[FIX] ir_qweb: issue if multiple IRA are created for a bundle

If multiple transactions start knowing that they should generate the
bundle, each one will run lessc and create a ir.attachment record
referencing the path on the filestore. While the file is not duplicated
on the filestore (as it is stored according to its hash), the final
result of `t-call-assets` will source multiple time the same file.

This patch fixes this issue by adapting get_attachment to group its
results by file name and only select the one with the max id (latest
generated).

We also remove the `inc` argument as it is not used.

openerp/addons/base/ir/ir_qweb.py

@@ -1250,10 +1250,24 @@ class AssetsBundle(object):
         ]
         return ira.sudo().search(domain).unlink()
 
-    def get_attachments(self, type, inc=None):
-        ira = self.env['ir.attachment']
-        domain = [('url', '=like', '/web/content/%%-%s/%s%s.%s' % (self.version, self.xmlid, ('%%' if inc is None else '.%s' % inc), type))]
-        return ira.sudo().search(domain, order='name asc')
+    def get_attachments(self, type):
+        """ Return the ir.attachment records for a given bundle. This method takes care of mitigating
+        an issue happening when parallel transactions generate the same bundle: while the file is not
+        duplicated on the filestore (as it is stored according to its hash), there are multiple
+        ir.attachment records referencing the same version of a bundle. As we don't want to source
+        multiple time the same bundle in our `to_html` function, we group our ir.attachment records
+        by file name and only return the one with the max id for each group.
+        """
+        url_pattern = '/web/content/%-{0}/{1}{2}.{3}'.format(self.version, self.xmlid, '.%' if type == 'css' else '', type)
+        self.env.cr.execute("""
+             SELECT max(id)
+               FROM ir_attachment
+              WHERE url like %s
+           GROUP BY datas_fname
+           ORDER BY datas_fname
+         """, [url_pattern])
+        attachment_ids = [r[0] for r in self.env.cr.fetchall()]
+        return self.env['ir.attachment'].sudo().browse(attachment_ids)
 
     def save_attachment(self, type, content, inc=None):
         ira = self.env['ir.attachment']

openerp/addons/test_assetsbundle/tests/test_assetsbundle.py

@@ -276,6 +276,24 @@ class TestJavascriptAssetsBundle(TransactionCase):
         self.assertTrue(stylesheets[1].url.endswith('.1.css'))
         self.assertTrue(stylesheets[2].url.endswith('.2.css'))
 
+    def test_14_duplicated_css_assets(self):
+        """ Checks that if the bundle's ir.attachment record is duplicated, the bundle is only sourced once. This could
+        happen if multiple transactions try to render the bundle simultaneously.
+        """
+        bundle0 = AssetsBundle(self.cssbundle_xmlid, env=self.env)
+        bundle0.css()
+        self.assertEquals(len(self._any_ira_for_bundle('css')), 1)
+
+        # duplicate the asset bundle
+        ira0 = self.registry['ir.attachment'].browse(self.cr, self.uid, self._any_ira_for_bundle('css')[0])
+        ira1 = ira0.copy()
+        self.assertEquals(len(self._any_ira_for_bundle('css')), 2)
+        self.assertEquals(ira0.store_fname, ira1.store_fname)
+
+        # the ir.attachment records should be deduplicated in the bundle's content
+        content = bundle0.to_html()
+        self.assertEqual(content.count('test_assetsbundle.bundle2.0.css'), 1)
+
 
 class TestAssetsBundleInBrowser(HttpCase):
     def test_01_js_interpretation(self):