Remove backlinks when clearing list or set of Mixed containing links

CHANGELOG.md

@@ -8,6 +8,7 @@
 * Fixed an assertion failure when listening for changes to a list of primitive Mixed which contains links. ([#4767](https://github.com/realm/realm-core/issues/4767), since the beginning of Mixed v11.0.0)
 * Fixed an assertion failure when listening for changes to a dictionary or set which contains an invalidated link. ([#4770](https://github.com/realm/realm-core/pull/4770), since the beginning of v11)
 * Fixed an endless recursive loop that could cause a stack overflow when computing changes on a set of objects which contained cycles. ([#4770](https://github.com/realm/realm-core/pull/4770), since the beginning of v11)
+* Fixed a crash after clearing a list or set of Mixed containing links to objects ([#4774](https://github.com/realm/realm-core/issues/4774), since the beginning of v11)
 
 ### Breaking changes
 * None.

src/realm/list.cpp

@@ -351,6 +351,15 @@ void Lst<Mixed>::do_remove(size_t ndx)
     }
 }
 
+template <>
+void Lst<Mixed>::do_clear()
+{
+    size_t ndx = size();
+    while (ndx--) {
+        do_remove(ndx);
+    }
+}
+
 Obj LnkLst::create_and_insert_linked_object(size_t ndx)
 {
     Table& t = *get_target_table();

src/realm/list.hpp

@@ -197,6 +197,8 @@ template <>
 void Lst<Mixed>::do_insert(size_t, Mixed);
 template <>
 void Lst<Mixed>::do_remove(size_t);
+template <>
+void Lst<Mixed>::do_clear();
 extern template class Lst<Mixed>;
 
 // Specialization of Lst<ObjLink>:

src/realm/set.cpp

@@ -219,6 +219,15 @@ void Set<Mixed>::do_erase(size_t ndx)
     }
 }
 
+template <>
+void Set<Mixed>::do_clear()
+{
+    size_t ndx = size();
+    while (ndx--) {
+        do_erase(ndx);
+    }
+}
+
 void LnkSet::remove_target_row(size_t link_ndx)
 {
     // Deleting the object will automatically remove all links

src/realm/set.hpp

@@ -355,6 +355,8 @@ template <>
 void Set<Mixed>::do_insert(size_t, Mixed);
 template <>
 void Set<Mixed>::do_erase(size_t);
+template <>
+void Set<Mixed>::do_clear();
 
 /// Compare set elements.
 ///

test/test_typed_links.cpp

@@ -198,3 +198,28 @@ TEST(TypedLinks_Clear)
     person->clear();
     g.verify();
 }
+
+TEST(TypedLinks_CollectionClear)
+{
+    Group g;
+    auto dog = g.add_table("dog");
+    auto person = g.add_table("person");
+    auto col_list_mixed = person->add_column_list(type_Mixed, "mixed_list");
+    auto col_set_mixed = person->add_column_set(type_Mixed, "mixed_set");
+
+    auto pluto = dog->create_object();
+    auto paul = person->create_object();
+
+    auto list = paul.get_list<Mixed>(col_list_mixed);
+    auto set = paul.get_set<Mixed>(col_set_mixed);
+    list.add(pluto);
+    set.insert(pluto);
+    CHECK_EQUAL(pluto.get_backlink_count(), 2);
+    list.clear();
+    set.clear();
+    CHECK_EQUAL(pluto.get_backlink_count(), 0);
+
+    pluto.remove();
+
+    g.verify();
+}