Fix crash when removing dictionary key (#7569)

Author: danieltabacaru

CHANGELOG.md

@@ -12,6 +12,7 @@
 * App::all_users() included logged out users only if they were logged out while the App instance existed. It now always includes all logged out users. ([PR #7300](https://github.com/realm/realm-core/pull/7300)).
 * Deleting the active user left the active user unset rather than selecting another logged-in user as the active user like logging out and removing users did. ([PR #7300](https://github.com/realm/realm-core/pull/7300)).
 * Fix compilation errors when using command-line `swift build` ([#7587](https://github.com/realm/realm-core/pull/7587), since v14.5.1).
+* Fixed crash when integrating removal of already removed dictionary key ([#7488](https://github.com/realm/realm-core/issues/7488), since v10.0.0).
 
 ### Breaking changes
 * The following things have been renamed or moved as part of moving all of the App Services functionality to the app namespace:

src/realm/sync/instruction_applier.cpp

@@ -489,7 +489,7 @@ void InstructionApplier::operator()(const Instruction::Update& instr)
                     }
                 },
                 [&](const Instruction::Payload::Erased&) {
-                    dict.erase(key);
+                    dict.try_erase(key);
                 },
                 [&](const Instruction::Payload::ObjectValue&) {
                     dict.create_and_insert_linked_object(key);

test/test_transform.cpp

@@ -1487,7 +1487,6 @@ TEST(Transform_ArrayInsert_EraseObject)
     client_2.get()->integrate_next_changeset_from(*server);
 }
 
-
 TEST(Transform_ArrayClearVsArrayClear_TimestampBased)
 {
     auto changeset_dump_dir_gen = get_changeset_dump_dir_generator(test_context);
@@ -2081,7 +2080,9 @@ TEST(Transform_Dictionary)
             auto& tr = *c.group;
             auto table = tr.add_table_with_primary_key("class_Table", type_Int, "id");
             table->add_column_dictionary(type_Mixed, "dict");
-            table->create_object_with_primary_key(0);
+            auto obj0 = table->create_object_with_primary_key(0);
+            auto dict = obj0.get_dictionary("dict");
+            dict.insert("key", 42);
             table->create_object_with_primary_key(1);
         });
 
@@ -2096,6 +2097,7 @@ TEST(Transform_Dictionary)
             auto dict0 = obj0.get_dictionary("dict");
             auto dict1 = obj1.get_dictionary("dict");
 
+            dict0.erase("key");
             dict0.insert("a", 123);
             dict0.insert("b", "Hello");
             dict0.insert("c", 45.0);
@@ -2112,6 +2114,7 @@ TEST(Transform_Dictionary)
             auto dict0 = obj0.get_dictionary("dict");
             auto dict1 = obj1.get_dictionary("dict");
 
+            dict0.erase("key");
             dict0.insert("b", "Hello, World!");
             dict0.insert("d", true);
 
@@ -2200,6 +2203,48 @@ TEST(Transform_Set)
     });
 }
 
+TEST(Transform_SetEraseVsSetErase)
+{
+    auto changeset_dump_dir_gen = get_changeset_dump_dir_generator(test_context);
+    auto server = Peer::create_server(test_context, changeset_dump_dir_gen.get());
+    auto client_1 = Peer::create_client(test_context, 2, changeset_dump_dir_gen.get());
+    auto client_2 = Peer::create_client(test_context, 3, changeset_dump_dir_gen.get());
+
+    // Baseline: insert one element in the set ('set' property)
+    client_1->create_schema([](WriteTransaction& tr) {
+        auto t = tr.get_group().add_table_with_primary_key("class_A", type_Int, "pk");
+        t->add_column_set(type_Int, "set");
+        auto obj = t->create_object_with_primary_key(1);
+        auto ss = obj.get_set<Int>("set");
+        ss.insert(42);
+    });
+
+    synchronize(server.get(), {client_1.get(), client_2.get()});
+
+    // Client 1 removes the element from the set
+    client_1->transaction([](Peer& p) {
+        auto ss = p.table("class_A")->begin()->get_set<Int>("set");
+        ss.erase(42);
+    });
+
+    // Client 2 removes the element from the set
+    client_2->transaction([](Peer& p) {
+        auto ss = p.table("class_A")->begin()->get_set<Int>("set");
+        ss.erase(42);
+    });
+
+    synchronize(server.get(), {client_1.get(), client_2.get()});
+
+    // Result: the set is empty
+    ReadTransaction read_server(server->shared_group);
+    ReadTransaction read_client_1(client_1->shared_group);
+    ReadTransaction read_client_2(client_2->shared_group);
+    CHECK(compare_groups(read_server, read_client_1));
+    CHECK(compare_groups(read_server, read_client_2, *test_context.logger));
+    auto table = read_server.get_table("class_A");
+    CHECK(table->begin()->get_set<Int>("set").is_empty());
+}
+
 TEST(Transform_ArrayEraseVsArrayErase)
 {
     // This test case recreates the problem that the above test exposes