ash: bash compat: "shift $BIGNUM" is equivalent to "shift 1"

shell/ash.c

@@ -9665,7 +9665,7 @@ shiftcmd(int argc UNUSED_PARAM, char **argv)
 	if (argv[1])
 		n = number(argv[1]);
 	if (n > shellparam.nparam)
-		n = shellparam.nparam;
+		n = 0; /* bash compat, was = shellparam.nparam; */
 	INT_OFF;
 	shellparam.nparam -= n;
 	for (ap1 = shellparam.p; --n >= 0; ap1++) {

shell/ash_test/ash-misc/shift1.right

@@ -0,0 +1,9 @@
+2 3 4
+0: shift: line 1: Illegal number: -1
+1 2 3 4
+2 3 4
+3 4
+4
+
+1 2 3 4
+1 2 3 4

shell/ash_test/ash-misc/shift1.tests

@@ -0,0 +1,10 @@
+$THIS_SH -c 'shift;    echo "$@"' 0 1 2 3 4
+#We do abort on -1, but then we abort. bash executes echo.
+$THIS_SH -c 'shift -1; echo "$@"' 0 1 2 3 4
+$THIS_SH -c 'shift  0; echo "$@"' 0 1 2 3 4
+$THIS_SH -c 'shift  1; echo "$@"' 0 1 2 3 4
+$THIS_SH -c 'shift  2; echo "$@"' 0 1 2 3 4
+$THIS_SH -c 'shift  3; echo "$@"' 0 1 2 3 4
+$THIS_SH -c 'shift  4; echo "$@"' 0 1 2 3 4
+$THIS_SH -c 'shift  5; echo "$@"' 0 1 2 3 4
+$THIS_SH -c 'shift  6; echo "$@"' 0 1 2 3 4