Backport the ksh93v- rm builtin to fix 'rm -d' (#348)

The -d flag implemented in the rm builtin is completely broken. No
matter what you do it refuses to remove directories, even if -r is
also passed. Reproducer:

  $ mkdir /tmp/empty
  $ PATH=/opt/ast/bin rm -d /tmp/empty
  rm: /tmp/empty: directory
  $ PATH=/opt/ast/bin rm -dr /tmp/empty
  rm: /tmp/empty: directory not removed [Is a directory]

Additionally, the description of 'rm -d' in the man page contradicts
how it's specified in <https://www.austingroupbugs.net/view.php?id=802>.

The ksh93v- rm builtin fixed nearly all of these issues, so I've
backported it to 93u+m and applied one additional fix for 'rm -rd'.

src/lib/libcmd/rm.c:
- Backported the fixes from the ksh93v- rm builtin's -d flag when
  used on empty directories.
- Backported the man page update for rm(1) from ksh93v-.
- The ksh93v- rm builtin had one additional bug that caused the -r
  option to fail when combined with -d. This was fixed by
  overriding -d if -r is also passed.

src/cmd/ksh93/tests/builtins.sh:
- Add regression tests for the rm builtin's -d option.

NEWS

@@ -9,6 +9,11 @@ Any uppercase BUG_* names are modernish shell bug IDs.
   looking up functions defined with the 'function' keyword. In the POSIX
   standard and on other shells, the '.' command finds only script files.
 
+- The rm built-in's -d/--directory option has been fixed. It now properly
+  removes empty directories and refuses to remove non-empty directories
+  (as specified in https://www.austingroupbugs.net/view.php?id=802). Note
+  that the rm built-in command isn't compiled in by default.
+
 2021-11-23:
 
 - A bug was fixed that allowed arithmetic expressions to assign out-of-range

src/cmd/ksh93/tests/builtins.sh

@@ -1311,5 +1311,46 @@ printf -v 'got[1][two][3]' 'ok\f%012d\n' $ver 2>/dev/null
 	"(expected $(printf %q "$exp"), got $(printf %q "$got"))"
 unset got ver
 
+# ======
+# The rm builtin's -d option should remove files and empty directories without
+# removing non-empty directories (unless the -r option is also passed).
+# https://www.austingroupbugs.net/view.php?id=802
+if builtin rm 2> /dev/null; then
+	echo foo > "$tmp/bar"
+	mkdir "$tmp/emptydir"
+	mkdir -p "$tmp/nonemptydir1/subfolder"
+	mkdir "$tmp/nonemptydir2"
+	echo dummyfile > "$tmp/nonemptydir2/shouldexist"
+
+	# Tests for lone -d option
+	got=$(rm -d "$tmp/emptydir" 2>&1)
+	[[ $? == 0 ]] || err_exit 'rm builtin fails to remove empty directory with -d option' \
+		"(got $(printf %q "$got"))"
+	[[ -d $tmp/emptydir ]] && err_exit 'rm builtin fails to remove empty directory with -d option'
+	got=$(rm -d $tmp/bar 2>&1)
+	[[ $? == 0 ]] || err_exit 'rm builtin fails to remove files with -d option' \
+		"(got $(printf %q "$got"))"
+	[[ -f $tmp/bar ]] && err_exit 'rm builtin fails to remove files with -d option'
+	rm -d "$tmp/nonemptydir1" 2> /dev/null
+	[[ ! -d $tmp/nonemptydir1/subfolder ]] && err_exit 'rm builtin has unwanted recursion with -d option on folder containing folder'
+	rm -d "$tmp/nonemptydir2" 2> /dev/null
+	[[ ! -f $tmp/nonemptydir2/shouldexist ]] && err_exit 'rm builtin has unwanted recursion with -d option on folder containing file'
+
+	# Recreate non-empty directories in case the above tests failed
+	mkdir -p "$tmp/nonemptydir1/subfolder"
+	mkdir -p "$tmp/nonemptydir2"
+	echo dummyfile > "$tmp/nonemptydir2/shouldexist"
+
+	# Tests combining -d with -r
+	got=$(rm -rd "$tmp/nonemptydir1" 2>&1)
+	[[ $? == 0 ]] || err_exit 'rm builtin fails to remove non-empty directory and subdirectory with -rd options' \
+		"(got $(printf %q "$got"))"
+	[[ -d $tmp/nonemptydir1/subfolder || -d $tmp/nonemptydir1 ]] && err_exit 'rm builtin fails to remove all folders with -rd options'
+	got=$(rm -rd "$tmp/nonemptydir2" 2>&1)
+	[[ $? == 0 ]] || err_exit 'rm builtin fails to remove non-empty directory and file with -rd options' \
+		"(got $(printf %q "$got"))"
+	[[ -f $tmp/nonemptydir2/shouldexist || -d $tmp/nonemptydir2 ]] && err_exit 'rm builtin fails to remove all folders and files with -rd options'
+fi
+
 # ======
 exit $((Errors<125?Errors:125))

src/lib/libcmd/rm.c

@@ -1,7 +1,7 @@
 /***********************************************************************
 *                                                                      *
 *               This software is part of the ast package               *
-*          Copyright (c) 1992-2012 AT&T Intellectual Property          *
+*          Copyright (c) 1992-2013 AT&T Intellectual Property          *
 *          Copyright (c) 2020-2021 Contributors to ksh 93u+m           *
 *                      and is licensed under the                       *
 *                 Eclipse Public License, Version 1.0                  *
@@ -15,8 +15,8 @@
 *                            AT&T Research                             *
 *                           Florham Park NJ                            *
 *                                                                      *
-*                 Glenn Fowler <gsf@research.att.com>                  *
+*               Glenn Fowler <glenn.s.fowler@gmail.com>                *
-*                  David Korn <dgk@research.att.com>                   *
+*                    David Korn <dgkorn@gmail.com>                     *
 *                                                                      *
 ***********************************************************************/
 #pragma prototyped
@@ -28,7 +28,7 @@
  */
 
 static const char usage[] =
-"[-?\n@(#)$Id: rm (AT&T Research) 2012-02-14 $\n]"
+"[-?\n@(#)$Id: rm (AT&T Research) 2013-12-01 $\n]"
 "[--catalog?" ERROR_CATALOG "]"
 "[+NAME?rm - remove files]"
 "[+DESCRIPTION?\brm\b removes the named \afile\a arguments. By default it"
@@ -43,11 +43,9 @@ static const char usage[] =
 "	writing a 0 filled buffer the same size as the file, executing"
 "	\bfsync\b(2) and closing before attempting to remove. Implemented"
 "	only on systems that support \bfsync\b(2).]"
-"[d:directory?\bremove\b(3) (or \bunlink\b(2)) directories rather than"
+"[d:directory?If the current entry is a directory then remove it using "
-"	\brmdir\b(2), and don't require that they be empty before removal."
+    "\brmdir\b(3) instead of the default \bunlink\b(2). If \b--recursive\b "
-"	The caller requires sufficient privilege, not to mention a strong"
+    "is not specified then non-empty directories will not be removed.]"
-"	constitution, to use this option. Even though the directory must"
-"	not be empty, \brm\b still attempts to empty it before removal.]"
 "[f:force?Ignore nonexistent files, ignore no file operands specified,"
 "	and never prompt the user.]"
 "[i:interactive|prompt?Prompt whether to remove each file."
@@ -84,7 +82,7 @@ typedef struct State_s			/* program state		*/
 {
 	Shbltin_t*	context;	/* builtin context		*/
 	int		clobber;	/* clear out file data first	*/
-	int		directory;	/* remove(dir) not rmdir(dir)	*/
+	int		directory;	/* rmdir(dir) not unlink(dir)	*/
 	int		force;		/* force actions		*/
 	int		interactive;	/* prompt for approval		*/
 	int		recursive;	/* remove subtrees too		*/
@@ -151,9 +149,12 @@ rm(State_t* state, register FTSENT* ent)
 		if (!state->recursive)
 		{
 			fts_set(NiL, ent, FTS_SKIP);
+			if (!state->directory)
+			{
 				error(2, "%s: directory", ent->fts_path);
 				break;
 			}
+		}
 		if (!beenhere(ent))
 		{
 			if (state->unconditional && (ent->fts_statp->st_mode & S_IRWXU) != S_IRWXU)
@@ -188,7 +189,7 @@ rm(State_t* state, register FTSENT* ent)
 						nonempty(ent);
 					}
 				}
-				if (ent->fts_info == FTS_D)
+				if (!state->directory && ent->fts_info == FTS_D)
 					break;
 			}
 			else
@@ -209,7 +210,7 @@ rm(State_t* state, register FTSENT* ent)
 				path = ent->fts_accpath;
 				if (state->verbose)
 					sfputr(sfstdout, ent->fts_path, '\n');
-				if ((ent->fts_info == FTS_DC || state->directory) ? remove(path) : rmdir(path))
+				if ((state->recursive || state->directory) ? rmdir(path) : unlink(path))
 					switch (errno)
 					{
 					case ENOENT:
@@ -385,6 +386,8 @@ b_rm(int argc, register char** argv, Shbltin_t* context)
 	}
 	if (!*argv)
 		return 0;
+	if (state.directory && state.recursive)
+		state.directory = 0;  /* the -r option overrides -d */
 
 	/*
 	 * do it