From 107e8b3d23a933b8cdc1f14045d7d42742be53a9 Mon Sep 17 00:00:00 2001
From: Matt Davis <matteius@gmail.com>
Date: Mon, 25 Sep 2017 09:36:31 -0400
Subject: [PATCH] Make `DEFAULT_PAGINATION_CLASS` `None` by default.  (#5170)

* Changes to the paginator defaults and settings

Require a default paginator be specified when using the page size
setting.
https://github.com/encode/django-rest-framework/issues/5168

* DRF-5168 import warnings

missed this in last commit

* Add a system checks file

Add a check for pagination settings for the 3.7 upgrade cycle.

* more compatible import approach

* missing bactic

* revised language and approach to import the system check

Adds a rest framework app config.

* Adjust doc wording
---
 docs/api-guide/pagination.md |  6 +++---
 rest_framework/__init__.py   |  2 ++
 rest_framework/apps.py       | 10 ++++++++++
 rest_framework/checks.py     | 18 ++++++++++++++++++
 rest_framework/settings.py   |  2 +-
 5 files changed, 34 insertions(+), 4 deletions(-)
 create mode 100644 rest_framework/apps.py
 create mode 100644 rest_framework/checks.py

diff --git a/docs/api-guide/pagination.md b/docs/api-guide/pagination.md
index 496886473..7b5e5b3f6 100644
--- a/docs/api-guide/pagination.md
+++ b/docs/api-guide/pagination.md
@@ -21,14 +21,14 @@ Pagination can be turned off by setting the pagination class to `None`.
 
 ## Setting the pagination style
 
-The default pagination style may be set globally, using the `DEFAULT_PAGINATION_CLASS` and `PAGE_SIZE` setting keys. For example, to use the built-in limit/offset pagination, you would do something like this:
+The pagination style may be set globally, using the `DEFAULT_PAGINATION_CLASS` and `PAGE_SIZE` setting keys. For example, to use the built-in limit/offset pagination, you would do something like this:
 
     REST_FRAMEWORK = {
         'DEFAULT_PAGINATION_CLASS': 'rest_framework.pagination.LimitOffsetPagination',
         'PAGE_SIZE': 100
     }
 
-Note that you need to set both the pagination class, and the page size that should be used.
+Note that you need to set both the pagination class, and the page size that should be used.  Both `DEFAULT_PAGINATION_CLASS` and `PAGE_SIZE` are `None` by default.
 
 You can also set the pagination class on an individual view by using the `pagination_class` attribute. Typically you'll want to use the same pagination style throughout your API, although you might want to vary individual aspects of the pagination, such as default or maximum page size, on a per-view basis.
 
@@ -85,7 +85,7 @@ This pagination style accepts a single number page number in the request query p
 
 #### Setup
 
-To enable the `PageNumberPagination` style globally, use the following configuration, modifying the `PAGE_SIZE` as desired:
+To enable the `PageNumberPagination` style globally, use the following configuration, and set the `PAGE_SIZE` as desired:
 
     REST_FRAMEWORK = {
         'DEFAULT_PAGINATION_CLASS': 'rest_framework.pagination.PageNumberPagination',
diff --git a/rest_framework/__init__.py b/rest_framework/__init__.py
index 9da9989e9..ae130a4d4 100644
--- a/rest_framework/__init__.py
+++ b/rest_framework/__init__.py
@@ -21,3 +21,5 @@ HTTP_HEADER_ENCODING = 'iso-8859-1'
 
 # Default datetime input and output formats
 ISO_8601 = 'iso-8601'
+
+default_app_config = 'rest_framework.apps.RestFrameworkConfig'
diff --git a/rest_framework/apps.py b/rest_framework/apps.py
new file mode 100644
index 000000000..f6013eb7e
--- /dev/null
+++ b/rest_framework/apps.py
@@ -0,0 +1,10 @@
+from django.apps import AppConfig
+
+
+class RestFrameworkConfig(AppConfig):
+    name = 'rest_framework'
+    verbose_name = "Django REST framework"
+
+    def ready(self):
+        # Add System checks
+        from .checks import pagination_system_check  # NOQA
diff --git a/rest_framework/checks.py b/rest_framework/checks.py
new file mode 100644
index 000000000..af6634d1e
--- /dev/null
+++ b/rest_framework/checks.py
@@ -0,0 +1,18 @@
+from django.core.checks import Tags, Warning, register
+
+
+@register(Tags.compatibility)
+def pagination_system_check(app_configs, **kwargs):
+    errors = []
+    # Use of default page size setting requires a default Paginator class
+    from rest_framework.settings import api_settings
+    if api_settings.PAGE_SIZE and not api_settings.DEFAULT_PAGINATION_CLASS:
+        errors.append(
+            Warning(
+                "You have specified a default PAGE_SIZE pagination rest_framework setting,"
+                "without specifying also a DEFAULT_PAGINATION_CLASS.",
+                hint="The default for DEFAULT_PAGINATION_CLASS is None. "
+                     "In previous versions this was PageNumberPagination",
+            )
+        )
+    return errors
diff --git a/rest_framework/settings.py b/rest_framework/settings.py
index bc42c38a6..86b577219 100644
--- a/rest_framework/settings.py
+++ b/rest_framework/settings.py
@@ -51,7 +51,7 @@ DEFAULTS = {
     'DEFAULT_VERSIONING_CLASS': None,
 
     # Generic view behavior
-    'DEFAULT_PAGINATION_CLASS': 'rest_framework.pagination.PageNumberPagination',
+    'DEFAULT_PAGINATION_CLASS': None,
     'DEFAULT_FILTER_BACKENDS': (),
 
     # Throttling