Generate fixture mixin without accessors

Remove the accessor-dependent early return so the DSL RBI always records the Rails test mixin. Combine the no-fixture output and typechecking coverage, and clarify why the runtime `include` is otherwise missing.

Author: KaanOzkan

lib/tapioca/dsl/compilers/active_record_fixtures.rb

@@ -37,10 +37,10 @@ module Compilers
       # ~~~
       #
       # The `include` is generated because Rails mixes `ActiveRecord::TestFixtures` into
-      # `ActiveSupport::TestCase` from a `:active_support_test_case` load hook in `rails/test_help.rb`,
-      # which is only required from an app's `test_helper.rb` and therefore never runs during RBI
-      # generation. Without it, Sorbet does not see the class methods the module contributes via
-      # `mixes_in_class_methods`, such as `fixtures`.
+      # `ActiveSupport::TestCase` through the `:active_support_test_case` load hook in
+      # `rails/test_help.rb`. Since RBI generation does not load an app's test helper, this runtime
+      # include is not captured. Without it, Sorbet does not see the class methods the module
+      # contributes via `mixes_in_class_methods`, such as `fixtures`.
       #: [ConstantType = singleton(ActiveSupport::TestCase)]
       class ActiveRecordFixtures < Compiler
         MISSING = Object.new
@@ -54,8 +54,6 @@ def decorate
             method_names_from_eager_fixture_loader
           end
 
-          return if method_names.empty?
-
           method_names.select! { |name| fixture_class_mapping_from_fixture_files[name] != MISSING }
 
           root.create_path(constant) do |mod|

manual/compiler_activerecordfixtures.md

@@ -29,7 +29,7 @@ end
 ~~~
 
 The `include` is generated because Rails mixes `ActiveRecord::TestFixtures` into
-`ActiveSupport::TestCase` from a `:active_support_test_case` load hook in `rails/test_help.rb`,
-which is only required from an app's `test_helper.rb` and therefore never runs during RBI
-generation. Without it, Sorbet does not see the class methods the module contributes via
-`mixes_in_class_methods`, such as `fixtures`.
+`ActiveSupport::TestCase` through the `:active_support_test_case` load hook in
+`rails/test_help.rb`. Since RBI generation does not load an app's test helper, this runtime
+include is not captured. Without it, Sorbet does not see the class methods the module
+contributes via `mixes_in_class_methods`, such as `fixtures`.

spec/tapioca/dsl/compilers/active_record_fixtures_spec.rb

@@ -47,12 +47,42 @@ class User
               assert_equal(["ActiveSupport::TestCase"], gathered_constants)
             end
 
-            it "does nothing if there are no fixtures" do
+            it "makes fixture class methods available when there are no fixtures" do
               expected = <<~RBI
                 # typed: strong
+
+                class ActiveSupport::TestCase
+                  include ActiveRecord::TestFixtures
+                end
               RBI
 
-              assert_equal(expected, rbi_for("ActiveSupport::TestCase"))
+              generated_rbi = rbi_for("ActiveSupport::TestCase")
+              dependencies_rbi = add_content_file("dependencies.rbi", <<~RBI)
+                # typed: true
+
+                module ActiveRecord::TestFixtures
+                  mixes_in_class_methods ::ActiveRecord::TestFixtures::ClassMethods
+                end
+
+                module ActiveRecord::TestFixtures::ClassMethods
+                  def fixtures(*fixture_set_names); end
+                end
+
+                class ActiveSupport::TestCase; end
+              RBI
+              generated_rbi_file = add_content_file("generated.rbi", generated_rbi)
+              test_file = add_content_file("test_case.rb", <<~RUBY)
+                # typed: true
+
+                class PostTest < ActiveSupport::TestCase
+                  fixtures :all
+                end
+              RUBY
+
+              result = context.sorbet("--no-config", dependencies_rbi, generated_rbi_file, test_file)
+
+              assert(result.status, result.err)
+              assert_equal(expected, generated_rbi)
             end
 
             it "ignores fixtures that do not have an associated model" do
@@ -242,7 +272,7 @@ def posts(fixture_name = nil, *other_fixtures); end
               assert_equal(expected, rbi_for("ActiveSupport::TestCase"))
             end
 
-            it "generates no methods for file fixtures" do
+            it "generates only the include for file fixtures" do
               add_content_file("test/fixtures/files/posts.yml", <<~YAML)
                 super_post:
                   title: An incredible Ruby post
@@ -253,6 +283,10 @@ def posts(fixture_name = nil, *other_fixtures); end
 
               expected = <<~RBI
                 # typed: strong
+
+                class ActiveSupport::TestCase
+                  include ActiveRecord::TestFixtures
+                end
               RBI
 
               assert_equal(expected, rbi_for("ActiveSupport::TestCase"))