Fix Unreachable() test to property EXPECT_DEATH in NDEBUG mode.

EXPECT_DEBUG_DEATH runs the statement without expecting a death in NDEBUG mode, causing a test failure in asan due to reaching `__builtin_unreachable`.
Also, improve a bit the definition of Unreachable to be more readable/useful.

PiperOrigin-RevId: 584133307

src/google/protobuf/port.h

@@ -202,17 +202,21 @@ inline constexpr bool DebugHardenStringValues() {
 #endif
 }
 
-#if ABSL_HAVE_BUILTIN(__builtin_FILE) && ABSL_HAVE_BUILTIN(__builtin_LINE)
-[[noreturn]] inline void Unreachable(const char* file = __builtin_FILE(),
-                                     int line = __builtin_LINE()) {
-#else
-[[noreturn]] inline void Unreachable(const char* file = "", int line = 0) {
-#endif
 #if defined(NDEBUG) && ABSL_HAVE_BUILTIN(__builtin_unreachable)
+[[noreturn]] ABSL_ATTRIBUTE_COLD PROTOBUF_ALWAYS_INLINE inline void
+Unreachable() {
   __builtin_unreachable();
-#endif
+}
+#elif ABSL_HAVE_BUILTIN(__builtin_FILE) && ABSL_HAVE_BUILTIN(__builtin_LINE)
+[[noreturn]] ABSL_ATTRIBUTE_COLD inline void Unreachable(
+    const char* file = __builtin_FILE(), int line = __builtin_LINE()) {
   protobuf_assumption_failed("Unreachable", file, line);
 }
+#else
+[[noreturn]] ABSL_ATTRIBUTE_COLD inline void Unreachable() {
+  protobuf_assumption_failed("Unreachable", "", 0);
+}
+#endif
 
 }  // namespace internal
 }  // namespace protobuf

src/google/protobuf/port_test.cc

@@ -33,10 +33,15 @@ TEST(PortTest, ProtobufAssume) {
 
 TEST(PortTest, UnreachableTrapsOnDebugMode) {
 #ifdef GTEST_HAS_DEATH_TEST
-  EXPECT_DEBUG_DEATH(Unreachable(), "Assumption failed: 'Unreachable'");
-#if ABSL_HAVE_BUILTIN(__builtin_FILE)
-  EXPECT_DEBUG_DEATH(Unreachable(),
-                     "port_test\\.cc:.*Assumption failed: 'Unreachable'");
+#if defined(NDEBUG)
+  // In NDEBUG we crash with a UD instruction, so we don't get the "Assumption
+  // failed" error.
+  GTEST_SKIP() << "Can't test __builtin_unreachable()";
+#elif ABSL_HAVE_BUILTIN(__builtin_FILE)
+  EXPECT_DEATH(Unreachable(),
+               "port_test\\.cc:.*Assumption failed: 'Unreachable'");
+#else
+  EXPECT_DEATH(Unreachable(), "Assumption failed: 'Unreachable'");
 #endif
 #endif
 }