compiler.h

// Copyright 2023 Google LLC. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd
 
#ifndef PACKAGER_MACROS_COMPILER_H_
#define PACKAGER_MACROS_COMPILER_H_
 
#define UNUSED(x) (void)(x)
 
// The FALLTHROUGH_INTENDED macro can be used to annotate implicit fall-through
// between switch labels:
//  switch (x) {
//    case 40:
//    case 41:
//      if (truth_is_out_there) {
//        ++x;
//        FALLTHROUGH_INTENDED;  // Use instead of/along with annotations in
//                               // comments.
//      } else {
//        return x;
//      }
//    case 42:
//      ...
//
//  As shown in the example above, the FALLTHROUGH_INTENDED macro should be
//  followed by a semicolon. It is designed to mimic control-flow statements
//  like 'break;', so it can be placed in most places where 'break;' can, but
//  only if there are no statements on the execution path between it and the
//  next switch label.
//
//  When compiled with clang in C++11 mode, the FALLTHROUGH_INTENDED macro is
//  expanded to [[clang::fallthrough]] attribute, which is analysed when
//  performing switch labels fall-through diagnostic ('-Wimplicit-fallthrough').
//  See clang documentation on language extensions for details:
//  http://clang.llvm.org/docs/AttributeReference.html#fallthrough-clang-fallthrough
//
//  When used with unsupported compilers, the FALLTHROUGH_INTENDED macro has no
//  effect on diagnostics.
//
//  In either case this macro has no effect on runtime behavior and performance
//  of code.
#if defined(__clang__) && __cplusplus >= 201103L && 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 [[fallthrough]]
#endif
 
#endif  // PACKAGER_MACROS_COMPILER_H_