iOS: don't override EXCLUDED_ARCHS when installing Hermes (#39060)

Summary:
- if an existing iOS project specifies `EXCLUDED_ARCHS`, these settings are overwritten by the `react_native_post_install` step as part of the Cocoapods install
- this can break the build of existing iOS apps that want to include React Native
- a previous PR (#38132) updated the Cocoapods utils to that we only update `EXCLUDED_ARCHS` when using Hermes
- this worked around the issue for apps that opted to use JSC
- however if you _do_ want to use Hermes (the default) this problem persists

### Existing Behaviour

- one of the functions called as part of the `react_native_post_install` step is `exclude_i386_architecture_while_using_hermes`
  - see [/packages/react-native/scripts/cocoapods/utils.rb](https://github.com/facebook/react-native/blob/v0.72.1/packages/react-native/scripts/cocoapods/utils.rb#L56-L69)
```
    def self.exclude_i386_architecture_while_using_hermes(installer)
        projects = self.extract_projects(installer)

        # Hermes does not support `i386` architecture
        excluded_archs_default = self.has_pod(installer, 'hermes-engine') ? "i386" : ""

        projects.each do |project|
            project.build_configurations.each do |config|
                config.build_settings["EXCLUDED_ARCHS[sdk=iphonesimulator*]"] = excluded_archs_default
            end

            project.save()
        end
    end
```

🐛 **However** 🐛

- this means existing projects that have `EXCLUDED_ARCHS` set, the existing value will be overwritten either to `"i386"` or a blank string

### Changed Behaviour

- appends `"i386"` to existing string if set, or just sets the value to `"i386"` if there is no existing value

## Changelog:

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[IOS] [FIXED] don't override `EXCLUDED_ARCHS` when installing Hermes

Pull Request resolved: #39060

Reviewed By: dmytrorykun

Differential Revision: D48515441

Pulled By: cipolleschi

fbshipit-source-id: 8cb3c8b680d92272da0b106553179af051d0f84e

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

@@ -220,7 +220,7 @@ def test_SetGCCPreprocessorDefinitionForHermes_itSetsThePreprocessorForDebug
     # ============================ #
     # Test - Exclude Architectures #
     # ============================ #
-    def test_excludeArchitectures_whenHermesEngineIsNotIncluded_excludeNothing
+    def test_excludeArchitectures_whenHermesEngineIsNotIncluded_withNoValue_leaveUnset
         # Arrange
         user_project_mock = prepare_empty_user_project_mock()
         pods_projects_mock = PodsProjectMock.new()
@@ -233,13 +233,36 @@ def test_excludeArchitectures_whenHermesEngineIsNotIncluded_excludeNothing
 
         # Assert
         user_project_mock.build_configurations.each do |config|
-            assert_equal(config.build_settings["EXCLUDED_ARCHS[sdk=iphonesimulator*]"], "")
+            assert_equal(config.build_settings["EXCLUDED_ARCHS[sdk=iphonesimulator*]"], nil)
         end
-        assert_equal(user_project_mock.save_invocation_count, 1)
+        assert_equal(user_project_mock.save_invocation_count, 0)
+        assert_equal(pods_projects_mock.save_invocation_count, 0)
+    end
+
+    def test_excludeArchitectures_whenHermesEngineIsNotIncluded_withExistingValue_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, 0)
         assert_equal(pods_projects_mock.save_invocation_count, 0)
     end
 
-    def test_excludeArchitectures_whenHermesEngineIsIncluded_excludeI386
+    def test_excludeArchitectures_whenHermesEngineIsIncluded_withNoValue_onlyExcludeI386
         # Arrange
         user_project_mock = prepare_empty_user_project_mock()
         pods_projects_mock = PodsProjectMock.new([], {"hermes-engine" => {}})
@@ -259,6 +282,29 @@ def test_excludeArchitectures_whenHermesEngineIsIncluded_excludeI386
         assert_equal(pods_projects_mock.save_invocation_count, 1)
     end
 
+    def test_excludeArchitectures_whenHermesEngineIsIncluded_withExistingValue_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

@@ -59,17 +59,27 @@ def self.turn_off_resource_bundle_react_core(installer)
     end
 
     def self.exclude_i386_architecture_while_using_hermes(installer)
-        projects = self.extract_projects(installer)
+        is_using_hermes = self.has_pod(installer, 'hermes-engine')
 
-        # Hermes does not support `i386` architecture
-        excluded_archs_default = self.has_pod(installer, 'hermes-engine') ? "i386" : ""
+        if is_using_hermes
+            key = "EXCLUDED_ARCHS[sdk=iphonesimulator*]"
 
-        projects.each do |project|
-            project.build_configurations.each do |config|
-                config.build_settings["EXCLUDED_ARCHS[sdk=iphonesimulator*]"] = excluded_archs_default
-            end
+            projects = self.extract_projects(installer)
 
-            project.save()
+            projects.each do |project|
+                project.build_configurations.each do |config|
+                    current_setting = config.build_settings[key] || ""
+
+                    excluded_archs_includes_I386 = current_setting.include?("i386")
+
+                    if !excluded_archs_includes_I386
+                        # Hermes does not support `i386` architecture
+                        config.build_settings[key] = "#{current_setting} i386".strip
+                    end
+                end
+
+                project.save()
+            end
         end
     end