Compile- and run-time assertions for the construction of Ref<const>.

Eigen/src/Core/Ref.h

diff --git a/Eigen/src/Core/Ref.h b/Eigen/src/Core/Ref.h
index 81de5f9..11866f7 100644
--- a/Eigen/src/Core/Ref.h
+++ b/Eigen/src/Core/Ref.h
@@ -332,6 +332,16 @@
   : public RefBase<Ref<const TPlainObjectType, Options, StrideType> >
 {
     typedef internal::traits<Ref> Traits;
+
+    static constexpr bool may_map_m_object_successfully = 
+      (StrideType::InnerStrideAtCompileTime == 0 ||
+       StrideType::InnerStrideAtCompileTime == 1 ||
+       StrideType::InnerStrideAtCompileTime == Dynamic) &&
+      (TPlainObjectType::IsVectorAtCompileTime ||
+       StrideType::OuterStrideAtCompileTime == 0 ||
+       StrideType::OuterStrideAtCompileTime == Dynamic ||
+       StrideType::OuterStrideAtCompileTime == TPlainObjectType::InnerSizeAtCompileTime ||
+       TPlainObjectType::InnerSizeAtCompileTime == Dynamic);
   public:
 
     typedef RefBase<Ref> Base;
@@ -344,6 +354,8 @@
 //      std::cout << match_helper<Derived>::HasDirectAccess << "," << match_helper<Derived>::OuterStrideMatch << "," << match_helper<Derived>::InnerStrideMatch << "\n";
 //      std::cout << int(StrideType::OuterStrideAtCompileTime) << " - " << int(Derived::OuterStrideAtCompileTime) << "\n";
 //      std::cout << int(StrideType::InnerStrideAtCompileTime) << " - " << int(Derived::InnerStrideAtCompileTime) << "\n";
+      EIGEN_STATIC_ASSERT(Traits::template match<Derived>::type::value || may_map_m_object_successfully,
+                          STORAGE_LAYOUT_DOES_NOT_MATCH);
       construct(expr.derived(), typename Traits::template match<Derived>::type());
     }
 
@@ -353,6 +365,8 @@
 
     template<typename OtherRef>
     EIGEN_DEVICE_FUNC inline Ref(const RefBase<OtherRef>& other) {
+      EIGEN_STATIC_ASSERT(Traits::template match<OtherRef>::type::value || may_map_m_object_successfully,
+                          STORAGE_LAYOUT_DOES_NOT_MATCH);
       construct(other.derived(), typename Traits::template match<OtherRef>::type());
     }
 
@@ -371,7 +385,9 @@
     EIGEN_DEVICE_FUNC void construct(const Expression& expr, internal::false_type)
     {
       internal::call_assignment_no_alias(m_object,expr,internal::assign_op<Scalar,Scalar>());
-      Base::construct(m_object);
+      const bool success = Base::construct(m_object);
+      EIGEN_ONLY_USED_FOR_DEBUG(success)
+      eigen_assert(success);
     }
 
   protected:

failtest/CMakeLists.txt

diff --git a/failtest/CMakeLists.txt b/failtest/CMakeLists.txt
index 2c5fc33..107c9e2 100644
--- a/failtest/CMakeLists.txt
+++ b/failtest/CMakeLists.txt
@@ -36,6 +36,8 @@
 ei_add_failtest("ref_3")
 ei_add_failtest("ref_4")
 ei_add_failtest("ref_5")
+ei_add_failtest("ref_6")
+ei_add_failtest("ref_7")
 
 ei_add_failtest("swap_1")
 ei_add_failtest("swap_2")

failtest/ref_6.cpp

diff --git a/failtest/ref_6.cpp b/failtest/ref_6.cpp
new file mode 100644
index 0000000..b246f97
--- /dev/null
+++ b/failtest/ref_6.cpp
@@ -0,0 +1,15 @@
+#include "../Eigen/Core"
+
+using namespace Eigen;
+
+void call_ref(Ref<const VectorXf, 0, InnerStride<2>>) {}
+
+int main() {
+  VectorXf a(10);
+  Map<const VectorXf, 0, InnerStride<2>> m(a.data(), 5);
+#ifdef EIGEN_SHOULD_FAIL_TO_BUILD
+  call_ref(a);
+#else
+  call_ref(m);
+#endif
+}

failtest/ref_7.cpp

diff --git a/failtest/ref_7.cpp b/failtest/ref_7.cpp
new file mode 100644
index 0000000..7d6a3cb
--- /dev/null
+++ b/failtest/ref_7.cpp
@@ -0,0 +1,16 @@
+#include "../Eigen/Core"
+
+using namespace Eigen;
+
+void call_ref(Ref<const Matrix3f, 0, OuterStride<2>>) {}
+
+int main() {
+  MatrixXf a(6, 2);
+  Map<const Matrix3f, 0, OuterStride<Dynamic>> md(a.data(), OuterStride<Dynamic>(2));
+  Map<const Matrix3f, 0, OuterStride<2>> m2(a.data());
+#ifdef EIGEN_SHOULD_FAIL_TO_BUILD
+  call_ref(md);
+#else
+  call_ref(m2);
+#endif
+}