Toposhape/Part: element methods in ComplexGeoData and TopoShape

src/App/ComplexGeoData.cpp

@@ -637,6 +637,82 @@ unsigned int ComplexGeoData::getMemSize() const
     return 0;
 }
 
+void ComplexGeoData::traceElement(const MappedName &name, TraceCallback cb) const
+{
+    long tag = this->Tag, encodedTag = 0;
+    int len = 0;
+
+    auto pos = findTagInElementName(name,&encodedTag,&len,nullptr,nullptr,true);
+    if(cb(name, len, encodedTag, tag) || pos < 0)
+        return;
+
+    if (name.startsWith(externalTagPostfix(), len))
+        return;
+
+    std::set<long> tagSet;
+
+    std::vector<MappedName> names;
+    if (tag)
+        tagSet.insert(std::abs(tag));
+    if (encodedTag)
+        tagSet.insert(std::abs(encodedTag));
+    names.push_back(name);
+
+    tag = encodedTag;
+    MappedName tmp;
+    bool first = true;
+
+    // TODO: element tracing without object is inheriently unsafe, because of
+    // possible external linking object which means the element may be encoded
+    // using external string table. Looking up the wrong table may accidentally
+    // cause circular mapping, and is actually quite easy to reproduce. See
+    //
+    // https://github.com/realthunder/FreeCAD_assembly3/issues/968
+    //
+    // A random depth limit is set here to not waste time. 'tagSet' above is
+    // also used for early detection of 'recursive' mapping.
+
+    for (int i=0; i<50; ++i) {
+        if(!len || len>pos)
+            return;
+        if(first) {
+            first = false;
+            size_t offset = 0;
+            if(name.startsWith(elementMapPrefix()))
+                offset = elementMapPrefix().size();
+            tmp = MappedName(name, offset, len);
+        }else
+            tmp = MappedName(tmp, 0, len);
+        tmp = dehashElementName(tmp);
+        names.push_back(tmp);
+        encodedTag = 0;
+        pos = findTagInElementName(tmp,&encodedTag,&len,nullptr,nullptr,true);
+        if (pos >= 0 && tmp.startsWith(externalTagPostfix(), len))
+            break;
+
+        if (encodedTag && tag != std::abs(encodedTag)
+            && !tagSet.insert(std::abs(encodedTag)).second) {
+            if (FC_LOG_INSTANCE.isEnabled(FC_LOGLEVEL_LOG)) {
+                FC_WARN("circular element mapping");
+                if (FC_LOG_INSTANCE.isEnabled(FC_LOGLEVEL_TRACE)) {
+                    auto doc = App::GetApplication().getActiveDocument();
+                    if (doc) {
+                        auto obj = doc->getObjectByID(this->Tag);
+                        if (obj)
+                            FC_LOG("\t" << obj->getFullName() << obj->getFullName() << "." << getIndexedName(name));
+                    }
+                    for (auto &name : names)
+                        FC_ERR("\t" << name);
+                }
+            }
+            break;
+        }
+
+        if(cb(tmp, len, encodedTag, tag) || pos < 0)
+            return;
+        tag = encodedTag;
+    }
+}
 
 void ComplexGeoData::setMappedChildElements(const std::vector<Data::ElementMap::MappedChildElements> & children)
 {