Restore Lint/UselessElseWithoutRescue cop

This reverts commit 6d0b336 and tweaked.

Follow up #10577 (comment).

RuboCop 1.29.1 and higher can analyze Ruby 2.5 code again, so it can restore the cop.

Rakefile

@@ -95,9 +95,13 @@ task documentation_syntax_check: :yard_for_generate_documentation do
       buffer = Parser::Source::Buffer.new('<code>', 1)
       buffer.source = example.text
 
-      # Ruby 2.7 raises a syntax error in
-      # `Lint/CircularArgumentReference` cop's example.
-      parser = if cop == RuboCop::Cop::Lint::CircularArgumentReference
+      # Ruby 2.6 or higher does not support a syntax used in
+      # `Lint/UselessElseWithoutRescue` cop's example.
+      parser = if cop == RuboCop::Cop::Lint::UselessElseWithoutRescue
+                 Parser::Ruby25.new(RuboCop::AST::Builder.new)
+               # Ruby 2.7 raises a syntax error in
+               # `Lint/CircularArgumentReference` cop's example.
+               elsif cop == RuboCop::Cop::Lint::CircularArgumentReference
                  Parser::Ruby26.new(RuboCop::AST::Builder.new)
                # Ruby 3.0 raises a syntax error in
                # `Lint/NumberedParameterAssignment` cop's example.

changelog/change_restore_lint_useless_else_without_rescue_cop.md

@@ -0,0 +1 @@
+* [#10697](https://github.com/rubocop/rubocop/pull/10697): Restore `Lint/UselessElseWithoutRescue` cop. ([@koic][])

config/default.yml

@@ -2348,6 +2348,12 @@ Lint/UselessAssignment:
   Enabled: true
   VersionAdded: '0.11'
 
+Lint/UselessElseWithoutRescue:
+  Description: 'Checks for useless `else` in `begin..end` without `rescue`.'
+  Enabled: true
+  VersionAdded: '0.17'
+  VersionChanged: '<<next>>'
+
 Lint/UselessMethodDefinition:
   Description: 'Checks for useless method definitions.'
   Enabled: true

lib/rubocop.rb

@@ -387,6 +387,7 @@
 require_relative 'rubocop/cop/lint/uri_regexp'
 require_relative 'rubocop/cop/lint/useless_access_modifier'
 require_relative 'rubocop/cop/lint/useless_assignment'
+require_relative 'rubocop/cop/lint/useless_else_without_rescue'
 require_relative 'rubocop/cop/lint/useless_method_definition'
 require_relative 'rubocop/cop/lint/useless_ruby2_keywords'
 require_relative 'rubocop/cop/lint/useless_setter_call'

lib/rubocop/cop/lint/useless_else_without_rescue.rb

@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module Lint
+      # Checks for useless `else` in `begin..end` without `rescue`.
+      #
+      # NOTE: This syntax is no longer valid on Ruby 2.6 or higher.
+      #
+      # @example
+      #
+      #   # bad
+      #
+      #   begin
+      #     do_something
+      #   else
+      #     do_something_else # This will never be run.
+      #   end
+      #
+      # @example
+      #
+      #   # good
+      #
+      #   begin
+      #     do_something
+      #   rescue
+      #     handle_errors
+      #   else
+      #     do_something_else
+      #   end
+      class UselessElseWithoutRescue < Base
+        MSG = '`else` without `rescue` is useless.'
+
+        def on_new_investigation
+          processed_source.diagnostics.each do |diagnostic|
+            next unless diagnostic.reason == :useless_else
+
+            add_offense(diagnostic.location, severity: diagnostic.level)
+          end
+        end
+      end
+    end
+  end
+end

spec/rubocop/cop/lint/useless_else_without_rescue_spec.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Lint::UselessElseWithoutRescue, :config do
+  context 'with `else` without `rescue`', :ruby25 do
+    it 'registers an offense' do
+      expect_offense(<<~RUBY)
+        begin
+          do_something
+        else
+        ^^^^ `else` without `rescue` is useless.
+          handle_unknown_errors
+        end
+      RUBY
+    end
+  end
+
+  context 'with `else` with `rescue`' do
+    it 'accepts' do
+      expect_no_offenses(<<~RUBY)
+        begin
+          do_something
+        rescue ArgumentError
+          handle_argument_error
+        else
+          handle_unknown_errors
+        end
+      RUBY
+    end
+  end
+end