AudioProcessorGraph: Allow nodes with ID 0 to be added

BREAKING_CHANGES.md

@@ -2,6 +2,30 @@
 
 # develop
 
+## Change
+
+The NodeID argument to AudioProcessorGraph::addNode() has been changed to take
+a std::optional<NodeID>.
+
+**Possible Issues**
+
+The behavior of any code calling AudioProcessorGraph::addNode(), that explicitly
+passes a default constructed NodeID or a NodeID constructed with a value of 0,
+will change. Previously these values would have been treated as a null value
+resulting in the actual NodeID being automatically determined. These will now
+be treated as requests for an explicit value.
+
+**Workaround**
+
+Either remove the explicit NodeID argument and rely on the default argument or
+pass a std::nullopt instead.
+
+**Rationale**
+
+The previous version prevented users from specifying a NodeID of 0 and resulted
+in unexpected behavior.
+
+
 ## Change
 
 The signature of DynamicObject::writeAsJSON() has been changed to accept a

modules/juce_audio_processors/processors/juce_AudioProcessorGraph.cpp

@@ -1694,7 +1694,7 @@ public:
     }
 
     Node::Ptr addNode (std::unique_ptr<AudioProcessor> newProcessor,
-                       const NodeID nodeID,
+                       std::optional<NodeID> nodeID,
                        UpdateKind updateKind)
     {
         if (newProcessor.get() == owner)
@@ -1703,7 +1703,7 @@ public:
             return nullptr;
         }
 
-        const auto idToUse = nodeID == NodeID() ? NodeID { ++(lastNodeID.uid) } : nodeID;
+        const auto idToUse = nodeID.value_or (NodeID { lastNodeID.uid + 1 });
 
         auto added = nodes.addNode (std::move (newProcessor), idToUse);
 
@@ -1957,7 +1957,7 @@ bool AudioProcessorGraph::isAnInputTo (const Node& source, const Node& destinati
 bool AudioProcessorGraph::isAnInputTo (NodeID source, NodeID destination) const noexcept                    { return pimpl->isAnInputTo (source, destination); }
 
 AudioProcessorGraph::Node::Ptr AudioProcessorGraph::addNode (std::unique_ptr<AudioProcessor> newProcessor,
-                                                             NodeID nodeId,
+                                                             std::optional<NodeID> nodeId,
                                                              UpdateKind updateKind)
 {
     return pimpl->addNode (std::move (newProcessor), nodeId, updateKind);

modules/juce_audio_processors/processors/juce_AudioProcessorGraph.h

@@ -252,7 +252,7 @@ public:
 
         If this succeeds, it returns a pointer to the newly-created node.
     */
-    Node::Ptr addNode (std::unique_ptr<AudioProcessor> newProcessor, NodeID nodeId = {}, UpdateKind = UpdateKind::sync);
+    Node::Ptr addNode (std::unique_ptr<AudioProcessor> newProcessor, std::optional<NodeID> nodeId = std::nullopt, UpdateKind = UpdateKind::sync);
 
     /** Deletes a node within the graph which has the specified ID.
         This will also delete any connections that are attached to this node.