Use `did_you_mean` spell checker for option suggestions

Now that we require Ruby over `2.3`, we can replace the current
suggestion methods we have with tooling from the `did_you_mean` gem.

There is a small user visible change and this is that we now offer a
single suggestion for misspelled options. We are suggesting fixes during
generator invocation and during a mistyped rails server rack handler. In
both cases, if we don't make a proper prediction on the first match, we
won't do so in the second or third one, so in my mind, this is okay.

railties/lib/rails/command/spellchecker.rb

@@ -3,50 +3,8 @@
 module Rails
   module Command
     module Spellchecker # :nodoc:
-      class << self
-        def suggest(word, from:, count: 3)
-          from.sort_by { |w| levenshtein_distance(word, w) }.take(count)
-        end
-
-        private
-          # This code is based directly on the Text gem implementation.
-          # Copyright (c) 2006-2013 Paul Battley, Michael Neumann, Tim Fletcher.
-          #
-          # Returns a value representing the "cost" of transforming str1 into str2.
-          def levenshtein_distance(str1, str2) # :doc:
-            s = str1
-            t = str2
-            n = s.length
-            m = t.length
-
-            return m if (0 == n)
-            return n if (0 == m)
-
-            d = (0..m).to_a
-            x = nil
-
-            # avoid duplicating an enumerable object in the loop
-            str2_codepoint_enumerable = str2.each_codepoint
-
-            str1.each_codepoint.with_index do |char1, i|
-              e = i + 1
-
-              str2_codepoint_enumerable.with_index do |char2, j|
-                cost = (char1 == char2) ? 0 : 1
-                x = [
-                  d[j + 1] + 1, # insertion
-                  e + 1,        # deletion
-                  d[j] + cost   # substitution
-                ].min
-                d[j] = e
-                e = x
-              end
-
-              d[m] = x
-            end
-
-            x
-          end
+      def self.suggest(word, from:)
+        DidYouMean::SpellChecker.new(dictionary: from.map(&:to_s)).correct(word).first
       end
     end
   end

railties/lib/rails/commands/server/server_command.rb

@@ -283,10 +283,10 @@ module Rails
               Run `rails server --help` for more options.
             MSG
           else
-            suggestions = Rails::Command::Spellchecker.suggest(server, from: RACK_SERVERS).map(&:inspect)
+            suggestions = Rails::Command::Spellchecker.suggest(server, from: RACK_SERVERS)
 
             <<~MSG
-              Could not find server "#{server}". Maybe you meant #{suggestions.first} or #{suggestions.second}?
+              Could not find server "#{server}". Maybe you meant #{suggestions.inspect}?
               Run `rails server --help` for more options.
             MSG
           end

railties/lib/rails/generators.rb

@@ -276,12 +276,11 @@ module Rails
           klass.start(args, config)
         else
           options     = sorted_groups.flat_map(&:last)
-          suggestions = Rails::Command::Spellchecker.suggest(namespace.to_s, from: options, count: 3)
-          suggestions.map! { |s| "'#{s}'" }
-          msg =  "Could not find generator '#{namespace}'. ".dup
-          msg << "Maybe you meant #{ suggestions[0...-1].join(', ')} or #{suggestions[-1]}\n"
-          msg << "Run `rails generate --help` for more options."
-          puts msg
+          suggestion  = Rails::Command::Spellchecker.suggest(namespace.to_s, from: options)
+          puts <<~MSG
+            Could not find generator '#{namespace}'. Maybe you meant #{suggestion.inspect}?\n"
+            Run `rails generate --help` for more options."
+          MSG
         end
       end
 

railties/test/command/spellchecker_test.rb

@@ -5,6 +5,6 @@ require "rails/command/spellchecker"
 
 class Rails::Command::SpellcheckerTest < ActiveSupport::TestCase
   test "suggests a word correction from dictionary" do
-    assert_equal %w(thin cgi puma), Rails::Command::Spellchecker.suggest("tin", from: %w(puma thin cgi))
+    assert_equal "thin", Rails::Command::Spellchecker.suggest("tin", from: %w(puma thin cgi))
   end
 end

railties/test/commands/server_test.rb

@@ -29,7 +29,7 @@ class Rails::Command::ServerCommandTest < ActiveSupport::TestCase
   end
 
   def test_using_server_mistype
-    assert_match(/Could not find server "tin". Maybe you meant "thin" or "cgi"/, run_command("--using", "tin"))
+    assert_match(/Could not find server "tin". Maybe you meant "thin"?/, run_command("--using", "tin"))
   end
 
   def test_using_positional_argument_deprecation

railties/test/generators_test.rb

@@ -33,7 +33,7 @@ class GeneratorsTest < Rails::Generators::TestCase
   def test_generator_suggestions
     name = :migrationz
     output = capture(:stdout) { Rails::Generators.invoke name }
-    assert_match "Maybe you meant 'migration'", output
+    assert_match 'Maybe you meant "migration"?', output
   end
 
   def test_generator_suggestions_except_en_locale
@@ -43,7 +43,7 @@ class GeneratorsTest < Rails::Generators::TestCase
     I18n.default_locale = :ja
     name = :tas
     output = capture(:stdout) { Rails::Generators.invoke name }
-    assert_match "Maybe you meant 'task', 'job' or", output
+    assert_match 'Maybe you meant "task"?', output
   ensure
     I18n.available_locales = orig_available_locales
     I18n.default_locale = orig_default_locale
@@ -52,7 +52,7 @@ class GeneratorsTest < Rails::Generators::TestCase
   def test_generator_multiple_suggestions
     name = :tas
     output = capture(:stdout) { Rails::Generators.invoke name }
-    assert_match "Maybe you meant 'task', 'job' or", output
+    assert_match 'Maybe you meant "task"?', output
   end
 
   def test_help_when_a_generator_with_required_arguments_is_invoked_without_arguments