Warn about LADSPA problems

Introduce a method which checks if a file that's loaded has the LADSPA
controls saved in an old format that was written with a version before
commit e99efd5.

The method is run at the end so that problems in all file versions are
detected. If a real upgrade was to be implemented it would have to run
between `DataFile::upgrade_0_4_0_rc2` and `DataFile::upgrade_1_0_99`.

See LMMS#5738 for more details.

include/DataFile.h

@@ -130,6 +130,7 @@ class LMMS_EXPORT DataFile : public QDomDocument
 	void upgrade_loopsRename();
 	void upgrade_noteTypes();
 	void upgrade_fixCMTDelays();
+	void findProblematicLadspaPlugins();
 
 	// List of all upgrade methods
 	static const std::vector<UpgradeMethod> UPGRADE_METHODS;

src/core/DataFile.cpp

@@ -84,7 +84,7 @@ const std::vector<DataFile::UpgradeMethod> DataFile::UPGRADE_METHODS = {
 	&DataFile::upgrade_mixerRename      ,   &DataFile::upgrade_bbTcoRename,
 	&DataFile::upgrade_sampleAndHold    ,   &DataFile::upgrade_midiCCIndexing,
 	&DataFile::upgrade_loopsRename      ,   &DataFile::upgrade_noteTypes,
-	&DataFile::upgrade_fixCMTDelays
+	&DataFile::upgrade_fixCMTDelays     ,   &DataFile::findProblematicLadspaPlugins
 };
 
 // Vector of all versions that have upgrade routines.
@@ -1046,7 +1046,6 @@ void DataFile::upgrade_0_4_0_rc2()
 	}
 }
 
-
 void DataFile::upgrade_1_0_99()
 {
 	jo_id_t last_assigned_id = 0;
@@ -1957,6 +1956,39 @@ void DataFile::upgrade_midiCCIndexing()
 	}
 }
 
+void DataFile::findProblematicLadspaPlugins()
+{
+	// This is not an upgrade but a check for potentially problematic LADSPA
+	// controls. See #5738 for more details.
+
+	const QDomNodeList ladspacontrols = elementsByTagName("ladspacontrols");
+
+	auto problematicLadspaControlFound = false;
+
+	for (int i = 0; i < ladspacontrols.size(); ++i)
+	{
+		const QDomElement ladspacontrol = ladspacontrols.item(i).toElement();
+
+		const auto attributes = ladspacontrol.attributes();
+		for (int j = 0; j < attributes.length(); ++j)
+		{
+			const auto attribute = attributes.item(j);
+			const auto name = attribute.nodeName();
+			if (name != "ports" && name.startsWith("port"))
+			{
+				problematicLadspaControlFound = true;
+				break;
+			}
+		}
+	}
+
+	if (problematicLadspaControlFound)
+	{
+		QMessageBox::warning(nullptr, QObject::tr("LADSPA plugins"),
+			QObject::tr("The project contains LADSPA plugins which might have not been restored correctly! Please check the project."));
+	}
+}
+
 void DataFile::upgrade()
 {
 	// Runs all necessary upgrade methods