message when using empty soul gems, using preferentially filled ones with equip command

apps/openmw/mwclass/misc.cpp

@@ -201,6 +201,25 @@ namespace MWClass
         return newPtr;
     }
 
+    std::pair<int, std::string> Miscellaneous::canBeEquipped(const MWWorld::ConstPtr &ptr, const MWWorld::Ptr &npc) const
+    {
+        // Special checks for soul gems.
+        
+        if (::Misc::StringUtils::ciEqualPrefix("misc_soulgem", ptr.getCellRef().getRefId()))
+        {
+            if (npc != MWBase::Environment::get().getWorld()->getPlayerPtr())
+                return std::make_pair(0, "Only the player can use soul gems.");
+
+            if (ptr.getCellRef().getSoul().empty())
+                return std::make_pair(0, "#{sNotifyMessage32}");
+
+            if (!MWBase::Environment::get().getWorld()->getStore().get<ESM::Creature>().search(ptr.getCellRef().getSoul()))
+                return std::make_pair(0, "Unknown soul creature id.");
+        }
+
+        return std::make_pair(1, "");
+    }
+
     std::unique_ptr<MWWorld::Action> Miscellaneous::use (const MWWorld::Ptr& ptr, bool force) const
     {
         if (ptr.getCellRef().getSoul().empty() || !MWBase::Environment::get().getWorld()->getStore().get<ESM::Creature>().search(ptr.getCellRef().getSoul()))

apps/openmw/mwclass/misc.hpp

@@ -45,6 +45,10 @@ namespace MWClass
 
             std::string getModel(const MWWorld::ConstPtr &ptr) const override;
 
+            std::pair<int, std::string> canBeEquipped(const MWWorld::ConstPtr &ptr, const MWWorld::Ptr &npc) const override;
+            ///< Return 0 if player cannot equip item. 1 if can equip. 2 if it's twohanded weapon. 3 if twohanded weapon conflicts with that. \n
+            ///  Second item in the pair specifies the error message
+
             std::unique_ptr<MWWorld::Action> use (const MWWorld::Ptr& ptr, bool force=false) const override;
             ///< Generate action for using via inventory menu
 

apps/openmw/mwgui/inventorywindow.cpp

@@ -549,6 +549,19 @@ namespace MWGui
             }
         }
 
+        // Separate check for the soul gems.
+        else if (::Misc::StringUtils::ciEqualPrefix("misc_soulgem", ptr.getCellRef().getRefId()))
+        {
+            std::pair<int, std::string> canEquip = ptr.getClass().canBeEquipped(ptr, player);
+
+            if (canEquip.first == 0)
+            {
+                MWBase::Environment::get().getWindowManager()->messageBox(canEquip.second);
+                updateItemView();
+                return;
+            }
+        }
+
         // If the item has a script, set OnPCEquip or PCSkipEquip to 1
         if (!script.empty())
         {

apps/openmw/mwscript/containerextensions.cpp

@@ -304,11 +304,38 @@ namespace MWScript
 
                     MWWorld::InventoryStore& invStore = ptr.getClass().getInventoryStore (ptr);
                     MWWorld::ContainerStoreIterator it = invStore.begin();
-                    for (; it != invStore.end(); ++it)
+
+                    // With soul gems we prefer filled ones.
+
+                    if (::Misc::StringUtils::ciEqualPrefix("misc_soulgem", item))
                     {
-                        if (::Misc::StringUtils::ciEqual(it->getCellRef().getRefId(), item))
+                        it = invStore.end();
-                            break;
+
+                        for (auto it_any = invStore.begin(); it_any != invStore.end(); ++it_any)
+                        {
+                            if (::Misc::StringUtils::ciEqual(it_any->getCellRef().getRefId(), item))
+                            {
+                                if (!it_any->getCellRef().getSoul().empty() &&
+                                    MWBase::Environment::get().getWorld()->getStore().get<ESM::Creature>().search(it_any->getCellRef().getSoul()))
+                                {
+                                    it = it_any;
+                                    break;
+                                }
+                                else if (it == invStore.end())
+                                    it = it_any;
+                            }
+                        }
                     }
+
+                    else
+                    {
+                        for (; it != invStore.end(); ++it)
+                        {
+                            if (::Misc::StringUtils::ciEqual(it->getCellRef().getRefId(), item))
+                                break;
+                        }
+                    }
+
                     if (it == invStore.end())
                     {
                         MWWorld::ManualRef ref(MWBase::Environment::get().getWorld()->getStore(), item, 1);

components/misc/stringops.hpp

@@ -97,6 +97,34 @@ public:
         return ciEqual(x, std::string_view(y, n - 1));
     }
 
+    template <class X, class Y>
+    static bool ciEqualPrefix(const X& x, const Y& y)
+    {
+        return std::equal(std::begin(x), std::end(x), std::begin(y),
+                          [] (char l, char r) { return toLower(l) == toLower(r); });
+    }
+
+    template <std::size_t n>
+    static auto ciEqualPrefix(const char(& x)[n], const char(& y)[n])
+    {
+        static_assert(n > 0);
+        return ciEqualPrefix(std::string_view(x, n - 1), std::string_view(y, n - 1));
+    }
+
+    template <std::size_t n, class T>
+    static auto ciEqualPrefix(const char(& x)[n], const T& y)
+    {
+        static_assert(n > 0);
+        return ciEqualPrefix(std::string_view(x, n - 1), y);
+    }
+
+    template <std::size_t n, class T>
+    static auto ciEqualPrefix(const T& x, const char(& y)[n])
+    {
+        static_assert(n > 0);
+        return ciEqualPrefix(x, std::string_view(y, n - 1));
+    }
+
     static int ciCompareLen(std::string_view x, std::string_view y, std::size_t len)
     {
         std::string_view::const_iterator xit = x.begin();