MacOS Build with `USE_SYSTEM_EIGEN3=ON` Error on `#include <Eigen/Core>` in `cpp/open3d/ml/impl/misc/VoxelPooling.h`

[essandess]

Checklist

• I have searched for similar issues.
• For Python issues, I have tested with the latest development wheel.
• I have checked the release documentation and the latest documentation (for main branch).

Steps to reproduce the issue

I’ve submitted a MacPorts Portfile for Open3D at macports/macports-ports#32787

When building with USE_SYSTEM_EIGEN3=ON, there’s a clang++ signature error on #include <Eigen/Core> in cpp/open3d/ml/impl/misc/VoxelPooling.h

A fix is in this patch of cpp/open3d/ml/impl/misc/VoxelPooling.h, which specifies Substitution Failure Is Not An Error to the preprocessor:

--- ./cpp/open3d/ml/impl/misc/VoxelPooling.h	2026-05-19 09:34:55
+++ ./cpp/open3d/ml/impl/misc/VoxelPooling.h	2026-05-19 13:31:10
@@ -35,10 +35,14 @@
                       "CENTER is not allowed for feature vectors");
     }
 
-    template <class Derived, class Derived2, class Derived3>
+    // SFINAE to fix `#include <Eigen/Core>`
+    template <class Derived, class Derived2, class Derived3,
+              typename = typename std::enable_if<
+                  std::is_base_of<Eigen::ArrayBase<Derived3>, Derived3>::value>::type>
     inline void AddPoint(const Eigen::MatrixBase<Derived>& pos,
                          const Eigen::MatrixBase<Derived2>& voxel_center,
-                         const Eigen::ArrayBase<Derived3>& feat) {
+                         // const Eigen::ArrayBase<Derived3>& feat) {
+                         const Derived3& feat) {
         bool new_nearest_neighbor = false;
         TReal sqr_d = 0;
         if (POS_FN == NEAREST_NEIGHBOR || FEAT_FN == NEAREST_NEIGHBOR) {

Error message

Signature error on #include <Eigen/Core> in cpp/open3d/ml/impl/misc/VoxelPooling.h

Open3D, Python and System information

- Operating system: macOS 26
- Python version: Python 3.14`
- Open3D version: 0.19.0`
- System architecture: arm64
- Is this a remote workstation?: no
- How did you install Open3D?: build from source
- Compiler version (if built from source): clang

Additional information

No response