Fixes #6786: Lv2Proc: Fix losing automation on export (#6944)

This PR is a about reloading an `Lv2Proc`, e.g. in case of a sample rate
change.

Prior to this PR, #6419 handled this by first saving the models into
XML, then destroying and re-initializing the whole `Lv2Proc` and finally
reloading the saved XML. However, #6786 shows that the automation is not
properly restored in such a case.

This PR thus attempts to not destroy the automatable models, just
everything else. This is done by moving `Lv2Proc::createPorts` into the
CTOR before calling `Lv2Proc::initPlugin`, which makes `initPlugin()`
and `shutdownPlugin()` proper inverses of each other (note that in jalv,
the ports are also created before the features are). The new class
`Lv2ProcSuspender` adds an RAII interface for reloading the `Lv2Proc`.

Note that another, possibly more clean approach would be to separate the
features and the plugin from the models ("controls"), to then only
destroy the features and the plugin. This could be done by having
`Lv2Effect` contain an `Lv2Proc` and `Lv2FxControls` contain an
`Lv2ProcControls`. Then the effect classes are the usual way round, and
you still maintain the separation between processor and controls in the
core LV2 code. (Similarly for the instrument, except we don't have a
processor/control split for instruments, so an instance of each class
would be contained within the same instrument instance.) - Thanks for
this proposal to @DomClark .

include/Lv2Proc.h

@@ -66,6 +66,7 @@ namespace Lv2Ports
 //! For Mono effects, 1 Lv2ControlBase references 2 Lv2Proc.
 class Lv2Proc : public LinkedModelGroup
 {
+	friend class Lv2ProcSuspender;
 public:
 	static Plugin::Type check(const LilvPlugin* plugin,
 		std::vector<PluginIssue> &issues);

include/NoCopyNoMove.h

@@ -0,0 +1,47 @@
+/*
+ * NoCopyNoMove.h - NoCopyNoMove class
+ *
+ * Copyright (c) 2023-2023 Johannes Lorenz <jlsf2013$users.sourceforge.net, $=@>
+ *
+ * This file is part of LMMS - https://lmms.io
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program (see COPYING); if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+ * Boston, MA 02110-1301 USA.
+ *
+ */
+
+#ifndef LMMS_NOCOPYNOMOVE_H
+#define LMMS_NOCOPYNOMOVE_H
+
+namespace lmms
+{
+
+/**
+ * Inherit this class to make your class non-copyable and non-movable
+ */
+class NoCopyNoMove
+{
+protected:
+	NoCopyNoMove() = default;
+	NoCopyNoMove(const NoCopyNoMove& other) = delete;
+	NoCopyNoMove& operator=(const NoCopyNoMove& other) = delete;
+	NoCopyNoMove(NoCopyNoMove&& other) = delete;
+	NoCopyNoMove& operator=(NoCopyNoMove&& other) = delete;
+};
+
+} // namespace lmms
+
+#endif // LMMS_NOCOPYNOMOVE_H
+

src/core/lv2/Lv2Proc.cpp

@@ -45,6 +45,7 @@
 #include "Lv2Evbuf.h"
 #include "MidiEvent.h"
 #include "MidiEventToByteSeq.h"
+#include "NoCopyNoMove.h"
 
 
 namespace lmms
@@ -168,6 +169,27 @@ Plugin::Type Lv2Proc::check(const LilvPlugin *plugin,
 
 
 
+class Lv2ProcSuspender : NoCopyNoMove
+{
+public:
+	Lv2ProcSuspender(Lv2Proc* proc)
+		: m_proc(proc)
+		, m_wasActive(proc->m_instance)
+	{
+		if (m_wasActive) { m_proc->shutdownPlugin(); }
+	}
+	~Lv2ProcSuspender()
+	{
+		if (m_wasActive) { m_proc->initPlugin(); }
+	}
+private:
+	Lv2Proc* const m_proc;
+	const bool m_wasActive;
+};
+
+
+
+
 Lv2Proc::Lv2Proc(const LilvPlugin *plugin, Model* parent) :
 	LinkedModelGroup(parent),
 	m_plugin(plugin),
@@ -175,6 +197,7 @@ Lv2Proc::Lv2Proc(const LilvPlugin *plugin, Model* parent) :
 	m_midiInputBuf(m_maxMidiInputEvents),
 	m_midiInputReader(m_midiInputBuf)
 {
+	createPorts();
 	initPlugin();
 }
 
@@ -186,22 +209,7 @@ Lv2Proc::~Lv2Proc() { shutdownPlugin(); }
 
 
 
-void Lv2Proc::reload()
-{
-	// save controls, which we want to keep
-	QDomDocument doc;
-	QDomElement controls = doc.createElement("controls");
-	saveValues(doc, controls);
-	// backup construction variables
-	const LilvPlugin* plugin = m_plugin;
-	Model* parent = Model::parentModel();
-	// destroy everything using RAII ...
-	this->~Lv2Proc();
-	// ... and reuse it ("placement new")
-	new (this) Lv2Proc(plugin, parent);
-	// reload the controls
-	loadValues(controls);
-}
+void Lv2Proc::reload() { Lv2ProcSuspender(this); }
 
 
 
@@ -434,8 +442,6 @@ void Lv2Proc::initPlugin()
 	initPluginSpecificFeatures();
 	m_features.createFeatureVectors();
 
-	createPorts();
-
 	m_instance = lilv_plugin_instantiate(m_plugin,
 		Engine::audioEngine()->processingSampleRate(),
 		m_features.featurePointers());