Support TargetRubyVersion 3.4 (experimental)

RuboCop AST 1.31 supports Ruby 3.4.
rubocop/rubocop-ast#276

This PR supports `TargetRubyVersion 3.4`.

changelog/new_support_ruby_3_3_experimental.md

@@ -0,0 +1 @@
+* [#12725](https://github.com/rubocop/rubocop/pull/12725): Support `TargetRubyVersion 3.4` (experimental). ([@koic][])

docs/modules/ROOT/pages/compatibility.adoc

@@ -35,6 +35,7 @@ The following table is the runtime support matrix.
 | 3.1 | -
 | 3.2 | -
 | 3.3 | -
+| 3.4 (experimental) | -
 |===
 
 RuboCop targets Ruby 2.0+ code analysis since RuboCop 1.30. It restored code analysis support that had been removed earlier by mistake, together with dropping runtime support for unsupported Ruby versions.

lib/rubocop/rspec/shared_contexts.rb

@@ -185,3 +185,7 @@ def source_range(range, buffer: source_buffer)
 RSpec.shared_context 'ruby 3.3' do
   let(:ruby_version) { 3.3 }
 end
+
+RSpec.shared_context 'ruby 3.4' do
+  let(:ruby_version) { 3.4 }
+end

lib/rubocop/target_ruby.rb

@@ -4,7 +4,7 @@ module RuboCop
   # The kind of Ruby that code inspected by RuboCop is written in.
   # @api private
   class TargetRuby
-    KNOWN_RUBIES = [2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 3.0, 3.1, 3.2, 3.3].freeze
+    KNOWN_RUBIES = [2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 3.0, 3.1, 3.2, 3.3, 3.4].freeze
     DEFAULT_VERSION = 2.7
 
     OBSOLETE_RUBIES = {

rubocop.gemspec

@@ -38,7 +38,7 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency('rainbow', '>= 2.2.2', '< 4.0')
   s.add_runtime_dependency('regexp_parser', '>= 1.8', '< 3.0')
   s.add_runtime_dependency('rexml', '>= 3.2.5', '< 4.0')
-  s.add_runtime_dependency('rubocop-ast', '>= 1.30.0', '< 2.0')
+  s.add_runtime_dependency('rubocop-ast', '>= 1.31.0', '< 2.0')
   s.add_runtime_dependency('ruby-progressbar', '~> 1.7')
   s.add_runtime_dependency('unicode-display_width', '>= 2.4.0', '< 3.0')
 end

spec/rubocop/cli_spec.rb

@@ -1903,7 +1903,7 @@ def method(foo, bar, qux, fred, arg5, f) end #{'#' * 85}
           'Error: RuboCop found unknown Ruby version 4.0 in `TargetRubyVersion`'
         )
         expect($stderr.string.strip).to match(
-          /Supported versions: 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 3.0, 3.1, 3.2, 3.3/
+          /Supported versions: 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 3.0, 3.1, 3.2, 3.3, 3.4/
         )
       end
     end