ManifestRegistrar#finalize! avoids duplicates (#295)

Fix a small bug introduced by #286. When a container is finalizing, providers are finalized first. If one of those providers loads a manifest-registered dependency, that manifest will already have been loaded by the time the manifest registrar finalizes. Keep track of loaded manifest files to avoid attempting to load them a second time, which would result in errors around duplicate registrations.

---------

Co-authored-by: Tim Riley <tim@riley.id.au>

Author: alassek

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Break Versioning](https://www.taoensso.com/break-ve
 
 ## [Unreleased]
 
+### Fixed
+
+- Avoid errors from attempted duplicate registrations when finalizing a container with manifest-registered dependencies that have already been loaded as part of finalizing providers. (@alassek, @timriley in #295)
+
 [Unreleased]: https://github.com/dry-rb/dry-system/compare/v1.2.5...main
 
 ## [1.2.5] - 2025-12-01

lib/dry/system/manifest_registrar.rb

@@ -22,17 +22,24 @@ class ManifestRegistrar
       def initialize(container)
         @container = container
         @config = container.config
+        @loaded = Set.new
       end
 
       # @api private
       def finalize!
         ::Dir[registrations_dir.join(RB_GLOB)].each do |file|
-          call(Identifier.new(File.basename(file, RB_EXT)))
+          ident = Identifier.new(File.basename(file, RB_EXT))
+
+          # Skip files already loaded during earlier stages of finalization, such as a provider
+          # resolving a component satisfied via a manifest. Since `#call` uses `load`, re-running
+          # here would attempt a duplicate registration and raise an error.
+          call(ident) unless @loaded.include?(ident.root_key)
         end
       end
 
       # @api private
       def call(component)
+        @loaded << component.root_key
         load(root.join(config.registrations_dir, "#{component.root_key}#{RB_EXT}"))
       end
 

spec/integration/container/providers/lazy_loading_manifest_during_finalize_spec.rb

@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+RSpec.describe "Providers / Lazy loading a manifest-registered dependency as part of finalize" do
+  before :context do
+    @dir = make_tmp_directory
+
+    with_directory(@dir) do
+      write "system/registrations/deps.rb", <<~RUBY
+        Test::Container.namespace(:deps) do |container|
+          container.register(:thing) { Object.new }
+        end
+      RUBY
+    end
+  end
+
+  before do
+    root = @dir
+    Test::Container = Class.new(Dry::System::Container) do
+      configure do |config|
+        config.root = root
+      end
+
+      register_provider :my_provider do
+        start do
+          target["deps.thing"]
+        end
+      end
+    end
+  end
+
+  it "does not register the manifest dependency more than once" do
+    expect { Test::Container.finalize! }.not_to raise_error
+    expect(Test::Container["deps.thing"]).to be
+  end
+end