Undeprecate :class_name

We tried to remove `:class_name` (along with some others), as it didn't
seem like they had a legitimate use as of thoughtbot#2384 and thoughtbot#2546. But we've
been seeing various cases where it's still helpful to have.

Closes thoughtbot#2384.

docs/customizing_dashboards.md

@@ -106,12 +106,12 @@ For example:
 with this, you will be able to search through the column `name` from the
 association `belongs_to :country`, from your model.
 
+`:class_name` - Specifies the name of the associated class.
+
 `:primary_key` (deprecated) - Specifies the association's primary_key.
 
 `:foreign_key` (deprecated) - Specifies the name of the foreign key directly.
 
-`:class_name` (deprecated) - Specifies the name of the associated class.
-
 **Field::HasMany**
 
 `:collection_attributes` - Set the columns to display in the show view.
@@ -124,12 +124,12 @@ set this to `0` or `false`. Default is `5`.
 
 `:direction` - What direction the sort should be in, `:asc` (default) or `:desc`.
 
+`:class_name` - Specifies the name of the associated class.
+
 `:primary_key` (deprecated) - Specifies object's primary_key.
 
 `:foreign_key` (deprecated) - Specifies the name of the foreign key directly.
 
-`:class_name` (deprecated) - Specifies the name of the associated class.
-
 **Field::HasOne**
 
 `:order` - Specifies the column used to order the records. It will apply both in
@@ -154,7 +154,7 @@ For example:
 with this, you will be able to search through the column `name` from the
 association `has_one :city`, from your model.
 
-`:class_name` (deprecated) - Specifies the name of the associated class.
+`:class_name` - Specifies the name of the associated class.
 
 **Field::Number**
 

docs/guides/scoping_has_many_relations.md

@@ -18,10 +18,10 @@ Since ActiveRecord infers the class name from the first argument, the new `has_m
 
 ## Add new relationship to dashboard
 
-Your new scoped relation can be used in the dashboard just like the original `HasMany`. Notice the new field needs to specifiy the class name as an option like you did in the model.
+Your new scoped relation can be used in the dashboard just like the original `HasMany`.
 
 ```ruby
 ATTRIBUTE_TYPES = {
   orders: Field::HasMany,
-  processed_orders: Field::HasMany.with_options(class_name: 'Order')
+  processed_orders: Field::HasMany
 ```

lib/administrate/field/associative.rb

@@ -37,7 +37,7 @@ def associated_class
 
       def associated_class_name
         if option_given?(:class_name)
-          deprecated_option(:class_name)
+          options.fetch(:class_name)
         else
           self.class.associated_class_name(
             resource.class,

spec/lib/fields/belongs_to_spec.rb

@@ -133,22 +133,6 @@
         /^Line Item \#\d\d\d\d$/
       )
     end
-
-    it "triggers a deprecation warning" do
-      line_item = create(:line_item)
-      field_class = Administrate::Field::BelongsTo.with_options(
-        class_name: "Customer"
-      )
-      field = field_class.new(
-        :product,
-        line_item.product,
-        :show,
-        resource: line_item
-      )
-      field.associated_class
-      expect(Administrate.deprecator).to have_received(:warn)
-        .with(/:class_name is deprecated/)
-    end
   end
 
   describe ":include_blank option" do

spec/lib/fields/has_many_spec.rb

@@ -64,16 +64,6 @@
       expect(dashboard_double).to have_received(:collection_attributes)
       expect(attributes).to eq([])
     end
-
-    it "triggers a deprecation warning" do
-      association = Administrate::Field::HasMany
-        .with_options(class_name: "Foo")
-      field = association.new(:customers, [], :show)
-      field.associated_collection
-
-      expect(Administrate.deprecator).to have_received(:warn)
-        .with(/:class_name is deprecated/)
-    end
   end
 
   describe "primary_key option" do