Fix static linking on iOS

[tomekzaw]

Summary

Fixes #6607.

This is more of a workaround to fix issue with missing headers when building Reanimated with static linkage for iOS. I spent several hours on trying to make it right but it would work correctly only partially. I will post my findings here or internally later on and I hope to find a better solution sometime in the future.

This workaround adds paths to Common/cpp and apple/ directories to HEADER_SEARCH_PATHS – the preprocessor looks for headers in these locations. I can't use an absolute path (calculated in Ruby) because it would make the output setup-dependent and thus affect checksums in Podfile.lock which is unwanted as some apps check against checksum changes on CI.

Test plan

Tested on fabric-example app with USE_FRAMEWORKS=static and without.

---

My findings

When installing pods in fabric-example with cd ios && bundle install && bundle exec pod install, the headers are visible in ios/Pods directory:

$ find . -name "REAUIKit.h"
./Pods/Headers/Public/RNReanimated/reanimated/apple/REAUIKit.h
./Pods/Headers/Private/RNReanimated/reanimated/apple/REAUIKit.h

However, after running USE_FRAMEWORKS=static bundle exec pod install, the headers are no longer present:

$ find . -name "REAUIKit.h"
<no output>

Because of this, #import <reanimated/apple/REAUIKit.h> doesn't work, but when changed back to #import <RNReanimated/REAUIKit.h> it works fine (jump to file also works in Xcode).

This made me wonder what's the location of REAUIKit.h. Obviously, the file is located in react-native-reanimated/packages/react-native-reanimated/apple/reanimated/apple/REAUIKit.h (using symlinks as a Development Pod), but the path is not included in header search paths. Hence, I decided to add react-native-reanimated/packages/react-native-reanimated/apple/ to header search paths. However, this can't be done using absolute paths because they are likely to be machine-specific (e.g. containing the home directory name) which also affects checksum in Podfile.lock which is inconvenient since some setups assume the checksum to be stable (unless the version of the library is changed) due to security concerns.

A better idea would be to take inspiration from react-native itself. I've noticed that ReactCommon has a similar feature – the headers are in nested subdirectories (e.g. react/renderer/core/ShadowNode.h) and the imports don't assume flat structure (e.g. it's #import <react/renderer/core/ShadowNode.h> instead of #import <ReactCommon/ShadowNode.h>).

I remembered that frameworks create FrameworkName.framework directories. I finally found RNReanimated.framework in Xcode build folder that you can open from menu bar:

Taking a quick look inside and comparing ReactCommon and RNReanimated, I've noticed that RNReanimated.framework doesn't contain any header files (except for umbrella header) while ReactCommon does:

When I commented out all 3 occurrences of header_mappings_dir in RNReanimated.podspec and run the Xcode build (first build lasts until the first error, if you hit the play button once again then, I assume it runs the remaining tasks), the headers were finally there but the directory structure was flattened:

-ss.header_mappings_dir = "Common/cpp/reanimated"
+#ss.header_mappings_dir = "Common/cpp/reanimated"

Then I tried passing an absolute path to appropriate directories to see if this would fix the structure:

-ss.header_mappings_dir = "Common/cpp/reanimated"
+ss.header_mappings_dir = "/Users/tomekzaw/RNOS/react-native-reanimated/packages/react-native-reanimated/Common/cpp"

-sss.header_mappings_dir = "apple/reanimated"
+sss.header_mappings_dir = "/Users/tomekzaw/RNOS/react-native-reanimated/packages/react-native-reanimated/

-ss.header_mappings_dir = "Common/cpp/worklets"
+ss.header_mappings_dir = "/Users/tomekzaw/RNOS/react-native-reanimated/packages/react-native-reanimated/Common/cpp"

After this change, the headers were present and in correct tree structure:

However, the headers were still not found by Xcode when building the project.

While reviewing the changes, I found the following diff in project.pbxproj (file is generated by CocoaPods):

HEADER_SEARCH_PATHS = (
	"$(inherited)",
	"${PODS_CONFIGURATION_BUILD_DIR}/ReactCommon/ReactCommon.framework/Headers",
	"${PODS_CONFIGURATION_BUILD_DIR}/ReactCommon/ReactCommon.framework/Headers/react/nativemodule/core",
	"${PODS_CONFIGURATION_BUILD_DIR}/ReactCommon-Samples/ReactCommon_Samples.framework/Headers",
	"${PODS_CONFIGURATION_BUILD_DIR}/ReactCommon-Samples/ReactCommon_Samples.framework/Headers/platform/ios",
	"${PODS_CONFIGURATION_BUILD_DIR}/React-Fabric/React_Fabric.framework/Headers/react/renderer/components/view/platform/cxx",
	"${PODS_CONFIGURATION_BUILD_DIR}/React-NativeModulesApple/React_NativeModulesApple.framework/Headers",
	"${PODS_CONFIGURATION_BUILD_DIR}/React-graphics/React_graphics.framework/Headers",
	"${PODS_CONFIGURATION_BUILD_DIR}/React-graphics/React_graphics.framework/Headers/react/renderer/graphics/platform/ios",
);

It looks like react-native overrides HEADER_SEARCH_PATHS when use_frameworks! :static is used. So I tried doing the same in RNReanimated.podspec:

s.pod_target_xcconfig = {
    "HEADER_SEARCH_PATHS" => '"${PODS_CONFIGURATION_BUILD_DIR}/RNReanimated/RNReanimated.framework/Headers" (...)",
}

Now the headers were correctly found but I got an error about redefinitions:

---

Then I investigated ReactCommon.podspec inside react-native repository and found several interesting lines of code:

s.header_dir = "ReactCommon" # Use global header_dir for all subspecs for use_frameworks! compatibility

It looks like header_dir must contain header_mappings_dir for the latter to work properly when use_frameworks! is enabled.

if ENV['USE_FRAMEWORKS']
  s.header_mappings_dir     = './'
end

For some reason, s.header_mappings_dir is set to the current directory only if USE_FRAMEWORKS is set.

[efstathiosntonas]

@tomekzaw hi, quick question:

when pod install after the changes in the podspec, is it necessary to clean derived data/build folder/Pods folder before rebuilding?

[tomekzaw]

@efstathiosntonas It's definitely recommended but not sure if required, I usually run rm -rf Pods Podfile.lock build prior to bundle exec pod install but I hardly ever clean DerivedData folder.