Make incorrect_length_validation use column name (#111)

This commit fixes a bug that caused incorrect_length_validation to use
the first length validator on _any_ column when identifying the
model-level maximum. This is naturally incorrect, and the code was
modified to take the column name into account.

Author: julianlires

lib/active_record_doctor/detectors/incorrect_length_validation.rb

@@ -38,7 +38,7 @@ def detect
             next if config(:ignore_attributes).include?("#{model.name}.#{column.name}")
             next if ![:string, :text].include?(column.type)
 
-            model_maximum = maximum_allowed_by_validations(model)
+            model_maximum = maximum_allowed_by_validations(model, column.name.to_sym)
             next if model_maximum == column.limit
 
             problem!(
@@ -52,9 +52,11 @@ def detect
         end
       end
 
-      def maximum_allowed_by_validations(model)
+      def maximum_allowed_by_validations(model, column)
         length_validator = model.validators.find do |validator|
-          validator.kind == :length && validator.options.include?(:maximum)
+          validator.kind == :length &&
+            validator.options.include?(:maximum) &&
+            validator.attributes.include?(column)
         end
         length_validator ? length_validator.options[:maximum] : nil
       end

test/active_record_doctor/detectors/incorrect_length_validation_test.rb

@@ -4,8 +4,10 @@ class ActiveRecordDoctor::Detectors::IncorrectLengthValidationTest < Minitest::T
   def test_validation_and_limit_equal_is_ok
     create_table(:users) do |t|
       t.string :email, limit: 64
+      t.string :name, limit: 32
     end.create_model do
       validates :email, length: { maximum: 64 }
+      validates :name, length: { maximum: 32 }
     end
 
     refute_problems