There is a model 

    class project_tag(models.Model):
    
        _name = 'project_tags.project_tag'
        _description = 'project_tag'
    
        name = fields.Char(string='Name', required=True, size=64)

Then there is project model

    class project(models.Model):
        _inherit = 'project.project'
    
        project_tag_ids = fields.Many2many(
            'project_tags.project_tag',
            'project_project_tag_ids_rel',
            'project_id',
            'project_tag_id',
            string='Tags')

And finally a model

    class ProjectTask(models.Model):
        """docstring"""
        _inherit = 'project.task'
    
        tag_ids = fields.Many2many(
            'project_tags.project_tag',
            'project_project_tag_ids_rel',
            'project_id',
            'project_tag_id',
            string='Tags',
            domain="[('project_id', 'in', project_id)]") .

The view for project task (model ProjectTask) contains field 

    <field name="tag_ids" widget="many2many_tags" options="{'no_create_edit': True}"/>

The user would like to see in tag_ids only those tags, that are configured for the project this task belongs to. For the given task's project there are no tags configured, so tag_ids should be empty but it's not :(.

Project tags (in this example it's empty).

I am hoping that domain would help. Unfortunately when tag_ids field definition is with domain    

    tag_ids = fields.Many2many(
            'project_tags.project_tag',
            'project_project_tag_ids_rel',
            'project_id',
            'project_tag_id',
            string='Tags',
            domain="[('project_id', 'in', project_id)]") .

the user sees an error

    ValueError: Invalid field u'project_id' in leaf "<osv.ExtendedLeaf: (u'project_id', u'=', 10) on project_tags_project_tag (ctx: )>"

When without a domain it shows all the tags 

    tag_ids = fields.Many2many(
        'project_tags.project_tag',
        'project_project_tag_ids_rel',
        'project_id',
        'project_tag_id',
        string='Tags') 

User expects to see only those tags that are assigned for the project.

The project manager can on the project window add tags to the project. The user that edits  or creates a task should be allowed to choose only those tags that are added for the project.

How can I modify code so that tag_ids shows only those tags that are for the project_id the task belongs to?