On 5/12/2018 9:35 AM, Martin Ågren wrote:

+static int verify_commit_graph_error;
+
+static void graph_report(const char *fmt, ...)
+{
+       va_list ap;
+       struct strbuf sb = STRBUF_INIT;
+       verify_commit_graph_error = 1;
+
+       va_start(ap, fmt);
+       strbuf_vaddf(&sb, fmt, ap);
+
+       fprintf(stderr, "%s\n", sb.buf);
+       strbuf_release(&sb);
+       va_end(ap);
+}

That's a good idea. Makes that patch a bit less trivial and this one a 
bit less difficult.