rm: do not skip files upon failure to remove an empty dir

When removing a directory fails for some reason, and that directory
is empty, the rm_fts code gets the return value of the excise call
confused with the return value of its earlier call to prompt,
causing fts_skip_tree to be called again and the next file
that rm would otherwise have deleted to survive.

* src/remove.c (rm_fts): Ensure we only skip a single fts entry,
when processing empty dirs.  I.e. only skip the entry
having successfully removed it.
* tests/rm/empty-immutable-skip.sh: New root-only test.
* tests/local.mk: Add it.
* NEWS: Mention the bug fix.
Fixes https://bugs.gnu.org/44883

tests/rm/empty-immutable-skip.sh

@@ -0,0 +1,46 @@
+#!/bin/sh
+# Ensure that rm does not skip extra files after hitting an empty immutable dir.
+# Requires root access to do chattr +i, as well as an ext[23] or xfs file system
+
+# Copyright (C) 2020 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 3 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, see <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ rm
+require_root_
+
+# These simple one-file operations are expected to work even in the
+# presence of this bug, and we need them to set up the rest of the test.
+chattr_i_works=1
+touch f
+chattr +i f 2>/dev/null || chattr_i_works=0
+rm f 2>/dev/null
+test -f f || chattr_i_works=0
+chattr -i f 2>/dev/null || chattr_i_works=0
+rm f 2>/dev/null || chattr_i_works=0
+test -f f && chattr_i_works=0
+
+if test $chattr_i_works = 0; then
+  skip_ "chattr +i doesn't work on this file system"
+fi
+
+mkdir empty || framework_failure_
+touch x y || framework_failure_
+chattr +i empty || framework_failure_
+rm -rf empty x y
+{ test -f x || test -f y; } && fail=1
+chattr -i empty
+
+Exit $fail