Ensure the receiver is modifiable before shrinking [Bug #17736]

* Ensure the receiver is modifiable before shinking [Bug #17736]

* Assert the receivers are not modified

1 files changed, 1 insertions, 0 deletions

diff --git a/array.c b/array.c
index 2876548085..0f7ccdeb90 100644
--- a/array.c
+++ b/array.c
@@ -3846,6 +3846,7 @@ select_bang_ensure(VALUE a)
 
     if (i2 < len && i2 < i1) {
 	long tail = 0;
+        rb_ary_modify(ary);
 	if (i1 < len) {
 	    tail = len - i1;
             RARRAY_PTR_USE_TRANSIENT(ary, ptr, {