[FIX] purchase: purchases button on product variants

This rev. is related to 8381d47543

The action action_purchase_line_product_tree is used in both
product templates and product variants forms.
Therefore, the default_product_id: active_id in the context
cannot be used,
As sometimes it will active_id will be a product template,
sometimes it will be a product variant.

I believe two different window actions should be used,
instead of sharing a common one and making hacks.
Nevertheless, as we avoid taking risks in stable releases
This should be done in master.

addons/purchase/purchase.py

@@ -1444,6 +1444,13 @@ class product_product(osv.Model):
             for product_id in ids
         }
 
+    def action_view_purchases(self, cr, uid, ids, context=None):
+        if isinstance(ids, (int, long)):
+            ids = [ids]
+        result = self.pool['product.template']._get_act_window_dict(cr, uid, 'purchase.action_purchase_line_product_tree', context=context)
+        result['domain'] = "[('product_id','in',[" + ','.join(map(str, ids)) + "])]"
+        return result
+
     _columns = {
         'purchase_count': fields.function(_purchase_count, string='# Purchases', type='integer'),
     }

addons/purchase/purchase_view.xml

@@ -648,7 +648,7 @@
             <field name="groups_id" eval="[(4, ref('purchase.group_purchase_user'))]"/>
             <field name="arch" type="xml">
                 <xpath expr="//div[@name='buttons']" position="inside">
-                   <button class="oe_inline oe_stat_button" name="%(action_purchase_line_product_tree)d" type="action" 
+                   <button class="oe_inline oe_stat_button" name="action_view_purchases" type="object"
                        icon="fa-shopping-cart">
                        <field string="Purchases" name="purchase_count" widget="statinfo"/>
                    </button>