vim-patch:8.2.2533: Vim9: cannot use a range with :unlet

Problem:    Vim9: cannot use a range with :unlet.
Solution:   Implement ISN_UNLETRANGE.

https://github.com/vim/vim/commit/5b5ae29bd3d7b832b6f15320430f7f191e0abd1f

Co-authored-by: Bram Moolenaar <Bram@vim.org>

3 files changed, 44 insertions, 25 deletions

diff --git a/src/nvim/eval.c b/src/nvim/eval.c
index ec5437a0b2..50da0a8657 100644
--- a/src/nvim/eval.c
+++ b/src/nvim/eval.c
@@ -1604,13 +1604,7 @@ char *get_lval(char *const name, typval_T *const rettv, lval_T *const lp, const
 
       lp->ll_dict = NULL;
       lp->ll_list = lp->ll_tv->vval.v_list;
-      lp->ll_li = tv_list_find(lp->ll_list, (int)lp->ll_n1);
-      if (lp->ll_li == NULL) {
-        if (lp->ll_n1 < 0) {
-          lp->ll_n1 = 0;
-          lp->ll_li = tv_list_find(lp->ll_list, (int)lp->ll_n1);
-        }
-      }
+      lp->ll_li = tv_list_find_index(lp->ll_list, &lp->ll_n1);
       if (lp->ll_li == NULL) {
         tv_clear(&var2);
         if (!quiet) {
diff --git a/src/nvim/eval/typval.c b/src/nvim/eval/typval.c
index a392d441cf..9e697d6144 100644
--- a/src/nvim/eval/typval.c
+++ b/src/nvim/eval/typval.c
@@ -1507,6 +1507,21 @@ const char *tv_list_find_str(list_T *const l, const int n)
   return tv_get_string(TV_LIST_ITEM_TV(li));
 }
 
+/// Like tv_list_find() but when a negative index is used that is not found use
+/// zero and set "idx" to zero.  Used for first index of a range.
+listitem_T *tv_list_find_index(list_T *const l, long *const idx)
+  FUNC_ATTR_WARN_UNUSED_RESULT
+{
+  listitem_T *li = tv_list_find(l, (int)(*idx));
+  if (li == NULL) {
+    if (*idx < 0) {
+      *idx = 0;
+      li = tv_list_find(l, (int)(*idx));
+    }
+  }
+  return li;
+}
+
 /// Locate item in a list and return its index
 ///
 /// @param[in]  l  List to search.
diff --git a/src/nvim/eval/vars.c b/src/nvim/eval/vars.c
index 0663c3c54c..f988a49e6c 100644
--- a/src/nvim/eval/vars.c
+++ b/src/nvim/eval/vars.c
@@ -1056,25 +1056,10 @@ static int do_unlet_var(lval_T *lp, char *name_end, exarg_T *eap, int deep FUNC_
                                      lp->ll_name_len))) {
     return FAIL;
   } else if (lp->ll_range) {
-    assert(lp->ll_list != NULL);
-    // Delete a range of List items.
-    listitem_T *const first_li = lp->ll_li;
-    listitem_T *last_li = first_li;
-    while (true) {
-      listitem_T *const li = TV_LIST_ITEM_NEXT(lp->ll_list, lp->ll_li);
-      if (value_check_lock(TV_LIST_ITEM_TV(lp->ll_li)->v_lock,
-                           lp->ll_name,
-                           lp->ll_name_len)) {
-        return false;
-      }
-      lp->ll_li = li;
-      lp->ll_n1++;
-      if (lp->ll_li == NULL || (!lp->ll_empty2 && lp->ll_n2 < lp->ll_n1)) {
-        break;
-      }
-      last_li = lp->ll_li;
+    if (list_unlet_range(lp->ll_list, lp->ll_li, lp->ll_name, lp->ll_name_len,
+                         lp->ll_n1, !lp->ll_empty2, lp->ll_n2) == FAIL) {
+      return FAIL;
     }
-    tv_list_remove_items(lp->ll_list, first_li, last_li);
   } else {
     if (lp->ll_list != NULL) {
       // unlet a List item.
@@ -1107,6 +1092,31 @@ static int do_unlet_var(lval_T *lp, char *name_end, exarg_T *eap, int deep FUNC_
   return ret;
 }
 
+/// Unlet one item or a range of items from a list.
+/// Return OK or FAIL.
+static int list_unlet_range(list_T *const l, listitem_T *const li_first, const char *const name,
+                            const size_t name_len, const long n1_arg, const bool has_n2,
+                            const long n2)
+{
+  assert(l != NULL);
+  // Delete a range of List items.
+  listitem_T *li_last = li_first;
+  long n1 = n1_arg;
+  while (true) {
+    if (value_check_lock(TV_LIST_ITEM_TV(li_last)->v_lock, name, name_len)) {
+      return FAIL;
+    }
+    listitem_T *const li = TV_LIST_ITEM_NEXT(l, li_last);
+    n1++;
+    if (li == NULL || (has_n2 && n2 < n1)) {
+      break;
+    }
+    li_last = li;
+  }
+  tv_list_remove_items(l, li_first, li_last);
+  return OK;
+}
+
 /// unlet a variable
 ///
 /// @param[in]  name  Variable name to unlet.