Adds information system check for PNG thumbnail existence

src/documents/__init__.py

@@ -1,5 +1,6 @@
 # this is here so that django finds the checks.
 from .checks import changed_password_check
 from .checks import parser_check
+from .checks import png_thumbnail_check
 
-__all__ = ["changed_password_check", "parser_check"]
+__all__ = ["changed_password_check", "parser_check", "png_thumbnail_check"]

src/documents/checks.py

@@ -1,7 +1,9 @@
 import textwrap
+from pathlib import Path
 
 from django.conf import settings
 from django.core.checks import Error
+from django.core.checks import Info
 from django.core.checks import register
 from django.core.exceptions import FieldError
 from django.db.utils import OperationalError
@@ -11,7 +13,6 @@ from documents.signals import document_consumer_declaration
 
 @register()
 def changed_password_check(app_configs, **kwargs):
-
     from documents.models import Document
     from paperless.db import GnuPG
 
@@ -67,3 +68,23 @@ def parser_check(app_configs, **kwargs):
         ]
     else:
         return []
+
+
+@register()
+def png_thumbnail_check(app_configs, **kwargs):
+    from documents.models import Document
+
+    try:
+        documents = Document.objects.all()
+        for document in documents:
+            existing_thumbnail = Path(document.thumbnail_path).resolve()
+            if existing_thumbnail.suffix == ".png":
+                return [
+                    Info(
+                        "PNG thumbnails found, consider running convert_thumbnails "
+                        "to convert to WebP",
+                    ),
+                ]
+        return []
+    except (OperationalError, ProgrammingError, FieldError):
+        return []  # No documents table yet