Re: [PATCH] git-compat-util: do not step on MAC_OS_X_VERSION_MIN_REQUIRED

On Feb 6, 2015, at 02:00, Eric Sunshine wrote:

On Fri, Feb 6, 2015 at 4:35 AM, Kyle J. McKay [off-list ref]  
wrote:

quoted

#ifndef NO_OPENSSL
+#ifdef __APPLE__
#define __AVAILABILITY_MACROS_USES_AVAILABILITY 0
-#define MAC_OS_X_VERSION_MIN_REQUIRED MAC_OS_X_VERSION_10_6
+#include <AvailabilityMacros.h>
+#undef DEPRECATED_ATTRIBUTE
+#define DEPRECATED_ATTRIBUTE
+#undef __AVAILABILITY_MACROS_USES_AVAILABILITY
+#endif
#include <openssl/ssl.h>
#include <openssl/err.h>
-#undef MAC_OS_X_VERSION_MIN_REQUIRED
-#undef __AVAILABILITY_MACROS_USES_AVAILABILITY

DEPRECATED_ATTRIBUTE is a fairly generic name. Do we want to be extra
careful and #undef it here to avoid potential unintended interactions
with other #includes (Apple or not)?

The new patch only mucks with it when we have #ifdef __APPLE__ and  
pretty much any apple code is going to end up including the  
availability stuff sooner or later which manipulates  
DEPRECATED_ATTRIBUTE.  Essentially that makes "DEPRECATED_ATTRIBUTE" a  
reserved macro name on __APPLE__.

   #ifdef __APPLE__
   #undef DEPRECATED_ATTRIBUTE
   #endif

If we do that, won't the compiler then helpfully supply a "0" when the  
macro is used?  Or is that only when an undefined macro is used inside  
an #if or #elif ?

That would break all later declarations that use it.

On the other hand, we've already mucked with it, so #undef may be  
superfluous.

Actually I just tested it.  If we #undef it we could end up producing  
these:

   error: syntax error before ‘DEPRECATED_ATTRIBUTE’

So I think it needs to stay #define'd to nothing to be safe in case  
anything later on ends up including stuff that uses it.  The worst  
that happens is you don't see some deprecation warnings that you  
otherwise would.  It won't make any functions available that shouldn't  
be or make unavailable functions that should be.

-Kyle