[Fix #6914] Fix an error for Rails/RedundantAllowNil when with interpolations

[Blue-Pix]

Fixes #6914.

This PR fixes the following error for Rails/RedundantAllowNil when with interpolations.

class Foo < ActiveRecord::Base
  BAR = "sample"
  validates :name, "#{self::BAR}": true
end

class SampleValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    if value.size > 3
      record.errors.add(attribute, 'too long')
    end
  end
end

This is stacktrace.

$ rubocop app/models/foo.rb --only Rails/RedundantAllowNil -d
An error occurred while Rails/RedundantAllowNil cop was inspecting /myapp/app/models/foo.rb:3:2.
undefined method `value' for "s(:dsym,\n  s(:begin,\n    s(:const,\n      s(:self), :BAR)))":RuboCop::AST::Node

---

Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[koic]

A solution is to use Node#source.

diff --git a/lib/rubocop/cop/rails/redundant_allow_nil.rb b/lib/rubocop/cop/rails/redundant_allow_nil.rb
index be75c1592..2f5934b56 100644
--- a/lib/rubocop/cop/rails/redundant_allow_nil.rb
+++ b/lib/rubocop/cop/rails/redundant_allow_nil.rb
@@ -79,10 +79,10 @@ module RuboCop
           node.each_descendant do |descendant|
             next unless descendant.pair_type?

-            key = descendant.children.first.value
+            key = descendant.children.first.source

-            allow_nil = descendant if key == :allow_nil
-            allow_blank = descendant if key == :allow_blank
+            allow_nil = descendant if key == 'allow_nil'
+            allow_blank = descendant if key == 'allow_blank'

             break if allow_nil && allow_blank
           end

[Blue-Pix]

Thanks for a review!

[koic]

Please add a test case to reproduce.

diff --git a/spec/rubocop/cop/rails/redundant_allow_nil_spec.rb b/spec/rubocop/cop/rails/redundant_allow_nil_spec.rb
index 0ce9ffd5a..760661d4a 100644
--- a/spec/rubocop/cop/rails/redundant_allow_nil_spec.rb
+++ b/spec/rubocop/cop/rails/redundant_allow_nil_spec.rb
@@ -73,4 +73,12 @@ RSpec.describe RuboCop::Cop::Rails::RedundantAllowNil do
       RUBY
     end
   end
+
+  context 'when using string interpolation' do
+    it 'registers no offense' do
+      expect_no_offenses(<<-'RUBY'.strip_indent)
+        validates :details, "path_to_dynamic_validation/#{with_interpolation}": true
+      RUBY
+    end
+  end
 end

[koic]

Looks good to me.
Can you squash your commits into one?

[bbatsov]

Thanks!