switch to standard C++ fallthrough attribute

We require C++20 now, so we can switch to the C++17 [[fallthrough]].

Change-Id: I5c34cd4154bca28f4d950524e5b2ffb1e7ec8afd
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/6388177
Reviewed-by: Lei Zhang <[email protected]>

Author: vapier

src/common/convert_UTF.cc

@@ -297,15 +297,15 @@ ConversionResult ConvertUTF16toUTF8 (const UTF16** sourceStart, const UTF16* sou
       case 4:
         *--target = (UTF8)((ch | byteMark) & byteMask);
         ch >>= 6;
-        BP_FALLTHROUGH;
+        [[fallthrough]];
       case 3:
         *--target = (UTF8)((ch | byteMark) & byteMask);
         ch >>= 6;
-        BP_FALLTHROUGH;
+        [[fallthrough]];
       case 2:
         *--target = (UTF8)((ch | byteMark) & byteMask);
         ch >>= 6;
-        BP_FALLTHROUGH;
+        [[fallthrough]];
       case 1:
         *--target =  (UTF8)(ch | firstByteMark[bytesToWrite]);
     }
@@ -338,10 +338,10 @@ Boolean isLegalUTF8(const UTF8 *source, int length) {
       /* Everything else falls through when "true"... */
     case 4:
       if ((a = (*--srcptr)) < 0x80 || a > 0xBF) return false;
-      BP_FALLTHROUGH;
+      [[fallthrough]];
     case 3:
       if ((a = (*--srcptr)) < 0x80 || a > 0xBF) return false;
-      BP_FALLTHROUGH;
+      [[fallthrough]];
     case 2:
       if ((a = (*--srcptr)) > 0xBF) return false;
 
@@ -353,7 +353,7 @@ Boolean isLegalUTF8(const UTF8 *source, int length) {
         case 0xF4: if (a > 0x8F) return false; break;
         default:   if (a < 0x80) return false;
       }
-      BP_FALLTHROUGH;
+      [[fallthrough]];
     case 1: if (*source >= 0x80 && *source < 0xC2) return false;
   }
   if (*source > 0xF4) return false;
@@ -399,12 +399,12 @@ ConversionResult ConvertUTF8toUTF16 (const UTF8** sourceStart, const UTF8* sourc
      */
     switch (extraBytesToRead) {
       /* remember, illegal UTF-8 */
-      case 5: ch += *source++; ch <<= 6; BP_FALLTHROUGH;
+      case 5: ch += *source++; ch <<= 6; [[fallthrough]];
       /* remember, illegal UTF-8 */
-      case 4: ch += *source++; ch <<= 6; BP_FALLTHROUGH;
-      case 3: ch += *source++; ch <<= 6; BP_FALLTHROUGH;
-      case 2: ch += *source++; ch <<= 6; BP_FALLTHROUGH;
-      case 1: ch += *source++; ch <<= 6; BP_FALLTHROUGH;
+      case 4: ch += *source++; ch <<= 6; [[fallthrough]];
+      case 3: ch += *source++; ch <<= 6; [[fallthrough]];
+      case 2: ch += *source++; ch <<= 6; [[fallthrough]];
+      case 1: ch += *source++; ch <<= 6; [[fallthrough]];
       case 0: ch += *source++;
     }
     ch -= offsetsFromUTF8[extraBytesToRead];
@@ -493,15 +493,15 @@ ConversionResult ConvertUTF32toUTF8 (const UTF32** sourceStart, const UTF32* sou
       case 4:
         *--target = (UTF8)((ch | byteMark) & byteMask);
         ch >>= 6;
-        BP_FALLTHROUGH;
+        [[fallthrough]];
       case 3:
         *--target = (UTF8)((ch | byteMark) & byteMask);
         ch >>= 6;
-        BP_FALLTHROUGH;
+        [[fallthrough]];
       case 2:
         *--target = (UTF8)((ch | byteMark) & byteMask);
         ch >>= 6;
-        BP_FALLTHROUGH;
+        [[fallthrough]];
       case 1:
         *--target = (UTF8) (ch | firstByteMark[bytesToWrite]);
     }
@@ -534,11 +534,11 @@ ConversionResult ConvertUTF8toUTF32 (const UTF8** sourceStart, const UTF8* sourc
      * The cases all fall through. See "Note A" below.
      */
     switch (extraBytesToRead) {
-      case 5: ch += *source++; ch <<= 6; BP_FALLTHROUGH;
-      case 4: ch += *source++; ch <<= 6; BP_FALLTHROUGH;
-      case 3: ch += *source++; ch <<= 6; BP_FALLTHROUGH;
-      case 2: ch += *source++; ch <<= 6; BP_FALLTHROUGH;
-      case 1: ch += *source++; ch <<= 6; BP_FALLTHROUGH;
+      case 5: ch += *source++; ch <<= 6; [[fallthrough]];
+      case 4: ch += *source++; ch <<= 6; [[fallthrough]];
+      case 3: ch += *source++; ch <<= 6; [[fallthrough]];
+      case 2: ch += *source++; ch <<= 6; [[fallthrough]];
+      case 1: ch += *source++; ch <<= 6; [[fallthrough]];
       case 0: ch += *source++;
     }
     ch -= offsetsFromUTF8[extraBytesToRead];

src/common/macros.h

@@ -31,18 +31,6 @@
 
 #include <stddef.h>
 
-// Ensure that this macro definition stays in a private header file: clang
-// suggests the first macro expanding to [[clang::fallthrough]] in its
-// diagnostics, so if BP_FALLTHROUGH is visible in code depending on breakpad,
-// clang would suggest BP_FALLTHROUGH for code depending on breakpad, instead of
-// the client code's own fallthrough macro.
-// TODO(thakis): Once everyone uses C++17, use its [[fallthrough]] instead.
-#if defined(__clang__)
-#define BP_FALLTHROUGH [[clang::fallthrough]]
-#else
-#define BP_FALLTHROUGH
-#endif
-
 // TODO: Delete when we require C++23.
 #ifndef unreachable
 #define unreachable() __builtin_unreachable()

src/processor/minidump.cc

@@ -2469,7 +2469,7 @@ string MinidumpModule::code_identifier() const {
         break;
       }
       // Otherwise fall through to the case below.
-      BP_FALLTHROUGH;
+      [[fallthrough]];
     }
 
     case MD_OS_MAC_OS_X:
@@ -5823,7 +5823,7 @@ bool Minidump::Read() {
                             stream_type << ", but can only deal with one";
             return false;
           }
-          BP_FALLTHROUGH;
+          [[fallthrough]];
         }
 
         default: {