[grilo] core: support transform GValue to key's GType

[Victor Toso <victortoso src gnome org>]

commit bbad302f7fa63ccc0d13ba307e6e986a8271c3ae
Author: Victor Toso <me victortoso com>
Date:   Mon Sep 3 12:07:30 2018 +0200

    core: support transform GValue to key's GType
    
    Although some conversions might imply losing precision, there is a
    major gain over situations like deserializing data.
    
    APIs that might be affected by this are the ones handling GValue as
    argument. In grl_related_keys_set() is where the code rely on checking
    the GType and failing if needed.
    
    Signed-off-by: Victor Toso <victortoso gnome org>

 src/data/grl-related-keys.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)
---
diff --git a/src/data/grl-related-keys.c b/src/data/grl-related-keys.c
index 50a8038..f086ce3 100644
--- a/src/data/grl-related-keys.c
+++ b/src/data/grl-related-keys.c
@@ -236,6 +236,7 @@ grl_related_keys_set (GrlRelatedKeys *relkeys,
 {
   GValue *copy = NULL;
   GrlRegistry *registry;
+  GType key_type, value_type;
 
   g_return_if_fail (GRL_IS_RELATED_KEYS (relkeys));
   g_return_if_fail (key);
@@ -244,17 +245,26 @@ grl_related_keys_set (GrlRelatedKeys *relkeys,
     return;
   }
 
-  /* Dup value */
-  if (G_VALUE_TYPE (value) != GRL_METADATA_KEY_GET_TYPE (key)) {
+  key_type = GRL_METADATA_KEY_GET_TYPE (key);
+  value_type = G_VALUE_TYPE (value);
+
+  if (!g_value_type_transformable (value_type, key_type)) {
     GRL_WARNING ("value has type %s, but expected %s",
-                 g_type_name (G_VALUE_TYPE (value)),
-                 g_type_name (GRL_METADATA_KEY_GET_TYPE (key)));
+                 g_type_name (value_type),
+                 g_type_name (key_type));
     return;
   }
 
+  /* Dup value */
   copy = g_new0 (GValue, 1);
-  g_value_init (copy, G_VALUE_TYPE (value));
-  g_value_copy (value, copy);
+  g_value_init (copy, key_type);
+  if (!g_value_transform (value, copy)) {
+    GRL_WARNING ("transforming value type %s to key's type %s failed",
+                 g_type_name (value_type),
+                 g_type_name (key_type));
+    g_free (copy);
+    return;
+  }
 
   registry = grl_registry_get_default ();