[Fix rubocop#444] Mark Rails/Blank as unsafe auto-correction

Fixes #rubocop#444.

This PR marks `Rails/Blank` as unsafe auto-correction because `' '.empty?` returns false,
but `' '.blank?` returns true. Therefore, auto-correction is not compatible if receiver is
a non-empty blank string, tab, or newline meta characters.

CHANGELOG.md

@@ -15,6 +15,7 @@
 * [#432](https://github.com/rubocop/rubocop-rails/issues/432): Exclude gemspec file by default for `Rails/TimeZone` cop. ([@koic][])
 * [#440](https://github.com/rubocop/rubocop-rails/issues/440): This PR makes `Rails/TimeZone` aware of timezone specifier. ([@koic][])
 * [#381](https://github.com/rubocop/rubocop-rails/pull/381): Update `IgnoredMethods` list for `Lint/NumberConversion` to allow Rails' duration methods. ([@dvandersluis][])
+* [#444](https://github.com/rubocop/rubocop-rails/issues/444): Mark `Rails/Blank` as unsafe auto-correction. ([@koic][])
 
 ## 2.9.1 (2020-12-16)
 

config/default.yml

@@ -149,8 +149,9 @@ Rails/BelongsTo:
 Rails/Blank:
   Description: 'Enforces use of `blank?`.'
   Enabled: true
+  SafeAutoCorrect: false
   VersionAdded: '0.48'
-  VersionChanged: '0.67'
+  VersionChanged: '2.10'
   # Convert usages of `nil? || empty?` to `blank?`
   NilOrEmpty: true
   # Convert usages of `!present?` to `blank?`

docs/modules/ROOT/pages/cops_rails.adoc

@@ -590,14 +590,18 @@ end
 
 | Enabled
 | Yes
-| Yes
+| Yes (Unsafe)
 | 0.48
-| 0.67
+| 2.10
 |===
 
 This cop checks for code that can be written with simpler conditionals
 using `Object#blank?` defined by Active Support.
 
+This cop is marked as unsafe auto-correction, because `' '.empty?` returns false,
+but `' '.blank?` returns true. Therefore, auto-correction is not compatible
+if receiver is a non-empty blank string, tab, or newline meta characters.
+
 Interaction with `Style/UnlessElse`:
 The configuration of `NotPresent` will not produce an offense in the
 context of `unless else` if `Style/UnlessElse` is inabled. This is

lib/rubocop/cop/rails/blank.rb

@@ -6,6 +6,10 @@ module Rails
       # This cop checks for code that can be written with simpler conditionals
       # using `Object#blank?` defined by Active Support.
       #
+      # This cop is marked as unsafe auto-correction, because `' '.empty?` returns false,
+      # but `' '.blank?` returns true. Therefore, auto-correction is not compatible
+      # if receiver is a non-empty blank string, tab, or newline meta characters.
+      #
       # Interaction with `Style/UnlessElse`:
       # The configuration of `NotPresent` will not produce an offense in the
       # context of `unless else` if `Style/UnlessElse` is inabled. This is