FYI: fix misleading diagnostic from ln

[Jim Meyering]

I've just checked in this change:

        "ln --backup f f" produces a misleading diagnostic:
        ln: creating hard link `f' => `f': No such file or directory
        * src/ln.c (do_link): Give a better diagnostic in this unusual case.
        (do_link): Rename local: s/lstat_ok/dest_lstat_ok/.
        * tests/ln/Makefile.am (TESTS): Add hard-backup.
        * tests/ln/hard-backup: New test for the above.

diff --git a/src/ln.c b/src/ln.c
index 0aa5ac5..fae3708 100644
--- a/src/ln.c
+++ b/src/ln.c
@@ -133,7 +133,7 @@ do_link (const char *source, const char
   struct stat source_stats;
   struct stat dest_stats;
   char *dest_backup = NULL;
-  bool lstat_ok = false;
+  bool dest_lstat_ok = false;
   bool source_is_dir = false;
   bool ok;

@@ -171,8 +171,8 @@ do_link (const char *source, const char

   if (remove_existing_files || interactive || backup_type != no_backups)
     {
-      lstat_ok = (lstat (dest, &dest_stats) == 0);
-      if (!lstat_ok && errno != ENOENT)
+      dest_lstat_ok = (lstat (dest, &dest_stats) == 0);
+      if (!dest_lstat_ok && errno != ENOENT)
        {
          error (0, errno, _("accessing %s"), quote (dest));
          return false;
@@ -184,8 +184,14 @@ do_link (const char *source, const char
      (with --backup, it just renames any existing destination file)
      But if the source and destination are the same, don't remove
      anything and fail right here.  */
-  if (remove_existing_files
-      && lstat_ok
+  if ((remove_existing_files
+       /* Ensure that "ln --backup f f" fails here, with the
+         "... same file" diagnostic, below.  Otherwise, subsequent
+         code would give a misleading "file not found" diagnostic.
+         This case is different than the others handled here, since
+         the command in question doesn't use --force.  */
+       || (!symbolic_link && backup_type != no_backups))
+      && dest_lstat_ok
       /* Allow `ln -sf --backup k k' to succeed in creating the
         self-referential symlink, but don't allow the hard-linking
         equivalent: `ln -f k k' (with or without --backup) to get
@@ -205,7 +211,7 @@ do_link (const char *source, const char
       return false;
     }

-  if (lstat_ok)
+  if (dest_lstat_ok)
     {
       if (S_ISDIR (dest_stats.st_mode))
        {
diff --git a/tests/ln/Makefile.am b/tests/ln/Makefile.am
index 8048a98..79bedce 100644
--- a/tests/ln/Makefile.am
+++ b/tests/ln/Makefile.am
@@ -1,7 +1,7 @@
 ## Process this file with automake to produce Makefile.in -*-Makefile-*-.
 AUTOMAKE_OPTIONS = 1.2 gnits

-TESTS = target-1 sf-1 misc backup-1
+TESTS = hard-backup target-1 sf-1 misc backup-1
 EXTRA_DIST = $(TESTS)
 TESTS_ENVIRONMENT = \
   PATH="$(VG_PATH_PREFIX)`pwd`/../../src$(PATH_SEPARATOR)$$PATH"
diff --git a/tests/ln/hard-backup b/tests/ln/hard-backup
new file mode 100755
index 0000000..e37938d
--- /dev/null
+++ b/tests/ln/hard-backup
@@ -0,0 +1,54 @@
+#!/bin/sh
+# Ensure that 'ln --backup F F' gives a proper diagnostic.
+
+# Copyright (C) 2006 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+if test "$VERBOSE" = yes; then
+  set -x
+  ln --version
+fi
+
+. $srcdir/../envvar-check
+. $srcdir/../lang-default
+
+pwd=`pwd`
+t0=`echo "$0"|sed 's,.*/,,'`.tmp; tmp=$t0/$$
+trap 'status=$?; cd "$pwd" && chmod -R u+rwx $t0 && rm -rf $t0 && exit 
$status' 0
+trap '(exit $?); exit $?' 1 2 13 15
+
+framework_failure=0
+mkdir -p $tmp || framework_failure=1
+cd $tmp || framework_failure=1
+touch f || framework_failure=1
+
+if test $framework_failure = 1; then
+  echo "$0: failure in testing framework" 1>&2
+  (exit 1); exit 1
+fi
+
+fail=0
+
+ln --backup f f 2> out && fail=1
+cat <<\EOF > exp || fail=1
+ln: `f' and `f' are the same file
+EOF
+
+cmp out exp || fail=1
+test $fail = 1 && diff out exp 2> /dev/null
+
+(exit $fail); exit $fail