规范模块目录和第三方依赖结构

third_party/eigen3/failtest/sparse_ref_3.cpp

@@ -0,0 +1,15 @@
+#include "../Eigen/Sparse"
+
+using namespace Eigen;
+
+#ifdef EIGEN_SHOULD_FAIL_TO_BUILD
+void call_ref(Ref<SparseMatrix<float> > a) { }
+#else
+void call_ref(const Ref<const SparseMatrix<float> > &a) { }
+#endif
+
+int main()
+{
+  SparseMatrix<float> a(10,10);
+  call_ref(a+a);
+}