fix LinearRegressionOutput with empty label

cpp-package/example/CMakeLists.txt

@@ -27,6 +27,10 @@ endif()
 
 include_directories(${CMAKE_CURRENT_SOURCE_DIR}/../include)
 
+add_executable(test_regress_label test_regress_label.cpp ${CPP_PACKAGE_HAEDERS})
+target_link_libraries(test_regress_label ${CPP_EXAMPLE_LIBS})
+add_dependencies(test_regress_label ${CPPEX_DEPS})
+
 add_executable(lenet lenet.cpp ${CPP_PACKAGE_HEADERS})
 target_link_libraries(lenet ${CPP_EXAMPLE_LIBS})
 add_dependencies(lenet ${CPPEX_DEPS})

cpp-package/example/test_regress_label.cpp

@@ -0,0 +1,33 @@
+#include <iostream>
+#include <vector>
+#include <string>
+#include "mxnet-cpp/MxNetCpp.h"
+
+using namespace mxnet::cpp;
+
+
+int main() {
+    std::cout << "Running regress label test" << std::endl;
+    Symbol data = Symbol::Variable("data");
+    Symbol label = Symbol::Variable("regress_label");
+    Symbol symbol = LinearRegressionOutput(data, label);
+    std::map<std::string, mxnet::cpp::OpReqType> opReqMap;
+    for (const auto& iter : symbol.ListArguments()) {
+        opReqMap[iter] = mxnet::cpp::OpReqType::kNullOp;
+    }
+    std::map<std::string, mxnet::cpp::NDArray> argMap({
+        {"data", NDArray(Shape{1, 3}, Context::cpu(), true)}
+    });
+
+    try {
+        symbol.SimpleBind(Context::cpu(),
+                argMap,
+                std::map<std::string, mxnet::cpp::NDArray>(),
+                opReqMap,
+                std::map<std::string, mxnet::cpp::NDArray>());
+    } catch (const std::exception& e) {
+        std::cout << "Error while binding in mxnet: " << MXGetLastError() << std::endl;
+        throw;
+    }
+    return 0;
+}

cpp-package/tests/ci_test.sh

@@ -60,6 +60,9 @@ cp ../../build/cpp-package/example/test_score .
 cp ../../build/cpp-package/example/test_ndarray_copy .
 ./test_ndarray_copy
 
+cp ../../build/cpp-package/example/test_regress_label .
+./test_regress_label
+
 sh unittests/unit_test_mlp_csv.sh
 
 cd inference

src/operator/regression_output-inl.h

@@ -59,7 +59,8 @@ inline bool RegressionOpShape(const nnvm::NodeAttrs& attrs,
   const mxnet::TShape &dshape = in_attrs->at(0);
   if (!shape_is_known(dshape)) return false;
   auto &lshape = (*in_attrs)[1];
-  if (lshape.ndim() == 0) {
+  // if label is not defined, manually build the shape based on dshape
+  if (lshape.ndim() == -1) {
     // special treatment for 1D output, to allow 1D label by default.
     // Think about change convention later
     if (dshape.ndim() == 2 && dshape[1] == 1) {