Extract Newsletters module to phoenix_kit_newsletters package

[timujinne]

Summary

Extracts PhoenixKit.Modules.Newsletters from phoenix_kit core into a standalone package (phoenix_kit_newsletters), and adds a cross-module dependency system to PhoenixKit.ModuleRegistry.

Changes

New: required_modules/0 callback system

• PhoenixKit.Module — new optional callback required_modules/0 :: [String.t()] (default: [])
• PhoenixKit.ModuleRegistry — new dependency_warnings/0 function that detects enabled modules with disabled dependencies
• Admin Modules page — displays dependency warnings in UI when required modules are not enabled

New: Auto-discovery for external module public routes

• integration.ex — new compile_module_public_routes/1 that auto-discovers public (non-admin) routes from external PhoenixKit modules via route_module/0
• Replaces the previous hardcoded safe_route_call(NewslettersRoutes, ...) pattern
• Module public routes placed before publishing/localized catch-all routes to prevent /:language/:group from intercepting paths like /newsletters/unsubscribe

Removed: Newsletters module from core

• Deleted lib/modules/newsletters/ (15 files)
• Deleted lib/phoenix_kit_web/routes/newsletters.ex
• Removed PhoenixKit.Modules.Newsletters from internal_modules/0 in ModuleRegistry
• sqs_processor.ex and process_scheduled_jobs_worker.ex — replaced direct Newsletters.* calls with ModuleRegistry.get_by_key("newsletters") + Code.ensure_loaded? guards

V79 migration stays in core

Tables (phoenix_kit_newsletters_*) continue to be created by phoenix_kit's versioned migration system. The new package contains only Elixir code.

Related

New package: BeamLabEU/phoenix_kit_newsletters#1

Test plan

• mix compile --warnings-as-errors passes
• mix credo --strict — no issues
• mix dialyzer — passes
• Verified in Decor 3D Print parent app with {:phoenix_kit_newsletters, path: "..."} added:
  • ModuleRegistry.all_modules() includes PhoenixKit.Modules.Newsletters
  • dependency_warnings/0 returns correct warnings when Emails disabled
  • Auto-discovered unsubscribe routes load correctly

[timujinne]

Code review

Found 2 issues:

1. Test suite broken: PhoenixKit.Modules.Newsletters added to @all_internal_modules but the module was extracted and deleted in this same PR. setup_all calls Code.ensure_loaded!/1 on every entry in this list, which will raise ArgumentError: could not load module PhoenixKit.Modules.Newsletters due to reason :nofile, preventing all tests in the file from running. The entry should be removed (or replaced with the correct internal module name if Mailing → Newsletters was a rename).

phoenix_kit/test/phoenix_kit/module_test.exs

Lines 25 to 36 in 7b546bd

	PhoenixKit.Modules.Sync,
	PhoenixKit.Modules.CustomerService,
	PhoenixKit.Modules.Newsletters,
	PhoenixKit.Jobs
	]
	# Ensure all modules are loaded so function_exported? works even when
	# running individual tests (where the "loadable" test may be excluded).
	setup_all do
	Enum.each(@all_internal_modules, &Code.ensure_loaded!/1)
	:ok
	end

2. Asymmetric function_exported? guard in process_scheduled_jobs_worker.ex: The code guards newsletters_mod.enabled?() with function_exported?(newsletters_mod, :enabled?, 0) but calls newsletters_mod.process_scheduled_broadcasts() on the next line without a corresponding guard. If an external Newsletters package implements enabled?/0 but not process_scheduled_broadcasts/0 (e.g., a version mismatch), the Oban worker will crash with an UndefinedFunctionError. Compare with sqs_processor.ex which consistently applies function_exported? before every dynamic call.

phoenix_kit/lib/phoenix_kit/scheduled_jobs/workers/process_scheduled_jobs_worker.ex

Lines 77 to 84 in 7b546bd

	newsletters_mod = PhoenixKit.ModuleRegistry.get_by_key("newsletters")
	if newsletters_mod && Code.ensure_loaded?(newsletters_mod) &&
	function_exported?(newsletters_mod, :enabled?, 0) &&
	newsletters_mod.enabled?() do
	{:ok, newsletters_count} = newsletters_mod.process_scheduled_broadcasts()
	if newsletters_count > 0 do

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