Promote did_you_mean to default gem

At the moment, there are some problems with regard to bundler + did_you_mean because of did_you_mean being a bundled gem. Since the vendored version of thor inside bundler and ruby itself explicitly requires did_you_mean, it can become difficult to load it when using Bundler.setup. See this issue: https://github.com/yuki24/did_you_mean/issues/117#issuecomment-482733159 for more details.

20 files changed, 906 insertions, 0 deletions

diff --git a/lib/did_you_mean.rb b/lib/did_you_mean.rb
new file mode 100644
index 0000000000..b8f92579ca
--- /dev/null
+++ b/lib/did_you_mean.rb
@@ -0,0 +1,110 @@
+require_relative "did_you_mean/version"
+require_relative "did_you_mean/core_ext/name_error"
+
+require_relative "did_you_mean/spell_checker"
+require_relative 'did_you_mean/spell_checkers/name_error_checkers'
+require_relative 'did_you_mean/spell_checkers/method_name_checker'
+require_relative 'did_you_mean/spell_checkers/key_error_checker'
+require_relative 'did_you_mean/spell_checkers/null_checker'
+require_relative 'did_you_mean/formatters/plain_formatter'
+require_relative 'did_you_mean/tree_spell_checker'
+
+# The +DidYouMean+ gem adds functionality to suggest possible method/class
+# names upon errors such as +NameError+ and +NoMethodError+. In Ruby 2.3 or
+# later, it is automatically activated during startup.
+#
+# @example
+#
+#   methosd
+#   # => NameError: undefined local variable or method `methosd' for main:Object
+#   #   Did you mean?  methods
+#   #                  method
+#
+#   OBject
+#   # => NameError: uninitialized constant OBject
+#   #    Did you mean?  Object
+#
+#   @full_name = "Yuki Nishijima"
+#   first_name, last_name = full_name.split(" ")
+#   # => NameError: undefined local variable or method `full_name' for main:Object
+#   #    Did you mean?  @full_name
+#
+#   @@full_name = "Yuki Nishijima"
+#   @@full_anme
+#   # => NameError: uninitialized class variable @@full_anme in Object
+#   #    Did you mean?  @@full_name
+#
+#   full_name = "Yuki Nishijima"
+#   full_name.starts_with?("Y")
+#   # => NoMethodError: undefined method `starts_with?' for "Yuki Nishijima":String
+#   #    Did you mean?  start_with?
+#
+#   hash = {foo: 1, bar: 2, baz: 3}
+#   hash.fetch(:fooo)
+#   # => KeyError: key not found: :fooo
+#   #    Did you mean?  :foo
+#
+#
+# == Disabling +did_you_mean+
+#
+# Occasionally, you may want to disable the +did_you_mean+ gem for e.g.
+# debugging issues in the error object itself. You can disable it entirely by
+# specifying +--disable-did_you_mean+ option to the +ruby+ command:
+#
+#   $ ruby --disable-did_you_mean -e "1.zeor?"
+#   -e:1:in `<main>': undefined method `zeor?' for 1:Integer (NameError)
+#
+# When you do not have direct access to the +ruby+ command (e.g.
+# +rails console+, +irb+), you could applyoptions using the +RUBYOPT+
+# environment variable:
+#
+#   $ RUBYOPT='--disable-did_you_mean' irb
+#   irb:0> 1.zeor?
+#   # => NoMethodError (undefined method `zeor?' for 1:Integer)
+#
+#
+# == Getting the original error message
+#
+# Sometimes, you do not want to disable the gem entirely, but need to get the
+# original error message without suggestions (e.g. testing). In this case, you
+# could use the +#original_message+ method on the error object:
+#
+#   no_method_error = begin
+#                       1.zeor?
+#                     rescue NoMethodError => error
+#                       error
+#                     end
+#
+#   no_method_error.message
+#   # => NoMethodError (undefined method `zeor?' for 1:Integer)
+#   #    Did you mean?  zero?
+#
+#   no_method_error.original_message
+#   # => NoMethodError (undefined method `zeor?' for 1:Integer)
+#
+module DidYouMean
+  # Map of error types and spell checker objects.
+  SPELL_CHECKERS = Hash.new(NullChecker)
+
+  # Adds +DidYouMean+ functionality to an error using a given spell checker
+  def self.correct_error(error_class, spell_checker)
+    SPELL_CHECKERS[error_class.name] = spell_checker
+    error_class.prepend(Correctable) unless error_class < Correctable
+  end
+
+  correct_error NameError, NameErrorCheckers
+  correct_error KeyError, KeyErrorChecker
+  correct_error NoMethodError, MethodNameChecker
+
+  # Returns the currenctly set formatter. By default, it is set to +DidYouMean::Formatter+.
+  def self.formatter
+    @@formatter
+  end
+
+  # Updates the primary formatter used to format the suggestions.
+  def self.formatter=(formatter)
+    @@formatter = formatter
+  end
+
+  self.formatter = PlainFormatter.new
+end
diff --git a/lib/did_you_mean/core_ext/name_error.rb b/lib/did_you_mean/core_ext/name_error.rb
new file mode 100644
index 0000000000..77dcd520c0
--- /dev/null
+++ b/lib/did_you_mean/core_ext/name_error.rb
@@ -0,0 +1,25 @@
+module DidYouMean
+  module Correctable
+    def original_message
+      method(:to_s).super_method.call
+    end
+
+    def to_s
+      msg = super.dup
+      suggestion = DidYouMean.formatter.message_for(corrections)
+
+      msg << suggestion if !msg.end_with?(suggestion)
+      msg
+    rescue
+      super
+    end
+
+    def corrections
+      @corrections ||= spell_checker.corrections
+    end
+
+    def spell_checker
+      SPELL_CHECKERS[self.class.to_s].new(self)
+    end
+  end
+end
diff --git a/lib/did_you_mean/did_you_mean.gemspec b/lib/did_you_mean/did_you_mean.gemspec
new file mode 100644
index 0000000000..8a74db8cc4
--- /dev/null
+++ b/lib/did_you_mean/did_you_mean.gemspec
@@ -0,0 +1,23 @@
+# coding: utf-8
+lib = File.expand_path('../lib', __FILE__)
+$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
+require 'did_you_mean/version'
+
+Gem::Specification.new do |spec|
+  spec.name          = "did_you_mean"
+  spec.version       = DidYouMean::VERSION
+  spec.authors       = ["Yuki Nishijima"]
+  spec.email         = ["mail@yukinishijima.net"]
+  spec.summary       = '"Did you mean?" experience in Ruby'
+  spec.description   = 'The gem that has been saving people from typos since 2014.'
+  spec.homepage      = "https://github.com/ruby/did_you_mean"
+  spec.license       = "MIT"
+
+  spec.files         = `git ls-files`.split($/).reject{|path| path.start_with?('evaluation/') }
+  spec.test_files    = spec.files.grep(%r{^(test)/})
+  spec.require_paths = ["lib"]
+
+  spec.required_ruby_version = '>= 2.5.0'
+
+  spec.add_development_dependency "rake"
+end
diff --git a/lib/did_you_mean/experimental.rb b/lib/did_you_mean/experimental.rb
new file mode 100644
index 0000000000..f8e37e4532
--- /dev/null
+++ b/lib/did_you_mean/experimental.rb
@@ -0,0 +1,2 @@
+warn "Experimental features in the did_you_mean gem has been removed " \
+     "and `require \"did_you_mean/experimental\"' has no effect."
diff --git a/lib/did_you_mean/experimental/initializer_name_correction.rb b/lib/did_you_mean/experimental/initializer_name_correction.rb
new file mode 100644
index 0000000000..b59c98e774
--- /dev/null
+++ b/lib/did_you_mean/experimental/initializer_name_correction.rb
@@ -0,0 +1,20 @@
+# frozen-string-literal: true
+
+require_relative '../levenshtein'
+
+module DidYouMean
+  module Experimental
+    module InitializerNameCorrection
+      def method_added(name)
+        super
+
+        distance = Levenshtein.distance(name.to_s, 'initialize')
+        if distance != 0 && distance <= 2
+          warn "warning: #{name} might be misspelled, perhaps you meant initialize?"
+        end
+      end
+    end
+
+    ::Class.prepend(InitializerNameCorrection)
+  end
+end
diff --git a/lib/did_you_mean/experimental/ivar_name_correction.rb b/lib/did_you_mean/experimental/ivar_name_correction.rb
new file mode 100644
index 0000000000..322e422c6b
--- /dev/null
+++ b/lib/did_you_mean/experimental/ivar_name_correction.rb
@@ -0,0 +1,76 @@
+# frozen-string-literal: true
+
+require_relative '../../did_you_mean'
+
+module DidYouMean
+  module Experimental #:nodoc:
+    class IvarNameCheckerBuilder #:nodoc:
+      attr_reader :original_checker
+
+      def initialize(original_checker) #:nodoc:
+        @original_checker = original_checker
+      end
+
+      def new(no_method_error) #:nodoc:
+        IvarNameChecker.new(no_method_error, original_checker: @original_checker)
+      end
+    end
+
+    class IvarNameChecker #:nodoc:
+      REPLS = {
+        "(irb)" => -> { Readline::HISTORY.to_a.last }
+      }
+
+      TRACE = TracePoint.trace(:raise) do |tp|
+        e = tp.raised_exception
+
+        if SPELL_CHECKERS.include?(e.class.to_s) && !e.instance_variable_defined?(:@frame_binding)
+          e.instance_variable_set(:@frame_binding, tp.binding)
+        end
+      end
+
+      attr_reader :original_checker
+
+      def initialize(no_method_error, original_checker: )
+        @original_checker = original_checker.new(no_method_error)
+
+        @location   = no_method_error.backtrace_locations.first
+        @ivar_names = no_method_error.frame_binding.receiver.instance_variables
+
+        no_method_error.remove_instance_variable(:@frame_binding)
+      end
+
+      def corrections
+        original_checker.corrections + ivar_name_corrections
+      end
+
+      def ivar_name_corrections
+        @ivar_name_corrections ||= SpellChecker.new(dictionary: @ivar_names).correct(receiver_name.to_s)
+      end
+
+      private
+
+      def receiver_name
+        return unless @original_checker.receiver.nil?
+
+        abs_path = @location.absolute_path
+        lineno   = @location.lineno
+
+        /@(\w+)*\.#{@original_checker.method_name}/ =~ line(abs_path, lineno).to_s && $1
+      end
+
+      def line(abs_path, lineno)
+        if REPLS[abs_path]
+          REPLS[abs_path].call
+        elsif File.exist?(abs_path)
+          File.open(abs_path) do |file|
+            file.detect { file.lineno == lineno }
+          end
+        end
+      end
+    end
+  end
+
+  NameError.send(:attr, :frame_binding)
+  SPELL_CHECKERS['NoMethodError'] = Experimental::IvarNameCheckerBuilder.new(SPELL_CHECKERS['NoMethodError'])
+end
diff --git a/lib/did_you_mean/formatters/plain_formatter.rb b/lib/did_you_mean/formatters/plain_formatter.rb
new file mode 100644
index 0000000000..e2d995f587
--- /dev/null
+++ b/lib/did_you_mean/formatters/plain_formatter.rb
@@ -0,0 +1,33 @@
+# frozen-string-literal: true
+
+module DidYouMean
+  # The +DidYouMean::PlainFormatter+ is the basic, default formatter for the
+  # gem. The formatter responds to the +message_for+ method and it returns a
+  # human readable string.
+  class PlainFormatter
+
+    # Returns a human readable string that contains +corrections+. This
+    # formatter is designed to be less verbose to not take too much screen
+    # space while being helpful enough to the user.
+    #
+    # @example
+    #
+    #   formatter = DidYouMean::PlainFormatter.new
+    #
+    #   # displays suggestions in two lines with the leading empty line
+    #   puts formatter.message_for(["methods", "method"])
+    #
+    #   Did you mean?  methods
+    #                   method
+    #   # => nil
+    #
+    #   # displays an empty line
+    #   puts formatter.message_for([])
+    #
+    #   # => nil
+    #
+    def message_for(corrections)
+      corrections.empty? ? "" : "\nDid you mean?  #{corrections.join("\n               ")}"
+    end
+  end
+end
diff --git a/lib/did_you_mean/formatters/verbose_formatter.rb b/lib/did_you_mean/formatters/verbose_formatter.rb
new file mode 100644
index 0000000000..b8fe214d57
--- /dev/null
+++ b/lib/did_you_mean/formatters/verbose_formatter.rb
@@ -0,0 +1,49 @@
+# frozen-string-literal: true
+
+module DidYouMean
+  # The +DidYouMean::VerboseFormatter+ uses extra empty lines to make the
+  # suggestion stand out more in the error message.
+  #
+  # In order to activate the verbose formatter,
+  #
+  # @example
+  #
+  #   OBject
+  #   # => NameError: uninitialized constant OBject
+  #   #    Did you mean?  Object
+  #
+  #   require 'did_you_mean/verbose'
+  #
+  #   OBject
+  #   # => NameError: uninitialized constant OBject
+  #   #
+  #   #        Did you mean? Object
+  #   #
+  #
+  class VerboseFormatter
+
+    # Returns a human readable string that contains +corrections+. This
+    # formatter is designed to be less verbose to not take too much screen
+    # space while being helpful enough to the user.
+    #
+    # @example
+    #
+    #   formatter = DidYouMean::PlainFormatter.new
+    #
+    #   puts formatter.message_for(["methods", "method"])
+    #
+    #
+    #       Did you mean? methods
+    #                     method
+    #
+    #   # => nil
+    #
+    def message_for(corrections)
+      return "" if corrections.empty?
+
+      output = "\n\n    Did you mean? ".dup
+      output << corrections.join("\n                  ")
+      output << "\n "
+    end
+  end
+end
diff --git a/lib/did_you_mean/jaro_winkler.rb b/lib/did_you_mean/jaro_winkler.rb
new file mode 100644
index 0000000000..56db130af4
--- /dev/null
+++ b/lib/did_you_mean/jaro_winkler.rb
@@ -0,0 +1,87 @@
+module DidYouMean
+  module Jaro
+    module_function
+
+    def distance(str1, str2)
+      str1, str2 = str2, str1 if str1.length > str2.length
+      length1, length2 = str1.length, str2.length
+
+      m          = 0.0
+      t          = 0.0
+      range      = (length2 / 2).floor - 1
+      range      = 0 if range < 0
+      flags1     = 0
+      flags2     = 0
+
+      # Avoid duplicating enumerable objects
+      str1_codepoints = str1.codepoints
+      str2_codepoints = str2.codepoints
+
+      i = 0
+      while i < length1
+        last = i + range
+        j    = (i >= range) ? i - range : 0
+
+        while j <= last
+          if flags2[j] == 0 && str1_codepoints[i] == str2_codepoints[j]
+            flags2 |= (1 << j)
+            flags1 |= (1 << i)
+            m += 1
+            break
+          end
+
+          j += 1
+        end
+
+        i += 1
+      end
+
+      k = i = 0
+      while i < length1
+        if flags1[i] != 0
+          j = index = k
+
+          k = while j < length2
+            index = j
+            break(j + 1) if flags2[j] != 0
+
+            j += 1
+          end
+
+          t += 1 if str1_codepoints[i] != str2_codepoints[index]
+        end
+
+        i += 1
+      end
+      t = (t / 2).floor
+
+      m == 0 ? 0 : (m / length1 + m / length2 + (m - t) / m) / 3
+    end
+  end
+
+  module JaroWinkler
+    WEIGHT    = 0.1
+    THRESHOLD = 0.7
+
+    module_function
+
+    def distance(str1, str2)
+      jaro_distance = Jaro.distance(str1, str2)
+
+      if jaro_distance > THRESHOLD
+        codepoints2  = str2.codepoints
+        prefix_bonus = 0
+
+        i = 0
+        str1.each_codepoint do |char1|
+          char1 == codepoints2[i] && i < 4 ? prefix_bonus += 1 : break
+          i += 1
+        end
+
+        jaro_distance + (prefix_bonus * WEIGHT * (1 - jaro_distance))
+      else
+        jaro_distance
+      end
+    end
+  end
+end
diff --git a/lib/did_you_mean/levenshtein.rb b/lib/did_you_mean/levenshtein.rb
new file mode 100644
index 0000000000..098053470f
--- /dev/null
+++ b/lib/did_you_mean/levenshtein.rb
@@ -0,0 +1,57 @@
+module DidYouMean
+  module Levenshtein # :nodoc:
+    # 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 distance(str1, str2)
+      n = str1.length
+      m = str2.length
+      return m if n.zero?
+      return n if m.zero?
+
+      d = (0..m).to_a
+      x = nil
+
+      # to avoid duplicating an enumerable object, create it outside of the loop
+      str2_codepoints = str2.codepoints
+
+      str1.each_codepoint.with_index(1) do |char1, i|
+        j = 0
+        while j < m
+          cost = (char1 == str2_codepoints[j]) ? 0 : 1
+          x = min3(
+            d[j+1] + 1, # insertion
+            i + 1,      # deletion
+            d[j] + cost # substitution
+          )
+          d[j] = i
+          i = x
+
+          j += 1
+        end
+        d[m] = x
+      end
+
+      x
+    end
+    module_function :distance
+
+    private
+
+    # detects the minimum value out of three arguments. This method is
+    # faster than `[a, b, c].min` and puts less GC pressure.
+    # See https://github.com/ruby/did_you_mean/pull/1 for a performance
+    # benchmark.
+    def min3(a, b, c)
+      if a < b && a < c
+        a
+      elsif b < c
+        b
+      else
+        c
+      end
+    end
+    module_function :min3
+  end
+end
diff --git a/lib/did_you_mean/spell_checker.rb b/lib/did_you_mean/spell_checker.rb
new file mode 100644
index 0000000000..e5106abba2
--- /dev/null
+++ b/lib/did_you_mean/spell_checker.rb
@@ -0,0 +1,46 @@
+# frozen-string-literal: true
+
+require_relative "levenshtein"
+require_relative "jaro_winkler"
+
+module DidYouMean
+  class SpellChecker
+    def initialize(dictionary:)
+      @dictionary = dictionary
+    end
+
+    def correct(input)
+      input     = normalize(input)
+      threshold = input.length > 3 ? 0.834 : 0.77
+
+      words = @dictionary.select { |word| JaroWinkler.distance(normalize(word), input) >= threshold }
+      words.reject! { |word| input == word.to_s }
+      words.sort_by! { |word| JaroWinkler.distance(word.to_s, input) }
+      words.reverse!
+
+      # Correct mistypes
+      threshold   = (input.length * 0.25).ceil
+      corrections = words.select { |c| Levenshtein.distance(normalize(c), input) <= threshold }
+
+      # Correct misspells
+      if corrections.empty?
+        corrections = words.select do |word|
+          word   = normalize(word)
+          length = input.length < word.length ? input.length : word.length
+
+          Levenshtein.distance(word, input) < length
+        end.first(1)
+      end
+
+      corrections
+    end
+
+    private
+
+    def normalize(str_or_symbol) #:nodoc:
+      str = str_or_symbol.to_s.downcase
+      str.tr!("@", "")
+      str
+    end
+  end
+end
diff --git a/lib/did_you_mean/spell_checkers/key_error_checker.rb b/lib/did_you_mean/spell_checkers/key_error_checker.rb
new file mode 100644
index 0000000000..be4bea7789
--- /dev/null
+++ b/lib/did_you_mean/spell_checkers/key_error_checker.rb
@@ -0,0 +1,20 @@
+require_relative "../spell_checker"
+
+module DidYouMean
+  class KeyErrorChecker
+    def initialize(key_error)
+      @key = key_error.key
+      @keys = key_error.receiver.keys
+    end
+
+    def corrections
+      @corrections ||= exact_matches.empty? ? SpellChecker.new(dictionary: @keys).correct(@key).map(&:inspect) : exact_matches
+    end
+
+    private
+
+    def exact_matches
+      @exact_matches ||= @keys.select { |word| @key == word.to_s }.map(&:inspect)
+    end
+  end
+end
diff --git a/lib/did_you_mean/spell_checkers/method_name_checker.rb b/lib/did_you_mean/spell_checkers/method_name_checker.rb
new file mode 100644
index 0000000000..3ca8a37e08
--- /dev/null
+++ b/lib/did_you_mean/spell_checkers/method_name_checker.rb
@@ -0,0 +1,56 @@
+require_relative "../spell_checker"
+
+module DidYouMean
+  class MethodNameChecker
+    attr_reader :method_name, :receiver
+
+    NAMES_TO_EXCLUDE = { NilClass => nil.methods }
+    NAMES_TO_EXCLUDE.default = []
+
+    # +MethodNameChecker::RB_RESERVED_WORDS+ is the list of reserved words in
+    # Ruby that take an argument. Unlike
+    # +VariableNameChecker::RB_RESERVED_WORDS+, these reserved words require
+    # an argument, and a +NoMethodError+ is raised due to the presence of the
+    # argument.
+    #
+    # The +MethodNameChecker+ will use this list to suggest a reversed word if
+    # a +NoMethodError+ is raised and found closest matches.
+    #
+    # Also see +VariableNameChecker::RB_RESERVED_WORDS+.
+    RB_RESERVED_WORDS = %i(
+      alias
+      case
+      def
+      defined?
+      elsif
+      end
+      ensure
+      for
+      rescue
+      super
+      undef
+      unless
+      until
+      when
+      while
+      yield
+    )
+
+    def initialize(exception)
+      @method_name  = exception.name
+      @receiver     = exception.receiver
+      @private_call = exception.respond_to?(:private_call?) ? exception.private_call? : false
+    end
+
+    def corrections
+      @corrections ||= SpellChecker.new(dictionary: RB_RESERVED_WORDS + method_names).correct(method_name) - NAMES_TO_EXCLUDE[@receiver.class]
+    end
+
+    def method_names
+      method_names = receiver.methods + receiver.singleton_methods
+      method_names += receiver.private_methods if @private_call
+      method_names.uniq!
+      method_names
+    end
+  end
+end
diff --git a/lib/did_you_mean/spell_checkers/name_error_checkers.rb b/lib/did_you_mean/spell_checkers/name_error_checkers.rb
new file mode 100644
index 0000000000..6e2aaa4cb1
--- /dev/null
+++ b/lib/did_you_mean/spell_checkers/name_error_checkers.rb
@@ -0,0 +1,20 @@
+require_relative 'name_error_checkers/class_name_checker'
+require_relative 'name_error_checkers/variable_name_checker'
+
+module DidYouMean
+  class << (NameErrorCheckers = Object.new)
+    def new(exception)
+      case exception.original_message
+      when /uninitialized constant/
+        ClassNameChecker
+      when /undefined local variable or method/,
+           /undefined method/,
+           /uninitialized class variable/,
+           /no member '.*' in struct/
+        VariableNameChecker
+      else
+        NullChecker
+      end.new(exception)
+    end
+  end
+end
diff --git a/lib/did_you_mean/spell_checkers/name_error_checkers/class_name_checker.rb b/lib/did_you_mean/spell_checkers/name_error_checkers/class_name_checker.rb
new file mode 100644
index 0000000000..3bd048b27c
--- /dev/null
+++ b/lib/did_you_mean/spell_checkers/name_error_checkers/class_name_checker.rb
@@ -0,0 +1,50 @@
+# frozen-string-literal: true
+
+require 'delegate'
+require_relative "../../spell_checker"
+
+module DidYouMean
+  class ClassNameChecker
+    attr_reader :class_name
+
+    def initialize(exception)
+      @class_name, @receiver, @original_message = exception.name, exception.receiver, exception.original_message
+    end
+
+    def corrections
+      @corrections ||= SpellChecker.new(dictionary: class_names)
+                         .correct(class_name)
+                         .map(&:full_name)
+                         .reject {|qualified_name| @original_message.include?(qualified_name) }
+    end
+
+    def class_names
+      scopes.flat_map do |scope|
+        scope.constants.map do |c|
+          ClassName.new(c, scope == Object ? "" : "#{scope}::")
+        end
+      end
+    end
+
+    def scopes
+      @scopes ||= @receiver.to_s.split("::").inject([Object]) do |_scopes, scope|
+        _scopes << _scopes.last.const_get(scope)
+      end.uniq
+    end
+
+    class ClassName < SimpleDelegator
+      attr :namespace
+
+      def initialize(name, namespace = '')
+        super(name)
+        @namespace = namespace
+      end
+
+      def full_name
+        self.class.new("#{namespace}#{__getobj__}")
+      end
+    end
+
+    private_constant :ClassName
+  end
+end
diff --git a/lib/did_you_mean/spell_checkers/name_error_checkers/variable_name_checker.rb b/lib/did_you_mean/spell_checkers/name_error_checkers/variable_name_checker.rb
new file mode 100644
index 0000000000..3e51b4fa3a
--- /dev/null
+++ b/lib/did_you_mean/spell_checkers/name_error_checkers/variable_name_checker.rb
@@ -0,0 +1,82 @@
+# frozen-string-literal: true
+
+require_relative "../../spell_checker"
+
+module DidYouMean
+  class VariableNameChecker
+    attr_reader :name, :method_names, :lvar_names, :ivar_names, :cvar_names
+
+    NAMES_TO_EXCLUDE = { 'foo' => [:fork, :for] }
+    NAMES_TO_EXCLUDE.default = []
+
+    # +VariableNameChecker::RB_RESERVED_WORDS+ is the list of all reserved
+    # words in Ruby. They could be declared like methods are, and a typo would
+    # cause Ruby to raise a +NameError+ because of the way they are declared.
+    #
+    # The +:VariableNameChecker+ will use this list to suggest a reversed word
+    # if a +NameError+ is raised and found closest matches, excluding:
+    #
+    #   * +do+
+    #   * +if+
+    #   * +in+
+    #   * +or+
+    #
+    # Also see +MethodNameChecker::RB_RESERVED_WORDS+.
+    RB_RESERVED_WORDS = %i(
+      BEGIN
+      END
+      alias
+      and
+      begin
+      break
+      case
+      class
+      def
+      defined?
+      else
+      elsif
+      end
+      ensure
+      false
+      for
+      module
+      next
+      nil
+      not
+      redo
+      rescue
+      retry
+      return
+      self
+      super
+      then
+      true
+      undef
+      unless
+      until
+      when
+      while
+      yield
+      __LINE__
+      __FILE__
+      __ENCODING__
+    )
+
+    def initialize(exception)
+      @name       = exception.name.to_s.tr("@", "")
+      @lvar_names = exception.respond_to?(:local_variables) ? exception.local_variables : []
+      receiver    = exception.receiver
+
+      @method_names = receiver.methods + receiver.private_methods
+      @ivar_names   = receiver.instance_variables
+      @cvar_names   = receiver.class.class_variables
+      @cvar_names  += receiver.class_variables if receiver.kind_of?(Module)
+    end
+
+    def corrections
+      @corrections ||= SpellChecker
+                     .new(dictionary: (RB_RESERVED_WORDS + lvar_names + method_names + ivar_names + cvar_names))
+                     .correct(name) - NAMES_TO_EXCLUDE[@name]
+    end
+  end
+end
diff --git a/lib/did_you_mean/spell_checkers/null_checker.rb b/lib/did_you_mean/spell_checkers/null_checker.rb
new file mode 100644
index 0000000000..1306f69d4a
--- /dev/null
+++ b/lib/did_you_mean/spell_checkers/null_checker.rb
@@ -0,0 +1,6 @@
+module DidYouMean
+  class NullChecker
+    def initialize(*);  end
+    def corrections; [] end
+  end
+end
diff --git a/lib/did_you_mean/tree_spell_checker.rb b/lib/did_you_mean/tree_spell_checker.rb
new file mode 100644
index 0000000000..6a5b485413
--- /dev/null
+++ b/lib/did_you_mean/tree_spell_checker.rb
@@ -0,0 +1,137 @@
+module DidYouMean
+  # spell checker for a dictionary that has a tree
+  # structure, see doc/tree_spell_checker_api.md
+  class TreeSpellChecker
+    attr_reader :dictionary, :dimensions, :separator, :augment
+
+    def initialize(dictionary:, separator: '/', augment: nil)
+      @dictionary = dictionary
+      @separator = separator
+      @augment = augment
+      @dimensions = parse_dimensions
+    end
+
+    def correct(input)
+      plausibles = plausible_dimensions input
+      return no_idea(input) if plausibles.empty?
+      suggestions = find_suggestions input, plausibles
+      return no_idea(input) if suggestions.empty?
+      suggestions
+    end
+
+    private
+
+    def parse_dimensions
+      ParseDimensions.new(dictionary, separator).call
+    end
+
+    def find_suggestions(input, plausibles)
+      states = plausibles[0].product(*plausibles[1..-1])
+      paths = possible_paths states
+      leaf = input.split(separator).last
+      ideas = find_ideas(paths, leaf)
+      ideas.compact.flatten
+    end
+
+    def no_idea(input)
+      return [] unless augment
+      ::DidYouMean::SpellChecker.new(dictionary: dictionary).correct(input)
+    end
+
+    def find_ideas(paths, leaf)
+      paths.map do |path|
+        names = find_leaves(path)
+        ideas = CorrectElement.new.call names, leaf
+        ideas_to_paths ideas, leaf, names, path
+      end
+    end
+
+    def ideas_to_paths(ideas, leaf, names, path)
+      return nil if ideas.empty?
+      return [path + separator + leaf] if names.include? leaf
+      ideas.map { |str| path + separator + str }
+    end
+
+    def find_leaves(path)
+      dictionary.map do |str|
+        next unless str.include? "#{path}#{separator}"
+        str.gsub("#{path}#{separator}", '')
+      end.compact
+    end
+
+    def possible_paths(states)
+      states.map do |state|
+        state.join separator
+      end
+    end
+
+    def plausible_dimensions(input)
+      elements = input.split(separator)[0..-2]
+      elements.each_with_index.map do |element, i|
+        next if dimensions[i].nil?
+        CorrectElement.new.call dimensions[i], element
+      end.compact
+    end
+  end
+
+  # parses the elements in each dimension
+  class ParseDimensions
+    def initialize(dictionary, separator)
+      @dictionary = dictionary
+      @separator = separator
+    end
+
+    def call
+      leafless = remove_leaves
+      dimensions = find_elements leafless
+      dimensions.map do |elements|
+        elements.to_set.to_a
+      end
+    end
+
+    private
+
+    def remove_leaves
+      dictionary.map do |a|
+        elements = a.split(separator)
+        elements[0..-2]
+      end.to_set.to_a
+    end
+
+    def find_elements(leafless)
+      max_elements = leafless.map(&:size).max
+      dimensions = Array.new(max_elements) { [] }
+      (0...max_elements).each do |i|
+        leafless.each do |elements|
+          dimensions[i] << elements[i] unless elements[i].nil?
+        end
+      end
+      dimensions
+    end
+
+    attr_reader :dictionary, :separator
+  end
+
+  # identifies the elements close to element
+  class CorrectElement
+    def initialize
+    end
+
+    def call(names, element)
+      return names if names.size == 1
+      str = normalize element
+      return [str] if names.include? str
+      checker = ::DidYouMean::SpellChecker.new(dictionary: names)
+      checker.correct(str)
+    end
+
+    private
+
+    def normalize(leaf)
+      str = leaf.dup
+      str.downcase!
+      return str unless str.include? '@'
+      str.tr!('@', '  ')
+    end
+  end
+end
diff --git a/lib/did_you_mean/verbose.rb b/lib/did_you_mean/verbose.rb
new file mode 100644
index 0000000000..4e86f167ea
--- /dev/null
+++ b/lib/did_you_mean/verbose.rb
@@ -0,0 +1,4 @@
+require_relative '../did_you_mean'
+require_relative 'formatters/verbose_formatter'
+
+DidYouMean.formatter = DidYouMean::VerboseFormatter.new
diff --git a/lib/did_you_mean/version.rb b/lib/did_you_mean/version.rb
new file mode 100644
index 0000000000..cdfeea8026
--- /dev/null
+++ b/lib/did_you_mean/version.rb
@@ -0,0 +1,3 @@
+module DidYouMean
+  VERSION = "1.3.1"
+end