From 1b86d41c7844729768b2ffd096e1cded3c145a93 Mon Sep 17 00:00:00 2001
From: Elliott Hughes <enh@google.com>
Date: Fri, 6 Apr 2018 17:45:22 -0700
Subject: [PATCH] Add SIZEOF_MEMBER.

Bug: N/A
Test: ran tests
Change-Id: Icb7e8ae83d242c867b71a990b08eb1a62ed1482c
---
 base/Android.bp                    |  1 +
 base/include/android-base/macros.h |  4 ++++
 base/macros_test.cpp               | 30 ++++++++++++++++++++++++++++++
 3 files changed, 35 insertions(+)
 create mode 100644 base/macros_test.cpp

diff --git a/base/Android.bp b/base/Android.bp
index 7b0ba11d0..12b396957 100644
--- a/base/Android.bp
+++ b/base/Android.bp
@@ -124,6 +124,7 @@ cc_test {
         "errors_test.cpp",
         "file_test.cpp",
         "logging_test.cpp",
+        "macros_test.cpp",
         "parsedouble_test.cpp",
         "parseint_test.cpp",
         "parsenetaddress_test.cpp",
diff --git a/base/include/android-base/macros.h b/base/include/android-base/macros.h
index 25f2ff4ed..fd6efb2a8 100644
--- a/base/include/android-base/macros.h
+++ b/base/include/android-base/macros.h
@@ -20,6 +20,8 @@
 #include <stddef.h>  // for size_t
 #include <unistd.h>  // for TEMP_FAILURE_RETRY
 
+#include <utility>
+
 // bionic and glibc both have TEMP_FAILURE_RETRY, but eg Mac OS' libc doesn't.
 #ifndef TEMP_FAILURE_RETRY
 #define TEMP_FAILURE_RETRY(exp)            \
@@ -114,6 +116,8 @@ char(&ArraySizeHelper(T(&array)[N]))[N];  // NOLINT(readability/casting)
   ((sizeof(a) / sizeof(*(a))) / \
     static_cast<size_t>(!(sizeof(a) % sizeof(*(a)))))
 
+#define SIZEOF_MEMBER(t, f) sizeof(std::declval<t>().f)
+
 // Changing this definition will cause you a lot of pain.  A majority of
 // vendor code defines LIKELY and UNLIKELY this way, and includes
 // this header through an indirect path.
diff --git a/base/macros_test.cpp b/base/macros_test.cpp
new file mode 100644
index 000000000..2b522db5c
--- /dev/null
+++ b/base/macros_test.cpp
@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * 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 "android-base/macros.h"
+
+#include <stdint.h>
+
+#include <gtest/gtest.h>
+
+TEST(macros, SIZEOF_MEMBER_macro) {
+  struct S {
+    int32_t i32;
+    double d;
+  };
+  ASSERT_EQ(4U, SIZEOF_MEMBER(S, i32));
+  ASSERT_EQ(8U, SIZEOF_MEMBER(S, d));
+}