Clean up macOS framework creation scripts (flutter/engine#54658)

This refactors `create_fat_macos_framework`, `_regenerate_symlinks` and
`_set_framework_permissions` to be more generic and not hardcode "FlutterMacOS"
as a framework name. Further, it reuses several utility functions from the iOS
code in `sky_utils` to improve readability and eliminate duplication.

This is refactoring prior to embedding dSYMs in FlutterMacOS.xcframework in a
followup patch.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

engine/src/flutter/sky/tools/create_macos_framework.py

@@ -47,12 +47,12 @@ def main():
     print('Cannot find macOS x64 Framework at %s' % x64_framework)
     return 1
 
-  arm64_dylib = os.path.join(arm64_framework, 'FlutterMacOS')
+  arm64_dylib = sky_utils.get_mac_framework_dylib_path(arm64_framework)
   if not os.path.isfile(arm64_dylib):
     print('Cannot find macOS arm64 dylib at %s' % arm64_dylib)
     return 1
 
-  x64_dylib = os.path.join(x64_framework, 'FlutterMacOS')
+  x64_dylib = sky_utils.get_mac_framework_dylib_path(x64_framework)
   if not os.path.isfile(x64_dylib):
     print('Cannot find macOS x64 dylib at %s' % x64_dylib)
     return 1
@@ -71,15 +71,16 @@ def main():
   return 0
 
 
-def process_framework(dst, args, fat_framework):
-  fat_framework_binary = os.path.join(fat_framework, 'Versions', 'A', 'FlutterMacOS')
+def process_framework(dst, args, framework_path):
+  framework_binary = sky_utils.get_mac_framework_dylib_path(framework_path)
+
   if args.dsym:
-    dsym_out = os.path.splitext(fat_framework)[0] + '.dSYM'
-    sky_utils.extract_dsym(fat_framework_binary, dsym_out)
+    dsym_out = os.path.join(dst, 'FlutterMacOS.dSYM')
+    sky_utils.extract_dsym(framework_binary, dsym_out)
     if args.zip:
       dsym_dst = os.path.join(dst, 'FlutterMacOS.dSYM')
       sky_utils.create_zip(dsym_dst, 'FlutterMacOS.dSYM.zip', ['.'])
-      # Double zip to make it consistent with legacy artifacts.
+      # Create a zip of just the contents of the dSYM, then create a zip of that zip.
       # TODO(fujino): remove this once https://github.com/flutter/flutter/issues/125067 is resolved
       sky_utils.create_zip(dsym_dst, 'FlutterMacOS.dSYM_.zip', ['FlutterMacOS.dSYM.zip'])
 
@@ -90,7 +91,7 @@ def process_framework(dst, args, fat_framework):
 
   if args.strip:
     unstripped_out = os.path.join(dst, 'FlutterMacOS.unstripped')
-    sky_utils.strip_binary(fat_framework_binary, unstripped_out)
+    sky_utils.strip_binary(framework_binary, unstripped_out)
 
 
 def zip_framework(dst):

engine/src/flutter/sky/tools/sky_utils.py

@@ -119,36 +119,43 @@ def copy_tree(source_path, destination_path, symlinks=False):
 
 
 def create_fat_macos_framework(fat_framework, arm64_framework, x64_framework):
+  """Creates a fat framework from two arm64 and x64 frameworks."""
+  # Clone the arm64 framework bundle as a starting point.
   copy_tree(arm64_framework, fat_framework, symlinks=True)
   _regenerate_symlinks(fat_framework)
-
-  fat_framework_binary = os.path.join(fat_framework, 'Versions', 'A', 'FlutterMacOS')
-
-  # Create the arm64/x64 fat framework.
-  arm64_dylib = os.path.join(arm64_framework, 'FlutterMacOS')
-  x64_dylib = os.path.join(x64_framework, 'FlutterMacOS')
-  lipo([arm64_dylib, x64_dylib], fat_framework_binary)
+  lipo([get_mac_framework_dylib_path(arm64_framework),
+        get_mac_framework_dylib_path(x64_framework)], get_mac_framework_dylib_path(fat_framework))
   _set_framework_permissions(fat_framework)
 
 
 def _regenerate_symlinks(framework_dir):
-  """Regenerates the symlinks structure.
+  """Regenerates the framework symlink structure.
 
-  Recipes V2 upload artifacts in CAS before integration and CAS follows symlinks.
-  This logic regenerates the symlinks in the expected structure.
+  When building on the bots, the framework is produced in one shard, uploaded
+  to LUCI's content-addressable storage cache (CAS), then pulled down in
+  another shard. When that happens, symlinks are dereferenced, resulting a
+  corrupted framework. This regenerates the expected symlink farm.
   """
-  if os.path.islink(os.path.join(framework_dir, 'FlutterMacOS')):
+  # If the dylib is symlinked, assume symlinks are all fine and bail out.
+  # The shutil.rmtree calls below only work on directories, and fail on symlinks.
+  framework_name = get_framework_name(framework_dir)
+  if os.path.islink(os.path.join(framework_dir, framework_name)):
     return
-  os.remove(os.path.join(framework_dir, 'FlutterMacOS'))
+
+  # Delete any existing files/directories.
+  os.remove(os.path.join(framework_dir, framework_name))
   shutil.rmtree(os.path.join(framework_dir, 'Headers'), True)
   shutil.rmtree(os.path.join(framework_dir, 'Modules'), True)
   shutil.rmtree(os.path.join(framework_dir, 'Resources'), True)
   current_version_path = os.path.join(framework_dir, 'Versions', 'Current')
   shutil.rmtree(current_version_path, True)
+
+  # Recreate the expected framework symlinks.
   os.symlink('A', current_version_path)
+
   os.symlink(
-      os.path.join('Versions', 'Current', 'FlutterMacOS'),
-      os.path.join(framework_dir, 'FlutterMacOS')
+      os.path.join('Versions', 'Current', framework_name),
+      os.path.join(framework_dir, framework_name)
   )
   os.symlink(os.path.join('Versions', 'Current', 'Headers'), os.path.join(framework_dir, 'Headers'))
   os.symlink(os.path.join('Versions', 'Current', 'Modules'), os.path.join(framework_dir, 'Modules'))
@@ -158,6 +165,7 @@ def _regenerate_symlinks(framework_dir):
 
 
 def _set_framework_permissions(framework_dir):
+  """Sets framework contents to be world readable, and world executable if user-executable."""
   # Make the framework readable and executable: u=rwx,go=rx.
   subprocess.check_call(['chmod', '755', framework_dir])
 
@@ -190,6 +198,16 @@ def _dsymutil_path():
   return buildroot_relative_path(dsymutil_path)
 
 
+def get_framework_name(framework_dir):
+  """Returns Foo given /path/to/Foo.framework."""
+  return os.path.splitext(os.path.basename(framework_dir))[0]
+
+
+def get_mac_framework_dylib_path(framework_dir):
+  """Returns /path/to/Foo.framework/Versions/A/Foo given /path/to/Foo.framework."""
+  return os.path.join(framework_dir, 'Versions', 'A', get_framework_name(framework_dir))
+
+
 def extract_dsym(binary_path, dsym_out_path):
   """Extracts a dSYM bundle from the specified Mach-O binary."""
   arch_dir = 'mac-arm64' if platform.processor() == 'arm' else 'mac-x64'