Fix an error for Rails/WhereExists with EnforcedStyle: where and implicit recievers

changelog/fix_error_for_rails_where_exists.md

@@ -0,0 +1 @@
+* [#1241](https://github.com/rubocop/rubocop-rails/pull/1241): Fix an error for `Rails/WhereExists` with `EnforcedStyle: where` and implicit receivers. ([@earlopain][])

lib/rubocop/cop/rails/where_exists.rb

@@ -67,7 +67,7 @@ def on_send(node)
             return unless convertable_args?(args)
 
             range = correction_range(node)
-            good_method = build_good_method(args, dot_source: node.loc.dot.source)
+            good_method = build_good_method(args, dot: node.loc.dot)
             message = format(MSG, good_method: good_method, bad_method: range.source)
 
             add_offense(range, message: message) do |corrector|
@@ -109,11 +109,11 @@ def correction_range(node)
           end
         end
 
-        def build_good_method(args, dot_source: '.')
+        def build_good_method(args, dot:)
           if exists_style?
             build_good_method_exists(args)
           elsif where_style?
-            build_good_method_where(args, dot_source)
+            build_good_method_where(args, dot&.source || '.')
           end
         end
 

spec/rubocop/cop/rails/where_exists_spec.rb

@@ -59,6 +59,17 @@
       RUBY
     end
 
+    it 'registers an offense when using implicit receiver and arg' do
+      expect_offense(<<~RUBY)
+        where('name = ?', 'john').exists?
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `exists?(['name = ?', 'john'])` over `where('name = ?', 'john').exists?`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        exists?(['name = ?', 'john'])
+      RUBY
+    end
+
     it 'registers an offense when using `where(...).exists?` with an association' do
       expect_offense(<<~RUBY)
         user.posts.where(published: true).exists?
@@ -142,6 +153,17 @@
       RUBY
     end
 
+    it 'registers an offense when using implicit receiver and arg' do
+      expect_offense(<<~RUBY)
+        exists?('name = ?', 'john')
+        ^^^^^^^^^^^^^^^^^^^^^^^^^^^ Prefer `where('name = ?', 'john').exists?` over `exists?('name = ?', 'john')`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        where('name = ?', 'john').exists?
+      RUBY
+    end
+
     it 'registers an offense and corrects when using `exists?` with an association' do
       expect_offense(<<~RUBY)
         user.posts.exists?(published: true)