Did you mean functionality. (#2601)

* Add did_you_mean functionality to rspec-core.

The functionality provides for suggestions when a person enters an
rspec spec/some_file_path command with typographical errors.

If there are errors, then the code at lib/rspec/core/configuration.rb:2037
searches for suggestions. If useful suggestions are found
they are added to the reported exception at
lib/rspec/core/configuration.rb:2038.

The suggestions are done by the ::DidYouMean::SpellChecker API
where available.

Author: obromios

lib/rspec/core.rb

@@ -139,6 +139,7 @@ def self.world
   module Core
     autoload :ExampleStatusPersister, "rspec/core/example_status_persister"
     autoload :Profiler,               "rspec/core/profiler"
+    autoload :DidYouMean,             "rspec/core/did_you_mean"
 
     # @private
     # This avoids issues with reporting time caused by examples that

lib/rspec/core/configuration.rb

@@ -2032,6 +2032,11 @@ def bisect_runner_class
 
       def load_file_handling_errors(method, file)
         __send__(method, file)
+      rescue LoadError => ex
+        relative_file = Metadata.relative_path(file)
+        suggestions = DidYouMean.new(relative_file).call
+        reporter.notify_non_example_exception(ex, "An error occurred while loading #{relative_file}.#{suggestions}")
+        RSpec.world.wants_to_quit = true
       rescue Support::AllExceptionsExceptOnesWeMustNotRescue => ex
         relative_file = Metadata.relative_path(file)
         reporter.notify_non_example_exception(ex, "An error occurred while loading #{relative_file}.")

lib/rspec/core/did_you_mean.rb

@@ -0,0 +1,46 @@
+module RSpec
+  module Core
+    # @private
+    # Wrapper around Ruby's `DidYouMean::SpellChecker` when available to provide file name suggestions.
+    class DidYouMean
+      attr_reader :relative_file_name
+
+      def initialize(relative_file_name)
+        @relative_file_name = relative_file_name
+      end
+
+      if defined?(::DidYouMean::SpellChecker)
+        # provide probable suggestions
+        def call
+          checker = ::DidYouMean::SpellChecker.new(:dictionary => Dir["spec/**/*.rb"])
+          probables = checker.correct(relative_file_name.sub('./', ''))[0..2]
+          return '' unless probables.any?
+
+          formats probables
+        end
+      else
+        # return a hint if API for ::DidYouMean::SpellChecker not supported
+        def call
+          "\nHint: Install the `did_you_mean` gem in order to provide suggestions for similarly named files."
+        end
+      end
+
+      private
+
+      def formats(probables)
+        rspec_format = probables.map { |s, _| "rspec ./#{s}" }
+        red_font(top_and_tail rspec_format)
+      end
+
+      def top_and_tail(rspec_format)
+        spaces = ' ' * 20
+        rspec_format.insert(0, ' - Did you mean?').join("\n#{spaces}") + "\n"
+      end
+
+      def red_font(mytext)
+        colorizer = ::RSpec::Core::Formatters::ConsoleCodes
+        colorizer.wrap mytext, :failure
+      end
+    end
+  end
+end

spec/rspec/core/did_you_mean_spec.rb

@@ -0,0 +1,37 @@
+module RSpec
+  module Core
+    RSpec.describe DidYouMean do
+      describe '#call' do
+        context "when `DidYouMean::SpellChecker` is available", :skip => !defined?(::DidYouMean::SpellChecker) do
+          context 'Success' do
+            let(:name) { './spec/rspec/core/did_you_mean_spec.rb' }
+            it 'returns a useful suggestion' do
+              expect(DidYouMean.new(name[0..-2]).call).to include name
+            end
+            context 'numerous possibilities' do
+              it 'returns a small number of suggestions' do
+                name = './spec/rspec/core/drb_spec.r'
+                suggestions = DidYouMean.new(name).call
+                expect(suggestions.split("\n").size).to eq 4
+              end
+            end
+          end
+          context 'No suitable suggestions' do
+            it 'returns empty string' do
+              name = './' + 'x' * 50
+              expect(DidYouMean.new(name).call).to eq ''
+            end
+          end
+        end
+        context "when `DidYouMean::SpellChecker` is not available", :unless => defined?(::DidYouMean::SpellChecker) do
+          describe 'Success' do
+            let(:name) { './spec/rspec/core/did_you_mean_spec.rb' }
+            it 'returns a hint' do
+              expect(DidYouMean.new(name[0..-2]).call).to include 'Hint:'
+            end
+          end
+        end
+      end
+    end
+  end
+end