Restyle example formatting for Style/NonNilCheck

Follow up of #4880 (comment). This PR is a change of document format for `Style/NonNilCheck` cop.
rubocop · Oct 27, 2019 · 2f69571 · 2f69571
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diff --git a/lib/rubocop/cop/style/non_nil_check.rb b/lib/rubocop/cop/style/non_nil_check.rb
@@ -5,27 +5,39 @@ module Cop
     module Style
       # This cop checks for non-nil checks, which are usually redundant.
       #
-      # @example
+      # With `IncludeSemanticChanges` set to `false` by default, this cop
+      # does not report offenses for `!x.nil?` and does no changes that might
+      # change behavior.
+      #
+      # With `IncludeSemanticChanges` set to `true`, this cop reports offenses
+      # for `!x.nil?` and autocorrects that and `x != nil` to solely `x`, which
+      # is **usually** OK, but might change behavior.
       #
+      # @example
       #   # bad
       #   if x != nil
       #   end
       #
-      #   # good (when not allowing semantic changes)
-      #   # bad (when allowing semantic changes)
-      #   if !x.nil?
-      #   end
-      #
-      #   # good (when allowing semantic changes)
+      #   # good
       #   if x
       #   end
       #
-      # Non-nil checks are allowed if they are the final nodes of predicate.
-      #
+      #   # Non-nil checks are allowed if they are the final nodes of predicate.
       #   # good
       #   def signed_in?
       #     !current_user.nil?
       #   end
+      #
+      # @example IncludeSemanticChanges: false (default)
+      #   # good
+      #   if !x.nil?
+      #   end
+      #
+      # @example IncludeSemanticChanges: true
+      #   # bad
+      #   if !x.nil?
+      #   end
+      #
       class NonNilCheck < Cop
         def_node_matcher :not_equal_to_nil?, '(send _ :!= nil)'
         def_node_matcher :unless_check?, '(if (send _ :nil?) ...)'

diff --git a/manual/cops_style.md b/manual/cops_style.md
@@ -4410,12 +4410,13 @@ Enabled | Yes | Yes  | 0.20 | 0.22
 
 This cop checks for non-nil checks, which are usually redundant.
 
-Non-nil checks are allowed if they are the final nodes of predicate.
+With `IncludeSemanticChanges` set to `false` by default, this cop
+does not report offenses for `!x.nil?` and does no changes that might
+change behavior.
 
-  # good
-  def signed_in?
-    !current_user.nil?
-  end
+With `IncludeSemanticChanges` set to `true`, this cop reports offenses
+for `!x.nil?` and autocorrects that and `x != nil` to solely `x`, which
+is **usually** OK, but might change behavior.
 
 ### Examples
 
@@ -4424,13 +4425,28 @@ Non-nil checks are allowed if they are the final nodes of predicate.
 if x != nil
 end
 
-# good (when not allowing semantic changes)
-# bad (when allowing semantic changes)
+# good
+if x
+end
+
+# Non-nil checks are allowed if they are the final nodes of predicate.
+# good
+def signed_in?
+  !current_user.nil?
+end
+```
+#### IncludeSemanticChanges: false (default)
+
+```ruby
+# good
 if !x.nil?
 end
+```
+#### IncludeSemanticChanges: true
 
-# good (when allowing semantic changes)
-if x
+```ruby
+# bad
+if !x.nil?
 end
 ```