[ios] making objective-C smart pointers support ARC (#47612)

Moving the implementation from https://codereview.chromium.org/1855483004 into the code base, including:

- scoped_nsobject, scoped_nsprotocol, scoped_block will support both mrc and arc
- Added parent class scoped_typeref for shared code between scoped_block and scoped_nsobject
- moving OwnershipPolicy to its own file

The implementation of the smart pointers are almost identical to https://codereview.chromium.org/1855483004 besides some syntax preference differences between chromium and flutter.

This PR also migrated [VsyncWaiterIosTest.mm](https://github.com/flutter/engine/pull/47612/files#diff-c98ce1a2aca65c29bbc444523b66921a53ecce5ff39a420b4eda7dbfe8ca1cc7) to ARC with scoped_nsobject

fixes flutter/flutter#137802

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

Author: Chris Yang

BUILD.gn

@@ -159,6 +159,7 @@ group("unittests") {
       "//flutter/display_list:display_list_rendertests",
       "//flutter/display_list:display_list_unittests",
       "//flutter/flow:flow_unittests",
+      "//flutter/fml:fml_arc_unittests",
       "//flutter/fml:fml_unittests",
       "//flutter/lib/ui:ui_unittests",
       "//flutter/runtime:dart_plugin_registrant_unittests",

ci/licenses_golden/excluded_files

@@ -101,6 +101,8 @@
 ../../../flutter/fml/message_loop_unittests.cc
 ../../../flutter/fml/paths_unittests.cc
 ../../../flutter/fml/platform/darwin/cf_utils_unittests.mm
+../../../flutter/fml/platform/darwin/scoped_nsobject_arc_unittests.mm
+../../../flutter/fml/platform/darwin/scoped_nsobject_unittests.mm
 ../../../flutter/fml/platform/darwin/string_range_sanitization_unittests.mm
 ../../../flutter/fml/platform/win/file_win_unittests.cc
 ../../../flutter/fml/platform/win/wstring_conversion_unittests.cc

ci/licenses_golden/licenses_flutter

@@ -2795,6 +2795,8 @@ ORIGIN: ../../../flutter/fml/platform/darwin/scoped_nsautorelease_pool.cc + ../.
 ORIGIN: ../../../flutter/fml/platform/darwin/scoped_nsautorelease_pool.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/platform/darwin/scoped_nsobject.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/platform/darwin/scoped_nsobject.mm + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/fml/platform/darwin/scoped_policy.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/fml/platform/darwin/scoped_typeref.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/platform/darwin/string_range_sanitization.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/platform/darwin/string_range_sanitization.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/platform/fuchsia/message_loop_fuchsia.cc + ../../../flutter/LICENSE
@@ -5549,6 +5551,8 @@ FILE: ../../../flutter/fml/platform/darwin/scoped_nsautorelease_pool.cc
 FILE: ../../../flutter/fml/platform/darwin/scoped_nsautorelease_pool.h
 FILE: ../../../flutter/fml/platform/darwin/scoped_nsobject.h
 FILE: ../../../flutter/fml/platform/darwin/scoped_nsobject.mm
+FILE: ../../../flutter/fml/platform/darwin/scoped_policy.h
+FILE: ../../../flutter/fml/platform/darwin/scoped_typeref.h
 FILE: ../../../flutter/fml/platform/darwin/string_range_sanitization.h
 FILE: ../../../flutter/fml/platform/darwin/string_range_sanitization.mm
 FILE: ../../../flutter/fml/platform/fuchsia/message_loop_fuchsia.cc

fml/BUILD.gn

@@ -165,6 +165,8 @@ source_set("fml") {
       "platform/darwin/scoped_nsautorelease_pool.h",
       "platform/darwin/scoped_nsobject.h",
       "platform/darwin/scoped_nsobject.mm",
+      "platform/darwin/scoped_policy.h",
+      "platform/darwin/scoped_typeref.h",
       "platform/darwin/string_range_sanitization.h",
       "platform/darwin/string_range_sanitization.mm",
     ]
@@ -366,6 +368,10 @@ if (enable_unittests) {
       ]
     }
 
+    if (is_mac || is_ios) {
+      sources += [ "platform/darwin/scoped_nsobject_unittests.mm" ]
+    }
+
     if (is_win) {
       sources += [
         "platform/win/file_win_unittests.cc",
@@ -388,4 +394,18 @@ if (enable_unittests) {
           [ "${fuchsia_sdk_path}/arch/${target_cpu}/sysroot/lib/libzircon.so" ]
     }
   }
+
+  executable("fml_arc_unittests") {
+    testonly = true
+    if (is_mac || is_ios) {
+      cflags_objcc = flutter_cflags_objc_arc
+      sources = [ "platform/darwin/scoped_nsobject_arc_unittests.mm" ]
+    }
+
+    deps = [
+      ":fml_fixtures",
+      "//flutter/fml",
+      "//flutter/testing",
+    ]
+  }
 }

fml/platform/darwin/scoped_block.h

@@ -8,86 +8,40 @@
 #include <Block.h>
 
 #include "flutter/fml/compiler_specific.h"
+#include "flutter/fml/platform/darwin/scoped_typeref.h"
 
-namespace fml {
-
-// ScopedBlock<> is patterned after ScopedCFTypeRef<>, but uses Block_copy() and
-// Block_release() instead of CFRetain() and CFRelease().
+#if defined(__has_feature) && __has_feature(objc_arc)
+#define BASE_MAC_BRIDGE_CAST(TYPE, VALUE) (__bridge TYPE)(VALUE)
+#else
+#define BASE_MAC_BRIDGE_CAST(TYPE, VALUE) VALUE
+#endif
 
-enum class OwnershipPolicy {
-  // The scoped object takes ownership of an object by taking over an existing
-  // ownership claim.
-  kAssume,
+namespace fml {
 
-  // The scoped object will retain the object and any initial ownership is
-  // not changed.
-  kRetain,
-};
+namespace internal {
 
 template <typename B>
-class ScopedBlock {
- public:
-  explicit ScopedBlock(B block = nullptr,
-                       OwnershipPolicy policy = OwnershipPolicy::kAssume)
-      : block_(block) {
-    if (block_ && policy == OwnershipPolicy::kRetain) {
-      block_ = Block_copy(block);
-    }
+struct ScopedBlockTraits {
+  static B InvalidValue() { return nullptr; }
+  static B Retain(B block) {
+    return BASE_MAC_BRIDGE_CAST(
+        B, Block_copy(BASE_MAC_BRIDGE_CAST(const void*, block)));
   }
-
-  ScopedBlock(const ScopedBlock<B>& that) : block_(that.block_) {
-    if (block_) {
-      block_ = Block_copy(block_);
-    }
-  }
-
-  ~ScopedBlock() {
-    if (block_) {
-      Block_release(block_);
-    }
-  }
-
-  ScopedBlock& operator=(const ScopedBlock<B>& that) {
-    reset(that.get(), OwnershipPolicy::kRetain);
-    return *this;
-  }
-
-  void reset(B block = nullptr,
-             OwnershipPolicy policy = OwnershipPolicy::kAssume) {
-    if (block && policy == OwnershipPolicy::kRetain) {
-      block = Block_copy(block);
-    }
-    if (block_) {
-      Block_release(block_);
-    }
-    block_ = block;
+  static void Release(B block) {
+    Block_release(BASE_MAC_BRIDGE_CAST(const void*, block));
   }
+};
 
-  bool operator==(B that) const { return block_ == that; }
-
-  bool operator!=(B that) const { return block_ != that; }
-
-  // NOLINTNEXTLINE(google-explicit-constructor)
-  operator B() const { return block_; }
-
-  B get() const { return block_; }
-
-  void swap(ScopedBlock& that) {
-    B temp = that.block_;
-    that.block_ = block_;
-    block_ = temp;
-  }
+}  // namespace internal
 
-  [[nodiscard]] B release() {
-    B temp = block_;
-    block_ = nullptr;
-    return temp;
-  }
+// ScopedBlock<> is patterned after ScopedCFTypeRef<>, but uses Block_copy() and
+// Block_release() instead of CFRetain() and CFRelease().
 
- private:
-  B block_;
-};
+template <typename B>
+using ScopedBlock = ScopedTypeRef<B, internal::ScopedBlockTraits<B>>;
 
 }  // namespace fml
 
+#undef BASE_MAC_BRIDGE_CAST
+
 #endif  // FLUTTER_FML_PLATFORM_DARWIN_SCOPED_BLOCK_H_