Replace reference member with a pointer

As recommended by C++ Core Guidelines C.12. This doesn't change the
lifetime requirements of the class, but I've added a comment to
highlight them.

src/api/sorting/plugin_graph.cpp

@@ -215,7 +215,7 @@ void PluginGraph::AddPluginVertices(Game& game,
                             .GetPluginUserMetadata(plugin->GetName(), true)
                             .value_or(PluginMetadata(plugin->GetName()));
 
-    auto pluginSortingData = PluginSortingData(*plugin,
+    auto pluginSortingData = PluginSortingData(plugin,
                                                masterlistMetadata,
                                                userMetadata,
                                                loadOrder,

src/api/sorting/plugin_sorting_data.cpp

@@ -50,7 +50,7 @@ std::vector<const Plugin*> GetPluginsSubset(
 }
 
 PluginSortingData::PluginSortingData(
-    const Plugin& plugin,
+    const Plugin* plugin,
     const PluginMetadata& masterlistMetadata,
     const PluginMetadata& userMetadata,
     const std::vector<std::string>& loadOrder,
@@ -70,19 +70,19 @@ PluginSortingData::PluginSortingData(
   }
 
   for (size_t i = 0; i < loadOrder.size(); i++) {
-    if (CompareFilenames(plugin.GetName(), loadOrder.at(i)) == 0) {
+    if (CompareFilenames(plugin->GetName(), loadOrder.at(i)) == 0) {
       loadOrderIndex_ = i;
     }
   }
 
   if (gameType == GameType::tes3) {
-    auto masterNames = plugin.GetMasters();
+    auto masterNames = plugin->GetMasters();
     if (masterNames.empty()) {
       numOverrideFormIDs = 0;
     } else {
       auto masters = GetPluginsSubset(loadedPlugins, masterNames);
       if (masters.size() == masterNames.size()) {
-        numOverrideFormIDs = plugin.GetOverlapSize(masters);
+        numOverrideFormIDs = plugin->GetOverlapSize(masters);
       } else {
         // Not all masters are loaded, fall back to using the plugin's
         // total record count (Morrowind doesn't have groups). This is OK
@@ -93,25 +93,26 @@ PluginSortingData::PluginSortingData(
         // order with missing masters with potentially poorer results than
         // for it to error out, as masters may be missing for a variety of
         // development & testing reasons.
-        numOverrideFormIDs = plugin.GetRecordAndGroupCount();
+        numOverrideFormIDs = plugin->GetRecordAndGroupCount();
       }
     }
   } else {
-    numOverrideFormIDs = plugin.NumOverrideFormIDs();
+    numOverrideFormIDs = plugin->NumOverrideFormIDs();
   }
 }
 
-std::string PluginSortingData::GetName() const { return plugin_.GetName(); }
+std::string PluginSortingData::GetName() const { return plugin_->GetName(); }
 
 bool PluginSortingData::IsMaster() const {
-  return plugin_.IsMaster() || (plugin_.IsLightPlugin() &&
-                                !boost::iends_with(plugin_.GetName(), ".esp"));
+  return plugin_->IsMaster() ||
+         (plugin_->IsLightPlugin() &&
+          !boost::iends_with(plugin_->GetName(), ".esp"));
 }
 
-bool PluginSortingData::LoadsArchive() const { return plugin_.LoadsArchive(); }
+bool PluginSortingData::LoadsArchive() const { return plugin_->LoadsArchive(); }
 
 std::vector<std::string> PluginSortingData::GetMasters() const {
-  return plugin_.GetMasters();
+  return plugin_->GetMasters();
 }
 
 size_t PluginSortingData::NumOverrideFormIDs() const {
@@ -120,7 +121,7 @@ size_t PluginSortingData::NumOverrideFormIDs() const {
 
 bool PluginSortingData::DoFormIDsOverlap(
     const PluginSortingData& plugin) const {
-  return plugin_.DoFormIDsOverlap(plugin.plugin_);
+  return plugin_->DoFormIDsOverlap(*plugin.plugin_);
 }
 
 std::string PluginSortingData::GetGroup() const { return group_; }

src/api/sorting/plugin_sorting_data.h

@@ -31,7 +31,12 @@
 namespace loot {
 class PluginSortingData {
 public:
-  explicit PluginSortingData(const Plugin& plugin,
+  /**
+   * This stores a copy of the plugin pointer that is passed to it, so
+   * PluginSortingData objects must not live longer than the Plugin objects
+   * that they are constructed from.
+   */
+  explicit PluginSortingData(const Plugin* plugin,
                              const PluginMetadata& masterlistMetadata,
                              const PluginMetadata& userMetadata,
                              const std::vector<std::string>& loadOrder,
@@ -58,7 +63,7 @@ public:
   const std::optional<size_t>& GetLoadOrderIndex() const;
 
 private:
-  const Plugin& plugin_;
+  const Plugin* plugin_;
   std::string group_;
   std::unordered_set<std::string> afterGroupPlugins_;
 

src/tests/api/internals/sorting/plugin_sorting_data_test.h

@@ -84,27 +84,27 @@ TEST_P(PluginSortingDataTest, lightFlaggedEspFilesShouldNotBeTreatedAsMasters) {
 
   ASSERT_NO_THROW(loadInstalledPlugins(game_, false));
 
-  auto esp = PluginSortingData(
-      *dynamic_cast<const Plugin *>(game_.GetPlugin(blankEsp)),
-      PluginMetadata(),
-      PluginMetadata(),
-      getLoadOrder(),
-      game_.Type(),
-      game_.GetCache().GetPlugins());
+  auto esp =
+      PluginSortingData(dynamic_cast<const Plugin *>(game_.GetPlugin(blankEsp)),
+                        PluginMetadata(),
+                        PluginMetadata(),
+                        getLoadOrder(),
+                        game_.Type(),
+                        game_.GetCache().GetPlugins());
   EXPECT_FALSE(esp.IsMaster());
 
-  auto master = PluginSortingData(
-      *dynamic_cast<const Plugin *>(game_.GetPlugin(blankEsm)),
-      PluginMetadata(),
-      PluginMetadata(),
-      getLoadOrder(),
-      game_.Type(),
-      game_.GetCache().GetPlugins());
+  auto master =
+      PluginSortingData(dynamic_cast<const Plugin *>(game_.GetPlugin(blankEsm)),
+                        PluginMetadata(),
+                        PluginMetadata(),
+                        getLoadOrder(),
+                        game_.Type(),
+                        game_.GetCache().GetPlugins());
   EXPECT_TRUE(master.IsMaster());
 
   if (GetParam() == GameType::fo4 || GetParam() == GameType::tes5se) {
     auto lightMaster = PluginSortingData(
-        *dynamic_cast<const Plugin *>(game_.GetPlugin(blankEsl)),
+        dynamic_cast<const Plugin *>(game_.GetPlugin(blankEsl)),
         PluginMetadata(),
         PluginMetadata(),
         getLoadOrder(),
@@ -113,7 +113,7 @@ TEST_P(PluginSortingDataTest, lightFlaggedEspFilesShouldNotBeTreatedAsMasters) {
     EXPECT_TRUE(lightMaster.IsMaster());
 
     auto lightPlugin = PluginSortingData(
-        *dynamic_cast<const Plugin *>(game_.GetPlugin(blankEslEsp)),
+        dynamic_cast<const Plugin *>(game_.GetPlugin(blankEslEsp)),
         PluginMetadata(),
         PluginMetadata(),
         getLoadOrder(),
@@ -128,7 +128,7 @@ TEST_P(PluginSortingDataTest,
   ASSERT_NO_THROW(loadInstalledPlugins(game_, false));
 
   auto plugin = PluginSortingData(
-      *dynamic_cast<const Plugin *>(game_.GetPlugin(blankMasterDependentEsm)),
+      dynamic_cast<const Plugin *>(game_.GetPlugin(blankMasterDependentEsm)),
       PluginMetadata(),
       PluginMetadata(),
       getLoadOrder(),
@@ -157,7 +157,7 @@ TEST_P(
   }
 
   auto plugin = PluginSortingData(
-      *dynamic_cast<const Plugin *>(game_.GetPlugin(blankMasterDependentEsm)),
+      dynamic_cast<const Plugin *>(game_.GetPlugin(blankMasterDependentEsm)),
       PluginMetadata(),
       PluginMetadata(),
       getLoadOrder(),