From aef04b7dcefd0e1d4d3b1eb8c38cc145baf645dc Mon Sep 17 00:00:00 2001
From: Jane Tournois <jane.tournois@geometryfactory.com>
Date: Mon, 17 Aug 2015 12:08:50 +0200
Subject: [PATCH] make compilation more explicit when Eigen < 3.2 is used

---
 .../include/CGAL/Polygon_mesh_processing/fair.h       |  7 +++++++
 .../internal/named_params_helper.h                    | 11 +++++++++++
 2 files changed, 18 insertions(+)

diff --git a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/fair.h b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/fair.h
index 4fa38d88ff4..0a74ed1153a 100644
--- a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/fair.h
+++ b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/fair.h
@@ -29,6 +29,7 @@
 #include <CGAL/Eigen_solver_traits.h>  // for sparse linear system solver
 #endif
 
+#include <boost/type_traits/is_same.hpp>
 
 namespace CGAL {
 
@@ -122,6 +123,12 @@ namespace internal {
       //if no solver is provided and Eigen version < 3.2
 #endif
 
+    typedef typename GetSolver<NamedParameters, Default_solver>::type SparseLinearSolver;
+    if (boost::is_same<SparseLinearSolver, bool>::value)
+    {
+      BOOST_STATIC_ASSERT_MSG(EIGEN_VERSION_AT_LEAST(3, 2, 0),
+                              "The function `fair` requires Eigen3 version 3.2 or later.");
+    }
     typedef typename GetVertexPointMap < PolygonMesh, NamedParameters>::type VPMap;
     typedef CGAL::internal::Cotangent_weight_with_voronoi_area_fairing<PolygonMesh, VPMap>
       Default_Weight_calculator;
diff --git a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/named_params_helper.h b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/named_params_helper.h
index df4bdf685e2..c17daf4a0f9 100644
--- a/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/named_params_helper.h
+++ b/Polygon_mesh_processing/include/CGAL/Polygon_mesh_processing/internal/named_params_helper.h
@@ -100,6 +100,17 @@ public:
   > ::type  type;
 };
 
+template<typename NamedParameters, typename DefaultSolver>
+class GetSolver
+{
+public:
+  typedef typename boost::lookup_named_param_def <
+    CGAL::sparse_linear_solver_t,
+    NamedParameters,
+    DefaultSolver
+  > ::type type;
+};
+
 
 
 #endif //CGAL_NAMED_PARAMETERS_HELPERS_H