Fix recursively dumping a group with a nonexistent subgroup. (#4582)

[SC-38499](https://app.shortcut.com/tiledb-inc/story/38499/recursively-dumping-a-group-fails-when-a-subgroup-does-not-exist)

---
TYPE: BUG
DESC: Fix recursively dumping a group with a nonexistent subgroup.

Author: teo-tsirpanis

test/src/unit-capi-group.cc

@@ -1490,6 +1490,54 @@ TEST_CASE_METHOD(
   remove_temp_dir(temp_dir);
 }
 
+TEST_CASE_METHOD(GroupFx, "C API: Group, dump", "[capi][group][dump]") {
+  // Create and open group in write mode
+  // TODO: refactor for each supported FS.
+  std::string temp_dir = fs_vec_[0]->temp_dir();
+  create_temp_dir(temp_dir);
+
+  tiledb::sm::URI group1_uri(temp_dir + "group1");
+  REQUIRE(tiledb_group_create(ctx_, group1_uri.c_str()) == TILEDB_OK);
+
+  tiledb::sm::URI group2_uri(temp_dir + "group2");
+  REQUIRE(tiledb_group_create(ctx_, group2_uri.c_str()) == TILEDB_OK);
+
+  tiledb_group_t* group1;
+  int rc = tiledb_group_alloc(ctx_, group1_uri.c_str(), &group1);
+  REQUIRE(rc == TILEDB_OK);
+  set_group_timestamp(group1, 1);
+  rc = tiledb_group_open(ctx_, group1, TILEDB_WRITE);
+  REQUIRE(rc == TILEDB_OK);
+
+  rc = tiledb_group_add_member(ctx_, group1, group2_uri.c_str(), 0, "group2");
+  REQUIRE(rc == TILEDB_OK);
+  rc = tiledb_group_close(ctx_, group1);
+  REQUIRE(rc == TILEDB_OK);
+
+  // Delete the subgroup to test that recursively dumping its parent will not
+  // fail.
+  rc = tiledb_object_remove(ctx_, group2_uri.c_str());
+  REQUIRE(rc == TILEDB_OK);
+
+  rc = tiledb_group_open(ctx_, group1, TILEDB_READ);
+  REQUIRE(rc == TILEDB_OK);
+
+  char* group_dump;
+  rc = tiledb_group_dump_str(ctx_, group1, &group_dump, 1);
+  REQUIRE(rc == TILEDB_OK);
+  REQUIRE(group_dump != nullptr);
+  REQUIRE(
+      std::string(group_dump) ==
+      "group1 GROUP\n|-- group2 GROUP (does not exist)\n");
+  free(group_dump);
+
+  rc = tiledb_group_close(ctx_, group1);
+  REQUIRE(rc == TILEDB_OK);
+
+  tiledb_group_free(&group1);
+  remove_temp_dir(temp_dir);
+}
+
 #ifdef TILEDB_SERIALIZATION
 TEST_CASE_METHOD(
     GroupFx,

tiledb/sm/group/group.cc

@@ -669,13 +669,27 @@ std::string Group::dump(
 
   for (const auto& member_entry : members()) {
     const auto& it = member_entry.second;
-    ss << "|" << indent << l_indent << " " << *it << std::endl;
+    URI member_uri = it->uri();
+    if (it->relative()) {
+      member_uri = group_uri_.join_path(it->uri().to_string());
+    }
+
+    ss << "|" << indent << l_indent << " " << *it;
+    bool do_recurse = false;
     if (it->type() == ObjectType::GROUP && recursive) {
-      URI member_uri = it->uri();
-      if (it->relative()) {
-        member_uri = group_uri_.join_path(it->uri().to_string());
+      // Before listing the group's members, check if the group exists in
+      // storage. If it does not, leave a message in the string.
+      ObjectType member_type = ObjectType::INVALID;
+      throw_if_not_ok(storage_manager_->object_type(member_uri, &member_type));
+      if (member_type == ObjectType::GROUP) {
+        do_recurse = true;
+      } else {
+        ss << " (does not exist)";
       }
+    }
+    ss << std::endl;
 
+    if (do_recurse) {
       Group group_rec(member_uri, storage_manager_);
       throw_if_not_ok(group_rec.open(QueryType::READ));
       ss << group_rec.dump(indent_size, num_indents + 2, recursive, false);