Let an app move the notice flash key once

README.md

@@ -170,7 +170,17 @@ end
 ```
 
 The message is flashed only when the defaults actually took effect. Pass `flash_key:` to use
-something other than `:notice`.
+something other than `:notice`, or move the default for the whole application once:
+
+```ruby
+# config/initializers/active_admin_filter_extensions.rb
+ActiveAdminFilterExtensions.notice_flash_key = :filters_notice
+```
+
+Worth doing where the layout renders its own key for "why this page is cut down": Active Admin
+writes action results to `:notice`, and on a shared key the arriving message wins, so a batch
+action's result would silence the notice. The key is read when the notice is written and
+`flash_key:` on the resource still beats it.
 
 ## Required filters: the mandatory window
 

lib/active_admin_filter_extensions.rb

@@ -17,6 +17,21 @@
 require "active_admin_filter_extensions/notice"
 
 module ActiveAdminFilterExtensions
+  class << self
+    # Where a filters notice goes when the resource does not say. Active Admin writes action
+    # results to :notice, and an app whose layout renders its own key for "why this page is
+    # cut down" would otherwise repeat `flash_key:` on every index that declares a notice:
+    #
+    #   ActiveAdminFilterExtensions.notice_flash_key = :notice_message
+    #
+    # Read when the notice is written, not when the resource is registered, so initializer
+    # order does not decide it.
+    attr_writer :notice_flash_key
+
+    def notice_flash_key
+      @notice_flash_key ||= :notice
+    end
+  end
 end
 
 # `add_filter` stores whatever options it is given without a whitelist, so `default:` needs no

lib/active_admin_filter_extensions/notice.rb

@@ -12,7 +12,12 @@ module ActiveAdminFilterExtensions
   # message is only flashed when the defaults actually took effect, so it stays quiet once the
   # admin has filtered for themselves.
   module Notice
-    def default_filters_notice(message, flash_key: :notice)
+    # The key this resource's notice goes under: what it declared, else the app-wide default.
+    def self.flash_key_for(config)
+      config.default_filters_notice_flash_key || ActiveAdminFilterExtensions.notice_flash_key
+    end
+
+    def default_filters_notice(message, flash_key: nil)
       # Declared on the resource rather than closed over, so that the redirect - which answers
       # the request the notice belongs on with a 302 - can find it and carry it across.
       config.default_filters_notice = message
@@ -27,7 +32,8 @@ def default_filters_notice(message, flash_key: :notice)
         # default slice - the notice on top of it would be noise.
         next if filter_policy_errors.present?
 
-        flash.now[flash_key] = ::MethodOrProcHelper.render_in_context(self, message)
+        flash.now[Notice.flash_key_for(active_admin_config)] =
+          ::MethodOrProcHelper.render_in_context(self, message)
       end
     end
   end

lib/active_admin_filter_extensions/redirect.rb

@@ -71,7 +71,7 @@ def self.included(base)
            filter_policy_errors.empty? && filter_defaults_engaged?
           # On a shared key - the default is :notice, the same key a batch action writes - the
           # arriving message wins: it names what just happened, the notice can wait.
-          key = active_admin_config.default_filters_notice_flash_key
+          key = Notice.flash_key_for(active_admin_config)
           flash[key] = ::MethodOrProcHelper.render_in_context(self, message) if flash[key].blank?
         end
 

lib/active_admin_filter_extensions/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module ActiveAdminFilterExtensions
-  VERSION = "1.0.1"
+  VERSION = "1.1.0"
 end

spec/integration/filter_defaults_spec.rb

@@ -191,6 +191,33 @@
 
       expect(page).to have_no_content("Showing published posts by default")
     end
+
+    describe "the app-wide key" do
+      # Deliberately a key no resource declares, so an example cannot pass by coincidence:
+      # NoticePost's own key is :filters_notice.
+      around do |example|
+        previous = ActiveAdminFilterExtensions.notice_flash_key
+        ActiveAdminFilterExtensions.notice_flash_key = :app_wide_notice
+        example.run
+        ActiveAdminFilterExtensions.notice_flash_key = previous
+      end
+
+      it "takes a notice that named no key of its own" do
+        # The resource says only the message; the app said where its notices go. Asserted on
+        # the rendered flash class, which is what the layout keys off.
+        visit "/admin/colliding_notice_posts"
+
+        expect(page).to have_css(".flash_app_wide_notice", text: "Showing published posts by default")
+        expect(page).to have_no_css(".flash_notice")
+      end
+
+      it "loses to the key the resource declared" do
+        visit "/admin/notice_posts"
+
+        expect(page).to have_css(".flash_filters_notice", text: "Showing published posts by default")
+        expect(page).to have_no_css(".flash_app_wide_notice")
+      end
+    end
   end
 
   describe "requests that carry no q of their own" do