From efc8beccd496f275663826ed507dd76728a75952 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Kirill=20M=C3=BCller?= <krlmlr+r@mailbox.org>
Date: Tue, 16 May 2023 09:09:06 +0200
Subject: [PATCH] Better error message

---
 R/versions.R                           | 3 +++
 tests/testthat/_snaps/old-data-type.md | 4 ----
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/R/versions.R b/R/versions.R
index 08d888e7e0..cfda3984ae 100644
--- a/R/versions.R
+++ b/R/versions.R
@@ -104,6 +104,9 @@ check_version <- function(graph) {
 }
 
 warn_version <- function(graph) {
+  # Calling for side effect: error if R_SEXP_to_igraph() fails
+  vcount_impl(graph)
+
   if (graph_version() != graph_version(graph)) {
     message(
       "This graph was created by an old(er) igraph version.\n",
diff --git a/tests/testthat/_snaps/old-data-type.md b/tests/testthat/_snaps/old-data-type.md
index 79fbf7d5ff..7f19013e7d 100644
--- a/tests/testthat/_snaps/old-data-type.md
+++ b/tests/testthat/_snaps/old-data-type.md
@@ -2,10 +2,6 @@
 
     Code
       V(karate)
-    Message <simpleMessage>
-      This graph was created by an old(er) igraph version.
-        Call upgrade_graph() on it to use with the current igraph version
-        For now we convert it on the fly...
     Error <simpleError>
       This graph was created by a now unsupported old igraph version.
         Call upgrade_version() before using igraph functions on that object.