[Fix rubocop#6956] Prevent auto-correct confliction of Lint/Lambda …

…and `Lint/UnusedBlockArgument`

Fixes rubocop#6956.

This PR prevents auto-correct confliction of `Lint/Lambda` and `Lint/UnusedBlockArgument`.

The following is the reproduction procedure.

```ruby
# example.rb
c = -> event do
  puts 'Hello world'
end
```

```console
% rubocop example.rb -a --only Style/Lambda,Lint/UnusedBlockArgument
```

## Before

A reserved word `lambda` is broken.

```diff
% git diff
diff --git a/example.rb b/example.rb
index 3445c6f..b8e24f4 100644
--- a/example.rb
+++ b/example.rb
@@ -1,3 +1,3 @@
-c = -> event do
+c = lambda_ do |_event|
   puts 'Hello world'
 end
```

## After

It will be a valid code.

```diff
% git diff
diff --git a/example.rb b/example.rb
index 3445c6f..9c22b37 100644
--- a/example.rb
+++ b/example.rb
@@ -1,3 +1,3 @@
-c = -> event do
+c = lambda do |_event|
   puts 'Hello world'
 end
```

CHANGELOG.md

@@ -21,6 +21,7 @@
 * [#6902](https://github.com/rubocop-hq/rubocop/issues/6902): Fix a bug where `Naming/RescuedExceptionsVariableName` would handle an only first rescue for multiple rescue groups. ([@tatsuyafw][])
 * [#6860](https://github.com/rubocop-hq/rubocop/issues/6860): Prevent auto-correct conflict of `Style/InverseMethods` and `Style/Not`. ([@hoshinotsuyoshi][])
 * [#6935](https://github.com/rubocop-hq/rubocop/issues/6935): `Layout/AccessModifierIndentation` should ignore access modifiers that apply to specific methods. ([@deivid-rodriguez][])
+* [#6956](https://github.com/rubocop-hq/rubocop/issues/6956): Prevent auto-correct confliction of `Lint/Lambda` and `Lint/UnusedBlockArgument`. ([@koic][])
 
 ### Changes
 

lib/rubocop/cop/correctors/unused_arg_corrector.rb

@@ -15,14 +15,26 @@ def correct(processed_source, node)
           @processed_source = processed_source
 
           if node.blockarg_type?
+            correct_for_blockarg_type(node)
+          else
             lambda do |corrector|
-              range = range_with_surrounding_space(range: node.source_range,
-                                                   side: :left)
-              range = range_with_surrounding_comma(range, :left)
-              corrector.remove(range)
+              variable_name = if node.optarg_type?
+                                node.node_parts[0]
+                              else
+                                # Extract only a var name without splat (`*`)
+                                node.source.gsub(/\A\*+/, '')
+                              end
+              corrector.replace(node.loc.name, "_#{variable_name}")
             end
-          else
-            ->(corrector) { corrector.insert_before(node.loc.name, '_') }
+          end
+        end
+
+        def correct_for_blockarg_type(node)
+          lambda do |corrector|
+            range = range_with_surrounding_space(range: node.source_range,
+                                                 side: :left)
+            range = range_with_surrounding_comma(range, :left)
+            corrector.remove(range)
           end
         end
       end

spec/rubocop/cli/cli_autocorrect_spec.rb

@@ -467,6 +467,25 @@ def verify_section
     expect(IO.read('example.rb')).to eq(corrected)
   end
 
+  it 'corrects `Lint/Lambda` and `Lint/UnusedBlockArgument` offenses' do
+    source = <<-'RUBY'.strip_indent
+      c = -> event do
+        puts 'Hello world'
+      end
+    RUBY
+    create_file('example.rb', source)
+    expect(cli.run([
+                     '--auto-correct',
+                     '--only', 'Lint/Lambda,Lint/UnusedBlockArgument'
+                   ])).to eq(0)
+    corrected = <<-'RUBY'.strip_indent
+      c = lambda do |_event|
+        puts 'Hello world'
+      end
+    RUBY
+    expect(IO.read('example.rb')).to eq(corrected)
+  end
+
   describe 'caching' do
     let(:cache) do
       instance_double(RuboCop::ResultCache, 'valid?' => true,