Drop support for Ruby 2.3

### Summary

This PR drops support for Ruby 2.3.

It is discussed in #6945.
And this suggestion would mean that RuboCop 1.0 (and pre-release)
requires Ruby 2.4 or higher.

The following is a plan after this PR.
There was a build error report for a dependent jaro_winkler gem.
#5989, #6754, #7447, and #7564. And #7673 was trying to solve it.

After dropping Ruby 2.3, replace jaro_winkler with did_you_mean.
did_you_mean is written in Ruby, so the build error due to native
extensions no longer occur. That change opens as anther PR.

### Other Information

The latest did_you_mean (1.4.0) supports Ruby 2.5 or higher,
so it needs to be confirmed old versions it works with Ruby 2.4.

.circleci/config.yml

@@ -44,29 +44,6 @@ rubocop_steps: &rubocop_steps
 
 jobs:
 
-  # Ruby 2.3
-  ruby-2.3-spec:
-    docker:
-      - image: circleci/ruby:2.3
-    environment:
-      <<: *common_env
-    steps:
-      *spec_steps
-  ruby-2.3-ascii_spec:
-    docker:
-      - image: circleci/ruby:2.3
-    environment:
-      <<: *common_env
-    steps:
-      *ascii_spec_steps
-  ruby-2.3-rubocop:
-    docker:
-      - image: circleci/ruby:2.3
-    environment:
-      <<: *common_env
-    steps:
-      *rubocop_steps
-
   # Ruby 2.4
   ruby-2.4-spec:
     docker:
@@ -240,7 +217,7 @@ jobs:
       - run:
           name: Upload coverage results to Code Climate
           command: |
-            ./tmp/cc-test-reporter sum-coverage tmp/codeclimate.*.json --parts 6 --output tmp/codeclimate.total.json
+            ./tmp/cc-test-reporter sum-coverage tmp/codeclimate.*.json --parts 5 --output tmp/codeclimate.total.json
             ./tmp/cc-test-reporter upload-coverage --input tmp/codeclimate.total.json
 
   # Miscellaneous tasks
@@ -265,11 +242,6 @@ workflows:
     jobs:
       - documentation-checks
       - cc-setup
-      - ruby-2.3-spec:
-          requires:
-            - cc-setup
-      - ruby-2.3-ascii_spec
-      - ruby-2.3-rubocop
       - ruby-2.4-spec:
           requires:
             - cc-setup
@@ -303,7 +275,6 @@ workflows:
 
       - cc-upload-coverage:
           requires:
-            - ruby-2.3-spec
             - ruby-2.4-spec
             - ruby-2.5-spec
             - ruby-2.6-spec

.rubocop.yml

@@ -12,7 +12,7 @@ AllCops:
     - 'spec/fixtures/**/*'
     - 'tmp/**/*'
     - '.git/**/*'
-  TargetRubyVersion: 2.3
+  TargetRubyVersion: 2.4
 
 Naming/PredicateName:
   # Method define macros for dynamically generated method.

CHANGELOG.md

@@ -16,6 +16,10 @@
 * [#7834](https://github.com/rubocop-hq/rubocop/issues/7834): Fix `Lint/UriRegexp` to register offense with array arguments. ([@tejasbubane][])
 * [#7841](https://github.com/rubocop-hq/rubocop/issues/7841): Fix an error for `Style/TrailingCommaInBlockArgs` when lambda literal (`->`) has multiple arguments. ([@koic][])
 
+### Changes
+
+* [#7840](https://github.com/rubocop-hq/rubocop/pull/7840): **(BREAKING)** Drop support for Ruby 2.3. ([@koic][])
+
 ## 0.81.0 (2020-04-01)
 
 ### New features

README.md

@@ -73,7 +73,7 @@ You can read a lot more about RuboCop in its [official docs](https://docs.ruboco
 
 RuboCop supports the following Ruby implementations:
 
-* MRI 2.3+
+* MRI 2.4+
 * JRuby 9.2+
 
 ## Team

config/default.yml

@@ -133,7 +133,7 @@ AllCops:
   # followed by the Gemfile.lock or gems.locked file. (Although the Ruby version
   # is specified in the Gemfile or gems.rb file, RuboCop reads the final value
   # from the lock file.) If the Ruby version is still unresolved, RuboCop will
-  # use the oldest officially supported Ruby version (currently Ruby 2.3).
+  # use the oldest officially supported Ruby version (currently Ruby 2.4).
   TargetRubyVersion: ~
 
 #################### Bundler ###############################
@@ -2831,7 +2831,7 @@ Style/FrozenStringLiteralComment:
     # `always` will always add the frozen string literal comment to a file
     # regardless of the Ruby version or if `freeze` or `<<` are called on a
     # string literal. If you run code against multiple versions of Ruby, it is
-    # possible that this will create errors in Ruby 2.3.0+.
+    # possible that this will create errors in Ruby 2.4.0+.
     - always
     # `always_true` will add the frozen string literal comment to a file,
     # similarly to the `always` style, but will also change any disabled

lib/rubocop/config_loader.rb

@@ -79,10 +79,8 @@ def merge(base_hash, derived_hash)
       # user's home directory is checked. If there's no .rubocop.yml
       # there either, the path to the default file is returned.
       def configuration_file_for(target_dir)
-        find_project_dotfile(target_dir) ||
-          find_user_dotfile ||
-          find_user_xdg_config ||
-          DEFAULT_FILE
+        find_project_dotfile(target_dir) || find_user_dotfile ||
+          find_user_xdg_config || DEFAULT_FILE
       end
 
       def configuration_from_file(config_file)
@@ -208,7 +206,9 @@ def existing_configuration(config_file)
       def write_config_file(file_name, file_string, rubocop_yml_contents)
         File.open(file_name, 'w') do |f|
           f.write "inherit_from:#{file_string}\n"
-          f.write "\n#{rubocop_yml_contents}" if rubocop_yml_contents =~ /\S/
+          if /\S/.match?(rubocop_yml_contents)
+            f.write "\n#{rubocop_yml_contents}"
+          end
         end
       end
 

lib/rubocop/cop/correctors/alignment_corrector.rb

@@ -51,7 +51,7 @@ def autocorrect_line(corrector, line_begin_pos, expr, column_delta,
             unless range.resize(1).source == "\n"
               corrector.insert_before(range, ' ' * column_delta)
             end
-          elsif range.source =~ /\A[ \t]+\z/
+          elsif /\A[ \t]+\z/.match?(range.source)
             remove(range, corrector)
           end
         end
@@ -112,7 +112,7 @@ def remove(range, corrector)
           corrector.remove(range)
         rescue RuntimeError
           range = range_between(range.begin_pos + 1, range.end_pos + 1)
-          retry if range.source =~ /^ +$/
+          retry if /^ +$/.match?(range.source)
         ensure
           $stderr = original_stderr
         end

lib/rubocop/cop/layout/end_of_line.rb

@@ -75,8 +75,8 @@ def offense_message(line)
                               style
                             end
           case effective_style
-          when :lf then MSG_DETECTED if line =~ /\r$/
-          else MSG_MISSING if line !~ /\r$/
+          when :lf then MSG_DETECTED if /\r$/.match?(line)
+          else MSG_MISSING unless /\r$/.match?(line)
           end
         end
 

lib/rubocop/cop/layout/first_array_element_indentation.rb

@@ -125,21 +125,15 @@ def check(array_node, left_parenthesis)
 
         def check_right_bracket(right_bracket, left_bracket, left_parenthesis)
           # if the right bracket is on the same line as the last value, accept
-          return if right_bracket.source_line[0...right_bracket.column] =~ /\S/
+          if /\S/.match?(right_bracket.source_line[0...right_bracket.column])
+            return
+          end
 
           expected_column = base_column(left_bracket, left_parenthesis)
           @column_delta = expected_column - right_bracket.column
           return if @column_delta.zero?
 
-          msg = if style == :align_brackets
-                  'Indent the right bracket the same as the left bracket.'
-                elsif style == :special_inside_parentheses && left_parenthesis
-                  'Indent the right bracket the same as the first position ' \
-                  'after the preceding left parenthesis.'
-                else
-                  'Indent the right bracket the same as the start of the line' \
-                  ' where the left bracket is.'
-                end
+          msg = msg(left_parenthesis)
           add_offense(right_bracket, location: right_bracket, message: msg)
         end
 
@@ -161,6 +155,18 @@ def message(base_description)
             base_description: base_description
           )
         end
+
+        def msg(left_parenthesis)
+          if style == :align_brackets
+            'Indent the right bracket the same as the left bracket.'
+          elsif style == :special_inside_parentheses && left_parenthesis
+            'Indent the right bracket the same as the first position ' \
+            'after the preceding left parenthesis.'
+          else
+            'Indent the right bracket the same as the start of the line' \
+            ' where the left bracket is.'
+          end
+        end
       end
     end
   end

lib/rubocop/cop/layout/first_hash_element_indentation.rb

@@ -128,7 +128,7 @@ def check(hash_node, left_parenthesis)
 
         def check_right_brace(right_brace, left_brace, left_parenthesis)
           # if the right brace is on the same line as the last value, accept
-          return if right_brace.source_line[0...right_brace.column] =~ /\S/
+          return if /\S/.match?(right_brace.source_line[0...right_brace.column])
 
           expected_column = base_column(left_brace, left_parenthesis)
           @column_delta = expected_column - right_brace.column

lib/rubocop/cop/layout/leading_comment_space.rb

@@ -56,7 +56,7 @@ class LeadingCommentSpace < Cop
 
         def investigate(processed_source)
           processed_source.each_comment do |comment|
-            next unless comment.text =~ /\A#+[^#\s=:+-]/
+            next unless /\A#+[^#\s=:+-]/.match?(comment.text)
             next if comment.loc.line == 1 && allowed_on_first_line?(comment)
             next if doxygen_comment_style?(comment)
             next if gemfile_ruby_comment?(comment)

lib/rubocop/cop/layout/line_length.rb

@@ -145,7 +145,7 @@ def breakable_range_after_semicolon(semicolon_token)
           return nil unless next_range.line == range.line
 
           next_char = next_range.source
-          return nil if /[\r\n]/ =~ next_char
+          return nil if /[\r\n]/.match?(next_char)
           return nil if next_char == ';'
 
           next_range

lib/rubocop/cop/layout/space_around_block_parameters.rb

@@ -47,7 +47,7 @@ def autocorrect(target)
               else
                 corrector.insert_after(target, ' ')
               end
-            elsif target.source =~ /^\s+$/
+            elsif /^\s+$/.match?(target.source)
               corrector.remove(target)
             else
               corrector.insert_after(target, ' ')

lib/rubocop/cop/layout/space_around_operators.rb

@@ -175,7 +175,7 @@ def offense_message(type, operator, with_space, right_operand)
             return if with_space.is?(operator.source)
 
             "Space around operator `#{operator.source}` detected."
-          elsif with_space.source !~ /^\s.*\s$/
+          elsif !/^\s.*\s$/.match?(with_space.source)
             "Surrounding space missing for operator `#{operator.source}`."
           elsif excess_leading_space?(type, operator, with_space) ||
                 excess_trailing_space?(right_operand, with_space)

lib/rubocop/cop/layout/space_inside_block_braces.rb

@@ -117,7 +117,7 @@ def check_inside(node, left_brace, right_brace)
             range = range_between(left_brace.end_pos, right_brace.begin_pos)
             inner = range.source
 
-            if inner =~ /\S/
+            if /\S/.match?(inner)
               braces_with_contents_inside(node, inner)
             elsif style_for_empty_braces == :no_space
               offense(range.begin_pos, range.end_pos,
@@ -142,7 +142,7 @@ def braces_with_contents_inside(node, inner)
         end
 
         def check_left_brace(inner, left_brace, args_delimiter)
-          if inner =~ /\A\S/
+          if /\A\S/.match?(inner)
             no_space_inside_left_brace(left_brace, args_delimiter)
           else
             space_inside_left_brace(left_brace, args_delimiter)

lib/rubocop/cop/layout/space_inside_range_literal.rb

@@ -53,7 +53,7 @@ def check(node)
           # account for multiline range literals
           expression.sub!(/#{escaped_op}\n\s*/, op)
 
-          return unless expression =~ /(\s#{escaped_op})|(#{escaped_op}\s)/
+          return unless /(\s#{escaped_op})|(#{escaped_op}\s)/.match?(expression)
 
           add_offense(node)
         end

lib/rubocop/cop/lint/debugger.rb

@@ -69,7 +69,7 @@ def message(node)
         end
 
         def binding_irb?(node)
-          target_ruby_version >= 2.4 && binding_irb_call?(node)
+          binding_irb_call?(node)
         end
       end
     end

lib/rubocop/cop/lint/implicit_string_concatenation.rb

@@ -81,7 +81,7 @@ def string_literals?(node1, node2)
         end
 
         def display_str(node)
-          if node.source =~ /\n/
+          if /\n/.match?(node.source)
             str_content(node).inspect
           else
             node.source

lib/rubocop/cop/lint/interpolation_check.rb

@@ -25,7 +25,7 @@ def on_str(node)
 
           parent = node.parent
           return if parent && (parent.dstr_type? || parent.regexp_type?)
-          return unless node.source.scrub =~ /(?<!\\)#\{.*\}/
+          return unless /(?<!\\)#\{.*\}/.match?(node.source.scrub)
 
           add_offense(node)
         end

lib/rubocop/cop/lint/percent_string_array.rb

@@ -48,7 +48,7 @@ def autocorrect(node)
               match = range.source.match(TRAILING_QUOTE)
               corrector.remove_trailing(range, match[0].length) if match
 
-              if range.source =~ LEADING_QUOTE
+              if LEADING_QUOTE.match?(range.source)
                 corrector.remove_leading(range, 1)
               end
             end

lib/rubocop/cop/lint/unified_integer.rb

@@ -33,8 +33,6 @@ def on_const(node)
         end
 
         def autocorrect(node)
-          return false if target_ruby_version <= 2.3
-
           lambda do |corrector|
             corrector.replace(node.loc.name, 'Integer')
           end

lib/rubocop/cop/mixin/trailing_comma.rb

@@ -135,7 +135,7 @@ def on_same_line?(range1, range2)
 
       def avoid_comma(kind, comma_begin_pos, extra_info)
         range = range_between(comma_begin_pos, comma_begin_pos + 1)
-        article = kind =~ /array/ ? 'an' : 'a'
+        article = /array/.match?(kind) ? 'an' : 'a'
         msg = format(
           MSG,
           command: 'Avoid',

lib/rubocop/cop/naming/class_and_module_camel_case.rb

@@ -22,7 +22,7 @@ class ClassAndModuleCamelCase < Cop
         MSG = 'Use CamelCase for classes and modules.'
 
         def on_class(node)
-          return unless node.loc.name.source =~ /_/
+          return unless /_/.match?(node.loc.name.source)
 
           add_offense(node, location: :name)
         end

lib/rubocop/cop/naming/constant_name.rb

@@ -45,8 +45,9 @@ def on_casgn(node)
           # SomeClass = Class.new(...)
           # SomeClass = Struct.new(...)
           return if allowed_assignment?(value)
+          return if SNAKE_CASE.match?(const_name)
 
-          add_offense(node, location: :name) if const_name !~ SNAKE_CASE
+          add_offense(node, location: :name)
         end
 
         private

lib/rubocop/cop/naming/heredoc_delimiter_naming.rb

@@ -39,7 +39,7 @@ def on_heredoc(node)
         def meaningful_delimiters?(node)
           delimiters = delimiter_string(node)
 
-          return false unless delimiters =~ /\w/
+          return false unless /\w/.match?(delimiters)
 
           forbidden_delimiters.none? do |forbidden_delimiter|
             delimiters =~ Regexp.new(forbidden_delimiter)

lib/rubocop/cop/style/and_or.rb

@@ -136,7 +136,7 @@ def whitespace_before_arg(node)
           end_paren = begin_paren
           # Increment position of parenthesis, unless message is a predicate
           # method followed by a non-whitespace char (e.g. is_a?String).
-          end_paren += 1 unless node.source =~ /\?\S/
+          end_paren += 1 unless /\?\S/.match?(node.source)
           range_between(begin_paren, end_paren)
         end
       end

lib/rubocop/cop/style/copyright.rb

@@ -55,7 +55,7 @@ def verify_autocorrect_notice!
           raise Warning, AUTOCORRECT_EMPTY_WARNING if autocorrect_notice.empty?
 
           regex = Regexp.new(notice)
-          return if autocorrect_notice =~ regex
+          return if autocorrect_notice&.match?(regex)
 
           raise Warning, "AutocorrectNotice '#{autocorrect_notice}' must " \
                          "match Notice /#{notice}/"

lib/rubocop/cop/style/exponential_notation.rb

@@ -74,11 +74,11 @@ def scientific?(node)
 
         def engineering?(node)
           mantissa, exponent = node.source.split('e')
-          return false unless exponent =~ /^-?\d+$/
+          return false unless /^-?\d+$/.match?(exponent)
           return false unless (exponent.to_i % 3).zero?
-          return false if mantissa =~ /^-?\d{4}/
-          return false if mantissa =~ /^-?0\d/
-          return false if mantissa =~ /^-?0.0/
+          return false if /^-?\d{4}/.match?(mantissa)
+          return false if /^-?0\d/.match?(mantissa)
+          return false if /^-?0.0/.match?(mantissa)
 
           true
         end