[Fixes rubocop#7979] SpellChecker may not be available

In rubocop#7979 it was reported
that DidYouMean::SpellChecker may not always be available. We can work
around it by doing a feature check before using the SpellChecker class.

CHANGELOG.md

@@ -11,6 +11,7 @@
 
 * [#8115](https://github.com/rubocop-hq/rubocop/issues/8115): Fix false negative for `Lint::FormatParameterMismatch` when argument contains formatting. ([@andrykonchin][])
 * [#8124](https://github.com/rubocop-hq/rubocop/issues/8124): Fix a false positive for `Lint/FormatParameterMismatch` when using named parameters with escaped `%`. ([@koic][])
+* [#7979](https://github.com/rubocop-hq/rubocop/issues/7979): Fix "uninitialized constant DidYouMean::SpellChecker" exception. ([@bquorning][])
 
 ## 0.85.1 (2020-06-07)
 

lib/rubocop/name_similarity.rb

@@ -12,6 +12,12 @@ def find_similar_name(target_name, names)
     end
 
     def find_similar_names(target_name, names)
+      # DidYouMean::SpellChecker is not available in all versions of Ruby, and
+      # even on versions where it *is* available (>= 2.3), it is not always
+      # required correctly. So we do a feature check first.
+      # See: https://github.com/rubocop-hq/rubocop/issues/7979
+      return [] unless defined?(DidYouMean::SpellChecker)
+
       names = names.dup
       names.delete(target_name)