bug #1381: fix sparse.diagonal() used as a rvalue.

The problem was that is "sparse" is not const, then sparse.diagonal() must have the
LValueBit flag meaning that sparse.diagonal().coeff(i) must returns a const reference,
const Scalar&. However, sparse::coeff() cannot returns a reference for a non-existing
zero coefficient. The trick is to return a reference to a local member of
evaluator<SparseMatrix>.

1 files changed, 4 insertions, 0 deletions

diff --git a/test/sparse_basic.cpp b/test/sparse_basic.cpp
index 208a66f12..91b7cb335 100644
--- a/test/sparse_basic.cpp
+++ b/test/sparse_basic.cpp
@@ -485,6 +485,10 @@ template<typename SparseMatrixType> void sparse_basic(const SparseMatrixType& re
     SparseMatrixType m2(rows, cols);
     initSparse<Scalar>(density, refMat2, m2);
     VERIFY_IS_APPROX(m2.diagonal(), refMat2.diagonal().eval());
+    DenseVector d = m2.diagonal();
+    VERIFY_IS_APPROX(d, refMat2.diagonal().eval());
+    d = m2.diagonal().array();
+    VERIFY_IS_APPROX(d, refMat2.diagonal().eval());
     VERIFY_IS_APPROX(const_cast<const SparseMatrixType&>(m2).diagonal(), refMat2.diagonal().eval());
     
     initSparse<Scalar>(density, refMat2, m2, ForceNonZeroDiag);