Protect from_hepevt against invalid parents/children record (#47)

This protects from_hepevt from invalid parent/children ranges.
Previously the code would abort or even crash on such input. Now it
raises a Python RuntimeError.

src/from_hepevt.cpp

@@ -8,15 +8,6 @@
 #include <utility>
 #include <vector>
 
-// template <>
-// struct std::hash<std::pair<int, int>> {
-//   std::size_t operator()(const std::pair<int, int>& p) const noexcept {
-//     auto h1 = std::hash<int>{}(p.first);
-//     auto h2 = std::hash<int>{}(p.second);
-//     return h1 ^ (h2 << 1); // or use boost::hash_combine
-//   }
-// };
-
 template <>
 struct std::less<std::pair<int, int>> {
   bool operator()(const std::pair<int, int>& a,
@@ -35,9 +26,10 @@ void normalize(int& m1, int& m2) {
   // m1 < m2, both > 0: interaction
   // m2 < m1, both > 0: same, needs swapping
 
-  if (m1 > 0 && m2 > 0 && m2 < m1) std::swap(m1, m2);
-
-  if (m1 > 0 && m2 == 0) m2 = m1;
+  if (m1 > 0 && m2 == 0)
+    m2 = m1;
+  else if (m2 < m1)
+    std::swap(m1, m2);
 
   --m1; // fortran to c index
 }
@@ -102,14 +94,28 @@ void connect_parents_and_children(GenEvent& event, bool parents,
 
     int m1 = vi.first.first;
     int m2 = vi.first.second;
+
     // there must be at least one parent or child when we arrive here...
     normalize(m1, m2);
-    assert(m1 < m2);
+    assert(m1 < m2); // postcondition after normalize
+
+    if (m1 < 0 || m2 > n) {
+      std::ostringstream os;
+      os << "invalid " << (parents ? "parents" : "children") << " range for vertex "
+         << event.vertices().size() << " [" << m1 << ", " << m2
+         << ") total number of particles " << n;
+      throw std::runtime_error(os.str().c_str());
+    }
 
     // ...with at least one child or parent
     const auto& co = vi.second;
-    assert(!co.empty());
 
+    if (co.empty()) {
+      std::ostringstream os;
+      os << "invalid empty " << (!parents ? "parents" : "children")
+         << " list for vertex " << event.vertices().size();
+      throw std::runtime_error(os.str().c_str());
+    }
     FourVector pos;
     if (has_vertex) {
       // we assume this is a production vertex

tests/test_from_hepevt.py

@@ -0,0 +1,57 @@
+import pyhepmc as hep
+import numpy as np
+import pytest
+
+
+def test_no_vertex_info():
+    px = py = pz = en = m = np.linspace(0, 1, 4)
+
+    pid = np.arange(4) + 1
+    sta = np.zeros(4, dtype=np.int32)
+    parents = [(0, 0), (1, 1), (0, 0), (0, 0)]
+    hev = hep.GenEvent()
+    hev.from_hepevt(0, px, py, pz, en, m, pid, sta, parents)
+    assert len(hev.vertices) == 1
+    assert len(hev.particles) == 4
+
+
+def test_parents_range_exceeding_particle_range():
+    px = py = pz = en = m = np.linspace(0, 1, 6)
+    pid = np.arange(6) + 1
+    sta = np.zeros(6, dtype=np.int32)
+    parents = [(0, 0), (1, 1), (2, 0), (3, 5), (4, 10), (3, 5)]
+    with pytest.raises(RuntimeError):
+        hep.GenEvent().from_hepevt(0, px, py, pz, en, m, pid, sta, parents)
+
+
+def test_invalid_length_of_parents():
+    px = py = pz = en = m = np.linspace(0, 1, 3)
+    pid = np.arange(3) + 1
+    sta = np.zeros(3, dtype=np.int32)
+    parents = [(0, 0), (1, 2)]
+    with pytest.raises(RuntimeError):
+        hep.GenEvent().from_hepevt(0, px, py, pz, en, m, pid, sta, parents)
+
+
+def test_inverted_parents_range():
+    px = py = pz = en = m = vx = vy = vz = vt = np.linspace(0, 1, 4)
+    pid = np.arange(4) + 1
+    sta = np.zeros(4, dtype=np.int32)
+    # inverted range is not an error (2, 1) will be converted to (1, 2)
+    parents = [(0, 0), (2, 1), (3, 3), (3, 3)]
+    hev = hep.GenEvent()
+    hev.from_hepevt(0, px, py, pz, en, m, pid, sta, parents)
+    expected = [[0, 1], [2]]
+    got = [[p.id - 1 for p in v.particles_in] for v in hev.vertices]
+    assert expected == got
+
+
+@pytest.mark.parametrize("bad", ([-4, 1], [1, -4]))
+def test_negative_parents_range(bad):
+    px = py = pz = en = m = vx = vy = vz = vt = np.linspace(0, 1, 4)
+    pid = np.arange(4) + 1
+    sta = np.zeros(4, dtype=np.int32)
+    # inverted range is not an error (2, 1) will be converted to (1, 2)
+    parents = [(0, 0), bad, (3, 3), (3, 3)]
+    with pytest.raises(RuntimeError):
+        hep.GenEvent().from_hepevt(0, px, py, pz, en, m, pid, sta, parents)