fix compute _url variable of workflow data uploads (#17233)

tests/test_formdata.py

@@ -1,3 +1,4 @@
+import collections
 import pytest
 import sys
 import shutil
@@ -481,3 +482,19 @@ def test_private_history(pub, local_user):
 
     local_user.roles = [role.id]
     assert formdef.is_user_allowed_read_status_and_history(local_user, formdata=formdata) is True
+
+def test_workflow_data_file_url(pub):
+    upload = Upload('test.txt', 'text/plain', 'ascii')
+    upload.receive(['first line', 'second line'])
+
+    formdata = formdef.data_class()()
+    formdata.store()
+    # create workflow_data as ordered dict to be sure _url comes last, to
+    # trigger #17233.
+    formdata.workflow_data = collections.OrderedDict(
+       foo_var_file='test.txt',
+       foo_var_file_raw=upload,
+       foo_var_file_url=None,
+    )
+    substvars = formdata.get_substitution_variables()
+    assert substvars['foo_var_file_url']

wcs/formdata.py

@@ -649,6 +649,8 @@ class FormData(StorableObject):
                 if k[0] == '_':
                     continue
                 d[k] = v
+            # recompute _url variable of attached files
+            for k, v in self.workflow_data.items():
                 if isinstance(v, Upload):
                     try:
                         formvar, fieldvar = re.match('(.*)_var_(.*)_raw$', k).groups()