Add system check for libjpeg / zlib

wagtail/wagtailimages/apps.py

@@ -1,5 +1,7 @@
 from django.apps import AppConfig
 
+from . import checks
+
 
 class WagtailImagesAppConfig(AppConfig):
     name = 'wagtail.wagtailimages'

wagtail/wagtailimages/checks.py

@@ -0,0 +1,58 @@
+import os
+
+from django.core.checks import register, Warning
+
+from willow.image import Image
+
+
+def has_jpeg_support():
+    wagtail_jpg = os.path.join(os.path.dirname(__file__), 'check_files', 'wagtail.jpg')
+    is_ok = True
+    f = open(wagtail_jpg, 'rb')
+
+    try:
+        Image.open(f)
+    except (IOError, Image.LoaderError):
+        is_ok = False
+    finally:
+        f.close()
+
+    return is_ok
+
+
+def has_png_support():
+    wagtail_png = os.path.join(os.path.dirname(__file__), 'check_files', 'wagtail.png')
+    is_ok = True
+    f = open(wagtail_png, 'rb')
+
+    try:
+        Image.open(f)
+    except (IOError, Image.LoaderError):
+        is_ok = False
+    finally:
+        f.close()
+
+    return is_ok
+
+
+@register()
+def image_library_check(app_configs, **kwargs):
+    errors = []
+
+    if not has_jpeg_support():
+        errors.append(
+            Warning(
+                'JPEG image support is not available',
+                hint="Check that the 'libjpeg' library is installed, then reinstall Pillow."
+            )
+        )
+
+    if not has_png_support():
+        errors.append(
+            Warning(
+                'PNG image support is not available',
+                hint="Check that the 'zlib' library is installed, then reinstall Pillow."
+            )
+        )
+
+    return errors