rakefile", "README\.md"\]/
+    assert_file "bukkits.gemspec", /spec\.files = Dir.chdir\(File\.expand_path\(__dir__\)\)\s+do\s+Dir\["\{app,config,db,lib\}\/\*\*\/\*", "MIT-LICENSE", "Rakefile", "README\.md"\]\s+end/
     assert_file "bukkits.gemspec", /spec\.version\s+ = Bukkits::VERSION/
   end