Add defer, a general facility for ad-hoc RAII. (#5554)

Firestore/Example/Firestore.xcodeproj/project.pbxproj

@@ -108,6 +108,7 @@
 		1733601ECCEA33E730DEAF45 /* autoid_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 54740A521FC913E500713A1A /* autoid_test.cc */; };
 		17473086EBACB98CDC3CC65C /* view_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = C7429071B33BDF80A7FA2F8A /* view_test.cc */; };
 		17638F813B9B556FE7718C0C /* FIRQuerySnapshotTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 5492E04F202154AA00B64F25 /* FIRQuerySnapshotTests.mm */; };
+		17DC97DE15D200932174EC1F /* defer_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 8ABAC2E0402213D837F73DC3 /* defer_test.cc */; };
 		17DFF30CF61D87883986E8B6 /* executor_std_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = B6FB4687208F9B9100554BA2 /* executor_std_test.cc */; };
 		1817DEF8FF479D218381C541 /* FSTGoogleTestTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 54764FAE1FAA21B90085E60A /* FSTGoogleTestTests.mm */; };
 		18638EAED9E126FC5D895B14 /* common.pb.cc in Sources */ = {isa = PBXBuildFile; fileRef = 544129D221C2DDC800EFB9CC /* common.pb.cc */; };
@@ -168,6 +169,7 @@
 		26777815544F549DD18D87AF /* message_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = CE37875365497FFA8687B745 /* message_test.cc */; };
 		268FC3360157A2DCAF89F92D /* snapshot_version_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = ABA495B9202B7E79008A7851 /* snapshot_version_test.cc */; };
 		26B52236C9D049847042E1BD /* FSTMockDatastore.mm in Sources */ = {isa = PBXBuildFile; fileRef = 5492E02D20213FFC00B64F25 /* FSTMockDatastore.mm */; };
+		26C4E52128C8E7B5B96BECC4 /* defer_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 8ABAC2E0402213D837F73DC3 /* defer_test.cc */; };
 		26C577D159CFFD73E24D543C /* memory_mutation_queue_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 74FBEFA4FE4B12C435011763 /* memory_mutation_queue_test.cc */; };
 		26CB3D7C871BC56456C6021E /* timestamp_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = ABF6506B201131F8005F2C74 /* timestamp_test.cc */; };
 		276A563D546698B6AAC20164 /* annotations.pb.cc in Sources */ = {isa = PBXBuildFile; fileRef = 618BBE9520B89AAC00B5BCE7 /* annotations.pb.cc */; };
@@ -502,6 +504,7 @@
 		5DDEC1A08F13226271FE636E /* resource_path_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = B686F2B02024FFD70028D6BE /* resource_path_test.cc */; };
 		5E5B3B8B3A41C8EB70035A6B /* FSTTransactionTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 5492E07B202154EB00B64F25 /* FSTTransactionTests.mm */; };
 		5E6F9184B271F6D5312412FF /* mutation_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = C8522DE226C467C54E6788D8 /* mutation_test.cc */; };
+		5E7812753D960FBB373435BD /* defer_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 8ABAC2E0402213D837F73DC3 /* defer_test.cc */; };
 		5E89B1A5A5430713C79C4854 /* FirestoreEncoderTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 1235769422B86E65007DDFA9 /* FirestoreEncoderTests.swift */; };
 		5ECE040F87E9FCD0A5D215DB /* pretty_printing_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB323F9553050F4F6490F9FF /* pretty_printing_test.cc */; };
 		5EE21E86159A1911E9503BC1 /* transform_operation_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 33607A3AE91548BD219EC9C6 /* transform_operation_test.cc */; };
@@ -547,6 +550,7 @@
 		62DA31B79FE97A90EEF28B0B /* delayed_constructor_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = D0A6E9136804A41CEC9D55D4 /* delayed_constructor_test.cc */; };
 		62F86BBE7DDA5B295B57C8DA /* string_apple_test.mm in Sources */ = {isa = PBXBuildFile; fileRef = 0EE5300F8233D14025EF0456 /* string_apple_test.mm */; };
 		6300709ECDE8E0B5A8645F8D /* time_testing.cc in Sources */ = {isa = PBXBuildFile; fileRef = 5497CB76229DECDE000FB92F /* time_testing.cc */; };
+		6325D0E43A402BC5866C9C0E /* defer_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 8ABAC2E0402213D837F73DC3 /* defer_test.cc */; };
 		6359EA7D5C76D462BD31B5E5 /* watch_change_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 2D7472BC70C024D736FF74D9 /* watch_change_test.cc */; };
 		6369DE4E258556FE3382DD78 /* field_filter_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = E8551D6C6FB0B1BACE9E5BAD /* field_filter_test.cc */; };
 		6380CACCF96A9B26900983DC /* leveldb_target_cache_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = E76F0CDF28E5FA62D21DE648 /* leveldb_target_cache_test.cc */; };
@@ -736,6 +740,7 @@
 		95ED06D2B0078D3CDB821B68 /* FIRArrayTransformTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 73866A9F2082B069009BB4FF /* FIRArrayTransformTests.mm */; };
 		9617B75E9E27E7BA46D87EF3 /* query_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = B9C261C26C5D311E1E3C0CB9 /* query_test.cc */; };
 		96552D8E218F68DDCFE210A0 /* status_apple_test.mm in Sources */ = {isa = PBXBuildFile; fileRef = 5493A423225F9990006DE7BA /* status_apple_test.mm */; };
+		96898170B456EAF092F73BBC /* defer_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 8ABAC2E0402213D837F73DC3 /* defer_test.cc */; };
 		974FF09E6AFD24D5A39B898B /* local_serializer_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = F8043813A5D16963EC02B182 /* local_serializer_test.cc */; };
 		97729B53698C0E52EB165003 /* field_filter_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = E8551D6C6FB0B1BACE9E5BAD /* field_filter_test.cc */; };
 		9774A6C2AA02A12D80B34C3C /* database_id_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = AB71064B201FA60300344F18 /* database_id_test.cc */; };
@@ -784,6 +789,7 @@
 		A61BB461F3E5822175F81719 /* memory_remote_document_cache_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 1CA9800A53669EFBFFB824E3 /* memory_remote_document_cache_test.cc */; };
 		A62CDCEBE56E37FBB085CFF9 /* fake_credentials_provider.cc in Sources */ = {isa = PBXBuildFile; fileRef = DCC17AF218430D8BB28DD197 /* fake_credentials_provider.cc */; };
 		A6A916A7DEA41EE29FD13508 /* watch_change_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 2D7472BC70C024D736FF74D9 /* watch_change_test.cc */; };
+		A6A9946A006AA87240B37E31 /* defer_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 8ABAC2E0402213D837F73DC3 /* defer_test.cc */; };
 		A6D57EC3A0BF39060705ED29 /* string_format_apple_test.mm in Sources */ = {isa = PBXBuildFile; fileRef = 9CFD366B783AE27B9E79EE7A /* string_format_apple_test.mm */; };
 		A6E236CE8B3A47BE32254436 /* array_sorted_map_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 54EB764C202277B30088B8F3 /* array_sorted_map_test.cc */; };
 		A7309DAD4A3B5334536ECA46 /* remote_event_test.cc in Sources */ = {isa = PBXBuildFile; fileRef = 584AE2C37A55B408541A6FF3 /* remote_event_test.cc */; };
@@ -1427,6 +1433,7 @@
 		87553338E42B8ECA05BA987E /* grpc_stream_tester.cc */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.cpp.cpp; path = grpc_stream_tester.cc; sourceTree = "<group>"; };
 		88CF09277CFA45EE1273E3BA /* leveldb_transaction_test.cc */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.cpp.cpp; path = leveldb_transaction_test.cc; sourceTree = "<group>"; };
 		8A41BBE832158C76BE901BC9 /* mutation_queue_test.h */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.c.h; path = mutation_queue_test.h; sourceTree = "<group>"; };
+		8ABAC2E0402213D837F73DC3 /* defer_test.cc */ = {isa = PBXFileReference; includeInIndex = 1; path = defer_test.cc; sourceTree = "<group>"; };
 		8C058C8BE2723D9A53CCD64B /* persistence_testing.h */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.c.h; path = persistence_testing.h; sourceTree = "<group>"; };
 		8E002F4AD5D9B6197C940847 /* Firestore.podspec */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text; name = Firestore.podspec; path = ../Firestore.podspec; sourceTree = "<group>"; };
 		9098A0C535096F2EE9C35DE0 /* create_noop_connectivity_monitor.h */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.c.h; path = create_noop_connectivity_monitor.h; sourceTree = "<group>"; };
@@ -1743,6 +1750,7 @@
 				54740A521FC913E500713A1A /* autoid_test.cc */,
 				AB380D01201BC69F00D97691 /* bits_test.cc */,
 				548DB928200D59F600E00ABC /* comparison_test.cc */,
+				8ABAC2E0402213D837F73DC3 /* defer_test.cc */,
 				D0A6E9136804A41CEC9D55D4 /* delayed_constructor_test.cc */,
 				B6FB4689208F9B9100554BA2 /* executor_libdispatch_test.mm */,
 				B6FB4687208F9B9100554BA2 /* executor_std_test.cc */,
@@ -3314,6 +3322,7 @@
 				9774A6C2AA02A12D80B34C3C /* database_id_test.cc in Sources */,
 				11F8EE69182C9699E90A9E3D /* database_info_test.cc in Sources */,
 				E2B7AEDCAAC5AD74C12E85C1 /* datastore_test.cc in Sources */,
+				5E7812753D960FBB373435BD /* defer_test.cc in Sources */,
 				62DA31B79FE97A90EEF28B0B /* delayed_constructor_test.cc in Sources */,
 				FF4FA5757D13A2B7CEE40F04 /* document.pb.cc in Sources */,
 				5B62003FEA9A3818FDF4E2DD /* document_key_test.cc in Sources */,
@@ -3488,6 +3497,7 @@
 				58E377DCCC64FE7D2C6B59A1 /* database_id_test.cc in Sources */,
 				8F3AE423677A4C50F7E0E5C0 /* database_info_test.cc in Sources */,
 				9A7CF567C6FF0623EB4CFF64 /* datastore_test.cc in Sources */,
+				17DC97DE15D200932174EC1F /* defer_test.cc in Sources */,
 				D22B96C19A0F3DE998D4320C /* delayed_constructor_test.cc in Sources */,
 				25A75DFA730BAD21A5538EC5 /* document.pb.cc in Sources */,
 				D6E0E54CD1640E726900828A /* document_key_test.cc in Sources */,
@@ -3673,6 +3683,7 @@
 				1465E362F7BA7A3D063E61C7 /* database_id_test.cc in Sources */,
 				A8AF92A35DFA30EEF9C27FB7 /* database_info_test.cc in Sources */,
 				B99452AB7E16B72D1C01FBBC /* datastore_test.cc in Sources */,
+				6325D0E43A402BC5866C9C0E /* defer_test.cc in Sources */,
 				2ABA80088D70E7A58F95F7D8 /* delayed_constructor_test.cc in Sources */,
 				1F38FD2703C58DFA69101183 /* document.pb.cc in Sources */,
 				BB1A6F7D8F06E74FB6E525C5 /* document_key_test.cc in Sources */,
@@ -3858,6 +3869,7 @@
 				1D618761796DE311A1707AA2 /* database_id_test.cc in Sources */,
 				E8495A8D1E11C0844339CCA3 /* database_info_test.cc in Sources */,
 				7B74447D211586D9D1CC82BB /* datastore_test.cc in Sources */,
+				A6A9946A006AA87240B37E31 /* defer_test.cc in Sources */,
 				4EE1ABA574FBFDC95165624C /* delayed_constructor_test.cc in Sources */,
 				E27C0996AF6EC6D08D91B253 /* document.pb.cc in Sources */,
 				B3F3DCA51819F1A213E00D9C /* document_key_test.cc in Sources */,
@@ -4042,6 +4054,7 @@
 				ABE6637A201FA81900ED349A /* database_id_test.cc in Sources */,
 				AB38D93020236E21000A432D /* database_info_test.cc in Sources */,
 				D3B470C98ACFAB7307FB3800 /* datastore_test.cc in Sources */,
+				26C4E52128C8E7B5B96BECC4 /* defer_test.cc in Sources */,
 				6EC28BB8C38E3FD126F68211 /* delayed_constructor_test.cc in Sources */,
 				544129DD21C2DDC800EFB9CC /* document.pb.cc in Sources */,
 				B6152AD7202A53CB000E5744 /* document_key_test.cc in Sources */,
@@ -4246,6 +4259,7 @@
 				61976CE9C088131EC564A503 /* database_id_test.cc in Sources */,
 				65FC1A102890C02EF1A65213 /* database_info_test.cc in Sources */,
 				4D6761FB02F4D915E466A985 /* datastore_test.cc in Sources */,
+				96898170B456EAF092F73BBC /* defer_test.cc in Sources */,
 				C663A8B74B57FD84717DEA21 /* delayed_constructor_test.cc in Sources */,
 				C426C6E424FB2199F5C2C5BC /* document.pb.cc in Sources */,
 				93E5620E3884A431A14500B0 /* document_key_test.cc in Sources */,

Firestore/core/src/util/defer.h

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2020 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef FIRESTORE_CORE_SRC_UTIL_DEFER_H_
+#define FIRESTORE_CORE_SRC_UTIL_DEFER_H_
+
+#include <functional>
+#include <utility>
+
+namespace firebase {
+namespace firestore {
+namespace util {
+
+/**
+ * Creates a deferred action object that will execute the given `action` when
+ * the `Defer` object is destroyed at the close of the lexical scope containing
+ * it. You must declare a local variable of type `Defer` for it to have any
+ * useful effect; otherwise the `Defer` is destroyed at the end of the
+ * statement, which is equivalent to just directly running the `action`.
+ *
+ * `Defer` is useful for performing ad-hoc RAII-style actions, without having
+ * to create the wrapper class. For example:
+ *
+ *     FILE* file = fopen(filename, "rb");
+ *     Defer cleanup([&] {
+ *       if (file) {
+ *         fclose(file);
+ *       }
+ *     });
+ */
+class Defer {
+  // TODO(C++17): Make Action a template argument and use CTAD in the callers.
+ public:
+  using Action = std::function<void()>;
+
+  /**
+   * Constructs a `Defer` object.
+   *
+   * @param action a callable object; usually a lambda. Even if exceptions are
+   *     enabled, when `action` is invoked it must not throw. This is similar
+   *     to the restriction that exists on destructors generally.
+   */
+  explicit Defer(Action&& action) : action_(std::move(action)) {
+  }
+
+  ~Defer() {
+    action_();
+  }
+
+  // Defer can be neither copied nor moved.
+  Defer(const Defer&) = delete;
+  Defer& operator=(const Defer&) = delete;
+
+ private:
+  Action action_;
+};
+
+}  // namespace util
+}  // namespace firestore
+}  // namespace firebase
+
+#endif  // FIRESTORE_CORE_SRC_UTIL_DEFER_H_

Firestore/core/src/util/filesystem_posix.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018 Google
+ * Copyright 2018 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -168,7 +168,7 @@ Status Filesystem::IsDirectory(const Path& path) {
 
 StatusOr<int64_t> Filesystem::FileSize(const Path& path) {
   struct stat st {};
-  if (stat(path.c_str(), &st) == 0) {
+  if (::stat(path.c_str(), &st) == 0) {
     return st.st_size;
   } else {
     return Status::FromErrno(

Firestore/core/src/util/filesystem_win.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018 Google
+ * Copyright 2018 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,7 @@
 #include <cerrno>
 #include <string>
 
+#include "Firestore/core/src/util/defer.h"
 #include "Firestore/core/src/util/hard_assert.h"
 #include "Firestore/core/src/util/path.h"
 #include "Firestore/core/src/util/statusor.h"
@@ -36,16 +37,16 @@ namespace util {
 
 StatusOr<Path> Filesystem::AppDataDir(absl::string_view app_name) {
   wchar_t* path = nullptr;
+  auto cleanup = defer([&] { CoTaskMemFree(path); });
+
   HRESULT hr = SHGetKnownFolderPath(FOLDERID_LocalAppData, 0, nullptr, &path);
   if (FAILED(hr)) {
-    CoTaskMemFree(path);
     return Status::FromLastError(
         HRESULT_CODE(hr),
         "Failed to find the local application data directory");
   }
 
   Path result = Path::FromUtf16(path, wcslen(path)).AppendUtf8(app_name);
-  CoTaskMemFree(path);
   return std::move(result);
 }
 

Firestore/core/src/util/string_apple.h

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018 Google
+ * Copyright 2018 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -46,6 +46,15 @@ inline CFStringRef MakeCFString(absl::string_view contents) {
                                  kCFStringEncodingUTF8, false);
 }
 
+/**
+ * CFRelease that safely ignores null values.
+ */
+inline void SafeCFRelease(CFTypeRef cf) {
+  if (cf) {
+    CFRelease(cf);
+  }
+}
+
 #if defined(__OBJC__)
 
 // Translates a string_view string to the equivalent NSString by making a copy.

Firestore/core/test/unit/model/field_value_test.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018 Google
+ * Copyright 2018 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,6 +28,8 @@
 #include "Firestore/core/src/model/field_mask.h"
 #include "Firestore/core/src/model/field_path.h"
 #include "Firestore/core/src/nanopb/byte_string.h"
+#include "Firestore/core/src/util/defer.h"
+#include "Firestore/core/src/util/string_apple.h"
 #include "Firestore/core/test/unit/testutil/equals_tester.h"
 #include "Firestore/core/test/unit/testutil/testutil.h"
 #include "Firestore/core/test/unit/testutil/time_testing.h"
@@ -312,10 +314,10 @@ TEST_F(FieldValueTest, Equality) {
 TEST_F(FieldValueTest, CanonicalBitsAreCanonical) {
   double input = ToDouble(kAlternateNanBits);
   CFNumberRef number = CFNumberCreate(nullptr, kCFNumberDoubleType, &input);
+  util::Defer cleanup([&] { util::SafeCFRelease(number); });
 
   double actual = 0.0;
   CFNumberGetValue(number, kCFNumberDoubleType, &actual);
-  CFRelease(number);
 
   ASSERT_EQ(kCanonicalNanBits, ToBits(actual));
 }

Firestore/core/test/unit/util/defer_test.cc

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2020 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Firestore/core/src/util/defer.h"
+
+#include "gtest/gtest.h"
+
+namespace firebase {
+namespace firestore {
+namespace util {
+
+TEST(DeferTest, Defers) {
+  int value = 0;
+  {
+    Defer cleanup([&] { ++value; });
+    ASSERT_EQ(value, 0);
+  }
+
+  ASSERT_EQ(value, 1);
+}
+
+}  // namespace util
+}  // namespace firestore
+}  // namespace firebase

Firestore/core/test/unit/util/filesystem_test.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018 Google
+ * Copyright 2018 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@
 #include <fstream>
 
 #include "Firestore/core/src/util/autoid.h"
+#include "Firestore/core/src/util/defer.h"
 #include "Firestore/core/src/util/log.h"
 #include "Firestore/core/src/util/path.h"
 #include "Firestore/core/src/util/statusor.h"
@@ -43,9 +44,12 @@ using testutil::Touch;
 static void WriteStringToFile(const Path& path, const std::string& text) {
   std::ofstream out{path.native_value()};
   ASSERT_TRUE(out.good());
+  Defer cleanup([&] {
+    out.close();
+    ASSERT_TRUE(out.good());
+  });
+
   out << text;
-  out.close();
-  ASSERT_TRUE(out.good());
 }
 
 static void WriteBytesToFile(const Path& path, int byte_count) {

Firestore/core/test/unit/util/string_apple_test.mm

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018 Google
+ * Copyright 2018 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 #include <string>
 #include <vector>
 
+#include "Firestore/core/src/util/defer.h"
 #include "gtest/gtest.h"
 
 namespace firebase {
@@ -50,9 +51,10 @@ class StringAppleTest : public testing::Test {
 TEST_F(StringAppleTest, MakeStringFromCFStringRef) {
   for (const std::string& string_value : StringTestCases()) {
     CFStringRef cf_string = MakeCFString(string_value);
+    Defer cleanup([&] { SafeCFRelease(cf_string); });
+
     std::string actual = MakeString(cf_string);
     EXPECT_EQ(string_value, actual);
-    CFRelease(cf_string);
   }
 }