GNU bug report logs - #35427
Conflicting declarations of GC_is_heap_ptr

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From: Sören Jonsson <sorjon02 <at> gmail.com>
To: 35427 <at> debbugs.gnu.org
Subject: bug#35427: Conflicting declarations of GC_is_heap_ptr
Date: Thu, 25 Apr 2019 08:20:31 +0200

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Hello,

I'm working on building guile 2.2.4 for Cygwin/Windows. I have now 
resolved a couple of library issues, and have run into a problem with 
conflicting declarations.

Environment:

   Cygwin

   $ gcc --version
   gcc (GCC) 7.4.0
   Copyright © 2017 Free Software Foundation, Inc.

   guile-2.2.4

   gc-8.0.4

Error message:

   make  all-am
   make[3]: Entering directory '/tmp/guile-2.2.4/libguile'
      CC       guile-guile.o
   In file included from ../libguile.h:81:0,
                     from guile.c:34:
   ../libguile/pairs.h:182:1: error: conflicting types for 'GC_is_heap_ptr'
     GC_is_heap_ptr (void *ptr)
     ^~~~~~~~~~~~~~
   In file included from ../libguile/bdw-gc.h:47:0,
                     from ../libguile/gc.h:156,
                     from ../libguile/atomic.h:25,
                     from ../libguile.h:37,
                     from guile.c:34:
   /usr/local/include/gc/gc.h:551:20: note: previous declaration of
   'GC_is_heap_ptr' was here
     GC_API int GC_CALL GC_is_heap_ptr(const void *);
                        ^~~~~~~~~~~~~~
   make[3]: *** [Makefile:3575: guile-guile.o] Error 1
   make[3]: Leaving directory '/tmp/guile-2.2.4/libguile'

Analysis:

   This appears to be a simple problem with the the function
   GC_is_heap_ptr declared in two different ways in two different
   files: /usr/local/include/gc/gc.h.156 and
   /tmp/guile/2.2.4/libguile/pairs.h. The first file declares it as
   "GC_API int GC_CALL GC_is_heap_ptr(const void *);", and the second
   as "static int
   GC_is_heap_ptr (void *ptr)
   {
      return GC_base (ptr) != NULL;
   }
   ".

Proposed solution:

   The obvious solution would be to surround the definition in
   libguile/pairs.h with a conditional #ifndef HAVE_GC_IS_HEAP_PTR, but
   i get the impression that libguile/pairs.h is auto-generated, so I
   might brake your code.  What would be your preferred solution?

With my best regards,

-- 
Sören Jonsson
Kärnvägen 237
906 27 UMEÅ
SWEDEN
Tel: 090-180 339, 070-603 3896

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