[lldb] [Windows] Provide vasprintf only for MSVC

[mati865]

Summary

Mingw-w64 provides this function and it has been causing issues for MSYS2 when building lldb.

[mstorsjo]

+1 from me on this, I'm ok with this change. I'm a bit curious as I haven't seen any issues regarding this myself though. I wonder if it something very MSYS2-specific, or is the difference in building with gcc vs clang?

[mati865]

Perhaps you are building with Clang?
I don't remember the message but GCC emits error about incompatible definition and declaration of vasprintf. I can build it without the patch and paste the error if you want.

[mstorsjo]

In D79999#2039069, @mati865 wrote:

Perhaps you are building with Clang?
I don't remember the message but GCC emits error about incompatible definition and declaration of vasprintf. I can build it without the patch and paste the error if you want.

I took a look now, and I see that the mingw-w64 vasprintf only is visible if _GNU_SOURCE is defined. So apparently something is setting that in your build, but not in mine - and thus this patch would actually break my build...

[mati865]

Indeed, I'll see if I can build all LLVM related packages without _GNU_SOURCE. Otherwise I'll guard it with #ifndef _GNU_SOURCE instead.

[mati865]

With _GNU_SOURCE removed I was able to successfully build everything without this diff.
I cannot test it today but I believe this updated diff would have fixed the error.

It's up to you whether this should be considered as user error and unsupported configuration.

lldb/include/lldb/Host/windows/PosixApi.h

 #define S_IFDIR _S_IFDIR
 
 #ifndef S_ISDIR
 #define S_ISDIR(mode) (((mode)&S_IFMT) == S_IFDIR)
 #endif
 
 #endif // _MSC_VER
 
-// Various useful posix functions that are not present in Windows.  We provide
-// custom implementations.
+// Various useful posix functions that are typically not present in Windows.
+// We provide custom implementations.
+#ifndef _GNU_SOURCE
 int vasprintf(char **ret, const char *fmt, va_list ap);
+#endif
 char *strcasestr(const char *s, const char *find);
 char *realpath(const char *name, char *resolved);
 
 #ifdef _MSC_VER
 
 char *basename(char *path);
 char *dirname(char *path);
 

lldb/source/Host/windows/Windows.cpp

bool wideToUtf8(const wchar_t *wide, char *buf, size_t bufSize) {
   size_t sourceLen = wcslen(wide) + 1 /* convert null too */;
   llvm::UTF8 *target = reinterpret_cast<llvm::UTF8 *>(buf);
   llvm::ConversionFlags flags = llvm::strictConversion;
   return llvm::ConvertUTF16toUTF8(&sourceStart, sourceStart + sourceLen, &target,
                             target + bufSize, flags) == llvm::conversionOK;
 }
 }
 
+#ifndef _GNU_SOURCE
 int vasprintf(char **ret, const char *fmt, va_list ap) {
   char *buf;
   int len;
   size_t buflen;
   va_list ap2;
 
   va_copy(ap2, ap);
   len = vsnprintf(NULL, 0, fmt, ap2);
 
   if (len >= 0 &&
       (buf = (char *)malloc((buflen = (size_t)(len + 1)))) != NULL) {
     len = vsnprintf(buf, buflen, fmt, ap);
     *ret = buf;
   } else {
     *ret = NULL;
     len = -1;
   }
 
   va_end(ap2);
   return len;
 }
+#endif
 
 char *strcasestr(const char *s, const char *find) {
   char c, sc;
   size_t len;
 
   if ((c = *find++) != 0) {
     c = tolower((unsigned char)c);
     len = strlen(find);