Check admin classes not in admin.py

This is because registering an admin class implies a call to
models.get_apps() which attempts to import *every* models.py in
the project.

Whilst your project should probably not have significant
inter-app dependencies, importing every possible models.py does
not help the situation and can cause ImportError when models are
loaded in different scenarios.

Signed-off-by: Chris Lamb <lamby@debian.org>

DjangoLint/AstCheckers/__init__.py

@@ -20,11 +20,13 @@
 
 def register(linter):
     from size import SizeChecker
+    from admin import AdminChecker
     from settings import SettingsChecker
     from model_fields import ModelFieldsChecker
     from model_methods import ModelMethodsChecker
 
     linter.register_checker(SizeChecker(linter))
+    linter.register_checker(AdminChecker(linter))
     linter.register_checker(SettingsChecker(linter))
     linter.register_checker(ModelFieldsChecker(linter))
     linter.register_checker(ModelMethodsChecker(linter))

DjangoLint/AstCheckers/admin.py

@@ -0,0 +1,57 @@
+# -*- coding: utf-8 -*-
+
+# django-lint -- Static analysis tool for Django projects and applications
+# Copyright (C) 2008-2009 Chris Lamb <chris@chris-lamb.co.uk>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+from pylint.interfaces import IASTNGChecker
+from pylint.checkers import BaseChecker
+
+from .utils import nodeisinstance
+
+class AdminChecker(BaseChecker):
+    __implements__ = IASTNGChecker
+
+    name = 'django_admin'
+    msgs = {
+        'W8020': (
+            'Admin class %r not in admin.py',
+            'loldongs',),
+    }
+
+    ADMIN_BASE_CLASSES = (
+        'django.contrib.admin.options.ModelAdmin',
+    )
+
+    def visit_module(self, node):
+        self.module = node
+
+    def leave_class(self, node):
+        if not nodeisinstance(node, self.ADMIN_BASE_CLASSES):
+            return
+
+        if not self.module.file.endswith('admin.py'):
+            # Admin classes not in an app's admin.py can cause circular import
+            # problems throughout a project.
+            #
+            # This is because registering an admin class implies a call to
+            # models.get_apps() which attempts to import *every* models.py in
+            # the project.
+            #
+            # Whilst your project should probably not have significant
+            # inter-app dependencies, importing every possible models.py does
+            # not help the situation and can cause ImportError when models are
+            # loaded in different scenarios.
+            self.add_message('W8020', node=node, args=(node.name,))

django_lint_example/example/models/__init__.py

@@ -1,4 +1,5 @@
 from django.db import models
+from django.contrib import admin
 
 class NullableModel(models.Model):
     TRUTH_VALUE = True
@@ -165,3 +166,9 @@ class WeirdPrimaryKeyModel(models.Model):
 class ManyToManyModel(models.Model):
     nullable = models.ManyToManyField(Model2, null=True)
     blank = models.ManyToManyField(Model3, blank=True)
+
+class AdminKlass(admin.ModelAdmin):
+    search_fields = ('nullable',)
+
+    class Meta:
+        model = ManyToManyModel