From 87112908be917c37aa2c22bd238a43c60528ec5b Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Thu, 23 Jun 2016 10:25:04 +0200
Subject: [PATCH] Biug 1242: fix comma init with empty matrices. (grafted from
 a3f7edf7e7672094190e04a0b4417de1abfa3de5 )

---
 Eigen/src/Core/CommaInitializer.h |  7 +++++--
 test/commainitializer.cpp         | 23 +++++++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/Eigen/src/Core/CommaInitializer.h b/Eigen/src/Core/CommaInitializer.h
index a036d8c3b..73e2a6418 100644
--- a/Eigen/src/Core/CommaInitializer.h
+++ b/Eigen/src/Core/CommaInitializer.h
@@ -76,8 +76,11 @@ struct CommaInitializer
   template<typename OtherDerived>
   CommaInitializer& operator,(const DenseBase<OtherDerived>& other)
   {
-    if(other.cols()==0 || other.rows()==0)
+    if(other.rows()==0)
+    {
+      m_col += other.cols();
       return *this;
+    }
     if (m_col==m_xpr.cols())
     {
       m_row+=m_currentBlockRows;
@@ -86,7 +89,7 @@ struct CommaInitializer
       eigen_assert(m_row+m_currentBlockRows<=m_xpr.rows()
         && "Too many rows passed to comma initializer (operator<<)");
     }
-    eigen_assert(m_col<m_xpr.cols()
+    eigen_assert(m_col<m_xpr.cols() || (m_xpr.cols()==0 && m_col==0)
       && "Too many coefficients passed to comma initializer (operator<<)");
     eigen_assert(m_currentBlockRows==other.rows());
     if (OtherDerived::SizeAtCompileTime != Dynamic)
diff --git a/test/commainitializer.cpp b/test/commainitializer.cpp
index 99102b966..86bdb040e 100644
--- a/test/commainitializer.cpp
+++ b/test/commainitializer.cpp
@@ -43,4 +43,27 @@ void test_commainitializer()
         4, 5, 6,
         vec[2].transpose();
   VERIFY_IS_APPROX(m3, ref);
+
+
+  // Check with empty matrices (bug #1242)
+  {
+    int const M = 0;
+    int const N1 = 2;
+    int const N2 = 1;
+
+    {
+      Matrix<double, M, N1> A1;
+      Matrix<double, M, N2> A2;
+      Matrix<double, M, N1 + N2> B;
+      B << A1, A2;
+    }
+    {
+      Matrix<double, N1, M> A1;
+      Matrix<double, N2, M> A2;
+      Matrix<double, N1 + N2, M> B;
+      B << A1,
+           A2;
+    }
+  }
+
 }