[tracker/wip/carlosg/unbound-vars: 1/3] libtracker-data: Allow looking up variables in context by name

[Carlos Garnacho <carlosg src gnome org>]

commit 97474303800141fbd4db71d91684474dc32cbba0
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sat Aug 29 14:25:10 2020 +0200

    libtracker-data: Allow looking up variables in context by name
    
    Getting a TrackerVariable first is a bit of an egg/chicken problem,
    since getting a TrackerVariable ensures it's referenced in the context
    in all code paths.
    
    Soften this a bit, and allow to look up variables by name, without
    necessarily creating a TrackerVariable for it.

 src/libtracker-data/tracker-sparql-types.c | 22 ++++++++++++++--------
 src/libtracker-data/tracker-sparql-types.h |  2 ++
 src/libtracker-data/tracker-sparql.c       | 10 +++++-----
 3 files changed, 21 insertions(+), 13 deletions(-)
---
diff --git a/src/libtracker-data/tracker-sparql-types.c b/src/libtracker-data/tracker-sparql-types.c
index a029a275e..a638620b2 100644
--- a/src/libtracker-data/tracker-sparql-types.c
+++ b/src/libtracker-data/tracker-sparql-types.c
@@ -653,8 +653,7 @@ tracker_context_class_init (TrackerContextClass *klass)
 static void
 tracker_context_init (TrackerContext *context)
 {
-       context->variable_set = g_hash_table_new (tracker_variable_hash,
-                                                 tracker_variable_equal);
+       context->variable_set = g_hash_table_new (g_str_hash, g_str_equal);
 }
 
 TrackerContext *
@@ -684,27 +683,34 @@ void
 tracker_context_add_variable_ref (TrackerContext  *context,
                                  TrackerVariable *variable)
 {
-       g_hash_table_add (context->variable_set, variable);
+       g_hash_table_insert (context->variable_set, variable->name, variable);
 }
 
 gboolean
 tracker_context_lookup_variable_ref (TrackerContext  *context,
                                      TrackerVariable *variable)
 {
-       return g_hash_table_lookup (context->variable_set, variable) != NULL;
+       return g_hash_table_lookup (context->variable_set, variable->name) != NULL;
+}
+
+gboolean
+tracker_context_lookup_variable_by_name (TrackerContext  *context,
+                                         const gchar     *name)
+{
+       return g_hash_table_lookup (context->variable_set, name) != NULL;
 }
 
 void
 tracker_context_propagate_variables (TrackerContext *context)
 {
        GHashTableIter iter;
-       gpointer key;
+       gpointer key, value;
 
        g_assert (context->parent != NULL);
        g_hash_table_iter_init (&iter, context->variable_set);
 
-       while (g_hash_table_iter_next (&iter, &key, NULL))
-               g_hash_table_add (context->parent->variable_set, key);
+       while (g_hash_table_iter_next (&iter, &key, &value))
+               g_hash_table_insert (context->parent->variable_set, key, value);
 }
 
 /* Select context */
@@ -985,7 +991,7 @@ tracker_triple_context_get_variable_binding_list (TrackerTripleContext *context,
                                 */
                                if (TRACKER_IS_SELECT_CONTEXT (current_context) &&
                                    tracker_context_get_parent (current_context) &&
-                                   g_hash_table_lookup (parent_context->variable_set, variable)) {
+                                   g_hash_table_lookup (parent_context->variable_set, variable->name)) {
                                        TrackerVariableBinding *sample;
                                        TrackerBinding *binding;
 
diff --git a/src/libtracker-data/tracker-sparql-types.h b/src/libtracker-data/tracker-sparql-types.h
index fc79798b7..8dc551234 100644
--- a/src/libtracker-data/tracker-sparql-types.h
+++ b/src/libtracker-data/tracker-sparql-types.h
@@ -346,6 +346,8 @@ void tracker_context_add_variable_ref    (TrackerContext  *context,
                                          TrackerVariable *variable);
 gboolean tracker_context_lookup_variable_ref (TrackerContext  *context,
                                               TrackerVariable *variable);
+gboolean tracker_context_lookup_variable_by_name (TrackerContext  *context,
+                                                  const gchar     *name);
 
 /* Select context */
 GType            tracker_select_context_get_type (void) G_GNUC_CONST;
diff --git a/src/libtracker-data/tracker-sparql.c b/src/libtracker-data/tracker-sparql.c
index 5a2795af9..91382f5db 100644
--- a/src/libtracker-data/tracker-sparql.c
+++ b/src/libtracker-data/tracker-sparql.c
@@ -5550,13 +5550,13 @@ intersect_var_set (GHashTable *ht1,
 {
        GHashTableIter iter;
        GList *intersection = NULL;
-       gpointer key;
+       gpointer key, value;
 
        g_hash_table_iter_init (&iter, ht1);
 
-       while (g_hash_table_iter_next (&iter, &key, NULL)) {
+       while (g_hash_table_iter_next (&iter, &key, &value)) {
                if (g_hash_table_contains (ht2, key))
-                       intersection = g_list_prepend (intersection, key);
+                       intersection = g_list_prepend (intersection, value);
        }
 
        return intersection;
@@ -5587,7 +5587,7 @@ translate_MinusGraphPattern (TrackerSparql  *sparql,
 
        intersection = intersect_var_set (cur_context->variable_set, context->variable_set);
 
-       vars = g_hash_table_get_keys (cur_context->variable_set);
+       vars = g_hash_table_get_values (cur_context->variable_set);
        cur = tracker_sparql_swap_builder (sparql, pre);
        append_subquery_select_vars (sparql, cur_context, vars);
        tracker_sparql_swap_builder (sparql, cur);
@@ -5654,7 +5654,7 @@ translate_GroupOrUnionGraphPattern (TrackerSparql  *sparql,
                }
        } while (_accept (sparql, RULE_TYPE_LITERAL, LITERAL_UNION));
 
-       vars = g_hash_table_get_keys (context->variable_set);
+       vars = g_hash_table_get_values (context->variable_set);
 
        if (placeholders->len > 1) {
                /* We are performing an union of multiple GroupGraphPattern,