Ensure prepare_container works as expected in App (#1185)

We want to ensure that the `prepare_container` block is run at the _last moment_ before the container is marked as `configured!`. With this change, this is now true for both `App` and `Slice`.

Before this change, the `prepare_container` block for `App` was being run before the app-specific configuration was applied.

lib/hanami/slice.rb

@@ -219,6 +219,7 @@ module Hanami
 
         prepare_all
 
+        instance_exec(container, &@prepare_container_block) if @prepare_container_block
         container.configured!
 
         @prepared = true
@@ -258,7 +259,6 @@ module Hanami
         prepare_container_imports
         prepare_container_providers
         prepare_autoloader
-        instance_exec(container, &@prepare_container_block) if @prepare_container_block
 
         prepare_slices
       end

spec/new_integration/container/prepare_container_spec.rb

@@ -0,0 +1,123 @@
+# frozen_string_literal: true
+
+RSpec.describe "Container / prepare_container", :app_integration do
+  # (Most of) the examples below make their expectations on a `container_to_prepare`,
+  # which is the container yielded to the `Slice.prepare_container` block _at the moment
+  # it is called_.
+  #
+  # This around hook ensures the examples are run at the right time and container is
+  # available to each.
+  around(in_prepare_container: true) do |example|
+    # Eagerly capture @loaded_features here (see spec/support/app_integration.rb) since
+    # around hooks are run before any before hooks (where we ordinarily capture
+    # @loaded_features), and by invoking `example_group_instance.subject` below, we're
+    # making requires that we want to ensure are properly cleaned between examples.
+    @loaded_features = $LOADED_FEATURES.dup
+
+    slice = example.example_group_instance.subject
+
+    slice.prepare_container do |container|
+      example.example.example_group.let(:container_to_prepare) { container }
+      example.run
+    end
+
+    # The prepare_container block is called when the slice is prepared
+    slice.prepare
+  end
+
+  describe "in app", :in_prepare_container do
+    before :context do
+      with_directory(@dir = make_tmp_directory) do
+        write "config/app.rb", <<~'RUBY'
+          module TestApp
+            class App < Hanami::App
+            end
+          end
+        RUBY
+
+        write "app/.keep", ""
+      end
+    end
+
+    subject {
+      with_directory(@dir) { require "hanami/setup" }
+      Hanami.app
+    }
+
+    it "receives the container for the app" do
+      expect(container_to_prepare).to be TestApp::Container
+    end
+
+    specify "the container has been already configured by the app" do
+      expect(container_to_prepare.config.component_dirs.dir("app")).to be
+    end
+
+    specify "the container is not yet marked as configured" do
+      expect(container_to_prepare).not_to be_configured
+    end
+
+    describe "after app is prepared", in_prepare_container: false do
+      before do
+        subject.prepare_container do |container|
+          container.config.name = :custom_name
+        end
+      end
+
+      it "preserves any container configuration changes made via the block" do
+        expect { subject.prepare }
+          .to change { subject.container.config.name }
+          .to :custom_name
+
+        expect(subject.container).to be_configured
+      end
+    end
+  end
+
+  describe "in slice", :in_prepare_container do
+    before :context do
+      with_directory(@dir = make_tmp_directory) do
+        write "config/app.rb", <<~'RUBY'
+          module TestApp
+            class App < Hanami::App
+            end
+          end
+        RUBY
+
+        write "slices/main/.keep", ""
+      end
+    end
+
+    subject {
+      with_directory(@dir) { require "hanami/setup" }
+      Hanami.app.register_slice(:main)
+    }
+
+    it "receives the container for the slice" do
+      expect(container_to_prepare).to be Main::Container
+    end
+
+    specify "the container has been already configured by the slice" do
+      expect(container_to_prepare.config.component_dirs.dir("")).to be
+    end
+
+    specify "the container is not yet marked as configured" do
+      expect(container_to_prepare).not_to be_configured
+    end
+
+    describe "after slice is prepared", in_prepare_container: false do
+      before do
+        subject.prepare_container do |container|
+          container.config.name = :custom_name
+        end
+      end
+
+      it "preserves any container configuration changes made via the block" do
+        expect { subject.prepare }
+          .to change { subject.container.config.name }
+          .to :custom_name
+
+        expect(subject.container).to be_configured
+      end
+    end
+  end
+end

spec/support/app_integration.rb

@@ -29,8 +29,10 @@ RSpec.configure do |config|
   config.include_context "Application integration", :app_integration
 
   config.before :each, :app_integration do
-    @load_paths = $LOAD_PATH.dup
-    @loaded_features = $LOADED_FEATURES.dup
+    # Conditionally assign these in case they have been assigned earlier for specific
+    # example groups (e.g. container/prepare_container_spec.rb)
+    @load_paths ||= $LOAD_PATH.dup
+    @loaded_features ||= $LOADED_FEATURES.dup
   end
 
   config.after :each, :app_integration do
@@ -56,7 +58,7 @@ RSpec.configure do |config|
 
     $LOAD_PATH.replace(@load_paths)
 
-    # Remove any specific LOADED_FEATURES added over the course of running each example
+    # Remove example-specific LOADED_FEATURES added when running each example
     new_features_to_keep = ($LOADED_FEATURES - @loaded_features).tap { |feats|
       feats.delete_if do |path|
         path =~ %r{hanami/(setup|prepare|boot|application/container/providers)} ||

spec/unit/hanami/slice_spec.rb

@@ -14,20 +14,4 @@ RSpec.describe Hanami::Slice, :app_integration do
         .to raise_error Hanami::SliceLoadError, /Slice must have a class name/
     end
   end
-
-  describe ".prepare_container" do
-    let(:app_modules) { %i[TestApp Slice1 Slice2] }
-
-    it "allows the user to configure the container after defaults settings have been applied" do
-      slice = Hanami.app.register_slice(:slice1).prepare
-      expect(slice.container.config.name).to eq :slice1
-
-      slice = Hanami.app.register_slice(:slice2) {
-        prepare_container do |container|
-          container.config.name = :my_slice
-        end
-      }.prepare
-      expect(slice.container.config.name).to eq :my_slice
-    end
-  end
 end