add support for Rails 6, Hyrax 4, and Blacklight 7

this makes no attempt to ensure UI-layer support for BL7 and whatever bootstrap
versions it requires (excepting whatever is tested by RSpec). the scope here is
simply to make it *possible* for a Hyrax 4 application to install and use
Bulkrax.

Gemfile

@@ -12,11 +12,11 @@ gemspec
 # Git. Remember to move these dependencies to your gemspec before releasing
 # your gem to rubygems.org.
 
-gem 'blacklight', '~> 6.25.0'
+gem 'blacklight'
 gem 'bootstrap-sass', '~> 3.0'
 gem 'coderay'
 gem 'factory_bot_rails'
-gem 'hyrax', '>= 2.3'
+gem 'hyrax', '>= 2.3', '< 4.999'
 gem 'oai'
 gem 'rsolr', '>= 1.0'
 gem 'rspec-rails'
@@ -28,6 +28,7 @@ group :development, :test do
   gem 'database_cleaner'
   gem 'pry-byebug'
   gem 'solr_wrapper', '>= 0.3'
+  gem 'sqlite3', '~> 1.4'
 end
 
 group :lint do

app/factories/bulkrax/object_factory.rb

@@ -117,7 +117,7 @@ def search_by_identifier
     def create
       attrs = transform_attributes
       @object = klass.new
-      object.reindex_extent = Hyrax::Adapters::NestingIndexAdapter::LIMITED_REINDEX if object.respond_to?(:reindex_extent)
+      object.reindex_extent = Hyrax::Adapters::NestingIndexAdapter::LIMITED_REINDEX if defined?(Hyrax::Adapters::NestingIndexAdapter) && object.respond_to?(:reindex_extent)
       run_callbacks :save do
         run_callbacks :create do
           if klass == Collection

app/jobs/bulkrax/create_relationships_job.rb

@@ -114,7 +114,8 @@ def process(relationship:, importer_run_id:, parent_record:, ability:)
     end
 
     def add_to_collection(child_record, parent_record)
-      parent_record.try(:reindex_extent=, Hyrax::Adapters::NestingIndexAdapter::LIMITED_REINDEX)
+      parent_record.try(:reindex_extent=, Hyrax::Adapters::NestingIndexAdapter::LIMITED_REINDEX) if
+        defined?(Hyrax::Adapters::NestingIndexAdapter)
       child_record.member_of_collections << parent_record
       child_record.save!
     end

app/services/bulkrax/remove_relationships_for_importer.rb

@@ -63,7 +63,8 @@ def break_relationships!
           remove_relationships_from_work(obj)
         end
 
-        obj.try(:reindex_extent=, Hyrax::Adapters::NestingIndexAdapter::LIMITED_REINDEX) if defined?(Hyrax)
+        obj.try(:reindex_extent=, Hyrax::Adapters::NestingIndexAdapter::LIMITED_REINDEX) if
+          defined?(Hyrax::Adapters::NestingIndexAdapter)
         obj.save!
       end
     end

spec/test_app/app/controllers/application_controller.rb

@@ -5,7 +5,7 @@ class ApplicationController < ActionController::Base
   include Blacklight::Controller
   include Hyrax::ThemedLayoutController
   with_themed_layout '1_column'
-  skip_after_action :discard_flash_if_xhr
+  skip_after_action :discard_flash_if_xhr if
+    Rails.version.split('.').first.to_i < 6
   protect_from_forgery with: :exception
-
 end

spec/test_app/config/application.rb

@@ -19,7 +19,6 @@ module TestApp
   class Application < Rails::Application
     # Initialize configuration defaults for originally generated Rails version.
     config.load_defaults 5.1
-    config.active_record.sqlite3.represent_boolean_as_integer = true
     # Settings in config/environments/* take precedence over those specified here.
     # Application configuration should go into files in config/initializers
     # -- all .rb files in that directory are automatically loaded.