Refactor cell XML parsing into shared free functions

Extract parse_cell_material_xml() and parse_cell_temperature_xml() from
CSGCell::CSGCell() into free functions in cell.h/cell.cpp so that
DAGUniverse can reuse the same logic when parsing <cell> override
sub-elements. Both handle void/material-id conversion, empty-array
validation, and non-negative temperature validation. Each call site
retains its own higher-level policy (fill/material exclusivity in
CSGCell, forbidden-attribute guards and duplicate detection in
DAGUniverse).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: pshriwise

include/openmc/cell.h

@@ -145,6 +145,23 @@ class Region {
   bool simple_; //!< Does the region contain only intersections?
 };
 
+//==============================================================================
+// XML parsing helpers for <cell> nodes
+//==============================================================================
+
+//! Parse material IDs from a <cell> XML node.
+//! \param node XML node containing a "material" attribute or child element
+//! \param cell_id Cell ID used in error messages
+//! \return Vector of material IDs (MATERIAL_VOID for "void")
+vector<int32_t> parse_cell_material_xml(pugi::xml_node node, int32_t cell_id);
+
+//! Parse temperatures (in Kelvin) from a <cell> XML node.
+//! Validates that all values are non-negative and the list is non-empty.
+//! \param node XML node containing a "temperature" attribute or child element
+//! \param cell_id Cell ID used in error messages
+//! \return Vector of temperatures in Kelvin
+vector<double> parse_cell_temperature_xml(pugi::xml_node node, int32_t cell_id);
+
 //==============================================================================
 
 class Cell {

src/cell.cpp

@@ -340,6 +340,45 @@ void Cell::to_hdf5(hid_t cell_group) const
   close_group(group);
 }
 
+//==============================================================================
+// XML parsing helpers for <cell> nodes
+//==============================================================================
+
+vector<int32_t> parse_cell_material_xml(pugi::xml_node node, int32_t cell_id)
+{
+  vector<std::string> mats {get_node_array<std::string>(node, "material", true)};
+  if (mats.empty()) {
+    fatal_error(fmt::format(
+      "An empty material element was specified for cell {}", cell_id));
+  }
+  vector<int32_t> material;
+  material.reserve(mats.size());
+  for (const auto& mat : mats) {
+    if (mat == "void") {
+      material.push_back(MATERIAL_VOID);
+    } else {
+      material.push_back(std::stoi(mat));
+    }
+  }
+  return material;
+}
+
+vector<double> parse_cell_temperature_xml(pugi::xml_node node, int32_t cell_id)
+{
+  auto temperatures = get_node_array<double>(node, "temperature");
+  if (temperatures.empty()) {
+    fatal_error(fmt::format(
+      "An empty temperature element was specified for cell {}", cell_id));
+  }
+  for (auto T : temperatures) {
+    if (T < 0) {
+      fatal_error(fmt::format(
+        "Cell {} was specified with a negative temperature", cell_id));
+    }
+  }
+  return temperatures;
+}
+
 //==============================================================================
 // CSGCell implementation
 //==============================================================================
@@ -390,26 +429,12 @@ CSGCell::CSGCell(pugi::xml_node cell_node)
   // universe), more than one material (distribmats), and some materials may
   // be "void".
   if (material_present) {
-    vector<std::string> mats {
-      get_node_array<std::string>(cell_node, "material", true)};
-    if (mats.size() > 0) {
-      material_.reserve(mats.size());
-      for (std::string mat : mats) {
-        if (mat.compare("void") == 0) {
-          material_.push_back(MATERIAL_VOID);
-        } else {
-          material_.push_back(std::stoi(mat));
-        }
-      }
-    } else {
-      fatal_error(fmt::format(
-        "An empty material element was specified for cell {}", id_));
-    }
+    material_ = parse_cell_material_xml(cell_node, id_);
   }
 
   // Read the temperature element which may be distributed like materials.
   if (check_for_node(cell_node, "temperature")) {
-    sqrtkT_ = get_node_array<double>(cell_node, "temperature");
+    sqrtkT_ = parse_cell_temperature_xml(cell_node, id_);
     sqrtkT_.shrink_to_fit();
 
     // Make sure this is a material-filled cell.
@@ -420,14 +445,6 @@ CSGCell::CSGCell(pugi::xml_node cell_node)
         id_));
     }
 
-    // Make sure all temperatures are non-negative.
-    for (auto T : sqrtkT_) {
-      if (T < 0) {
-        fatal_error(fmt::format(
-          "Cell {} was specified with a negative temperature", id_));
-      }
-    }
-
     // Convert to sqrt(k*T).
     for (auto& T : sqrtkT_) {
       T = std::sqrt(K_BOLTZMANN * T);

src/dagmc.cpp

@@ -115,45 +115,16 @@ DAGUniverse::DAGUniverse(pugi::xml_node node)
           "DAGMC cell {} override must specify material.", cell_id));
       }
 
-      vector<std::string> mats =
-        get_node_array<std::string>(cell_node, "material", true);
-      if (mats.empty()) {
-        fatal_error(fmt::format(
-          "DAGMC cell {} override has an empty material specification.",
-          cell_id));
-      }
-
-      vector<int32_t> override_mats;
-      override_mats.reserve(mats.size());
-      for (const auto& mat : mats) {
-        if (mat == "void") {
-          override_mats.push_back(MATERIAL_VOID);
-        } else {
-          override_mats.push_back(std::stoi(mat));
-        }
-      }
-
-      auto inserted = material_overrides.emplace(cell_id, override_mats);
+      auto inserted = material_overrides.emplace(
+        cell_id, parse_cell_material_xml(cell_node, cell_id));
       if (!inserted.second) {
         fatal_error(fmt::format(
           "Duplicate DAGMC cell override specified for cell {}", cell_id));
       }
 
       if (check_for_node(cell_node, "temperature")) {
-        auto temperatures = get_node_array<double>(cell_node, "temperature");
-        if (temperatures.empty()) {
-          fatal_error(fmt::format(
-            "DAGMC cell {} override has an empty temperature specification.",
-            cell_id));
-        }
-        for (auto T : temperatures) {
-          if (T < 0.0) {
-            fatal_error(fmt::format(
-              "DAGMC cell {} was specified with a negative temperature",
-              cell_id));
-          }
-        }
-        temperature_overrides.emplace(cell_id, temperatures);
+        temperature_overrides.emplace(
+          cell_id, parse_cell_temperature_xml(cell_node, cell_id));
       }
     }
   } else if (check_for_node(node, "material_overrides")) {