Add lib/ to $LOAD_PATH before loading app file (#1251)

This makes it possible to require files from lib/ at conventional spot at the top of the file, rather than inside the body of the app class.

lib/hanami.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
+require "pathname"
 require "zeitwerk"
 require_relative "hanami/constants"
 
@@ -36,7 +37,8 @@ module Hanami
     app_path = self.app_path
 
     if app_path
-      require(app_path)
+      prepare_load_path
+      require(app_path.to_s)
       app
     elsif raise_exception
       raise(
@@ -47,6 +49,23 @@ module Hanami
     end
   end
 
+  # Prepare the load path as early as possible (based on the default root inferred from the location
+  # of `config/app.rb`), so `require` can work at the top of `config/app.rb`. This may be useful
+  # when external classes are needed for configuring certain aspects of the app.
+  #
+  # @api private
+  # @since 2.0.0
+  private_class_method def self.prepare_load_path
+    lib_path = app_path&.join("..", "..", LIB_DIR)
+
+    if lib_path&.directory?
+      path = lib_path.realpath.to_s
+      $LOAD_PATH.prepend(path) unless $LOAD_PATH.include?(path)
+    end
+
+    lib_path
+  end
+
   # Returns the Hamami app class.
   #
   # To ensure your Hanami app is loaded, run {.setup} (or `require "hanami/setup"`) first.
@@ -98,10 +117,10 @@ module Hanami
   # Searches within the given directory, then searches upwards through parent directories until the
   # app file can be found.
   #
-  # @param dir [String] The directory from which to start searching. Defaults to the current
-  #   directory.
+  # @param dir [String, Pathname] The directory from which to start searching. Defaults to the
+  #   current directory.
   #
-  # @return [String, nil] the app file path, or nil if not found.
+  # @return [Pathname, nil] the app file path, or nil if not found.
   #
   # @api public
   # @since 2.0.0
@@ -110,7 +129,7 @@ module Hanami
     path = dir.join(APP_PATH)
 
     if path.file?
-      path.to_s
+      path
     elsif !dir.root?
       app_path(dir.parent)
     end

lib/hanami/app.rb

@@ -29,11 +29,6 @@ module Hanami
         subclass.class_eval do
           @config = Hanami::Config.new(app_name: slice_name, env: Hanami.env)
 
-          # Prepare the load path (based on the default root of `Dir.pwd`) as early as possible, so
-          # you can make a `require` inside the body of an `App` subclass, which may be useful for
-          # certain kinds of app configuration.
-          prepare_load_path
-
           load_dotenv
         end
       end

spec/integration/code_loading/loading_from_lib_spec.rb

@@ -82,6 +82,40 @@ RSpec.describe "Code loading / Loading from lib directory", :app_integration do
     end
   end
 
+  describe "default root with requires at top of app file" do
+    before :context do
+      with_directory(@dir = make_tmp_directory.realpath) do
+        write "config/app.rb", <<~'RUBY'
+          require "hanami"
+          require "external_class"
+
+          module TestApp
+            class App < Hanami::App
+              @class_from_lib = ExternalClass
+
+              def self.class_from_lib
+                @class_from_lib
+              end
+            end
+          end
+        RUBY
+
+        write "lib/external_class.rb", <<~'RUBY'
+          class ExternalClass
+          end
+        RUBY
+      end
+    end
+
+    before do
+      with_directory(@dir) { require "hanami/setup" }
+    end
+
+    specify "classes in lib/ can be required directly from the top of the app file" do
+      expect(Hanami.app.class_from_lib).to be ExternalClass
+    end
+  end
+
   context "app root reconfigured" do
     before :context do
       with_directory(@dir = make_tmp_directory.realpath) do

spec/integration/setup_spec.rb

@@ -126,7 +126,7 @@ RSpec.describe "Hanami setup", :app_integration do
         with_tmp_directory(Dir.mktmpdir) do
           write "config/app.rb"
 
-          expect(app_path).to match(%r{^/.*/config/app.rb$})
+          expect(app_path.to_s).to match(%r{^/.*/config/app.rb$})
         end
       end
     end
@@ -138,7 +138,7 @@ RSpec.describe "Hanami setup", :app_integration do
           write "lib/foo/bar/.keep"
 
           Dir.chdir("lib/foo/bar") do
-            expect(app_path).to match(%r{^/.*/config/app.rb$})
+            expect(app_path.to_s).to match(%r{^/.*/config/app.rb$})
           end
         end
       end