[tracker/wip/carlosg/handle-recursive-resources: 2/2] libtracker-sparql: Handle correctly backreferences in TrackerResource tree

[Carlos Garnacho <carlosg src gnome org>]

commit 72337af163ef0582961ef94b493fb365778cc472
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sun Mar 31 15:11:18 2019 +0200

    libtracker-sparql: Handle correctly backreferences in TrackerResource tree
    
    We do keep a notion of already visited TrackerResources when generating the
    output. However that could go wrong if the TrackerResource references itself
    or a "parent" TrackerResource.
    
    Add the resources to the done list beforehand, so they are ensured not to be
    visited again if such backreferences exist.
    
    Related: https://gitlab.gnome.org/GNOME/tracker-miners/issues/60

 src/libtracker-sparql/tracker-resource.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)
---
diff --git a/src/libtracker-sparql/tracker-resource.c b/src/libtracker-sparql/tracker-resource.c
index 33fc65416..a5d006270 100644
--- a/src/libtracker-sparql/tracker-resource.c
+++ b/src/libtracker-sparql/tracker-resource.c
@@ -1025,11 +1025,9 @@ generate_nested_turtle_resource (TrackerResource    *resource,
                return;
 
        if (g_list_find_custom (data->done_list, resource, (GCompareFunc) tracker_resource_compare) == NULL) {
+               data->done_list = g_list_prepend (data->done_list, resource);
                generate_turtle (resource, data);
-
                g_string_append (data->string, "\n");
-
-               data->done_list = g_list_prepend (data->done_list, resource);
        }
 }
 
@@ -1260,7 +1258,7 @@ tracker_resource_print_turtle (TrackerResource         *self,
        context.all_namespaces = namespaces;
        context.our_namespaces = tracker_namespace_manager_new ();
        context.string = g_string_new ("");
-       context.done_list = NULL;
+       context.done_list = g_list_prepend (NULL, self);
 
        maybe_intern_prefix_of_compact_uri (context.all_namespaces, context.our_namespaces, 
tracker_resource_get_identifier(self));
 
@@ -1300,8 +1298,8 @@ generate_sparql_relation_deletes_foreach (gpointer key,
                TrackerResource *relation = g_value_get_object (value);
 
                if (g_list_find_custom (data->done_list, relation, (GCompareFunc) tracker_resource_compare) 
== NULL) {
-                       generate_sparql_deletes (relation, data);
                        data->done_list = g_list_prepend (data->done_list, relation);
+                       generate_sparql_deletes (relation, data);
                }
        }
 }
@@ -1323,8 +1321,8 @@ generate_sparql_relation_inserts_foreach (gpointer key,
                        return;
 
                if (g_list_find_custom (data->done_list, relation, (GCompareFunc) tracker_resource_compare) 
== NULL) {
-                       generate_sparql_insert_pattern (relation, data);
                        data->done_list = g_list_prepend (data->done_list, relation);
+                       generate_sparql_insert_pattern (relation, data);
                }
        } else if (G_VALUE_HOLDS (value, G_TYPE_PTR_ARRAY)) {
                GPtrArray *array = g_value_get_boxed (value);
@@ -1349,8 +1347,8 @@ generate_sparql_relation_inserts_foreach (gpointer key,
                                                (GCompareFunc) tracker_resource_compare) != NULL)
                                continue;
 
-                       generate_sparql_insert_pattern (relation, data);
                        data->done_list = g_list_prepend (data->done_list, relation);
+                       generate_sparql_insert_pattern (relation, data);
                }
        }
 }
@@ -1507,7 +1505,7 @@ tracker_resource_print_sparql_update (TrackerResource         *resource,
        /* Resources can be recursive, and may have repeated or even cyclic
         * relationships. This list keeps track of what we already processed.
         */
-       context.done_list = NULL;
+       context.done_list = g_list_prepend (NULL, resource);
 
        /* Delete the existing data. If we don't do this, we may get constraint
         * violations due to trying to add a second value to a single-valued
@@ -1516,7 +1514,7 @@ tracker_resource_print_sparql_update (TrackerResource         *resource,
        generate_sparql_deletes (resource, &context);
 
        g_list_free (context.done_list);
-       context.done_list = NULL;
+       context.done_list = g_list_prepend (NULL, resource);
 
        /* Finally insert the data */
        g_string_append (context.string, "INSERT DATA {\n");
@@ -1577,13 +1575,12 @@ generate_jsonld_value (const GValue       *value,
                resource = TRACKER_RESOURCE (g_value_get_object (value));
 
                if (g_list_find_custom (data->done_list, resource, (GCompareFunc) tracker_resource_compare) 
== NULL) {
+                       data->done_list = g_list_prepend (data->done_list, resource);
                        json_builder_begin_object (data->builder);
 
                        tracker_resource_generate_jsonld (resource, data);
 
                        json_builder_end_object (data->builder);
-
-                       data->done_list = g_list_prepend (data->done_list, resource);
                } else {
                        json_builder_add_string_value (data->builder, 
tracker_resource_get_identifier(resource));
                }
@@ -1680,7 +1677,7 @@ tracker_resource_print_jsonld (TrackerResource         *self,
        context.all_namespaces = namespaces;
        context.our_namespaces = tracker_namespace_manager_new ();
        context.builder = json_builder_new ();
-       context.done_list = NULL;
+       context.done_list = g_list_prepend (NULL, self);
 
        maybe_intern_prefix_of_compact_uri (context.all_namespaces, context.our_namespaces, 
tracker_resource_get_identifier (self));