Remove support for Ruby 2.6 (#21477)

As pointed out by https://github.com/mastodon/mastodon/pull/21297#discussion_r1028372193
at least one of our dependencies already dropped support for Ruby 2.6, and we
had removed Ruby 2.6 tests from the CI over a year ago (#16861).

So stop advertising Ruby 2.6 support, bump targeted version, and drop some
compatibility code.

.rubocop.yml

@@ -2,7 +2,7 @@ require:
   - rubocop-rails
 
 AllCops:
-  TargetRubyVersion: 2.5
+  TargetRubyVersion: 2.7
   NewCops: disable
   Exclude:
     - 'spec/**/*'

Gemfile

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 source 'https://rubygems.org'
-ruby '>= 2.6.0', '< 3.1.0'
+ruby '>= 2.7.0', '< 3.1.0'
 
 gem 'pkg-config', '~> 1.4'
 gem 'rexml', '~> 3.2'

README.md

@@ -72,7 +72,7 @@ Mastodon acts as an OAuth2 provider, so 3rd party apps can use the REST and Stre
 
 - **PostgreSQL** 9.5+
 - **Redis** 4+
-- **Ruby** 2.6+
+- **Ruby** 2.7+
 - **Node.js** 14+
 
 The repository includes deployment configurations for **Docker and docker-compose** as well as specific platforms like **Heroku**, **Scalingo**, and **Nanobox**. The [**standalone** installation guide](https://docs.joinmastodon.org/admin/install/) is available in the documentation.

config/application.rb

@@ -22,7 +22,6 @@ require 'mail'
 Bundler.require(*Rails.groups)
 
 require_relative '../lib/exceptions'
-require_relative '../lib/enumerable'
 require_relative '../lib/sanitize_ext/sanitize_config'
 require_relative '../lib/redis/namespace_extensions'
 require_relative '../lib/paperclip/url_generator_extensions'

lib/enumerable.rb

@@ -1,26 +0,0 @@
-# frozen_string_literal: true
-
-module Enumerable
-  # TODO: Remove this once stop to support Ruby 2.6
-  if RUBY_VERSION < '2.7.0'
-    def filter_map
-      if block_given?
-        result = []
-        each do |element|
-          res = yield element
-          result << res if res
-        end
-        result
-      else
-        Enumerator.new do |yielder|
-          result = []
-          each do |element|
-            res = yielder.yield element
-            result << res if res
-          end
-          result
-        end
-      end
-    end
-  end
-end