compat for old sessions with missing plugins (+doc)

1 files changed, 34 insertions, 0 deletions

diff --git a/libs/ardour/unknown_processor.cc b/libs/ardour/unknown_processor.cc
index 4bf4ebeaef..df40d4d040 100644
--- a/libs/ardour/unknown_processor.cc
+++ b/libs/ardour/unknown_processor.cc
@@ -69,6 +69,40 @@ UnknownProcessor::can_support_io_configuration (const ChanCount &in, ChanCount &
 	if (have_ioconfig && in == *saved_input) {
 		out = *saved_output;
 		return true;
+	} else if (!have_ioconfig) {
+		/* pass for old sessions.
+		 *
+		 * session load assumes processor config succeeds.
+		 * if initial configuration fails, processors downstream
+		 * remain unconfigured and at least the panner will assert/segfault.
+		 *
+		 * This may still result in impossible setup, however
+		 * Route::configure_processors_unlocked() ignores configure_io() return value
+		 * in the inner loop and configures all available processors.
+		 *
+		 * It can still lead to segfaults IFF the track has no inputs and this is a
+		 * generator (processor_max_streams will be zero).
+		 */
+		PBD::warning << _("Using plugin-stub with unknown i/o configuration for: ") << name() << endmsg;
+#if 0
+		/* No output channels are fine (or should be, there may be edge-cases with e.g sends).
+		 *
+		 * Discussion needed.
+		 *
+		 * This is the safer option (no audio output, no possible damage)
+		 * and the way to go in the long run.
+		 * An even better solution is to disable the route if there are missing plugins
+		 * and/or impossible configurations.
+		 *
+		 * Currently no output channels results in awkward GUI route display and also
+		 * breaks semantics in mixbus (which assumes that the route has channels required
+		 * for the always present mixer-strip plugin).
+		 */
+		out = ChanCount ();
+#else
+		out = in;
+#endif
+		return true;
 	}
 	return false;
 }