patch 8.0.0655: not easy to make sure a function does not exist commit https://github.com/vim/vim/commit/d6abcd154cdc6a8dd4b7c6ccad37617ea8a1b4aa Author: Bram Moolenaar <Bram@vim.org> Date: Thu Jun 22 19:15:24 2017 +0200 patch 8.0.0655: not easy to make sure a function does not exist Problem: Not easy to make sure a function does not exist. Solution: Add ! as an optional argument to :delfunc.

--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -2807,7 +2807,8 @@ ex_delfunction(exarg_T *eap)
     {
 	if (fp == NULL)
 	{
-	    EMSG2(_(e_nofunc), eap->arg);
+	    if (!eap->forceit)
+		EMSG2(_(e_nofunc), eap->arg);
 	    return;
 	}
 	if (fp->uf_calls > 0)