refactor: Add new concepts for Eigen types

This commit adds several new concepts for dealing with Eigen base types.
The motivation for this is superficially to simplify some of the
requirements in the track state proxy and the multi-trajectory, but it
also allows me to more easily deal with some clang compiler warnings
seen in #3949, as clang won't let me compare `A::ColsAtCompileTime` and
`B::ColsAtCompileTime` if `A` and `B` are different types; this allows
me to hide the conversion to integers inside a concept.

Core/include/Acts/EventData/TrackStateProxy.hpp

@@ -16,6 +16,7 @@
 #include "Acts/EventData/TrackStateType.hpp"
 #include "Acts/EventData/Types.hpp"
 #include "Acts/Surfaces/Surface.hpp"
+#include "Acts/Utilities/EigenConcepts.hpp"
 #include "Acts/Utilities/HashedString.hpp"
 #include "Acts/Utilities/Helpers.hpp"
 
@@ -782,12 +783,11 @@ class TrackStateProxy {
   template <typename val_t, typename cov_t>
   void allocateCalibrated(const Eigen::DenseBase<val_t>& val,
                           const Eigen::DenseBase<cov_t>& cov)
-    requires(Eigen::PlainObjectBase<val_t>::RowsAtCompileTime > 0 &&
-             Eigen::PlainObjectBase<val_t>::RowsAtCompileTime <= eBoundSize &&
-             Eigen::PlainObjectBase<val_t>::RowsAtCompileTime ==
-                 Eigen::PlainObjectBase<cov_t>::RowsAtCompileTime &&
-             Eigen::PlainObjectBase<cov_t>::RowsAtCompileTime ==
-                 Eigen::PlainObjectBase<cov_t>::ColsAtCompileTime)
+    requires(Concepts::eigen_base_is_fixed_size<val_t> &&
+             Concepts::eigen_bases_have_same_num_rows<val_t, cov_t> &&
+             Concepts::eigen_base_is_square<cov_t> &&
+             Eigen::PlainObjectBase<val_t>::RowsAtCompileTime <=
+                 static_cast<std::underlying_type_t<BoundIndices>>(eBoundSize))
   {
     m_traj->template allocateCalibrated<
         Eigen::PlainObjectBase<val_t>::RowsAtCompileTime>(m_istate, val, cov);

Core/include/Acts/EventData/VectorMultiTrajectory.hpp

@@ -16,6 +16,7 @@
 #include "Acts/EventData/Types.hpp"
 #include "Acts/EventData/detail/DynamicColumn.hpp"
 #include "Acts/EventData/detail/DynamicKeyIterator.hpp"
+#include "Acts/Utilities/EigenConcepts.hpp"
 #include "Acts/Utilities/HashedString.hpp"
 #include "Acts/Utilities/Helpers.hpp"
 #include "Acts/Utilities/ThrowAssert.hpp"
@@ -495,13 +496,11 @@ class VectorMultiTrajectory final
   void allocateCalibrated_impl(IndexType istate,
                                const Eigen::DenseBase<val_t>& val,
                                const Eigen::DenseBase<cov_t>& cov)
-
-    requires(Eigen::PlainObjectBase<val_t>::RowsAtCompileTime > 0 &&
-             Eigen::PlainObjectBase<val_t>::RowsAtCompileTime <= eBoundSize &&
-             Eigen::PlainObjectBase<val_t>::RowsAtCompileTime ==
-                 Eigen::PlainObjectBase<cov_t>::RowsAtCompileTime &&
-             Eigen::PlainObjectBase<cov_t>::RowsAtCompileTime ==
-                 Eigen::PlainObjectBase<cov_t>::ColsAtCompileTime)
+    requires(Concepts::eigen_base_is_fixed_size<val_t> &&
+             Concepts::eigen_bases_have_same_num_rows<val_t, cov_t> &&
+             Concepts::eigen_base_is_square<cov_t> &&
+             Eigen::PlainObjectBase<val_t>::RowsAtCompileTime <=
+                 static_cast<std::underlying_type_t<BoundIndices>>(eBoundSize))
   {
     constexpr std::size_t measdim = val_t::RowsAtCompileTime;
 

Core/include/Acts/Utilities/EigenConcepts.hpp

@@ -0,0 +1,56 @@
+// This file is part of the ACTS project.
+//
+// Copyright (C) 2016 CERN for the benefit of the ACTS project
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+#pragma once
+
+#include <Eigen/Dense>
+
+namespace Acts::Concepts {
+/// @brief Concept that is true iff T is a valid Eigen dense base.
+template <typename T>
+concept is_eigen_base = requires {
+  { T::RowsAtCompileTime };
+  { T::ColsAtCompileTime };
+};
+
+/// @brief Concept that is true iff T is a valid Eigen dense base with fixed
+/// size.
+template <typename T>
+concept eigen_base_is_fixed_size =
+    is_eigen_base<T> && Eigen::PlainObjectBase<T>::RowsAtCompileTime > 0 &&
+    Eigen::PlainObjectBase<T>::ColsAtCompileTime > 0;
+
+/// @brief Concept that is true iff T is a valid Eigen dense base with fixed,
+/// square size.
+template <typename T>
+concept eigen_base_is_square = eigen_base_is_fixed_size<T> &&
+                               Eigen::PlainObjectBase<T>::RowsAtCompileTime ==
+                                   Eigen::PlainObjectBase<T>::ColsAtCompileTime;
+
+/// @brief Concept that is true iff T1 and T2 have the same, known at compile
+/// time, number of rows.
+template <typename T1, typename T2>
+concept eigen_bases_have_same_num_rows =
+    eigen_base_is_fixed_size<T1> && eigen_base_is_fixed_size<T2> &&
+    static_cast<std::size_t>(Eigen::PlainObjectBase<T1>::RowsAtCompileTime) ==
+        static_cast<std::size_t>(Eigen::PlainObjectBase<T2>::RowsAtCompileTime);
+
+/// @brief Concept that is true iff T1 and T2 have the same, known at compile
+/// time, number of columns.
+template <typename T1, typename T2>
+concept eigen_bases_have_same_num_cols =
+    eigen_base_is_fixed_size<T1> && eigen_base_is_fixed_size<T2> &&
+    static_cast<std::size_t>(Eigen::PlainObjectBase<T1>::ColsAtCompileTime) ==
+        static_cast<std::size_t>(Eigen::PlainObjectBase<T2>::ColsAtCompileTime);
+
+/// @brief Concept that is true iff T1 and T2 have the same, known at compile
+/// time, size.
+template <typename T1, typename T2>
+concept eigen_bases_have_same_size = eigen_bases_have_same_num_rows<T1, T2> &&
+                                     eigen_bases_have_same_num_cols<T1, T2>;
+}  // namespace Acts::Concepts