Allow Provider Sources to choose a custom superclass

Relates to hanami/hanami#1417

The motivation for this is to allow consuming frameworks of dry-system
to define their own superclass for providers, in order to add their own
method apis to the class.

The is only used for user-defined providers with a block implementation.

External providers in a group do not allow this, because their
superclass is defined ahead of time when they are added to the source
registry. If an external provider source wants to use a different
superclass, they can define a concrete class of their own instead.

The custom superclass is assumed to be a child of
Dry::System::Provider::Source.

In addition to `provider_source_class`, ProviderRegistrar contains
`provider_source_options` as an extension point for subclasses to send
custom intialization params to the source class.

lib/dry/system/provider.rb

@@ -127,7 +127,8 @@ class Provider
       attr_reader :source
 
       # @api private
-      def initialize(name:, namespace: nil, target_container:, source_class:, &block) # rubocop:disable Style/KeywordParametersOrder
+      # rubocop:disable Layout/LineLength, Style/KeywordParametersOrder
+      def initialize(name:, namespace: nil, target_container:, source_class:, source_options: {}, &block)
         @name = name
         @namespace = namespace
         @target_container = target_container
@@ -137,11 +138,13 @@ def initialize(name:, namespace: nil, target_container:, source_class:, &block)
         @step_running = nil
 
         @source = source_class.new(
+          **source_options,
           provider_container: provider_container,
           target_container: target_container,
           &block
         )
       end
+      # rubocop:enable Layout/LineLength, Style/KeywordParametersOrder
 
       # Runs the `prepare` lifecycle step.
       #

lib/dry/system/provider/source.rb

@@ -37,10 +37,20 @@ class << self
           # @see Dry::System::Provider::SourceDSL
           #
           # @api private
-          def for(name:, group: nil, &block)
-            Class.new(self) { |klass|
+          def for(name:, group: nil, superclass: nil, &block)
+            superclass ||= self
+
+            Class.new(superclass) { |klass|
               klass.source_name name
               klass.source_group group
+
+              name_with_group = group ? "#{group}->#{name}" : name
+              klass.instance_eval <<~RUBY, __FILE__, __LINE__ + 1
+                def name
+                  "#{superclass.name}[#{name_with_group}]"
+                end
+              RUBY
+
               SourceDSL.evaluate(klass, &block) if block
             }
           end
@@ -58,14 +68,6 @@ def inherited(subclass)
             end
           end
 
-          # @api private
-          def name
-            source_str = source_name
-            source_str = "#{source_group}->#{source_str}" if source_group
-
-            "Dry::System::Provider::Source[#{source_str}]"
-          end
-
           # @api private
           def to_s
             "#<#{name}>"

lib/dry/system/provider_registrar.rb

@@ -136,6 +136,14 @@ def provider_files
         }.first
       end
 
+      # Extension point for subclasses
+      # @api private
+      def provider_source_class = Dry::System::Provider::Source
+
+      # Extension point for subclasses
+      # @api private
+      def provider_source_options = {}
+
       # @api private
       def finalize!
         provider_files.each do |path|
@@ -196,13 +204,18 @@ def provider_paths
       end
 
       def build_provider(name, options:, source: nil, &block)
-        source_class = source || Provider::Source.for(name: name, &block)
+        source_class = source || Provider::Source.for(
+          name: name,
+          superclass: provider_source_class,
+          &block
+        )
 
         Provider.new(
           **options,
           name: name,
           target_container: target_container,
-          source_class: source_class
+          source_class: source_class,
+          source_options: provider_source_options
         )
       end
 
@@ -215,6 +228,7 @@ def build_provider_from_source(name, source:, group:, options:, &block)
           name: name,
           target_container: target_container,
           source_class: provider_source.source,
+          source_options: provider_source_options,
           &block
         )
       end

spec/integration/container/providers/custom_provider_superclass_spec.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+RSpec.describe "Providers / Custom provider superclass" do
+  let!(:custom_superclass) do
+    module Test
+      class CustomSource < Dry::System::Provider::Source
+        attr_reader :custom_setting
+
+        def initialize(custom_setting:, **options, &block)
+          super(**options, &block)
+          @custom_setting = custom_setting
+        end
+      end
+    end
+
+    Test::CustomSource
+  end
+
+  let!(:custom_registrar) do
+    module Test
+      class CustomRegistrar < Dry::System::ProviderRegistrar
+        def provider_source_class = Test::CustomSource
+        def provider_source_options = {custom_setting: "hello"}
+      end
+    end
+
+    Test::CustomRegistrar
+  end
+
+  subject(:system) do
+    module Test
+      class Container < Dry::System::Container
+        configure do |config|
+          config.root = SPEC_ROOT.join("fixtures/app").realpath
+          config.provider_registrar = Test::CustomRegistrar
+        end
+      end
+    end
+
+    Test::Container
+  end
+
+  it "overrides the default Provider Source base class" do
+    system.register_provider(:test) {}
+
+    provider_source = system.providers[:test].source
+
+    expect(provider_source.class).to be < custom_superclass
+    expect(provider_source.class.name).to eq "Test::CustomSource[test]"
+    expect(provider_source.custom_setting).to eq "hello"
+  end
+end