From e5eb871419fc80799a8126fefe147d8fb4a04a2f Mon Sep 17 00:00:00 2001
From: Jiakai Liu <liujiakai@fb.com>
Date: Fri, 22 Mar 2019 14:01:41 -0700
Subject: [PATCH] Fix DCHECK to handle dangling else (#18295)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18295

Replace "if (false)" with "while (false)" which fixes potential dangling else issue as shown in added test case.

Reviewed By: ezyang

Differential Revision: D14569608

fbshipit-source-id: 407052db9182ce27b7a59841e90fa50d3eca262e
---
 c10/test/util/logging_test.cpp        |  7 +++++++
 c10/util/logging_is_not_google_glog.h | 16 ++++++++--------
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/c10/test/util/logging_test.cpp b/c10/test/util/logging_test.cpp
index e05d781..38f7787 100644
--- a/c10/test/util/logging_test.cpp
+++ b/c10/test/util/logging_test.cpp
@@ -77,6 +77,13 @@ TEST(LoggingTest, Join) {
   EXPECT_EQ(s, "1, 2, 3");
 }
 
+TEST(LoggingTest, TestDanglingElse) {
+  if (true)
+    DCHECK_EQ(1, 1);
+  else
+    GTEST_FAIL();
+}
+
 #if GTEST_HAS_DEATH_TEST
 TEST(LoggingDeathTest, TestEnforceUsingFatal) {
   bool kTrue = true;
diff --git a/c10/util/logging_is_not_google_glog.h b/c10/util/logging_is_not_google_glog.h
index 8d8f7f6..50b0c0d 100644
--- a/c10/util/logging_is_not_google_glog.h
+++ b/c10/util/logging_is_not_google_glog.h
@@ -120,7 +120,7 @@ static_assert(
 #else
 // Optimized version - generates no code.
 #define DCHECK(condition) \
-  if (false)              \
+  while (false)           \
   CHECK(condition)
 #endif // NDEBUG
 
@@ -146,22 +146,22 @@ static_assert(
 #else // !NDEBUG
 // These versions generate no code in optimized mode.
 #define DCHECK_EQ(val1, val2) \
-  if (false)                  \
+  while (false)               \
   CHECK_OP(val1, val2, ==)
 #define DCHECK_NE(val1, val2) \
-  if (false)                  \
+  while (false)               \
   CHECK_OP(val1, val2, !=)
 #define DCHECK_LE(val1, val2) \
-  if (false)                  \
+  while (false)               \
   CHECK_OP(val1, val2, <=)
 #define DCHECK_LT(val1, val2) \
-  if (false)                  \
+  while (false)               \
   CHECK_OP(val1, val2, <)
 #define DCHECK_GE(val1, val2) \
-  if (false)                  \
+  while (false)               \
   CHECK_OP(val1, val2, >=)
 #define DCHECK_GT(val1, val2) \
-  if (false)                  \
+  while (false)               \
   CHECK_OP(val1, val2, >)
 #endif // NDEBUG
 
@@ -178,7 +178,7 @@ static_assert(
 #else // !NDEBUG
 // Optimized version - generates no code.
 #define DCHECK_NOTNULL(val) \
-  if (false)                \
+  while (false)             \
   CHECK_NOTNULL(val)
 #endif // NDEBUG
 
-- 
2.7.4