Add injector mixin plugin

lib/dry/system/plugins.rb

@@ -134,6 +134,9 @@ def enabled_plugins
 
       require "dry/system/plugins/zeitwerk"
       register(:zeitwerk, Plugins::Zeitwerk)
+
+      require_relative "plugins/injector_mixin"
+      register(:injector_mixin, Plugins::InjectorMixin)
     end
   end
 end

lib/dry/system/plugins/injector_mixin.rb

@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+module Dry
+  module System
+    module Plugins
+      # @api private
+      class InjectorMixin < Module
+        MODULE_SEPARATOR = "::"
+
+        attr_reader :name
+
+        def initialize(name: "Deps")
+          @name = name
+        end
+
+        def extended(container)
+          container.after(:configure, &method(:define_mixin))
+        end
+
+        private
+
+        def define_mixin(container)
+          inflector = container.config.inflector
+
+          name_parts = name.split(MODULE_SEPARATOR)
+
+          if name_parts[0] == ""
+            name_parts.delete_at(0)
+            root_module = Object
+          else
+            root_module = container_parent_module(container)
+          end
+
+          mixin_parent_mod = define_parent_modules(
+            root_module,
+            name_parts,
+            inflector
+          )
+
+          mixin_parent_mod.const_set(
+            inflector.camelize(name_parts.last),
+            container.injector
+          )
+        end
+
+        def container_parent_module(container)
+          if container.name
+            parent_name = container.name.split(MODULE_SEPARATOR)[0..-2].join(MODULE_SEPARATOR)
+            container.config.inflector.constantize(parent_name)
+          else
+            Object
+          end
+        end
+
+        def define_parent_modules(parent_mod, name_parts, inflector)
+          return parent_mod if name_parts.length == 1
+
+          name_parts[0..-2].reduce(parent_mod) { |parent_mod, mod_name|
+            parent_mod.const_set(inflector.camelize(mod_name), Module.new)
+          }
+        end
+      end
+    end
+  end
+end

spec/integration/container/plugins/injector_mixin_spec.rb

@@ -0,0 +1,84 @@
+# frozen_string_literal: true
+
+RSpec.describe "Plugins / Injector mixin" do
+
+  describe "default options" do
+    it "creates a 'Deps' mixin in the container's parent module" do
+      module Test
+        class Container < Dry::System::Container
+          use :injector_mixin
+          configured!
+        end
+      end
+
+      component = Object.new
+      Test::Container.register "component", component
+
+      depending_obj = Class.new do
+        include Test::Deps["component"]
+      end.new
+
+      expect(depending_obj.component).to be component
+    end
+  end
+
+  describe "name given" do
+    it "creates a mixin with the given name in the container's parent module" do
+      module Test
+        class Container < Dry::System::Container
+          use :injector_mixin, name: "Inject"
+          configured!
+        end
+      end
+
+      component = Object.new
+      Test::Container.register "component", component
+
+      depending_obj = Class.new do
+        include Test::Inject["component"]
+      end.new
+
+      expect(depending_obj.component).to be component
+    end
+  end
+
+  describe "nested name given" do
+    it "creates a mixin with the given name in the container's parent module" do
+      module Test
+        class Container < Dry::System::Container
+          use :injector_mixin, name: "Inject::These::Pls"
+          configured!
+        end
+      end
+
+      component = Object.new
+      Test::Container.register "component", component
+
+      depending_obj = Class.new do
+        include Test::Inject::These::Pls["component"]
+      end.new
+
+      expect(depending_obj.component).to be component
+    end
+  end
+
+  describe "top-level name given" do
+    it "creates a mixin with the given name in the top-level module" do
+      module Test
+        class Container < Dry::System::Container
+          use :injector_mixin, name: "::Deps"
+          configured!
+        end
+      end
+
+      component = Object.new
+      Test::Container.register "component", component
+
+      depending_obj = Class.new do
+        include ::Deps["component"]
+      end.new
+
+      expect(depending_obj.component).to be component
+    end
+  end
+end