Fix static linking on iOS (#6614)

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.

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

---

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:

<img width="312" alt="Screenshot 2024-10-18 at 18 04 45"
src="https://github.com/user-attachments/assets/1db95b44-d21c-4e9a-a1d5-19674093094b">

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:

<img width="1178" alt="Screenshot 2024-10-18 at 18 05 33"
src="https://github.com/user-attachments/assets/2633ab64-a85e-4a04-b2b3-97a11e576d6c">

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:

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

<img width="1178" alt="Screenshot 2024-10-18 at 18 14 52"
src="https://github.com/user-attachments/assets/c25c1dfe-ce45-45ff-856f-be005907ffe2">

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

```diff
-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"
```

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

```rb
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.

```rb
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.

...

```
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",
);
```

Author: tomekzaw

apps/fabric-example/ios/Podfile.lock

@@ -2229,7 +2229,7 @@ SPEC CHECKSUMS:
   RNCPicker: d051e0647af8b2ad01a3d39a6b5dd9b7c0ccc166
   RNFlashList: 6f169ad83e52579b7754cbbcec1b004c27d82c93
   RNGestureHandler: c374c750a0a9bacd95f5c740d146ab9428549d6b
-  RNReanimated: 3eda8373a520a38427b68054026b5a8d40d42cfe
+  RNReanimated: 648a88c56c6881c93255e0eab431859b346e0b42
   RNScreens: de6e57426ba0e6cbc3fb5b4f496e7f08cb2773c2
   RNSVG: 08750404f92a36162a92522cc77dee437be1d257
   SocketRocket: d4aabe649be1e368d1318fdf28a022d714d65748

apps/macos-example/macos/Podfile.lock

@@ -1270,7 +1270,7 @@ SPEC CHECKSUMS:
   RNCAsyncStorage: ec53e44dc3e75b44aa2a9f37618a49c3bc080a7a
   RNCPicker: 0173dedc74776227ec6dcc61bb85cd9f07bbb2ac
   RNGestureHandler: bb81850add626ddd265294323310fec6e861c96b
-  RNReanimated: 857daa16ccc117c0491ad6950c9579cb436295df
+  RNReanimated: 8e5c163219a6444172d851df401a1e86721635f0
   RNSVG: 01eb8d8a0e2289ec3ecc9626ce920e00d2174992
   SocketRocket: f6c6249082c011e6de2de60ed641ef8bbe0cfac9
   Yoga: 329461de6a23b9e0c108d197fd0f6e87c8c8ecf2

apps/paper-example/ios/Podfile.lock

@@ -2019,7 +2019,7 @@ SPEC CHECKSUMS:
   RNCPicker: 0173dedc74776227ec6dcc61bb85cd9f07bbb2ac
   RNFlashList: 115dd44377580761bff386a0caebf165424cf16f
   RNGestureHandler: 6dfe7692a191ee224748964127114edf057a1475
-  RNReanimated: 3ffdf9d59cc891c4cbd29b5182ed845aea6ec187
+  RNReanimated: ac6bc4e337cfc694308e094f1d73487c21832bc8
   RNScreens: 19719a9c326e925498ac3b2d35c4e50fe87afc06
   RNSVG: 01eb8d8a0e2289ec3ecc9626ce920e00d2174992
   SocketRocket: d4aabe649be1e368d1318fdf28a022d714d65748

apps/tvos-example/ios/Podfile.lock

@@ -1267,7 +1267,7 @@ SPEC CHECKSUMS:
   React-runtimescheduler: 20b2202e3396589a71069d12ae9f328949c7c7b8
   React-utils: 0307d396f233e47a167b5aaf045b0e4e1dc19d74
   ReactCommon: 17891ca337bfa5a7263649b09f27a8c664537bf2
-  RNReanimated: fe28ce0f9e7a41852e6b0e0b5ac557236ae39db9
+  RNReanimated: 0552e8e7058dfe736c41ce163c0cd66eaf0ca906
   SocketRocket: f32cd54efbe0f095c4d7594881e52619cfe80b17
   Yoga: e7f2a2256464d4ef7b3825d216bd22aac3b449c1
 

packages/react-native-reanimated/RNReanimated.podspec

@@ -116,7 +116,17 @@ Pod::Spec.new do |s|
   }
   s.compiler_flags = "#{folly_compiler_flags} #{boost_compiler_flags}"
   s.xcconfig = {
-    "HEADER_SEARCH_PATHS" => "\"$(PODS_ROOT)/boost\" \"$(PODS_ROOT)/boost-for-react-native\" \"$(PODS_ROOT)/glog\" \"$(PODS_ROOT)/RCT-Folly\" \"$(PODS_ROOT)/Headers/Public/React-hermes\" \"$(PODS_ROOT)/Headers/Public/hermes-engine\" \"$(PODS_ROOT)/#{$config[:react_native_common_dir]}\"",
+    "HEADER_SEARCH_PATHS" => [
+      '"$(PODS_ROOT)/boost"',
+      '"$(PODS_ROOT)/boost-for-react-native"',
+      '"$(PODS_ROOT)/glog"',
+      '"$(PODS_ROOT)/RCT-Folly"',
+      '"$(PODS_ROOT)/Headers/Public/React-hermes"',
+      '"$(PODS_ROOT)/Headers/Public/hermes-engine"',
+      "\"$(PODS_ROOT)/#{$config[:react_native_common_dir]}\"",
+      "\"$(PODS_ROOT)/#{$config[:react_native_reanimated_dir_from_pods_root]}/apple\"",
+      "\"$(PODS_ROOT)/#{$config[:react_native_reanimated_dir_from_pods_root]}/Common/cpp\"",
+    ].join(' '),
     "OTHER_CFLAGS" => "$(inherited) #{folly_flags} #{fabric_flags} #{example_flag} #{version_flag} #{debug_flag} #{compilation_metadata_generation_flag}"
   }
   s.requires_arc = true

packages/react-native-reanimated/scripts/reanimated_utils.rb

@@ -14,6 +14,7 @@ def find_config()
     :is_tvos_target => nil,
     :react_native_node_modules_dir => nil,
     :react_native_common_dir => nil,
+    :react_native_reanimated_dir_from_pods_root => nil,
   }
 
   react_native_node_modules_dir = File.join(File.dirname(`cd "#{Pod::Config.instance.installation_root.to_s}" && node --print "require.resolve('react-native/package.json')"`), '..')
@@ -43,6 +44,10 @@ def find_config()
   react_native_common_dir_relative = Pathname.new(react_native_common_dir_absolute).relative_path_from(pods_root).to_s
   result[:react_native_common_dir] = react_native_common_dir_relative
 
+  react_native_reanimated_dir_absolute = File.join(__dir__, '..')
+  react_native_reanimated_dir_relative = Pathname.new(react_native_reanimated_dir_absolute).relative_path_from(pods_root).to_s
+  result[:react_native_reanimated_dir_from_pods_root] = react_native_reanimated_dir_relative
+
   return result
 end