Report incompatible roles in pg_upgrade checking

When checking for roles with a pg_ prefix in <= 9.5 servers, report
all found roles in a text file as how other checks are done instead
of just reporting that they exist. Rolenames are printed with their
Oids to match other reports.

Author: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Bruce Momjian <bruce@momjian.us>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/4BB2735C-C347-4CF7-AFB1-8573BE930066@yesql.se

Author: danielgustafsson

src/bin/pg_upgrade/check.c

@@ -1395,27 +1395,52 @@ check_for_pg_role_prefix(ClusterInfo *cluster)
 {
 	PGresult   *res;
 	PGconn	   *conn = connectToServer(cluster, "template1");
+	int			ntups;
+	int			i_roloid;
+	int			i_rolname;
+	FILE	   *script = NULL;
+	char		output_path[MAXPGPATH];
 
 	prep_status("Checking for roles starting with \"pg_\"");
 
+	snprintf(output_path, sizeof(output_path), "%s/%s",
+			 log_opts.basedir,
+			 "pg_role_prefix.txt");
+
 	res = executeQueryOrDie(conn,
-							"SELECT * "
+							"SELECT oid AS roloid, rolname "
 							"FROM pg_catalog.pg_roles "
 							"WHERE rolname ~ '^pg_'");
 
-	if (PQntuples(res) != 0)
+	ntups = PQntuples(res);
+	i_roloid = PQfnumber(res, "roloid");
+	i_rolname = PQfnumber(res, "rolname");
+	for (int rowno = 0; rowno < ntups; rowno++)
 	{
-		if (cluster == &old_cluster)
-			pg_fatal("The source cluster contains roles starting with \"pg_\"");
-		else
-			pg_fatal("The target cluster contains roles starting with \"pg_\"");
+		if (script == NULL && (script = fopen_priv(output_path, "w")) == NULL)
+			pg_fatal("could not open file \"%s\": %s",
+					 output_path, strerror(errno));
+		fprintf(script, "%s (oid=%s)\n",
+				PQgetvalue(res, rowno, i_rolname),
+				PQgetvalue(res, rowno, i_roloid));
 	}
 
 	PQclear(res);
 
 	PQfinish(conn);
 
-	check_ok();
+	if (script)
+	{
+		fclose(script);
+		pg_log(PG_REPORT, "fatal");
+		pg_fatal("Your installation contains roles starting with \"pg_\".\n"
+				 "\"pg_\" is a reserved prefix for system roles, the cluster\n"
+				 "cannot be upgraded until these roles are renamed.\n"
+				 "A list of roles starting with \"pg_\" is in the file:\n"
+				 "    %s", output_path);
+	}
+	else
+		check_ok();
 }
 
 /*