experiment with -Wimplicit-fallthrough

base/compiler_specific.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_COMPILER_SPECIFIC_H_
 #define BASE_COMPILER_SPECIFIC_H_
 
 #include "build/build_config.h"
 
 #if defined(COMPILER_MSVC)
@@ skipping 131 matching lines @@
 #elif defined(__clang__)
 #define OVERRIDE override
 #elif defined(COMPILER_GCC) && __cplusplus >= 201103 && \
       (__GNUC__ * 10000 + __GNUC_MINOR__ * 100) >= 40700
 // GCC 4.7 supports explicit virtual overrides when C++11 support is enabled.
 #define OVERRIDE override
 #else
 #define OVERRIDE
 #endif
 
+// XXX amazing comment
+#if defined(__clang__) && defined(__has_warning)
+#if __has_feature(cxx_attributes) && __has_warning("-Wimplicit-fallthrough")
+#define FALLTHROUGH_INTENDED [[clang::fallthrough]]  // NOLINT
+#endif
+#endif
+
+#ifndef FALLTHROUGH_INTENDED
+#define FALLTHROUGH_INTENDED do { } while (0)
+
 // Annotate a virtual method indicating that subclasses must not override it,
 // or annotate a class to indicate that it cannot be subclassed.
 // Use like:
 //   virtual void foo() FINAL;
 //   class B FINAL : public A {};
 #if defined(COMPILER_MSVC)
 // TODO(jered): Change this to "final" when chromium no longer uses MSVC 2010.
 #define FINAL sealed
 #elif defined(__clang__)
 #define FINAL final
 #elif defined(COMPILER_GCC) && __cplusplus >= 201103 && \
       (__GNUC__ * 10000 + __GNUC_MINOR__ * 100) >= 40700
 // GCC 4.7 supports explicit virtual overrides when C++11 support is enabled.
 #define FINAL final
 #else
 #define FINAL
 #endif
 
+// Annotate a virtual method indicating it must be overriding a virtual
+// method in the parent class.
+// Use like:
+//   virtual void foo() OVERRIDE;
+#if defined(COMPILER_MSVC)
+#define OVERRIDE override
+#elif defined(__clang__)
+#define OVERRIDE override
+#else
+#define OVERRIDE
+#endif
+
 // Annotate a function indicating the caller must examine the return value.
 // Use like:
 //   int foo() WARN_UNUSED_RESULT;
 // To explicitly ignore a result, see |ignore_result()| in <base/basictypes.h>.
 #if defined(COMPILER_GCC)
 #define WARN_UNUSED_RESULT __attribute__((warn_unused_result))
 #else
 #define WARN_UNUSED_RESULT
 #endif
 
 // Tell the compiler a function is using a printf-style format string.
 // |format_param| is the one-based index of the format string parameter;
 // |dots_param| is the one-based index of the "..." parameter.
 // For v*printf functions (which take a va_list), pass 0 for dots_param.
 // (This is undocumented but matches what the system C headers do.)
 #if defined(COMPILER_GCC)
 #define PRINTF_FORMAT(format_param, dots_param) \
     __attribute__((format(printf, format_param, dots_param)))
 #else
 #define PRINTF_FORMAT(format_param, dots_param)
 #endif
 
 // WPRINTF_FORMAT is the same, but for wide format strings.
 // This doesn't appear to yet be implemented in any compiler.
 // See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38308 .
 #define WPRINTF_FORMAT(format_param, dots_param)
 // If available, it would look like:
 //   __attribute__((format(wprintf, format_param, dots_param)))
 
-
 // MemorySanitizer annotations.
 #ifdef MEMORY_SANITIZER
 extern "C" {
 void __msan_unpoison(const void *p, unsigned long s);
 }  // extern "C"
 
 // Mark a memory region fully initialized.
 // Use this to annotate code that deliberately reads uninitialized data, for
 // example a GC scavenging root set pointers from the stack.
 #define MSAN_UNPOISON(p, s)  __msan_unpoison(p, s)
 #else  // MEMORY_SANITIZER
 #define MSAN_UNPOISON(p, s)
 #endif  // MEMORY_SANITIZER
 
 // Macro useful for writing cross-platform function pointers.
 #if !defined(CDECL)
 #if defined(OS_WIN)
 #define CDECL __cdecl
 #else  // defined(OS_WIN)
 #define CDECL
 #endif  // defined(OS_WIN)
 #endif  // !defined(CDECL)
 
 #endif  // BASE_COMPILER_SPECIFIC_H_