Overridden model managers shouldn't appear in _meta.managers

[Tim Graham]

The following models from the Django test suite validate on Django 1.9.x but result in this error on Django 1.10:

CustomArticle.on_site: (sites.E001) CurrentSiteManager could not find a field named 'sites'.

from django.contrib.sites.managers import CurrentSiteManager
from django.contrib.sites.models import Site
from django.db import models


class AbstractArticle(models.Model):
    on_site = CurrentSiteManager()

    class Meta:
        abstract = True


class CustomArticle(AbstractArticle):
    site_for_article = models.ForeignKey(Site, models.CASCADE)
    on_site = CurrentSiteManager('site_for_article')

Bisected to 3a47d42fa33012b2156bf04058d933df6b3082d2. CustomArticle._meta.managers shows both CurrentSiteManager instances and the one from the abstract model raises the error.

[Loic Bistuer]

I'm not sure I get it. The CustomArticle doesn't seem to have a site field, so why shouldn't the warning be raised?

[Adam Johnson]

Perhaps the real mistake is running check() for the shadowed CurrentSiteManager from the abstract model? It's not accessible from the concrete model once it's been shadowed right?

[Loic Bistuer]

OK got it, I missed the site_for_article part. I've got a fix in mind.

[Loic Bistuer]

PR ​https://github.com/django/django/pull/7115.

[GitHub <noreply@…>]

In d4eefc7e:

Fixed #27073 -- Removed duplicated managers in Model._meta.managers.

[Loïc Bistuer <loic.bistuer@…>]

In 21f18e53:

[1.10.x] Fixed #27073 -- Removed duplicated managers in Model._meta.managers.

Backport of d4eefc7e2af0d93283ed1c03e0af0a482982b6f0 from master