Uncommon permutation of #defines breaks compilation in Errno.cpp

[Gadal]

In llvm/lib/Support/Errno.cpp, we have the following (comments removed for brevity):

#include "llvm/Support/Errno.h"
#include "llvm/Config/config.h"
#include <cstring>

#if HAVE_ERRNO_H
#include <errno.h>
#endif

namespace llvm {
namespace sys {

#if HAVE_ERRNO_H
std::string StrError() {
  return StrError(errno);
}
#endif  // HAVE_ERRNO_H

std::string StrError(int errnum) {
  std::string str;
  if (errnum == 0)
    return str;
#if defined(HAVE_STRERROR_R) || HAVE_DECL_STRERROR_S
  const int MaxErrStrLen = 2000;
  char buffer[MaxErrStrLen];
  buffer[0] = '\0';
#endif

#ifdef HAVE_STRERROR_R
#if defined(__GLIBC__) && defined(_GNU_SOURCE)
  str = strerror_r(errnum, buffer, MaxErrStrLen - 1);
#else
  strerror_r(errnum, buffer, MaxErrStrLen - 1);
  str = buffer;
#endif
#elif HAVE_DECL_STRERROR_S // "Windows Secure API"
  strerror_s(buffer, MaxErrStrLen - 1, errnum);
  str = buffer;
#elif defined(HAVE_STRERROR)
  str = strerror(errnum);
#else
  raw_string_ostream stream(str);                            // Appears to be unable to compile.
  stream << "Error #" << errnum;
  stream.flush();
#endif
  return str;
}

}  // namespace sys
}  // namespace llvm

In the event that HAVE_STRERROR_R is undefined, HAVE_DECL_STRERROR_S evaluates to false, and HAVE_STRERROR is undefined, the portion of text marked above is inserted. Compilation fails with the following error:

llvm\lib\Support\Errno.cpp(66): error C2065: 'raw_string_ostream': undeclared identifier

It appears that raw_string_ostream is not defined by Errno.h, config.h, errno.h, or any of their transitive inclusions.

L66 was added 11 years ago here, and that commit added an inclusion for llvm/Support/raw_ostream.h. That inclusion was deleted here.

Adding back that inclusion resolves the compilation error.

[Gadal]

@serge-sans-paille It may be worth a look at fbbc41f to see if any of the other 70 deletions in that change are invalid for certain combinations of #defines.

[MaskRay]

In the event that HAVE_STRERROR_R is undefined, HAVE_DECL_STRERROR_S evaluates to false, and HAVE_STRERROR is undefined, the portion of text marked above is inserted. Compilation fails with the following error:

Does this scenario happen for a known supported OS?

strerror_r has great portability. It may not exist in MSVC but strerror is available there. If we cannot find a supported OS exercising this code path of the following lines, the real fix should be to remove these lines:

  raw_string_ostream stream(str);
  stream << "Error #" << errnum;
  stream.flush();

[Gadal]

@MaskRay

Does this scenario happen for a known supported OS?

Not to my knowledge. In my case, I bumped into the set of conditions I described above due to a misconfiguration, but that was easily resolved.