Improve detection for rails as the testing framework

lib/ruby_lsp/global_state.rb

@@ -1,6 +1,8 @@
 # typed: strict
 # frozen_string_literal: true
 
+require "ruby_lsp/listeners/rails_app"
+
 module RubyLsp
   class GlobalState
     extend T::Sig
@@ -133,9 +135,9 @@ def detect_test_library(dependencies)
         "rspec"
       # A Rails app may have a dependency on minitest, but we would instead want to use the Rails test runner provided
       # by ruby-lsp-rails. A Rails app doesn't need to depend on the rails gem itself, individual components like
-      # activestorage may be added to the gemfile so that other components aren't downloaded. Check for the presence
-      #  of bin/rails to support these cases.
-      elsif bin_rails_present
+      # activestorage may be added to the gemfile so that other components aren't downloaded. Check for inheritance of
+      # `Rails::Application` in config/application.rb to support these cases.
+      elsif rails_app?
         "rails"
       # NOTE: Intentionally ends with $ to avoid mis-matching minitest-reporters, etc. in a Rails app.
       elsif dependencies.any?(/^minitest$/)
@@ -166,8 +168,24 @@ def detect_typechecker(dependencies)
     end
 
     sig { returns(T::Boolean) }
-    def bin_rails_present
-      File.exist?(File.join(workspace_path, "bin/rails"))
+    def rails_app?
+      config = rails_app_config
+      return false unless config
+
+      result = Prism.parse(config)
+      return false unless result
+
+      dispatcher = Prism::Dispatcher.new
+      listener = Listeners::RailsApp.new(dispatcher)
+      dispatcher.dispatch(result.value)
+
+      listener.rails_app
+    end
+
+    sig { returns(T.nilable(String)) }
+    def rails_app_config
+      path = File.join(workspace_path, "config/application.rb")
+      File.read(path) if File.exist?(path)
     end
 
     sig { returns(T::Boolean) }

lib/ruby_lsp/listeners/rails_app.rb

@@ -0,0 +1,28 @@
+# typed: strict
+# frozen_string_literal: true
+
+module RubyLsp
+  module Listeners
+    class RailsApp
+      extend T::Sig
+
+      sig { returns(T::Boolean) }
+      attr_reader :rails_app
+
+      sig { params(dispatcher: Prism::Dispatcher).void }
+      def initialize(dispatcher)
+        @rails_app = T.let(false, T::Boolean)
+        dispatcher.register(self, :on_class_node_enter)
+      end
+
+      sig { params(node: Prism::ClassNode).void }
+      def on_class_node_enter(node)
+        superclass = node.superclass
+        case superclass
+        when Prism::ConstantPathNode
+          @rails_app = true if superclass.full_name == "Rails::Application"
+        end
+      end
+    end
+  end
+end

test/global_state_test.rb

@@ -37,15 +37,35 @@ def test_detects_test_unit
       assert_equal("test-unit", state.test_library)
     end
 
-    def test_detects_rails_if_minitest_is_present_and_bin_rails_exists
+    def test_detects_rails_if_minitest_is_present_and_rails_file_exists
       stub_direct_dependencies("minitest" => "1.2.3")
 
       state = GlobalState.new
-      state.stubs(:bin_rails_present).returns(true)
+      state.stubs(:rails_app_config).returns(<<~RUBY)
+        module MyApp
+          class Application < Rails::Application
+          end
+        end
+      RUBY
+
       state.apply_options({})
       assert_equal("rails", state.test_library)
     end
 
+    def test_doesnt_detects_rails_if_minitest_is_present_and_rails_file_contains_bogus
+      stub_direct_dependencies("minitest" => "1.2.3")
+
+      state = GlobalState.new
+      state.stubs(:rails_app_config).returns(<<~RUBY)
+        puts "Hello World!"
+        class Test
+        end
+      RUBY
+
+      state.apply_options({})
+      assert_equal("minitest", state.test_library)
+    end
+
     def test_detects_rspec_if_both_rails_and_rspec_are_present
       stub_direct_dependencies("rspec" => "1.2.3")