From 08ef815c7b55f28417b1a965eeab3640558d5f5a Mon Sep 17 00:00:00 2001
From: Stefan Becker <chemobejk@gmail.com>
Date: Sat, 7 Apr 2018 16:42:35 +0300
Subject: [PATCH] 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.
---
 src/build_log.cc |  6 ++++++
 src/hash_map.h   |  3 +++
 src/util.cc      |  2 +-
 src/util.h       | 14 ++++++++++++++
 4 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/src/build_log.cc b/src/build_log.cc
index c75be95..2a65f9d 100644
--- a/src/build_log.cc
+++ b/src/build_log.cc
@@ -76,11 +76,17 @@ uint64_t MurmurHash64A(const void* key, size_t len) {
   switch (len & 7)
   {
   case 7: h ^= uint64_t(data[6]) << 48;
+          NINJA_FALLTHROUGH;
   case 6: h ^= uint64_t(data[5]) << 40;
+          NINJA_FALLTHROUGH;
   case 5: h ^= uint64_t(data[4]) << 32;
+          NINJA_FALLTHROUGH;
   case 4: h ^= uint64_t(data[3]) << 24;
+          NINJA_FALLTHROUGH;
   case 3: h ^= uint64_t(data[2]) << 16;
+          NINJA_FALLTHROUGH;
   case 2: h ^= uint64_t(data[1]) << 8;
+          NINJA_FALLTHROUGH;
   case 1: h ^= uint64_t(data[0]);
           h *= m;
   };
diff --git a/src/hash_map.h b/src/hash_map.h
index a91aeb9..55d2c9d 100644
--- a/src/hash_map.h
+++ b/src/hash_map.h
@@ -18,6 +18,7 @@
 #include <algorithm>
 #include <string.h>
 #include "string_piece.h"
+#include "util.h"
 
 // MurmurHash2, by Austin Appleby
 static inline
@@ -40,7 +41,9 @@ unsigned int MurmurHash2(const void* key, size_t len) {
   }
   switch (len) {
   case 3: h ^= data[2] << 16;
+          NINJA_FALLTHROUGH;
   case 2: h ^= data[1] << 8;
+          NINJA_FALLTHROUGH;
   case 1: h ^= data[0];
     h *= m;
   };
diff --git a/src/util.cc b/src/util.cc
index 61a038b..760bc23 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -197,7 +197,7 @@ bool CanonicalizePath(char* path, size_t* len, uint64_t* slash_bits,
       case '\\':
         bits |= bits_mask;
         *c = '/';
-        // Intentional fallthrough.
+        NINJA_FALLTHROUGH;
       case '/':
         bits_mask <<= 1;
     }
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, ...);