From 721c95ba0b67eb46422dcf05a4274960e49c8894 Mon Sep 17 00:00:00 2001
From: Carles Pina i Estany <carles@pina.cat>
Date: Sun, 8 Nov 2020 14:57:51 +0000
Subject: [PATCH] Fixed #32180 -- Added system check for file system caches
 absolute location.

---
 django/core/checks/caches.py         | 16 ++++++++++++++++
 docs/ref/checks.txt                  |  2 ++
 tests/check_framework/test_caches.py | 27 +++++++++++++++++++++++++++
 3 files changed, 45 insertions(+)

diff --git a/django/core/checks/caches.py b/django/core/checks/caches.py
index 6fdecf5a1e..4baa23aeb6 100644
--- a/django/core/checks/caches.py
+++ b/django/core/checks/caches.py
@@ -53,3 +53,19 @@ def check_cache_location_not_exposed(app_configs, **kwargs):
                 id='caches.W002',
             ))
     return errors
+
+
+@register(Tags.caches)
+def check_file_based_cache_is_absolute(app_configs, **kwargs):
+    errors = []
+    for alias, config in settings.CACHES.items():
+        cache = caches[alias]
+        if not isinstance(cache, FileBasedCache):
+            continue
+        if not pathlib.Path(config['LOCATION']).is_absolute():
+            errors.append(Warning(
+                f"Your '{alias}' cache LOCATION path is relative. Use an "
+                f"absolute path instead.",
+                id='caches.W003',
+            ))
+    return errors
diff --git a/docs/ref/checks.txt b/docs/ref/checks.txt
index 0ff6d36a25..b7f941ff83 100644
--- a/docs/ref/checks.txt
+++ b/docs/ref/checks.txt
@@ -142,6 +142,8 @@ configured:
   lead to corruption of your data because its
   :setting:`LOCATION <CACHES-LOCATION>` matches/is inside/contains
   :setting:`MEDIA_ROOT`/:setting:`STATIC_ROOT`/:setting:`STATICFILES_DIRS`.
+* **caches.W003**: Your ``<cache>`` cache :setting:`LOCATION <CACHES-LOCATION>`
+  is relative. Use an absolute path instead.
 
 Database
 --------
diff --git a/tests/check_framework/test_caches.py b/tests/check_framework/test_caches.py
index 002528d1f5..a3ddfd64e7 100644
--- a/tests/check_framework/test_caches.py
+++ b/tests/check_framework/test_caches.py
@@ -3,6 +3,7 @@ import pathlib
 from django.core.checks import Warning
 from django.core.checks.caches import (
     E001, check_cache_location_not_exposed, check_default_cache_is_configured,
+    check_file_based_cache_is_absolute,
 )
 from django.test import SimpleTestCase
 from django.test.utils import override_settings
@@ -89,3 +90,29 @@ class CheckCacheLocationTest(SimpleTestCase):
             settings = self.get_settings(setting, root / 'cache', root / 'other')
             with self.subTest(setting=setting), self.settings(**settings):
                 self.assertEqual(check_cache_location_not_exposed(None), [])
+
+
+class CheckCacheAbsolutePath(SimpleTestCase):
+    def test_absolute_path(self):
+        with self.settings(CACHES={
+            'default': {
+                'BACKEND': 'django.core.cache.backends.filebased.FileBasedCache',
+                'LOCATION': pathlib.Path.cwd() / 'cache',
+            },
+        }):
+            self.assertEqual(check_file_based_cache_is_absolute(None), [])
+
+    def test_relative_path(self):
+        with self.settings(CACHES={
+            'default': {
+                'BACKEND': 'django.core.cache.backends.filebased.FileBasedCache',
+                'LOCATION': 'cache',
+            },
+        }):
+            self.assertEqual(check_file_based_cache_is_absolute(None), [
+                Warning(
+                    "Your 'default' cache LOCATION path is relative. Use an "
+                    "absolute path instead.",
+                    id='caches.W003',
+                ),
+            ])