[FIX] project, issue: change user_id + date_start

project.task: use an onchange to update date_start when changing user_id.
Indeed date_start is automatically updated in the create / write. Without
the onchange, this may lead to errors related to date_start being greater
then date_end.

project.issue: code in create and write now takes into account date_open
values given to the method and avoid erasing them.
In issue however the onchange is not added. Indeed the date_open and
date_closed fields are not visible in the view. They are automatically
computed and used to compute statistics.

addons/project/project_view.xml

@@ -396,6 +396,7 @@
                             <field name="project_id" domain="[('state','not in', ('close', 'cancelled'))]" on_change="onchange_project(project_id)" context="{'default_use_tasks':1}"/>
                             <field name="user_id"
                                 options='{"no_open": True}'
+                                on_change="onchange_user_id(user_id, context)"
                                 context="{'default_groups_ref': ['base.group_user', 'base.group_partner_manager', 'project.group_project_user']}"/>
                             <field name="reviewer_id"
                                 options='{"no_open": True}'

addons/project_issue/project_issue.py

@@ -303,7 +303,7 @@ def create(self, cr, uid, vals, context=None):
         context = dict(context or {})
         if vals.get('project_id') and not context.get('default_project_id'):
             context['default_project_id'] = vals.get('project_id')
-        if vals.get('user_id'):
+        if vals.get('user_id') and not vals.get('date_open'):
             vals['date_open'] = fields.datetime.now()
         if 'stage_id' in vals:
             vals.update(self.onchange_stage_id(cr, uid, None, vals.get('stage_id'), context=context)['value'])
@@ -319,8 +319,8 @@ def write(self, cr, uid, ids, vals, context=None):
             vals['date_last_stage_update'] = fields.datetime.now()
             if 'kanban_state' not in vals:
                 vals['kanban_state'] = 'normal'
-        # user_id change: update date_start
-        if vals.get('user_id'):
+        # user_id change: update date_open
+        if vals.get('user_id') and 'date_open' not in vals:
             vals['date_open'] = fields.datetime.now()
 
         return super(project_issue, self).write(cr, uid, ids, vals, context)