Fix #25145: Crash relating to StaffTypeChange

src/engraving/dom/measure.cpp

@@ -1395,6 +1395,9 @@ bool Measure::acceptDrop(EditData& data) const
             viewer->setDropRectangle(canvasBoundingRect());
             return true;
         case ActionIconType::STAFF_TYPE_CHANGE:
+            if (!canAddStaffTypeChange(staffIdx)) {
+                return false;
+            }
             viewer->setDropRectangle(staffRect);
             return true;
         case ActionIconType::SYSTEM_LOCK:
@@ -1736,6 +1739,9 @@ EngravingItem* Measure::drop(EditData& data)
             score()->insertMeasure(ElementType::MEASURE, this);
             break;
         case ActionIconType::STAFF_TYPE_CHANGE: {
+            if (!canAddStaffTypeChange(staffIdx)) {
+                return nullptr;
+            }
             EngravingItem* stc = Factory::createStaffTypeChange(this);
             stc->setParent(this);
             stc->setTrack(staffIdx * VOICES);
@@ -3475,6 +3481,21 @@ bool Measure::canAddStringTunings(staff_idx_t staffIdx) const
     return !alreadyHasStringTunings;
 }
 
+bool Measure::canAddStaffTypeChange(staff_idx_t staffIdx) const
+{
+    for (const EngravingObject* child : el()) {
+        if (!child || !child->isStaffTypeChange()) {
+            continue;
+        }
+        const StaffTypeChange* stc = toStaffTypeChange(child);
+        if (stc->staffIdx() == staffIdx) {
+            // Staff already has a StaffTypeChange at this measure...
+            return false;
+        }
+    }
+    return true;
+}
+
 Fraction Measure::maxTicks() const
 {
     Segment* s = first();

src/engraving/dom/measure.h

@@ -355,6 +355,7 @@ class Measure final : public MeasureBase
     void respaceSegments();
 
     bool canAddStringTunings(staff_idx_t staffIdx) const;
+    bool canAddStaffTypeChange(staff_idx_t staffIdx) const;
 
 private:
 

src/engraving/rw/read400/tread.cpp

@@ -3638,7 +3638,12 @@ void TRead::read(Spacer* s, XmlReader& e, ReadContext& ctx)
 
 void TRead::read(StaffType* t, XmlReader& e, ReadContext&)
 {
-    t->setGroup(TConv::fromXml(e.asciiAttribute("group"), StaffGroup::STANDARD));
+    const AsciiStringView group = e.asciiAttribute("group");
+    IF_ASSERT_FAILED(!group.empty()) {
+        return;
+    }
+
+    t->setGroup(TConv::fromXml(group, StaffGroup::STANDARD));
 
     if (t->group() == StaffGroup::TAB) {
         t->setGenKeysig(false);

src/engraving/rw/read410/tread.cpp

@@ -4107,7 +4107,12 @@ void TRead::read(Spacer* s, XmlReader& e, ReadContext& ctx)
 
 void TRead::read(StaffType* t, XmlReader& e, ReadContext&)
 {
-    t->setGroup(TConv::fromXml(e.asciiAttribute("group"), StaffGroup::STANDARD));
+    const AsciiStringView group = e.asciiAttribute("group");
+    IF_ASSERT_FAILED(!group.empty()) {
+        return;
+    }
+
+    t->setGroup(TConv::fromXml(group, StaffGroup::STANDARD));
 
     if (t->group() == StaffGroup::TAB) {
         t->setGenKeysig(false);

src/notation/internal/notationinteraction.cpp

@@ -2516,9 +2516,13 @@ bool NotationInteraction::dragMeasureAnchorElement(const PointF& pos)
         RectF measureRect = targetMeasure->staffPageBoundingRect(staffIdx);
         measureRect.adjust(page->x(), page->y(), page->x(), page->y());
         m_dropData.ed.pos = measureRect.center();
-        setAnchorLines({ LineF(pos, measureRect.topLeft()) });
 
-        return targetMeasure->acceptDrop(m_dropData.ed);
+        const bool dropAccepted = targetMeasure->acceptDrop(m_dropData.ed);
+        if (dropAccepted) {
+            setAnchorLines({ LineF(pos, measureRect.topLeft()) });
+        }
+
+        return dropAccepted;
     }
     dropElem->score()->addRefresh(dropElem->canvasBoundingRect());
     setDropTarget(nullptr);