15 minute fix: Add default argument to JsonApiSortParam (#13369)

* Add default argument to JsonApiSortParam

* Update usage

app/controllers/api/v0/followers_controller.rb

@@ -29,7 +29,6 @@ module Api
 
       def order_criteria
         parse_sort_param(
-          params[:sort],
           allowed_fields: [:created_at],
           default_sort: { created_at: :desc },
         )

app/controllers/concerns/json_api_sort_param.rb

@@ -6,7 +6,7 @@ module JsonApiSortParam
   #   array determines the sort order of the resulting hash.
   # @param default_sort [{Symbol => Symbol}] The default sort order. Used when
   #   the param string is nil/empty or when parsing it results in an empty hash.
-  def parse_sort_param(param_string, allowed_fields:, default_sort:)
+  def parse_sort_param(param_string = params[:sort], allowed_fields:, default_sort:)
     fields = param_string.to_s.split(",")
     unfiltered_hash = fields_to_hash(fields)
     sort = sort_and_filter(unfiltered_hash, allowed_fields)

spec/controllers/concerns/json_api_sort_param_spec.rb

@@ -1,7 +1,20 @@
 require "rails_helper"
 
 RSpec.describe JsonApiSortParam do
-  let!(:controller) { Class.new { include JsonApiSortParam }.new }
+  let!(:controller) do
+    Class.new(Api::V0::ApiController) { include JsonApiSortParam }.new
+  end
+
+  it "uses the `sort` param of the controller by default" do
+    params = ActionController::Parameters.new(sort: "created_at,-updated_at")
+    allow(controller).to receive(:params).and_return(params)
+
+    params = controller.parse_sort_param(
+      allowed_fields: %i[created_at updated_at],
+      default_sort: { created_at: :desc },
+    )
+    expect(params).to eq({ created_at: :asc, updated_at: :desc })
+  end
 
   it "returns a default sort order if there are no sorting params" do
     params = controller.parse_sort_param(