More LV2 buf-size features (#6254)

Implement `LV2_BUF_SIZE__boundedBlockLength` and
`LV2_BUF_SIZE__fixedBlockLength`.

src/core/lv2/Lv2Features.cpp

@@ -69,7 +69,15 @@ void Lv2Features::createFeatureVectors()
 	// create vector of features
 	for(std::pair<const char* const, void*>& pr : m_featureByUri)
 	{
-		Q_ASSERT(pr.second != nullptr);
+		/*
+			If pr.second is nullptr here, this means that the LV2_feature
+			has no "data". If this happens here, this means
+			* either that this feature is static
+			  (e.g. LV2_BUF_SIZE__boundedBlockLength)
+			* or that the programmer forgot to use operator[] before feature
+			  vector creation (This can be done in
+			  Lv2Proc::initPluginSpecificFeatures or in Lv2Features::initCommon)
+		*/
 		m_features.push_back(LV2_Feature { pr.first, pr.second });
 	}
 

src/core/lv2/Lv2Manager.cpp

@@ -31,6 +31,7 @@
 #include <cstring>
 #include <lilv/lilv.h>
 #include <lv2.h>
+#include <lv2/lv2plug.in/ns/ext/buf-size/buf-size.h>
 #include <lv2/lv2plug.in/ns/ext/options/options.h>
 #include <QDebug>
 #include <QDir>
@@ -78,6 +79,10 @@ Lv2Manager::Lv2Manager() :
 	m_supportedFeatureURIs.insert(LV2_URID__map);
 	m_supportedFeatureURIs.insert(LV2_URID__unmap);
 	m_supportedFeatureURIs.insert(LV2_OPTIONS__options);
+	// min/max is always passed in the options
+	m_supportedFeatureURIs.insert(LV2_BUF_SIZE__boundedBlockLength);
+	// block length is only changed initially in AudioEngine CTOR
+	m_supportedFeatureURIs.insert(LV2_BUF_SIZE__fixedBlockLength);
 
 	auto supportOpt = [this](Lv2UridCache::Id id)
 	{