Functional algorithms allow to mismatch collection types

[tmadlener]

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Issue

It is possible to run Functional algorithms with mismatched input types without any check catching that at runtime. I.e. if users put in a wrong collection name by accident, things will ideally explode without an apparent reason why or, even worse, run but produce garbage.

Operating System and Version

all

compiler

all

The version of the key4hep stack

nightlies

Package Version

main

Reproducer

As a minimal reproducer consider the following transformer

struct TypeMisMatchDemo final : k4FWCore::Transformer<edm4hep::MCParticleCollection(const edm4hep::TrackCollection&)> {
  TypeMisMatchDemo(const std::string& name, ISvcLocator* svcLoc)
      : Transformer(name, svcLoc, {KeyValues("InputCollection", {"MCParticles"})},
                    {KeyValues("OutputCollection", {"MCParticles2"})}) {}

  edm4hep::MCParticleCollection operator()(const edm4hep::TrackCollection& inputs) const final {
    debug() << inputs.size() << " type = " << inputs.getTypeName() << endmsg;
    auto track = inputs[0];
    // The next line goes boom if the input is not really a TrackerHitCollection
    debug() << track.getTrackerHits().size() << endmsg;

    return edm4hep::MCParticleCollection{};
  }
};

if we pair this with the following python config:

from Gaudi.Configuration import INFO, DEBUG
from Configurables import ExampleFunctionalProducer, TypeMisMatchDemo, EventDataSvc

from k4FWCore import ApplicationMgr

producer = ExampleFunctionalProducer("Producer", OutputCollection=["MCParticles"])

mismatch = TypeMisMatchDemo(InputCollection=["MCParticles"], OutputLevel=DEBUG)

ApplicationMgr(
    TopAlg=[producer, mismatch],
    EvtSel="NONE",
    EvtMax=1,
    ExtSvc=[EventDataSvc("EventDataSvc")],
    OutputLevel=INFO,
)

We get a segmentation fault, because inputs is not actually a edm4hep::TrackerHitCollection, but rather a edm4hep::MCParticleCollection. Depending on which functions we call on the input collection and its members, we either get a segmentation fault (yay) or simply apparently run without problems (but most likely not with what we intended to to).

I have added the simple reproducer as a test case on https://github.com/tmadlener/K4FWCore/tree/mismatch-repro

Additional context

The underlying issue is the static_cast here:

k4FWCore/k4FWCore/include/k4FWCore/FunctionalUtils.h

Line 147 in ce56844

std::get<Index>(inputTuple) = static_cast<std::tuple_element_t<Index, std::tuple<In...>>*>(in);