Conditionally produce/consume in GeneratorSmearedProducer

Only call produces and consumes if the data products the module
want appear to be in the job.
This solves the case where the module has been added to a job
just on the remote possibility it might be needed but infact
the values which are actually wanted come from the source.

Author: Dr15Jones

GeneratorInterface/Core/plugins/GeneratorSmearedProducer.cc

@@ -27,39 +27,80 @@ class GeneratorSmearedProducer : public edm::global::EDProducer<> {
   static void fillDescriptions(edm::ConfigurationDescriptions& descriptions);
 
 private:
-  const edm::EDGetTokenT<edm::HepMCProduct> newToken_;
-  const edm::EDGetTokenT<edm::HepMCProduct> oldToken_;
-  const edm::EDGetTokenT<edm::HepMC3Product> Token3_;
+  edm::EDGetTokenT<edm::HepMCProduct> newToken_;
+  edm::EDGetTokenT<edm::HepMCProduct> oldToken_;
+  edm::EDGetTokenT<edm::HepMC3Product> Token3_;
 };
 
-GeneratorSmearedProducer::GeneratorSmearedProducer(edm::ParameterSet const& ps)
-    : newToken_(consumes<edm::HepMCProduct>(ps.getUntrackedParameter<edm::InputTag>("currentTag"))),
-      oldToken_(consumes<edm::HepMCProduct>(ps.getUntrackedParameter<edm::InputTag>("previousTag"))),
-      Token3_(consumes<edm::HepMC3Product>(ps.getUntrackedParameter<edm::InputTag>("currentTag"))) {
+namespace {
+  template <typename T>
+  bool match(edm::InputTag const& iTag, edm::ProductDescription const& iDesc) {
+    if (iDesc.unwrappedTypeID() == edm::TypeID(typeid(T))) {
+      if (iDesc.moduleLabel() == iTag.label() and iDesc.productInstanceName() == iTag.instance()) {
+        if (iTag.process().empty() or iTag.willSkipCurrentProcess() or
+            iTag.process() == edm::InputTag::kCurrentProcess) {
+          return true;
+        }
+      } else {
+        return iTag.process() == iDesc.processName();
+      }
+    }
+    return false;
+  }
+}  // namespace
+
+GeneratorSmearedProducer::GeneratorSmearedProducer(edm::ParameterSet const& ps) {
   // This producer produces a HepMCProduct, a copy of the original one
   // It is used for backward compatibility
   // If HepMC3Product exists, it produces its copy
   // It adds "generatorSmeared" to description, which is needed for further processing
-  produces<edm::HepMCProduct>();
-  produces<edm::HepMC3Product>();
+  auto currentTag = ps.getUntrackedParameter<edm::InputTag>("currentTag");
+  auto previousTag = ps.getUntrackedParameter<edm::InputTag>("previousTag");
+  callWhenNewProductsRegistered([this, currentTag, previousTag](edm::ProductDescription const& desc) {
+    bool oldHep = false;
+    if (match<edm::HepMCProduct>(currentTag, desc)) {
+      if (newToken_.isUninitialized()) {
+        newToken_ = consumes<edm::HepMCProduct>(currentTag);
+        oldHep = true;
+      }
+    }
+    if (match<edm::HepMCProduct>(previousTag, desc)) {
+      if (oldToken_.isUninitialized()) {
+        oldToken_ = consumes<edm::HepMCProduct>(previousTag);
+        oldHep = true;
+      }
+    }
+    if (oldHep) {
+      produces<edm::HepMCProduct>();
+    }
+    if (match<edm::HepMC3Product>(currentTag, desc)) {
+      Token3_ = consumes<edm::HepMC3Product>(currentTag);
+      produces<edm::HepMC3Product>();
+    }
+  });
 }
 
 void GeneratorSmearedProducer::produce(edm::StreamID, edm::Event& iEvent, const edm::EventSetup& es) const {
   edm::Handle<edm::HepMCProduct> theHepMCProduct;
-  bool found = iEvent.getByToken(newToken_, theHepMCProduct);
-  if (!found) {
+  bool found = false;
+  if (not newToken_.isUninitialized()) {
+    found = iEvent.getByToken(newToken_, theHepMCProduct);
+  }
+  if (!found and not oldToken_.isUninitialized()) {
     found = iEvent.getByToken(oldToken_, theHepMCProduct);
   }
   if (found) {
     std::unique_ptr<edm::HepMCProduct> theCopy(new edm::HepMCProduct(*theHepMCProduct));
     iEvent.put(std::move(theCopy));
   }
 
-  edm::Handle<edm::HepMC3Product> theHepMC3Product;
-  found = iEvent.getByToken(Token3_, theHepMC3Product);
-  if (found) {
-    std::unique_ptr<edm::HepMC3Product> theCopy3(new edm::HepMC3Product(*theHepMC3Product));
-    iEvent.put(std::move(theCopy3));
+  if (not Token3_.isUninitialized()) {
+    edm::Handle<edm::HepMC3Product> theHepMC3Product;
+    found = iEvent.getByToken(Token3_, theHepMC3Product);
+    if (found) {
+      std::unique_ptr<edm::HepMC3Product> theCopy3(new edm::HepMC3Product(*theHepMC3Product));
+      iEvent.put(std::move(theCopy3));
+    }
   }
 }