patch: Option to not create backup files creates backup files

[nia <nia%NetBSD.org@localhost>]

I noticed some odd behaviour when I tried to use patch(1) without
creating backup files (-V none). It seems this option is ignored,
and backup files are created anyway. The PATCH_VERSION_CONTROL
environment variable can also override -V none, which is the
opposite of the behaviour stated in the man page.

The problem in the code seems to be that patch treats "none"
as the same as "undefined" (or "no option specified"), and
freely allows it to be overriden.

If there's no PATCH_VERSION_CONTROL environment variable and
the backup type is undefined ("none") after the command line
options are parsed, NULL is passed to get_version, which results
in numbered_existing being returned, making it impossible to
use -V none.

This diff introduces an "undefined" backup type and uses it
in places "none" was previously mistakenly used, allowing
"none" to be passed with -V and work as expected.

Please review.

Index: patch/backupfile.c
===================================================================
RCS file: /cvsroot/src/usr.bin/patch/backupfile.c,v
retrieving revision 1.15
diff -u -r1.15 backupfile.c
--- patch/backupfile.c	11 Apr 2014 17:30:03 -0000	1.15
+++ patch/backupfile.c	19 Feb 2021 12:39:45 -0000
@@ -38,7 +38,7 @@
 #define ISDIGIT(c) (isascii ((unsigned char)c) && isdigit ((unsigned char)c))
 
 /* Which type of backup file names are generated. */
-enum backup_type backup_type = none;
+enum backup_type backup_type = undefined;
 
 /*
  * The extension added to file names to produce a simple (as opposed to
Index: patch/backupfile.h
===================================================================
RCS file: /cvsroot/src/usr.bin/patch/backupfile.h,v
retrieving revision 1.6
diff -u -r1.6 backupfile.h
--- patch/backupfile.h	19 Sep 2008 18:33:34 -0000	1.6
+++ patch/backupfile.h	19 Feb 2021 12:39:45 -0000
@@ -19,6 +19,8 @@
 
 /* When to make backup files. */
 enum backup_type {
+	undefined,
+
 	/* Never make backups. */
 	none,
 
Index: patch/patch.c
===================================================================
RCS file: /cvsroot/src/usr.bin/patch/patch.c,v
retrieving revision 1.29
diff -u -r1.29 patch.c
--- patch/patch.c	6 Sep 2011 18:25:14 -0000	1.29
+++ patch/patch.c	19 Feb 2021 12:39:45 -0000
@@ -197,17 +197,18 @@
 	else
 		simple_backup_suffix = ORIGEXT;
 
+	if ((v = getenv("PATCH_VERSION_CONTROL")) == NULL)
+		v = getenv("VERSION_CONTROL");
+	if (v != NULL)
+		backup_type = get_version(v);
+
 	/* parse switches */
 	Argc = argc;
 	Argv = argv;
 	get_some_switches();
 
-	if (backup_type == none) {
-		if ((v = getenv("PATCH_VERSION_CONTROL")) == NULL)
-			v = getenv("VERSION_CONTROL");
-		if (v != NULL || !posix)
-			backup_type = get_version(v);	/* OK to pass NULL. */
-	}
+	if (backup_type == undefined)
+		backup_type = posix ? none : numbered_existing;
 
 	/* make sure we clean up /tmp in case of disaster */
 	set_signals(0);
@@ -493,7 +494,7 @@
 	while ((ch = getopt_long(Argc, Argv, options, longopts, NULL)) != -1) {
 		switch (ch) {
 		case 'b':
-			if (backup_type == none)
+			if (backup_type == undefined)
 				backup_type = numbered_existing;
 			if (optarg == NULL)
 				break;