patch 8.2.2301: Vim9: cannot unlet a dict or list item

Problem:    Vim9: cannot unlet a dict or list item.
Solution:   Add ISN_UNLETINDEX.  Refactor assignment code to use for unlet.

src/testdir/test_vim9_assign.vim

@@ -1349,14 +1349,47 @@ def Test_unlet()
   assert_false(exists('s:somevar'))
   unlet! s:somevar
 
+  # dict unlet
+  var dd = {a: 1, b: 2, c: 3}
+  unlet dd['a']
+  unlet dd.c
+  assert_equal({b: 2}, dd)
+
+  # list unlet
+  var ll = [1, 2, 3, 4]
+  unlet ll[1]
+  unlet ll[-1]
+  assert_equal([1, 3], ll)
+
+  # list of dict unlet
+  var dl = [{a: 1, b: 2}, {c: 3}]
+  unlet dl[0]['b']
+  assert_equal([{a: 1}, {c: 3}], dl)
+
+  CheckDefExecFailure([
+   'var ll = test_null_list()',
+   'unlet ll[0]',
+   ], 'E684:')
+  CheckDefExecFailure([
+   'var ll = [1]',
+   'unlet ll[2]',
+   ], 'E684:')
+  CheckDefExecFailure([
+   'var dd = test_null_dict()',
+   'unlet dd["a"]',
+   ], 'E716:')
+  CheckDefExecFailure([
+   'var dd = {a: 1}',
+   'unlet dd["b"]',
+   ], 'E716:')
+
   # can compile unlet before variable exists
-  # This doesn't work yet
+  g:someDict = {key: 'val'}
-  #g:someDict = {key: 'val'}
+  var k = 'key'
-  #var k = 'key'
+  unlet g:someDict[k]
-  #unlet g:someDict[k]
+  assert_equal({}, g:someDict)
-  #assert_equal({}, g:someDict)
+  unlet g:someDict
-  #unlet g:someDict
+  assert_false(exists('g:someDict'))
-  #assert_false(exists('g:someDict'))
 
   CheckScriptFailure([
    'vim9script',

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2301,
 /**/
     2300,
 /**/

src/vim9.h

@@ -60,6 +60,7 @@ typedef enum {
 
     ISN_UNLET,		// unlet variable isn_arg.unlet.ul_name
     ISN_UNLETENV,	// unlet environment variable isn_arg.unlet.ul_name
+    ISN_UNLETINDEX,	// unlet item of list or dict
 
     ISN_LOCKCONST,	// lock constant value
 

src/vim9execute.c

@@ -1783,6 +1783,10 @@ call_def_function(
 		    typval_T	*tv_dest = STACK_TV_BOT(-1);
 		    int		status = OK;
 
+		    // Stack contains:
+		    // -3 value to be stored
+		    // -2 index
+		    // -1 dict or list
 		    tv = STACK_TV_BOT(-3);
 		    SOURCING_LNUM = iptr->isn_lnum;
 		    if (dest_type == VAR_ANY)
@@ -1898,6 +1902,91 @@ call_def_function(
 		}
 		break;
 
+	    // unlet item in list or dict variable
+	    case ISN_UNLETINDEX:
+		{
+		    typval_T	*tv_idx = STACK_TV_BOT(-2);
+		    typval_T	*tv_dest = STACK_TV_BOT(-1);
+		    int		status = OK;
+
+		    // Stack contains:
+		    // -2 index
+		    // -1 dict or list
+		    if (tv_dest->v_type == VAR_DICT)
+		    {
+			// unlet a dict item, index must be a string
+			if (tv_idx->v_type != VAR_STRING)
+			{
+			    semsg(_(e_expected_str_but_got_str),
+					vartype_name(VAR_STRING),
+					vartype_name(tv_idx->v_type));
+			    status = FAIL;
+			}
+			else
+			{
+			    dict_T	*d = tv_dest->vval.v_dict;
+			    char_u	*key = tv_idx->vval.v_string;
+			    dictitem_T  *di = NULL;
+
+			    if (key == NULL)
+				key = (char_u *)"";
+			    if (d != NULL)
+				di = dict_find(d, key, (int)STRLEN(key));
+			    if (di == NULL)
+			    {
+				// NULL dict is equivalent to empty dict
+				semsg(_(e_dictkey), key);
+				status = FAIL;
+			    }
+			    else
+			    {
+				// TODO: check for dict or item locked
+				dictitem_remove(d, di);
+			    }
+			}
+		    }
+		    else if (tv_dest->v_type == VAR_LIST)
+		    {
+			// unlet a List item, index must be a number
+			if (tv_idx->v_type != VAR_NUMBER)
+			{
+			    semsg(_(e_expected_str_but_got_str),
+					vartype_name(VAR_NUMBER),
+					vartype_name(tv_idx->v_type));
+			    status = FAIL;
+			}
+			else
+			{
+			    list_T	*l = tv_dest->vval.v_list;
+			    varnumber_T	n = tv_idx->vval.v_number;
+			    listitem_T	*li = NULL;
+
+			    li = list_find(l, n);
+			    if (li == NULL)
+			    {
+				semsg(_(e_listidx), n);
+				status = FAIL;
+			    }
+			    else
+				// TODO: check for list or item locked
+				listitem_remove(l, li);
+			}
+		    }
+		    else
+		    {
+			status = FAIL;
+			semsg(_(e_cannot_index_str),
+						vartype_name(tv_dest->v_type));
+		    }
+
+		    clear_tv(tv_idx);
+		    clear_tv(tv_dest);
+		    ectx.ec_stack.ga_len -= 2;
+		    if (status == FAIL)
+			goto on_error;
+		}
+		break;
+
 	    // push constant
 	    case ISN_PUSHNR:
 	    case ISN_PUSHBOOL:
@@ -3649,6 +3738,9 @@ ex_disassemble(exarg_T *eap)
 			iptr->isn_arg.unlet.ul_forceit ? "!" : "",
 			iptr->isn_arg.unlet.ul_name);
 		break;
+	    case ISN_UNLETINDEX:
+		smsg("%4d UNLETINDEX", current);
+		break;
 	    case ISN_LOCKCONST:
 		smsg("%4d LOCKCONST", current);
 		break;