Add a stable sort

- This probably has a negative performance impact, so I’m not sure I’m going to
  merge this.

lib/mime/types.rb

@@ -131,9 +131,7 @@ def [](type_id, complete: false, registered: false)
                 @type_variants[MIME::Type.simplified(type_id)]
               end
 
-    prune_matches(matches, complete, registered).sort { |a, b|
-      a.priority_compare(b)
-    }
+    stable_sort(prune_matches(matches, complete, registered))
   end
 
   # Return the list of MIME::Types which belongs to the file based on its
@@ -149,11 +147,12 @@ def [](type_id, complete: false, registered: false)
   #   puts MIME::Types.type_for(%w(citydesk.xml citydesk.gif))
   #     => [application/xml, image/gif, text/xml]
   def type_for(filename)
-    Array(filename).flat_map { |fn|
+    results =
+      Array(filename).flat_map { |fn|
       @extension_index[fn.chomp.downcase[/\.?([^.]*?)$/, 1]]
-    }.compact.inject(Set.new, :+).sort { |a, b|
-      a.priority_compare(b)
-    }
+    }.compact.inject(Set.new, :+)
+
+    stable_sort(results)
   end
   alias of type_for
 
@@ -221,6 +220,12 @@ def match(pattern)
       k =~ pattern
     }.values.inject(Set.new, :+)
   end
+
+  def stable_sort(list)
+    list.lazy.each_with_index.sort { |(a, ai), (b, bi)|
+      a.priority_compare(b).nonzero? || ai <=> bi
+    }.map(&:first)
+  end
 end
 
 require 'mime/types/cache'

mime-types.gemspec

@@ -26,7 +26,7 @@ Gem::Specification.new do |s|
 
     if Gem::Version.new(Gem::VERSION) >= Gem::Version.new('1.2.0') then
       s.add_runtime_dependency(%q<mime-types-data>.freeze, ["~> 3.2015"])
-      s.add_development_dependency(%q<minitest>.freeze, ["~> 5.13"])
+      s.add_development_dependency(%q<minitest>.freeze, ["~> 5.14"])
       s.add_development_dependency(%q<hoe-doofus>.freeze, ["~> 1.0"])
       s.add_development_dependency(%q<hoe-gemspec2>.freeze, ["~> 1.1"])
       s.add_development_dependency(%q<hoe-git>.freeze, ["~> 1.6"])
@@ -38,10 +38,10 @@ Gem::Specification.new do |s|
       s.add_development_dependency(%q<rake>.freeze, [">= 10.0", "< 14.0"])
       s.add_development_dependency(%q<simplecov>.freeze, ["~> 0.7"])
       s.add_development_dependency(%q<rdoc>.freeze, [">= 4.0", "< 7"])
-      s.add_development_dependency(%q<hoe>.freeze, ["~> 3.20"])
+      s.add_development_dependency(%q<hoe>.freeze, ["~> 3.22"])
     else
       s.add_dependency(%q<mime-types-data>.freeze, ["~> 3.2015"])
-      s.add_dependency(%q<minitest>.freeze, ["~> 5.13"])
+      s.add_dependency(%q<minitest>.freeze, ["~> 5.14"])
       s.add_dependency(%q<hoe-doofus>.freeze, ["~> 1.0"])
       s.add_dependency(%q<hoe-gemspec2>.freeze, ["~> 1.1"])
       s.add_dependency(%q<hoe-git>.freeze, ["~> 1.6"])
@@ -53,11 +53,11 @@ Gem::Specification.new do |s|
       s.add_dependency(%q<rake>.freeze, [">= 10.0", "< 14.0"])
       s.add_dependency(%q<simplecov>.freeze, ["~> 0.7"])
       s.add_dependency(%q<rdoc>.freeze, [">= 4.0", "< 7"])
-      s.add_dependency(%q<hoe>.freeze, ["~> 3.20"])
+      s.add_dependency(%q<hoe>.freeze, ["~> 3.22"])
     end
   else
     s.add_dependency(%q<mime-types-data>.freeze, ["~> 3.2015"])
-    s.add_dependency(%q<minitest>.freeze, ["~> 5.13"])
+    s.add_dependency(%q<minitest>.freeze, ["~> 5.14"])
     s.add_dependency(%q<hoe-doofus>.freeze, ["~> 1.0"])
     s.add_dependency(%q<hoe-gemspec2>.freeze, ["~> 1.1"])
     s.add_dependency(%q<hoe-git>.freeze, ["~> 1.6"])
@@ -69,6 +69,6 @@ Gem::Specification.new do |s|
     s.add_dependency(%q<rake>.freeze, [">= 10.0", "< 14.0"])
     s.add_dependency(%q<simplecov>.freeze, ["~> 0.7"])
     s.add_dependency(%q<rdoc>.freeze, [">= 4.0", "< 7"])
-    s.add_dependency(%q<hoe>.freeze, ["~> 3.20"])
+    s.add_dependency(%q<hoe>.freeze, ["~> 3.22"])
   end
 end

test/test_mime_types.rb

@@ -18,7 +18,8 @@ def mime_types
                'content-type' => 'application/gzip',
                'extensions' => 'gz',
                'registered' => true
-             )
+             ),
+             *MIME::Types.type_for('foo.webm')
     }
   end
 
@@ -38,8 +39,8 @@ def mime_types
     end
 
     it 'is countable with an enumerator' do
-      assert_equal 6, mime_types.each.count
-      assert_equal 6, mime_types.lazy.count
+      assert_equal 8, mime_types.each.count
+      assert_equal 8, mime_types.lazy.count
     end
   end
 
@@ -159,11 +160,15 @@ def mime_types
       plain_text.add_extensions('xtxt')
       assert_includes mime_types.type_for('xtxt'), 'text/plain'
     end
+
+    it 'returns a stable order for types with equal priority' do
+      assert_equal %w(audio/webm video/webm), mime_types.type_for('foo.webm')
+    end
   end
 
   describe '#count' do
     it 'can count the number of types inside' do
-      assert_equal 6, mime_types.count
+      assert_equal 8, mime_types.count
     end
   end
 end

test/test_mime_types_class.rb

@@ -100,6 +100,10 @@ def setup
       plain_text.add_extensions('xtxt')
       assert_includes MIME::Types.type_for('xtxt'), 'text/plain'
     end
+
+    it 'returns a stable order for types with equal priority' do
+      assert_equal %w(audio/webm video/webm), MIME::Types.type_for('foo.webm')
+    end
   end
 
   describe '.count' do