patch 8.2.4304: Vim9: slice() makes a copy but doesn't change the type

Problem:    Vim9: slice() makes a copy but doesn't change the type.
Solution:   Change the declared type like copy(). (closes #9696)

src/evalfunc.c

@@ -1169,6 +1169,27 @@ ret_first_arg(int argcount,
     return &t_void;
 }
     static type_T *
+ret_slice(int argcount,
+	type2_T *argtypes,
+	type_T	**decl_type)
+{
+    if (argcount > 0)
+    {
+	if (argtypes[0].type_decl != NULL)
+	{
+	    switch (argtypes[0].type_decl->tt_type)
+	    {
+		case VAR_STRING: *decl_type = &t_string; break;
+		case VAR_BLOB: *decl_type = &t_blob; break;
+		case VAR_LIST: *decl_type = &t_list_any; break;
+		default: break;
+	    }
+	}
+	return argtypes[0].type_curr;
+    }
+    return &t_void;
+}
+    static type_T *
 ret_copy(int argcount,
 	type2_T *argtypes,
 	type_T	**decl_type)
@@ -2292,7 +2313,7 @@ static funcentry_T global_functions[] =
     {"sinh",		1, 1, FEARG_1,	    arg1_float_or_nr,
 			ret_float,	    FLOAT_FUNC(f_sinh)},
     {"slice",		2, 3, FEARG_1,	    arg23_slice,
-			ret_first_arg,	    f_slice},
+			ret_slice,	    f_slice},
     {"sort",		1, 3, FEARG_1,	    arg13_sortuniq,
 			ret_first_arg,	    f_sort},
     {"sound_clear",	0, 0, 0,	    NULL,

src/testdir/test_vim9_builtin.vim

@@ -3619,6 +3619,9 @@ def Test_slice()
   assert_equal([], slice(range(6), 1, -5))
   assert_equal([], slice(range(6), 1, -6))
 
+  var lds: list<dict<string>> = [{key: 'value'}]
+  assert_equal(['val'], lds->slice(0, 1)->map((_, v) => 'val'))
+
   assert_equal(0z1122334455, slice(0z001122334455, 1))
   assert_equal(0z112233, slice(0z001122334455, 1, 4))
   assert_equal(0z11223344, slice(0z001122334455, 1, -1))

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4304,
 /**/
     4303,
 /**/