From 4b2cebade8512abe05e94fd08ef901d818d8912b Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Wed, 21 Nov 2018 15:53:37 +0100
Subject: [PATCH] Workaround weird MSVC bug

---
 Eigen/src/SVD/SVDBase.h |  4 +++-
 test/jacobi.cpp         | 15 +++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/Eigen/src/SVD/SVDBase.h b/Eigen/src/SVD/SVDBase.h
index 429414797..1aede5ab0 100644
--- a/Eigen/src/SVD/SVDBase.h
+++ b/Eigen/src/SVD/SVDBase.h
@@ -180,8 +180,10 @@ public:
   RealScalar threshold() const
   {
     eigen_assert(m_isInitialized || m_usePrescribedThreshold);
+    // this temporary is needed to workaround a MSVC issue
+    Index diagSize = (std::max<Index>)(1,m_diagSize);
     return m_usePrescribedThreshold ? m_prescribedThreshold
-                                    : (std::max<Index>)(1,m_diagSize)*NumTraits<Scalar>::epsilon();
+                                    : diagSize*NumTraits<Scalar>::epsilon();
   }
 
   /** \returns true if \a U (full or thin) is asked for in this SVD decomposition */
diff --git a/test/jacobi.cpp b/test/jacobi.cpp
index 5604797f5..27b6e46d9 100644
--- a/test/jacobi.cpp
+++ b/test/jacobi.cpp
@@ -57,6 +57,19 @@ void jacobi(const MatrixType& m = MatrixType())
   }
 }
 
+namespace Foo {
+class Bar {};
+bool operator<(const Bar&, const Bar&) { return true; }
+}
+// regression test for a very strange MSVC issue for which simply
+// including SVDBase.h messes up with std::max and custom scalar type
+void msvc_workaround()
+{
+  const Foo::Bar a;
+  const Foo::Bar b;
+  std::max EIGEN_NOT_A_MACRO (a,b);
+}
+
 EIGEN_DECLARE_TEST(jacobi)
 {
   for(int i = 0; i < g_repeat; i++) {
@@ -77,4 +90,6 @@ EIGEN_DECLARE_TEST(jacobi)
     TEST_SET_BUT_UNUSED_VARIABLE(r);
     TEST_SET_BUT_UNUSED_VARIABLE(c);
   }
+
+  msvc_workaround();
 }