iOS: don't override EXCLUDED_ARCHS when installing Hermes

packages/react-native/scripts/cocoapods/__tests__/utils-test.rb

@@ -259,6 +259,52 @@ def test_excludeArchitectures_whenHermesEngineIsIncluded_excludeI386
         assert_equal(pods_projects_mock.save_invocation_count, 1)
     end
 
+    def test_excludeArchitectures_whenHermesEngineIsNotIncluded_preserveExistingValue
+        # Arrange
+        user_project_mock = prepare_empty_user_project_mock()
+        user_project_mock.build_configurations.each do |config|
+            config.build_settings["EXCLUDED_ARCHS[sdk=iphonesimulator*]"] = "arm64"
+        end
+        pods_projects_mock = PodsProjectMock.new()
+        installer = InstallerMock.new(pods_projects_mock, [
+            AggregatedProjectMock.new(user_project_mock)
+        ])
+
+        # Act
+        ReactNativePodsUtils.exclude_i386_architecture_while_using_hermes(installer)
+
+        # Assert
+        user_project_mock.build_configurations.each do |config|
+            assert_equal(config.build_settings["EXCLUDED_ARCHS[sdk=iphonesimulator*]"], "arm64")
+        end
+
+        assert_equal(user_project_mock.save_invocation_count, 1)
+        assert_equal(pods_projects_mock.save_invocation_count, 1)
+    end
+
+    def test_excludeArchitectures_whenHermesEngineIsIncluded_appendI386
+        # Arrange
+        user_project_mock = prepare_empty_user_project_mock()
+        user_project_mock.build_configurations.each do |config|
+            config.build_settings["EXCLUDED_ARCHS[sdk=iphonesimulator*]"] = "arm64"
+        end
+        pods_projects_mock = PodsProjectMock.new([], {"hermes-engine" => {}})
+        installer = InstallerMock.new(pods_projects_mock, [
+            AggregatedProjectMock.new(user_project_mock)
+        ])
+
+        # Act
+        ReactNativePodsUtils.exclude_i386_architecture_while_using_hermes(installer)
+
+        # Assert
+        user_project_mock.build_configurations.each do |config|
+            assert_equal(config.build_settings["EXCLUDED_ARCHS[sdk=iphonesimulator*]"], "arm64 i386")
+        end
+
+        assert_equal(user_project_mock.save_invocation_count, 1)
+        assert_equal(pods_projects_mock.save_invocation_count, 1)
+    end
+
     # ================= #
     # Test - Fix Config #
     # ================= #

packages/react-native/scripts/cocoapods/utils.rb

@@ -59,14 +59,24 @@ def self.turn_off_resource_bundle_react_core(installer)
     end
 
     def self.exclude_i386_architecture_while_using_hermes(installer)
-        projects = self.extract_projects(installer)
+        isUsingHermes = self.has_pod(installer, 'hermes-engine')
+        key = "EXCLUDED_ARCHS[sdk=iphonesimulator*]"
 
-        # Hermes does not support `i386` architecture
-        excluded_archs_default = self.has_pod(installer, 'hermes-engine') ? "i386" : ""
+        projects = self.extract_projects(installer)
 
         projects.each do |project|
             project.build_configurations.each do |config|
-                config.build_settings["EXCLUDED_ARCHS[sdk=iphonesimulator*]"] = excluded_archs_default
+                current_setting = config.build_settings[key] || ""
+
+                excludesI386 = current_setting.include?("i386")
+
+                if isUsingHermes and !excludesI386
+                    # Hermes does not support `i386` architecture
+                    config.build_settings[key] = "#{current_setting} i386".strip
+                else
+                    # leave EXCLUDED_ARCHS unchanged or set it to "" if it doesn't already exist
+                    config.build_settings[key] = current_setting
+                end
             end
 
             project.save()