Deprecate Rails 5.2

Rails 5.2 reached EOL on June 1st, 2022 [1]. We're going to deprecate it
on Solidus v3.2, and remove support on the next major.

- We warn when we detect that version is used.
- We remove the Rails 5.2 job in the CI.
- We remove branching on Rails 5.2 in the specs.

We've taken solidusio#3333 for inspiration.

- [1] - https://guides.rubyonrails.org/maintenance_policy.html

.circleci/config.yml

@@ -150,16 +150,6 @@ jobs:
       - setup
       - test
 
-  postgres_rails52:
-    executor: postgres
-    parallelism: *parallelism
-    environment:
-      RAILS_VERSION: '~> 5.2.0'
-      DISABLE_ACTIVE_STORAGE: true
-    steps:
-      - setup
-      - test
-
 workflows:
   build:
     jobs:
@@ -171,5 +161,4 @@ workflows:
       - mysql
       - postgres_rails61
       - postgres_rails60
-      - postgres_rails52
       - legacy_events

core/lib/spree/core.rb

@@ -85,6 +85,15 @@ class GatewayError < RuntimeError; end
   end
 end
 
+if Gem::Version.new(Rails.version) < Gem::Version.new('5.2')
+  Spree::Deprecation.warn <<~HEREDOC
+    Rails 5.2 (EOL) is deprecated and will not be supported anymore from the next Solidus version.
+    Please, upgrade to a more recent Rails version.
+    Read more on upgrading from Rails 5.2 to Rails 6.0 here:
+    https://guides.rubyonrails.org/upgrading_ruby_on_rails.html#upgrading-from-rails-5-2-to-rails-6-0
+  HEREDOC
+end
+
 require 'spree/core/version'
 
 require 'spree/core/active_merchant_dependencies'

core/spec/lib/spree/event_spec.rb

@@ -17,26 +17,17 @@
     before do
       # ActiveSupport::Notifications does not provide an interface to clean all
       # subscribers at once, so some low level brittle code is required
-      if Rails.gem_version >= Gem::Version.new('6.0.0')
-        @old_string_subscribers = notifier.instance_variable_get('@string_subscribers').dup
-        @old_other_subscribers = notifier.instance_variable_get('@other_subscribers').dup
-        notifier.instance_variable_get('@string_subscribers').clear
-        notifier.instance_variable_get('@other_subscribers').clear
-      else
-        @old_subscribers = notifier.instance_variable_get('@subscribers').dup
-        notifier.instance_variable_get('@subscribers').clear
-      end
+      @old_string_subscribers = notifier.instance_variable_get('@string_subscribers').dup
+      @old_other_subscribers = notifier.instance_variable_get('@other_subscribers').dup
+      notifier.instance_variable_get('@string_subscribers').clear
+      notifier.instance_variable_get('@other_subscribers').clear
       @old_listeners = notifier.instance_variable_get('@listeners_for').dup
       notifier.instance_variable_get('@listeners_for').clear
     end
 
     after do
-      if Rails.gem_version >= Gem::Version.new('6.0.0')
-        notifier.instance_variable_set '@string_subscribers', @old_string_subscribers
-        notifier.instance_variable_set '@other_subscribers', @old_other_subscribers
-      else
-        notifier.instance_variable_set '@subscribers', @old_subscribers
-      end
+      notifier.instance_variable_set '@string_subscribers', @old_string_subscribers
+      notifier.instance_variable_set '@other_subscribers', @old_other_subscribers
       notifier.instance_variable_set '@listeners_for', @old_listeners
     end