test for completely empty datasets (#281)

* test for completely empty datasets

* prevents failures with cryptic error message:
    HDF5-DIAG: Error detected in HDF5 (1.10.4) thread 140737340061504:
    #000: ../../../src/H5Shyper.c line 7057 in H5Sselect_hyperslab(): hyperslab doesn't support H5S_NULL space

src/population.hpp

@@ -29,15 +29,15 @@ namespace sonata {
 
 namespace {
 
-const char* H5_DYNAMICS_PARAMS = "dynamics_params";
-const char* H5_LIBRARY = "@library";
+constexpr const char* const H5_DYNAMICS_PARAMS = "dynamics_params";
+constexpr const char* const H5_LIBRARY = "@library";
 
 
 std::set<std::string> _listChildren(const HighFive::Group& group,
                                     const std::set<std::string>& ignoreNames = {}) {
     std::set<std::string> result;
     for (const auto& name : group.listObjectNames()) {
-        if (ignoreNames.count(name)) {
+        if (ignoreNames.count(name) > 0) {
             continue;
         }
         result.insert(name);
@@ -57,7 +57,6 @@ std::set<std::string> _listExplicitEnumerations(const HighFive::Group h5Group,
     return names;
 }
 
-
 template <typename T>
 std::vector<T> _readChunk(const HighFive::DataSet& dset, const Selection::Range& range) {
     std::vector<T> result;
@@ -70,6 +69,10 @@ std::vector<T> _readChunk(const HighFive::DataSet& dset, const Selection::Range&
 
 template <typename T, typename std::enable_if<!std::is_pod<T>::value>::type* = nullptr>
 std::vector<T> _readSelection(const HighFive::DataSet& dset, const Selection& selection) {
+    if (selection.ranges().empty() || dset.getElementCount() == 0) {
+        return {};
+    }
+
     if (selection.ranges().size() == 1) {
         return _readChunk<T>(dset, selection.ranges().front());
     }
@@ -89,7 +92,7 @@ std::vector<T> _readSelection(const HighFive::DataSet& dset, const Selection& se
 
 template <typename T, typename std::enable_if<std::is_pod<T>::value>::type* = nullptr>
 std::vector<T> _readSelection(const HighFive::DataSet& dset, const Selection& selection) {
-    if (selection.ranges().empty()) {
+    if (selection.ranges().empty() || dset.getElementCount() == 0) {
         return {};
     } else if (selection.ranges().size() == 1) {
         return _readChunk<T>(dset, selection.ranges().front());

tests/test_nodes.cpp

@@ -163,6 +163,13 @@ TEST_CASE("NodePopulationSelectAll", "[base]") {
 TEST_CASE("NodePopulationmatchAttributeValues", "[base]") {
     NodePopulation population("./data/nodes1.h5", "", "nodes-A");
 
+    SECTION("int") {
+        const auto sel = population.matchAttributeValues("A-int64", 1);
+        CHECK(sel.flatSize() == 0);
+
+        CHECK_THROWS_AS(population.matchAttributeValues("E-mapping-good", 1), SonataError);
+    }
+
     SECTION("String") {
         auto sel = population.matchAttributeValues<std::string>("attr-Z", "bb");
         CHECK(sel.flatSize() == 1);