Add NINJA_FALLTHROUGH macro

Borrow macro implementation from OpenSSL code.

Add the macro after each fallthrough switch case to indicate our
intention to the compiler. This silences GCC -Wimplicit-fallthrough
warnings, which is implied by GCC 7.x -Wextra.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/util.h b/src/util.h
index 4ee41a5..1b4227c 100644
--- a/src/util.h
+++ b/src/util.h
@@ -34,6 +34,20 @@ using namespace std;
 /// Log a fatal message and exit.
 NORETURN void Fatal(const char* msg, ...);
 
+// Have a generic fall-through for different versions of C/C++.
+#if defined(__cplusplus) && __cplusplus >= 201703L
+#define NINJA_FALLTHROUGH [[fallthrough]]
+#elif defined(__cplusplus) && __cplusplus >= 201103L && defined(__clang__)
+#define NINJA_FALLTHROUGH [[clang::fallthrough]]
+#elif defined(__cplusplus) && __cplusplus >= 201103L && defined(__GNUC__) && \
+    __GNUC__ >= 7
+#define NINJA_FALLTHROUGH [[gnu::fallthrough]]
+#elif defined(__GNUC__) && __GNUC__ >= 7 // gcc 7
+#define NINJA_FALLTHROUGH __attribute__ ((fallthrough))
+#else // C++11 on gcc 6, and all other cases
+#define NINJA_FALLTHROUGH
+#endif
+
 /// Log a warning message.
 void Warning(const char* msg, ...);