--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2010-03-20  Bruno Haible  <bruno@clisp.org>
+
+	Work around unlink() bug on MacOS X 10.5.6.
+	* lib/unlink.c (rpl_unlink): If UNLINK_PARENT_BUG is defined, fail when
+	attempting to unlink a parent directory.
+	* m4/unlink.m4 (gl_FUNC_UNLINK): Require AC_CANONICAL_HOST. Test for
+	MacOS X 10.5 bug. If the bug is present, define UNLINK_PARENT_BUG and
+	activate for the replacement function.
+	* doc/posix-functions/unlink.texi: Mention the MacOS X 10.5 bug.
+
 2010-03-20  Bruno Haible  <bruno@clisp.org>
 
 	Fix link errors on Solaris 8.

--- a/doc/posix-functions/unlink.texi
+++ b/doc/posix-functions/unlink.texi
@@ -11,6 +11,9 @@
 @item
 Some systems mistakenly succeed on @code{unlink("link-to-file/")}:
 GNU/Hurd, FreeBSD 7.2, Solaris 9.
+@item
+On MacOS X 10.5.6, in a writable HFS mount, @code{unlink("..")} succeeds
+without doing anything.
 @end itemize
 
 Portability problems not fixed by Gnulib:

--- a/lib/unlink.c
+++ b/lib/unlink.c
@@ -80,6 +80,16 @@
         }
     }
   if (!result)
-    result = unlink (name);
+    {
+#if UNLINK_PARENT_BUG
+      if (len >= 2 && name[len - 1] == '.' && name[len - 2] == '.'
+          && (len == 2 || ISSLASH (name[len - 3])))
+        {
+          errno = EISDIR; /* could also use EPERM */
+          return -1;
+        }
+#endif
+      result = unlink (name);
+    }
   return result;
 }

--- a/m4/unlink.m4
+++ b/m4/unlink.m4
@@ -1,4 +1,4 @@
-# unlink.m4 serial 3
+# unlink.m4 serial 4
 dnl Copyright (C) 2009, 2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -8,9 +8,10 @@
 [
   AC_REQUIRE([gl_AC_DOS])
   AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  AC_REQUIRE([AC_CANONICAL_HOST])
   dnl Detect Solaris 9 and FreeBSD 7.2 bug.
   AC_CACHE_CHECK([whether unlink honors trailing slashes],
-    [gl_cv_func_unlink_works],
+    [gl_cv_func_unlink_honors_slashes],
     [touch conftest.file
      # Assume that if we have lstat, we can also check symlinks.
      if test $ac_cv_func_lstat = yes; then
@@ -25,10 +26,70 @@
       if (!unlink ("conftest.lnk/") || errno != ENOTDIR) return 2;
 #endif
       ]])],
-      [gl_cv_func_unlink_works=yes], [gl_cv_func_unlink_works=no],
-      [gl_cv_func_unlink_works="guessing no"])
+      [gl_cv_func_unlink_honors_slashes=yes],
+      [gl_cv_func_unlink_honors_slashes=no],
+      [gl_cv_func_unlink_honors_slashes="guessing no"])
      rm -f conftest.file conftest.lnk])
-  if test x"$gl_cv_func_unlink_works" != xyes; then
+  dnl Detect MacOS X 10.5.6 bug: On read-write HFS mounts, unlink("..") or
+  dnl unlink("../..") succeeds without doing anything.
+  AC_CACHE_CHECK([whether unlink of a parent directory fails is it should],
+    [gl_cv_func_unlink_parent_fails],
+    [case "$host_os" in
+       darwin*)
+         if {
+              # Use the mktemp program if available. If not available, hide the error
+              # message.
+              tmp=`(umask 077 && mktemp -d /tmp/gtXXXXXX) 2>/dev/null` &&
+              test -n "$tmp" && test -d "$tmp"
+            } ||
+            {
+              # Use a simple mkdir command. It is guaranteed to fail if the directory
+              # already exists.  $RANDOM is bash specific and expands to empty in shells
+              # other than bash, ksh and zsh.  Its use does not increase security;
+              # rather, it minimizes the probability of failure in a very cluttered /tmp
+              # directory.
+              tmp=/tmp/gt$$-$RANDOM
+              (umask 077 && mkdir "$tmp")
+            }; then
+           mkdir "$tmp/subdir"
+           export tmp
+           AC_RUN_IFELSE(
+             [AC_LANG_SOURCE([[
+                #include <stdlib.h>
+                #include <unistd.h>
+                int main ()
+                {
+                  if (chdir (getenv ("tmp")) != 0)
+                    return 1;
+                  return unlink ("..") == 0;
+                }
+              ]])],
+             [gl_cv_func_unlink_parent_fails=yes],
+             [gl_cv_func_unlink_parent_fails=no],
+             [gl_cv_func_unlink_parent_fails="guessing no"])
+           rm -rf "$tmp"
+           unset tmp
+         else
+           gl_cv_func_unlink_parent_fails="guessing no"
+         fi
+         ;;
+       *)
+         gl_cv_func_unlink_parent_fails="guessing yes"
+         ;;
+     esac
+    ])
+  case "$gl_cv_func_unlink_parent_fails" in
+    *no)
+      AC_DEFINE([UNLINK_PARENT_BUG], [1],
+        [Define to 1 if unlink() on a parent directory may succeed])
+      ;;
+  esac
+  if test "$gl_cv_func_unlink_honors_slashes" != yes \
+     || { case "$gl_cv_func_unlink_parent_fails" in
+            *yes) false;;
+            *no) true;;
+          esac
+        }; then
     REPLACE_UNLINK=1
     AC_LIBOBJ([unlink])
   fi