Let format_offense add variable-width whitespace

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features
 
 * [#8111](https://github.com/rubocop-hq/rubocop/pull/8111): Add auto-correct for `Style/StructInheritance`. ([@tejasbubane][])
+* [#8113](https://github.com/rubocop-hq/rubocop/pull/8113): Let `expect_offense` templates add variable-length whitespace with `_{foo}`. ([@eugeneius][])
 
 ## 0.85.1 (2020-06-07)
 

lib/rubocop/rspec/expect_offense.rb

@@ -72,19 +72,29 @@ module RSpec
     #
     #   expect_no_corrections
     #
-    # If your code has variables of different lengths, you can use `%{foo}`
-    # and `^{foo}` to format your template:
+    # If your code has variables of different lengths, you can use `%{foo}`,
+    # `^{foo}`, and `_{foo}` to format your template:
     #
     #   %w[raise fail].each do |keyword|
     #     expect_offense(<<~RUBY, keyword: keyword)
     #       %{keyword}(RuntimeError, msg)
     #       ^{keyword}^^^^^^^^^^^^^^^^^^^ Redundant `RuntimeError` argument can be removed.
     #     RUBY
+    #
+    #   %w[has_one has_many].each do |type|
+    #     expect_offense(<<~RUBY, type: type)
+    #       class Book
+    #         %{type} :chapter, foreign_key: 'book_id'
+    #         _{type}           ^^^^^^^^^^^^^^^^^^^^^^ Specifying the default value is redundant.
+    #       end
+    #     RUBY
+    #   end
     module ExpectOffense
       def format_offense(source, **replacements)
         replacements.each do |keyword, value|
           source = source.gsub("%{#{keyword}}", value)
                          .gsub("^{#{keyword}}", '^' * value.size)
+                         .gsub("_{#{keyword}}", ' ' * value.size)
         end
         source
       end