From 8d7ebac6ec8a3e638e5f99d15a740bf886527b15 Mon Sep 17 00:00:00 2001
From: Sergiu Deitsch <sergiu.deitsch@gmail.com>
Date: Sat, 27 Sep 2025 14:03:07 +0200
Subject: [PATCH] Disambiguate multiplication of a permutation matrix and a
 homogeneous vector

---
 Eigen/src/Core/ProductEvaluators.h | 8 ++++++++
 test/geo_homogeneous.cpp           | 9 +++++++++
 2 files changed, 17 insertions(+)

diff --git a/Eigen/src/Core/ProductEvaluators.h b/Eigen/src/Core/ProductEvaluators.h
index 5955e496f..be55be5e8 100644
--- a/Eigen/src/Core/ProductEvaluators.h
+++ b/Eigen/src/Core/ProductEvaluators.h
@@ -1272,6 +1272,14 @@ template <typename Lhs, typename Rhs, int ProductTag, typename MatrixShape>
 struct generic_product_impl<Lhs, Rhs, HomogeneousShape, MatrixShape, ProductTag>
     : generic_product_impl<typename Lhs::PlainObject, Rhs, DenseShape, MatrixShape, ProductTag> {};
 
+template <typename Lhs, typename Rhs, int ProductTag>
+struct generic_product_impl<Lhs, Rhs, PermutationShape, HomogeneousShape, ProductTag>
+    : generic_product_impl<Lhs, Rhs, PermutationShape, DenseShape, ProductTag> {};
+
+template <typename Lhs, typename Rhs, int ProductTag>
+struct generic_product_impl<Lhs, Rhs, HomogeneousShape, PermutationShape, ProductTag>
+    : generic_product_impl<Lhs, Rhs, DenseShape, PermutationShape, ProductTag> {};
+
 }  // end namespace internal
 
 }  // end namespace Eigen
diff --git a/test/geo_homogeneous.cpp b/test/geo_homogeneous.cpp
index 638fbec1e..21be26d25 100644
--- a/test/geo_homogeneous.cpp
+++ b/test/geo_homogeneous.cpp
@@ -124,6 +124,15 @@ void homogeneous(void) {
     VERIFY_IS_APPROX(pts_xy1.transpose() * pts_xy1, pts_xy1.transpose() * pts_xy1.eval());
     VERIFY_IS_APPROX(pts_xy2 * pts_xy2.transpose(), pts_xy2.eval() * pts_xy2.transpose());
   }
+
+  {
+    const Eigen::PermutationMatrix<Size> P{Eigen::Vector<int, Size>::EqualSpaced(0, 1)};
+    const auto right = Eigen::Vector<Scalar, Size - 1>::Random().homogeneous();
+    const auto left = Eigen::RowVector<Scalar, Size - 1>::Random().homogeneous();
+
+    VERIFY_IS_APPROX(P * right, P * right.eval());
+    VERIFY_IS_APPROX(left * P, left.eval() * P);
+  }
 }
 
 EIGEN_DECLARE_TEST(geo_homogeneous) {