[Fix #10258] Recover Ruby 2.4 code analysis using `TargetRubyVersion:…

… 2.4`

Fixes #10258 and reverts part of #9648.

Only the Ruby version (2.4) to runtime should have been dropped,
not code analysis.
This PR makes Ruby 2.4 code analysis with `TargetRubyVersion: 2.4`.
So, this keeps it compatible with `TargetRubyVersion` up to
RuboCop 1.12.1 as semver.

It aims to solve essentially the same problem as #10626.

changelog/fix_recover_ruby_24_code_analysis.md

@@ -0,0 +1 @@
+* [#10258](https://github.com/rubocop/rubocop/issues/10258): Recover Ruby 2.4 code analysis using `TargetRubyVersion: 2.4`. ([@koic][])

lib/rubocop/cop/style/hash_transform_keys.rb

@@ -7,6 +7,8 @@ module Style
       # `_.map {...}.to_h`, and `Hash[_.map {...}]` that are actually just
       # transforming the keys of a hash, and tries to use a simpler & faster
       # call to `transform_keys` instead.
+      # It should only be enabled on Ruby version 2.5 or newer.
+      # (`transform_keys` was added in Ruby 2.5.)
       #
       # @safety
       #   This cop is unsafe, as it can produce false positives if we are
@@ -26,6 +28,9 @@ module Style
       class HashTransformKeys < Base
         include HashTransformMethod
         extend AutoCorrector
+        extend TargetRubyVersion
+
+        minimum_target_ruby_version 2.5
 
         # @!method on_bad_each_with_object(node)
         def_node_matcher :on_bad_each_with_object, <<~PATTERN

lib/rubocop/cop/style/redundant_begin.rb

@@ -36,6 +36,7 @@ module Style
       #   do_something
       #
       #   # bad
+      #   # When using Ruby 2.5 or later.
       #   do_something do
       #     begin
       #       something
@@ -75,6 +76,7 @@ def on_def(node)
         alias on_defs on_def
 
         def on_block(node)
+          return if target_ruby_version < 2.5
           return if node.send_node.lambda_literal?
           return if node.braces?
           return unless node.body&.kwbegin_type?

lib/rubocop/rspec/shared_contexts.rb

@@ -116,6 +116,10 @@ def source_range(range, buffer: source_buffer)
   end
 end
 
+RSpec.shared_context 'ruby 2.4', :ruby24 do
+  let(:ruby_version) { 2.4 }
+end
+
 RSpec.shared_context 'ruby 2.5', :ruby25 do
   let(:ruby_version) { 2.5 }
 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 = [2.5, 2.6, 2.7, 3.0, 3.1, 3.2].freeze
+    KNOWN_RUBIES = [2.4, 2.5, 2.6, 2.7, 3.0, 3.1, 3.2].freeze
     DEFAULT_VERSION = 2.6
 
     OBSOLETE_RUBIES = {

spec/rubocop/cli_spec.rb

@@ -1693,7 +1693,9 @@ def method(foo, bar, qux, fred, arg5, f) end #{'#' * 85}
         expect($stderr.string.strip).to start_with(
           'Error: RuboCop found unknown Ruby version 4.0 in `TargetRubyVersion`'
         )
-        expect($stderr.string.strip).to match(/Supported versions: 2.5, 2.6, 2.7, 3.0, 3.1, 3.2/)
+        expect($stderr.string.strip).to match(
+          /Supported versions: 2.4, 2.5, 2.6, 2.7, 3.0, 3.1, 3.2/
+        )
       end
     end
 
@@ -1714,7 +1716,7 @@ def method(foo, bar, qux, fred, arg5, f) end #{'#' * 85}
           /2\.0-compatible analysis was dropped after version 0\.50/
         )
 
-        expect($stderr.string.strip).to match(/Supported versions: 2.5/)
+        expect($stderr.string.strip).to match(/Supported versions: 2.4/)
       end
     end
   end

spec/rubocop/config_loader_spec.rb

@@ -1188,7 +1188,7 @@ class Loop < Base
       end
 
       context 'when the specified version is obsolete' do
-        let(:inherited_version) { '2.4' }
+        let(:inherited_version) { '2.3' }
 
         context 'and it is not overridden' do
           before do
@@ -1199,7 +1199,7 @@ class Loop < Base
 
           it 'raises a validation error' do
             expect { configuration_from_file }.to raise_error(RuboCop::ValidationError) do |error|
-              expect(error.message).to start_with('RuboCop found unsupported Ruby version 2.4')
+              expect(error.message).to start_with('RuboCop found unsupported Ruby version 2.3')
             end
           end
         end

spec/rubocop/cop/lint/suppressed_exception_spec.rb

@@ -114,25 +114,27 @@ def self.foo
       end
     end
 
-    context 'when empty rescue for `do` block' do
-      it 'registers an offense for empty rescue without comment' do
-        expect_offense(<<~RUBY)
-          foo do
-            do_something
-          rescue
-          ^^^^^^ Do not suppress exceptions.
-          end
-        RUBY
-      end
+    context 'Ruby 2.5 or higher', :ruby25 do
+      context 'when empty rescue for `do` block' do
+        it 'registers an offense for empty rescue without comment' do
+          expect_offense(<<~RUBY)
+            foo do
+              do_something
+            rescue
+            ^^^^^^ Do not suppress exceptions.
+            end
+          RUBY
+        end
 
-      it 'registers an offense for empty rescue with comment' do
-        expect_offense(<<~RUBY)
-          foo do
-          rescue
-          ^^^^^^ Do not suppress exceptions.
-            # do nothing
-          end
-        RUBY
+        it 'registers an offense for empty rescue with comment' do
+          expect_offense(<<~RUBY)
+            foo do
+            rescue
+            ^^^^^^ Do not suppress exceptions.
+              # do nothing
+            end
+          RUBY
+        end
       end
     end
   end
@@ -195,24 +197,26 @@ def self.foo
       end
     end
 
-    context 'when empty rescue for `do` block' do
-      it 'registers an offense for empty rescue without comment' do
-        expect_offense(<<~RUBY)
-          foo do
-            do_something
-          rescue
-          ^^^^^^ Do not suppress exceptions.
-          end
-        RUBY
-      end
+    context 'Ruby 2.5 or higher', :ruby25 do
+      context 'when empty rescue for `do` block' do
+        it 'registers an offense for empty rescue without comment' do
+          expect_offense(<<~RUBY)
+            foo do
+              do_something
+            rescue
+            ^^^^^^ Do not suppress exceptions.
+            end
+          RUBY
+        end
 
-      it 'does not register an offense for empty rescue with comment' do
-        expect_no_offenses(<<~RUBY)
-          foo do
-          rescue
-            # do nothing
-          end
-        RUBY
+        it 'does not register an offense for empty rescue with comment' do
+          expect_no_offenses(<<~RUBY)
+            foo do
+            rescue
+              # do nothing
+            end
+          RUBY
+        end
       end
     end