[Fix rubocop#5630] Fix false positive Style/FormatStringToken

Fixes rubocop#5630.

This PR fixes a false positive for `Style/FormatStringToken` when using
placeholder arguments in `format` method.

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * [#5623](https://github.com/bbatsov/rubocop/pull/5623): Fix `Bundler/OrderedGems` when a group includes duplicate gems. ([@colorbox][])
 * [#5633](https://github.com/bbatsov/rubocop/pull/5633): Fix broken `--fail-fast`. ([@mmyoji][])
+* [#5630](https://github.com/bbatsov/rubocop/issues/5630): Fix false positive for `Style/FormatStringToken` when using placeholder arguments in `format` method. ([@koic][])
 
 ### Changes
 * [#5626](https://github.com/bbatsov/rubocop/pull/5626): Change `Naming/UncommunicativeMethodParamName` add `to` to allowed names in default config. ([@unused][])
@@ -3235,4 +3236,4 @@
 [@elebow]: https://github.com/elebow
 [@colorbox]: https://github.com/colorbox
 [@mmyoji]: https://github.com/mmyoji
-[@unused]: https://github.com/unused
+[@unused]: https://github.com/unused

lib/rubocop/cop/style/format_string_token.rb

@@ -51,6 +51,7 @@ class FormatStringToken < Cop
         }.freeze
 
         def on_str(node)
+          return if placeholder_argument?(node)
           return if node.each_ancestor(:xstr, :regexp).any?
 
           tokens(node) do |detected_style, token_range|
@@ -156,6 +157,13 @@ def slice_source(source_range, new_begin, new_end)
             new_end
           )
         end
+
+        def placeholder_argument?(node)
+          return false unless node.parent
+          return true if node.parent.pair_type?
+
+          placeholder_argument?(node.parent)
+        end
       end
     end
   end

spec/rubocop/cop/style/format_string_token_spec.rb

@@ -127,6 +127,17 @@
     RUBY
   end
 
+  it 'ignores placeholder argumetns' do
+    expect_no_offenses(<<-RUBY.strip_indent)
+      format(
+        '%<day>s %<start>s-%<end>s',
+        day: open_house.starts_at.strftime('%a'),
+        start: open_house.starts_at.strftime('%l'),
+        end: open_house.ends_at.strftime('%l %p').strip
+      )
+    RUBY
+  end
+
   it 'handles __FILE__' do
     expect_no_offenses('__FILE__')
   end