sh: Recognize "--" in . and exec.

Although "--" historically has not been required to be recognized for
certain special builtins that do not take options in POSIX, some other
implementations recognize options for them, requiring scripts to use "--" or
avoid operands starting with "-".

Operands starting with "-" can be avoided with eval by prepending a space,
and cannot occur with break, continue, exit, return and shift as they only
take numbers, nor with times as it does not take operands. With . and exec,
avoiding "-" is not so easy as it may require reimplementing the PATH
search; therefore the current proposal for POSIX is to require recognition
of "--" for them.

We continue to accept other strings starting with "-" as operands to . and
exec, and also "--" if it is alone to . (which would otherwise be invalid
anyway).

bin/sh/eval.c

@@ -1170,6 +1170,12 @@ truecmd(int argc __unused, char **argv __unused)
 int
 execcmd(int argc, char **argv)
 {
+	/*
+	 * Because we have historically not supported any options,
+	 * only treat "--" specially.
+	 */
+	if (argc > 1 && strcmp(argv[1], "--") == 0)
+		argc--, argv++;
 	if (argc > 1) {
 		struct strlist *sp;
 

bin/sh/main.c

@@ -314,14 +314,20 @@ find_dot_file(char *basename)
 int
 dotcmd(int argc, char **argv)
 {
-	char *fullname;
+	char *filename, *fullname;
 
 	if (argc < 2)
 		error("missing filename");
 
 	exitstatus = 0;
 
-	fullname = find_dot_file(argv[1]);
+	/*
+	 * Because we have historically not supported any options,
+	 * only treat "--" specially.
+	 */
+	filename = argc > 2 && strcmp(argv[1], "--") == 0 ? argv[2] : argv[1];
+
+	fullname = find_dot_file(filename);
 	setinputfile(fullname, 1);
 	commandname = fullname;
 	cmdloop(0);

tools/regression/bin/sh/builtins/dot2.0

@@ -0,0 +1,21 @@
+# $FreeBSD$
+
+failures=
+failure() {
+	echo "Error at line $1" >&2
+	failures=x$failures
+}
+
+T=$(mktemp -d ${TMPDIR:-/tmp}/sh-test.XXXXXX) || exit
+trap 'rm -rf $T' 0
+cd $T || exit 3
+unset x
+echo 'x=2' >testscript
+. -- ./testscript
+[ "$x" = 2 ] || failure $LINENO
+cd / || exit 3
+x=1
+PATH=$T:$PATH . -- testscript
+[ "$x" = 2 ] || failure $LINENO
+
+test -z "$failures"

tools/regression/bin/sh/builtins/exec2.0

@@ -0,0 +1,25 @@
+# $FreeBSD$
+
+failures=
+failure() {
+	echo "Error at line $1" >&2
+	failures=x$failures
+}
+
+(
+	exec -- >/dev/null
+	echo bad
+)
+[ $? = 0 ] || failure $LINENO
+(
+	exec -- sh -c 'exit 42'
+	echo bad
+)
+[ $? = 42 ] || failure $LINENO
+(
+	exec -- /var/empty/nosuch
+	echo bad
+) 2>/dev/null
+[ $? = 127 ] || failure $LINENO
+
+test -z "$failures"