hush: do not assign to readonly VAR in "VAR=VAL CMD" syntax too

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/hush.c

@@ -2089,6 +2089,8 @@ static int set_local_var(char *str, unsigned flags)
 		if (cur->flg_read_only) {
 			bb_error_msg("%s: readonly variable", str);
 			free(str);
+//NOTE: in bash, assignment in "export READONLY_VAR=Z" fails, and sets $?=1,
+//but export per se succeeds (does put the var in env). We don't mimic that.
 			return -1;
 		}
 		if (flags & SETFLAG_UNEXPORT) { // && cur->flg_export ?
@@ -2283,8 +2285,12 @@ static struct variable *set_vars_and_save_old(char **strings)
 		if (eq) {
 			var_pp = get_ptr_to_local_var(*s, eq - *s);
 			if (var_pp) {
-				/* Remove variable from global linked list */
 				var_p = *var_pp;
+				if (var_p->flg_read_only) {
+					bb_error_msg("%s: readonly variable", *s);
+					goto next;
+				}
+				/* Remove variable from global linked list */
 				debug_printf_env("%s: removing '%s'\n", __func__, var_p->varstr);
 				*var_pp = var_p->next;
 				/* Add it to returned list */
@@ -2293,6 +2299,7 @@ static struct variable *set_vars_and_save_old(char **strings)
 			}
 			set_local_var(*s, SETFLAG_EXPORT);
 		}
+ next:
 		s++;
 	}
 	return old;

shell/hush_test/hush-vars/readonly0.right

@@ -5,8 +5,10 @@ hush: a=A: readonly variable
 Fail:1
 hush: a=A: readonly variable
 Fail:1
-hush: a=A: readonly variable
+hush: a=Z: readonly variable
 Fail:1
-Visible:0
+hush: a=Z: readonly variable
+b=B
+^^^a is not exported
 hush: a: readonly variable
 Fail:1

shell/hush_test/hush-vars/readonly0.tests

@@ -1,10 +1,12 @@
+unset a b
+
 readonly a=A
 b=B
 readonly b
-# readonly on already readonly var is harmless
+# readonly on already readonly var is harmless:
 readonly b a
 readonly | grep '^readonly [ab]='
-# this should work
+# this should work:
 export a b
 export -n a b
 echo Ok:$?
@@ -12,13 +14,23 @@ env | grep -e^a= -e^b=  # shows nothing
 
 # these should all fail (despite the same value being assigned)
 # bash does not abort even in non-interactive more (in script)
-true
-a=A
+true; a=A
+echo Fail:$?
+true; readonly a=A
+echo Fail:$?
+
+# in bash, assignment in export fails, but export succeeds! :)
+# we don't mimic that!
+true; export a=Z
 echo Fail:$?; true
-readonly a=A
-echo Fail:$?; true
-export a=A
-echo Fail:$?; true
-a=A echo Visible:$? # command still runs
+#env | grep '^a='
+#echo "^^^a is exported"
+export -n a  # undo that bashism, if it happens
+
+export b
+# this fails to both set and export a:
+a=Z env | grep '^[ab]='  # command still runs
+echo "^^^a is not exported"
+
 unset a
 echo Fail:$?; true