Drop Ruby 2.6 support

Follow up rubocop/rubocop#11791.

This PR drops Ruby 2.6 support. And JRuby has been dropped from the CI matrix because
no JRuby-specific issues have been found and prevents the following build error:

```console
#!/bin/bash -eo pipefail
bundle install
Fetching https://github.com/rubocop/rubocop.git
You need to install git to be able to use gems from git repositories. For help
installing git, please refer to GitHub's tutorial at
https://help.github.com/articles/set-up-git

Exited with code exit status 11
CircleCI received exit code 11
```

https://app.circleci.com/pipelines/github/rubocop/rubocop-minitest/926/workflows/68776b54-5856-4acd-a99a-f41df114634d/jobs/6034

This does not mean no support for JRuby. RuboCop Rails will continue to support JRuby 9.4+.

.circleci/config.yml

@@ -35,9 +35,6 @@ workflows:
   build:
     jobs:
       - documentation-checks
-      - rake_default:
-          name: Ruby 2.6
-          image: cimg/ruby:2.6
       - rake_default:
           name: Ruby 2.7
           image: cimg/ruby:2.7
@@ -53,6 +50,3 @@ workflows:
       - rake_default:
           name: Ruby HEAD
           image: rubocophq/circleci-ruby-snapshot:latest # Nightly snapshot build
-      - rake_default:
-          name: JRuby 9.3
-          image: circleci/jruby:9.3

.rubocop.yml

@@ -13,7 +13,7 @@ AllCops:
     - 'vendor/**/*'
     - 'spec/fixtures/**/*'
     - 'tmp/**/*'
-  TargetRubyVersion: 2.6
+  TargetRubyVersion: 2.7
   SuggestExtensions: false
 
 InternalAffairs/NodeMatcherDirective:

changelog/change_drop_ruby_2_6_support.md

@@ -0,0 +1 @@
+* [#986](https://github.com/rubocop/rubocop-rails/pull/986): **(Breaking)** Drop Ruby 2.6 support. ([@koic][])

lib/rubocop/cop/rails/lexically_scoped_action_filter.rb

@@ -176,14 +176,14 @@ def array_values(node) # rubocop:disable Metrics/MethodLength
           when :sym
             [node.value]
           when :array
-            node.values.map do |v|
+            node.values.filter_map do |v|
               case v.type
               when :str
                 v.str_content.to_sym
               when :sym
                 v.value
               end
-            end.compact
+            end
           else
             []
           end

lib/rubocop/rails/schema_loader/schema.rb

@@ -83,21 +83,21 @@ def with_column?(name:)
         private
 
         def build_columns(node)
-          each_content(node).map do |child|
+          each_content(node).filter_map do |child|
             next unless child&.send_type?
             next if child.method?(:index)
 
             Column.new(child)
-          end.compact
+          end
         end
 
         def build_indices(node)
-          each_content(node).map do |child|
+          each_content(node).filter_map do |child|
             next unless child&.send_type?
             next unless child.method?(:index)
 
             Index.new(child)
-          end.compact
+          end
         end
 
         def each_content(node, &block)

rubocop-rails.gemspec

@@ -8,7 +8,7 @@ Gem::Specification.new do |s|
   s.name = 'rubocop-rails'
   s.version = RuboCop::Rails::Version::STRING
   s.platform = Gem::Platform::RUBY
-  s.required_ruby_version = '>= 2.6.0'
+  s.required_ruby_version = '>= 2.7.0'
   s.authors = ['Bozhidar Batsov', 'Jonas Arvidsson', 'Yuji Nakayama']
   s.description = <<~DESCRIPTION
     Automatic Rails code style checking tool.

spec/project_spec.rb

@@ -138,9 +138,9 @@
 
       describe 'link to related issue' do
         let(:issues) do
-          entries.map do |entry|
+          entries.filter_map do |entry|
             entry.match(/\[(?<number>[#\d]+)\]\((?<url>[^)]+)\)/)
-          end.compact
+          end
         end
 
         it 'has an issue number prefixed with #' do

tasks/changelog.rb

@@ -1,10 +1,5 @@
 # frozen_string_literal: true
 
-if RUBY_VERSION < '2.6'
-  puts 'Changelog utilities available only for Ruby 2.6+'
-  exit(1)
-end
-
 # Changelog utility
 class Changelog
   ENTRIES_PATH = 'changelog/'