Silence macOS vfork deprecation warnings

The vfork system call exists and works in macOS 11.6 but the compiler
gives a deprecation message; silence it, because the performance is
still better than that of plain fork.  See discussion at
https://lists.gnu.org/archive/html/emacs-devel/2022-02/msg00260.html

* src/conf_post.h (VFORK): New #define.
* src/callproc.c (emacs_spawn):
* src/sysdep.c (sys_subshell): Use it.

3 files changed, 15 insertions, 2 deletions

diff --git a/src/callproc.c b/src/callproc.c
index 4d3b0bb8e06..dcee740043c 100644
--- a/src/callproc.c
+++ b/src/callproc.c
@@ -1500,7 +1500,7 @@ emacs_spawn (pid_t *newpid, int std_in, int std_out, int std_err,
   if (pty != NULL)
     pid = fork ();
   else
-    pid = vfork ();
+    pid = VFORK ();
 #else
   pid = vfork ();
 #endif
diff --git a/src/conf_post.h b/src/conf_post.h
index 6db76a2dfad..0b6260b287e 100644
--- a/src/conf_post.h
+++ b/src/conf_post.h
@@ -353,6 +353,19 @@ extern int emacs_setenv_TZ (char const *);
 # define vfork fork
 #endif
 
+/* vfork is deprecated on at least macOS 11.6 and later, but it still works
+   and is faster than fork, so silence the warning as if we knew what we
+   are doing.  */
+#ifdef DARWIN_OS
+#define VFORK()                                                         \
+  (_Pragma("clang diagnostic push")                                     \
+   _Pragma("clang diagnostic ignored \"-Wdeprecated-declarations\"")    \
+   vfork ()                                                             \
+   _Pragma("clang diagnostic pop"))
+#else
+#define VFORK() vfork ()
+#endif
+
 #if ! (defined __FreeBSD__ || defined GNU_LINUX || defined __MINGW32__)
 # undef PROFILING
 #endif
diff --git a/src/sysdep.c b/src/sysdep.c
index d682e87cc71..c772aff6a02 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -664,7 +664,7 @@ sys_subshell (void)
 #else
   {
     char *volatile str_volatile = str;
-    pid = vfork ();
+    pid = VFORK ();
     str = str_volatile;
   }
 #endif