Add error message for missing TLD

src/backend/InvenTree/InvenTree/settings.py

@@ -28,6 +28,7 @@
 from InvenTree.config import get_boolean_setting, get_oidc_private_key, get_setting
 from InvenTree.ready import isInMainThread, isRunningBackup
 from InvenTree.sentry import default_sentry_dsn, init_sentry
+from InvenTree.validators import invalid_site_url_hint
 from InvenTree.version import checkMinPythonVersion, inventreeCommitHash
 from users.oauth2_scopes import oauth2_scopes
 
@@ -771,7 +772,7 @@
         validator = URLValidator()
         validator(SITE_URL)
     except Exception:
-        msg = f"Invalid SITE_URL value: '{SITE_URL}'. InvenTree server cannot start."
+        msg = f"Invalid SITE_URL value: '{SITE_URL}'. InvenTree server cannot start.{invalid_site_url_hint(SITE_URL)}"
         logger.error(msg)
         print(msg)
         sys.exit(-1)

src/backend/InvenTree/InvenTree/validators.py

@@ -1,6 +1,8 @@
 """Custom field validators for InvenTree."""
 
+import ipaddress
 import tokenize
+from urllib.parse import urlsplit
 
 from django.conf import settings
 from django.core import validators
@@ -88,6 +90,39 @@ def __call__(self, value):
         super().__call__(value)
 
 
+def invalid_site_url_hint(site_url: str) -> str:
+    """Return an extra hint for *why* a SITE_URL value failed validation.
+
+    Django's URLValidator rejects any hostname that isn't 'localhost', an IP
+    address, or a fully qualified (dotted) name - so a bare LAN hostname like
+    'warehouse' fails with no indication of what's actually wrong. Returns an
+    empty string when nothing more specific than "invalid URL" applies.
+    """
+    hostname = urlsplit(site_url).hostname
+
+    if hostname is None and '//' not in site_url:
+        # No scheme was given at all, e.g. SITE_URL=warehouse
+        hostname = urlsplit(f'//{site_url}').hostname
+
+    if not hostname or hostname == 'localhost':
+        return ''
+
+    try:
+        ipaddress.ip_address(hostname)
+        return ''
+    except ValueError:
+        pass
+
+    if '.' not in hostname:
+        return (
+            f" '{hostname}' has no top-level domain. InvenTree requires a fully "
+            "qualified hostname (e.g. 'warehouse.local'), an IP address, or "
+            "'localhost' - a bare hostname is rejected by Django's URL validator."
+        )
+
+    return ''
+
+
 def validate_purchase_order_reference(value):
     """Validate the 'reference' field of a PurchaseOrder."""
     from order.models import PurchaseOrder