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Fix platform check for macOS #895

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Fix platform check for macOS #895

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6 changes: 1 addition & 5 deletions zutil.h
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Original file line number Diff line number Diff line change
Expand Up @@ -137,15 +137,11 @@ extern z_const char * const z_errmsg[10]; /* indexed by 2-zlib_error */
# endif
#endif

#if defined(MACOS) || defined(TARGET_OS_MAC)
#if TARGET_OS_OSX
# define OS_CODE 7
# ifndef Z_SOLO
# if defined(__MWERKS__) && __dest_os != __be_os && __dest_os != __win32_os
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@glandium glandium Jan 17, 2024 •
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The history of this code is interesting.
zlib 0.71 (the first version in git) had:

#ifdef MACOS
#  define OS_CODE  0x07
#endif

zlib 1.0.8 added the fdopen thing, but differently:

#if defined(MACOS) || defined(TARGET_OS_MAC)
#  define OS_CODE  0x07
#  ifndef fdopen
#    define fdopen(fd,mode) NULL /* No fdopen() */
#  endif
#endif
#if defined(__MWERKS__) && !defined(fdopen)
#  if __dest_os != __be_os && __dest_os != __win32_os
#    define fdopen(fd,mode) NULL
#  endif
#endif

The corresponding changelog:

  • check for TARGET_OS_MAC in addition to MACOS (Brad Pettit)
  • do not use fdopen for Metrowerks on Mac (Brad Pettit))

zlib 1.1.3 changed it to:

#if defined(MACOS) || defined(TARGET_OS_MAC)
#  define OS_CODE  0x07
#  if defined(__MWERKS__) && __dest_os != __be_os && __dest_os != __win32_os
#    include <unix.h> /* for fdopen */
#  else
#    ifndef fdopen
#      define fdopen(fd,mode) NULL /* No fdopen() */
#    endif
#  endif
#endif

I think the corresponding changelog entry is:

  • Support gzdopen on Mac with Metrowerks (Jason Linhart)

Presumably, Metrowerks was defining TARGET_OS_MAC, and probably didn't define TARGET_OS_OSX, so my assumption here is that this change breaks Metrowerks. However, it's also a long gone compiler, so maybe this part can go entirely, which leaves us with two different OS_CODE values for macOS, one of which was added in ce12c5c

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@markmentovai markmentovai Sep 20, 2025 •
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which leaves us with two different OS_CODE values for macOS, one of which was added in ce12c5c

Ever since ce12c5c, OS_CODE = 19 has meant macOS (or any other modern Apple OS). Prior to that, modern Apple OSes were reported as OS_CODE = 3, “assume Unix”. So what’s the story with OS_CODE = 7 mentioning TARGET_OS_MAC, then?

TARGET_OS_MAC has long been defined by the macOS SDK back to the very earliest days—I see it in the Mac OS X 10.1.5 SDK from Xcode 1.0 (2003-09-28)—but only by <TargetConditionals.h>, which would not normally have been #included into any translation unit that also #included zutil.h. zutil.h is zlib-internal and not generally made available to zlib consumers, so the lack of <TargetConditionals.h> in zlib code is largely dispositive.

The TARGET_OS_MAC macro as used in zutil.h (until 4bd9a71) was presumably used as another synonym for classic (pre-X, previous century) Mac OS, just as MACOS. It would never have meant macOS (or OS X or Mac OS X) in this code, until llvm/llvm-project@6e1f191 (in upstream Clang 18.1, 2024-01-29, and in Xcode 16.3, 2025-03-31).

The ce12c5c commit message says that appnote.txt defines the meaning of these bytes, and appnote.txt §4.4.2 makes it somewhat clear by stating assignments of 7 - Macintosh and 19 - OS X (Darwin).

# include <unix.h> /* for fdopen */
# else
# ifndef fdopen
# define fdopen(fd,mode) NULL /* No fdopen() */
# endif
# endif
# endif
#endif
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