feat!: Add IVertexFinder interface, use in vertexing (#2948)

This PR introduces a new `IVertexFinder` with an interface that can support the existing vertex finder implementations, with the exception of the seed vertex finder (which depends on specific spacepoint triplets).

The interface introduces a type-erased state holder that the client of the finder initializes via the `makeState` interface function, and which the finder implementation downcasts to manipulate the state. This enables the concrete interface without templating.

Since some vertex finders use *other* vertex finders as seeders, this also allows to have the seed finder property use this `IVertexFinder` interface.

I did not observe CPU performance degradation as documented in #2842.

Part of:
- #2842 

Blocked by:
- #2946

Core/include/Acts/Vertexing/AdaptiveGridDensityVertexFinder.hpp

@@ -9,9 +9,11 @@
 #pragma once
 
 #include "Acts/EventData/TrackParameters.hpp"
+#include "Acts/MagneticField/MagneticFieldContext.hpp"
 #include "Acts/Utilities/Result.hpp"
 #include "Acts/Vertexing/AdaptiveGridTrackDensity.hpp"
 #include "Acts/Vertexing/DummyVertexFitter.hpp"
+#include "Acts/Vertexing/IVertexFinder.hpp"
 #include "Acts/Vertexing/Vertex.hpp"
 #include "Acts/Vertexing/VertexingOptions.hpp"
 
@@ -28,10 +30,7 @@ namespace Acts {
 /// with the highest track density is returned as a vertex candidate.
 /// Unlike the GridDensityVertexFinder, this seeder implements an adaptive
 /// version where the density grid grows bigger with added tracks.
-///
-/// @tparam vfitter_t Vertex fitter type
-template <typename vfitter_t = DummyVertexFitter<>>
-class AdaptiveGridDensityVertexFinder {
+class AdaptiveGridDensityVertexFinder final : public IVertexFinder {
   using GridDensity = AdaptiveGridTrackDensity;
 
  public:
@@ -87,15 +86,28 @@ class AdaptiveGridDensityVertexFinder {
   ///
   /// @param trackVector Input track collection
   /// @param vertexingOptions Vertexing options
-  /// @param state The state object to cache the density grid
+  /// @param anyState The state object to cache the density grid
   /// and density contributions of each track, to be used
   /// if cacheGridStateForTrackRemoval == true
   ///
   /// @return Vector of vertices, filled with a single
   ///         vertex (for consistent interfaces)
-  Result<std::vector<Vertex>> find(const std::vector<InputTrack>& trackVector,
-                                   const VertexingOptions& vertexingOptions,
-                                   State& state) const;
+  Result<std::vector<Vertex>> find(
+      const std::vector<InputTrack>& trackVector,
+      const VertexingOptions& vertexingOptions,
+      IVertexFinder::State& anyState) const override;
+
+  IVertexFinder::State makeState(
+      const Acts::MagneticFieldContext& /*mctx*/) const override {
+    return IVertexFinder::State{State{}};
+  }
+
+  void setTracksToRemove(
+      IVertexFinder::State& anyState,
+      const std::vector<InputTrack>& removedTracks) const override {
+    auto& state = anyState.template as<State>();
+    state.tracksToRemove = removedTracks;
+  }
 
   /// @brief Constructor for user-defined InputTrack type
   ///

Core/include/Acts/Vertexing/AdaptiveGridDensityVertexFinder.ipp

@@ -6,11 +6,11 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
-template <typename vfitter_t>
-auto Acts::AdaptiveGridDensityVertexFinder<vfitter_t>::find(
+inline auto Acts::AdaptiveGridDensityVertexFinder::find(
     const std::vector<InputTrack>& trackVector,
-    const VertexingOptions& vertexingOptions, State& state) const
-    -> Result<std::vector<Vertex>> {
+    const VertexingOptions& vertexingOptions,
+    IVertexFinder::State& anyState) const -> Result<std::vector<Vertex>> {
+  auto& state = anyState.as<State>();
   // Remove density contributions from tracks removed from track collection
   if (m_cfg.cacheGridStateForTrackRemoval && state.isInitialized &&
       !state.tracksToRemove.empty()) {
@@ -95,8 +95,7 @@ auto Acts::AdaptiveGridDensityVertexFinder<vfitter_t>::find(
   return seedVec;
 }
 
-template <typename vfitter_t>
-auto Acts::AdaptiveGridDensityVertexFinder<vfitter_t>::doesPassTrackSelection(
+inline auto Acts::AdaptiveGridDensityVertexFinder::doesPassTrackSelection(
     const BoundTrackParameters& trk) const -> bool {
   // Get required track parameters
   const double d0 = trk.parameters()[BoundIndices::eBoundLoc0];

Core/include/Acts/Vertexing/AdaptiveMultiVertexFinder.hpp

@@ -11,13 +11,16 @@
 #include "Acts/Definitions/Algebra.hpp"
 #include "Acts/Definitions/Units.hpp"
 #include "Acts/EventData/TrackParameters.hpp"
+#include "Acts/MagneticField/MagneticFieldContext.hpp"
 #include "Acts/Utilities/Logger.hpp"
 #include "Acts/Utilities/Result.hpp"
 #include "Acts/Vertexing/AMVFInfo.hpp"
+#include "Acts/Vertexing/IVertexFinder.hpp"
 #include "Acts/Vertexing/ImpactPointEstimator.hpp"
 #include "Acts/Vertexing/TrackLinearizer.hpp"
 #include "Acts/Vertexing/VertexingOptions.hpp"
 
+#include <functional>
 #include <type_traits>
 
 namespace Acts {
@@ -32,19 +35,9 @@ namespace Acts {
 ///
 /// @tparam vfitter_t Vertex fitter type
 /// @tparam sfinder_t Seed finder type
-template <typename vfitter_t, typename sfinder_t>
-class AdaptiveMultiVertexFinder {
+template <typename vfitter_t>
+class AdaptiveMultiVertexFinder final : public IVertexFinder {
   using FitterState_t = typename vfitter_t::State;
-  using SeedFinderState_t = typename sfinder_t::State;
-
-  template <typename T, typename = int>
-  struct NeedsRemovedTracks : std::false_type {};
-
-#ifndef DOXYGEN
-  template <typename T>
-  struct NeedsRemovedTracks<T, decltype((void)T::tracksToRemove, 0)>
-      : std::true_type {};
-#endif
 
  public:
   /// Configuration struct
@@ -55,7 +48,8 @@ class AdaptiveMultiVertexFinder {
     /// @param sfinder The seed finder
     /// @param ipEst ImpactPointEstimator
     /// @param bIn Input magnetic field
-    Config(vfitter_t fitter, sfinder_t sfinder, ImpactPointEstimator ipEst,
+    Config(vfitter_t fitter, std::shared_ptr<const IVertexFinder> sfinder,
+           ImpactPointEstimator ipEst,
            std::shared_ptr<const MagneticFieldProvider> bIn)
         : vertexFitter(std::move(fitter)),
           seedFinder(std::move(sfinder)),
@@ -66,7 +60,7 @@ class AdaptiveMultiVertexFinder {
     vfitter_t vertexFitter;
 
     // Vertex seed finder
-    sfinder_t seedFinder;
+    std::shared_ptr<const IVertexFinder> seedFinder;
 
     // ImpactPointEstimator
     ImpactPointEstimator ipEstimator;
@@ -161,7 +155,9 @@ class AdaptiveMultiVertexFinder {
   };  // Config struct
 
   /// State struct for fulfilling interface
-  struct State {};
+  struct State {
+    std::reference_wrapper<const MagneticFieldContext> magContext;
+  };
 
   /// @brief Constructor for user-defined InputTrack_t type !=
   /// BoundTrackParameters
@@ -179,6 +175,12 @@ class AdaptiveMultiVertexFinder {
           "No function to extract parameters "
           "from InputTrack provided.");
     }
+
+    if (!m_cfg.seedFinder) {
+      throw std::invalid_argument(
+          "AdaptiveMultiVertexFinder: "
+          "No vertex fitter provided.");
+    }
   }
 
   AdaptiveMultiVertexFinder(AdaptiveMultiVertexFinder&&) = default;
@@ -188,12 +190,24 @@ class AdaptiveMultiVertexFinder {
   ///
   /// @param allTracks Input track collection
   /// @param vertexingOptions Vertexing options
-  /// @param state State for fulfilling interfaces
+  /// @param anyState The state object
   ///
   /// @return Vector of all reconstructed vertices
-  Result<std::vector<Vertex>> find(const std::vector<InputTrack>& allTracks,
-                                   const VertexingOptions& vertexingOptions,
-                                   State& state) const;
+  Result<std::vector<Vertex>> find(
+      const std::vector<InputTrack>& allTracks,
+      const VertexingOptions& vertexingOptions,
+      IVertexFinder::State& anyState) const override;
+
+  IVertexFinder::State makeState(
+      const Acts::MagneticFieldContext& mctx) const override {
+    return IVertexFinder::State{State{mctx}};
+  }
+
+  void setTracksToRemove(
+      IVertexFinder::State& /*state*/,
+      const std::vector<InputTrack>& /*removedTracks*/) const override {
+    // Nothing to do here
+  }
 
  private:
   /// Configuration object
@@ -203,9 +217,7 @@ class AdaptiveMultiVertexFinder {
   std::unique_ptr<const Logger> m_logger;
 
   /// Private access to logging instance
-  const Logger& logger() const {
-    return *m_logger;
-  }
+  const Logger& logger() const { return *m_logger; }
 
   /// @brief Calls the seed finder and sets constraints on the found seed
   /// vertex if desired
@@ -221,7 +233,7 @@ class AdaptiveMultiVertexFinder {
   Result<Vertex> doSeeding(
       const std::vector<InputTrack>& trackVector, Vertex& currentConstraint,
       const VertexingOptions& vertexingOptions,
-      SeedFinderState_t& seedFinderState,
+      IVertexFinder::State& seedFinderState,
       const std::vector<InputTrack>& removedSeedTracks) const;
 
   /// @brief Sets constraint vertex after seeding