Give visible error to user when there are no rights.

Currently bot does not give user-visible output when
user is not logged in or user does not have permissions.
Instead of silently failing inform user of a problem.

Bug: T345342
Change-Id: I3b7135a0e6ea6fb5c6280f611610b5c60376bbb2
---
M pywikibot/data/sparql.py
M tests/sparql_tests.py
2 files changed, 66 insertions(+), 6 deletions(-)

diff --git a/pywikibot/data/sparql.py b/pywikibot/data/sparql.py
index 23ffb1d..3417e32 100644
--- a/pywikibot/data/sparql.py
+++ b/pywikibot/data/sparql.py
@@ -4,7 +4,6 @@
 #
 # Distributed under the terms of the MIT license.
 #
-from contextlib import suppress
 from typing import Optional
 from urllib.parse import quote
 
@@ -14,7 +13,7 @@
 from pywikibot.backports import Dict, List, removeprefix
 from pywikibot.comms import http
 from pywikibot.data import WaitingMixin
-from pywikibot.exceptions import Error
+from pywikibot.exceptions import Error, NoUsernameError
 
 
 try:
@@ -144,17 +143,36 @@
         if headers is None:
             headers = DEFAULT_HEADERS
 
+        # force cleared
+        self.last_response = None
+
         url = f'{self.endpoint}?query={quote(query)}'
         while True:
             try:
                 self.last_response = http.fetch(url, headers=headers)
+                break
             except Timeout:
                 self.wait()
-                continue
 
-            with suppress(JSONDecodeError):
-                return self.last_response.json()
-            break
+        try:
+            return self.last_response.json()
+        except JSONDecodeError:
+            # There is no proper error given but server returns HTML page
+            # in case login isn't valid sotry to guess what the problem is
+            # and notify user instead of silently ignoring it.
+            # This could be made more reliable by fixing the backend.
+            # Note: only raise error when response starts with HTML,
+            # not in case the response otherwise might have it in between
+            strcontent = self.last_response.content.decode()
+            if (strcontent.startswith('<!DOCTYPE html>')
+               and 'https://commons-query.wikimedia.org' in url):
+                if ('Special:UserLogin' in strcontent
+                   or 'Special:OAuth' in strcontent):
+                    message = ('You need to log in to Wikimedia Commons '
+                               'and give OAUTH permission. '
+                               'Open https://commons-query.wikimedia.org '
+                               'with browser to login and give permission.')
+                    raise NoUsernameError('User not logged in. ' + message)
 
         return None
 
diff --git a/tests/sparql_tests.py b/tests/sparql_tests.py
index 706da60..a14f4f0 100755
--- a/tests/sparql_tests.py
+++ b/tests/sparql_tests.py
@@ -14,6 +14,7 @@
 import pywikibot.data.sparql as sparql
 from tests.aspects import TestCase, WikidataTestCase
 from tests.utils import skipping
+from pywikibot.exceptions import NoUsernameError
 
 
 # See: https://www.w3.org/TR/2013/REC-sparql11-results-json-20130321/
@@ -181,6 +182,33 @@
         self.assertFalse(res)
 
 
+class TestCommonsQueryService(TestCase):
+    """Test Commons Query Service auth."""
+
+    family = 'commons'
+    code = 'commons'
+
+    def testLoginAndOauthPermisson(self):
+        """Commons Query Service Login and Oauth permission."""
+        # Define the SPARQL query
+        query = 'SELECT ?a ?b WHERE { ?a wdt:P9478 ?b } LIMIT 4'
+
+        # Set up the SPARQL endpoint and entity URL
+        # Note: https://commons-query.wikimedia.org
+        # requires user to be logged in
+
+        entity_url = 'https://commons.wikimedia.org/entity/'
+        endpoint = 'https://commons-query.wikimedia.org/sparql'
+
+        # Create a SparqlQuery object
+        query_object = sparql.SparqlQuery(endpoint=endpoint,
+                                          entity_url=entity_url)
+
+        # Execute the SPARQL query and retrieve the data user not logged in
+        with self.assertRaisesRegex(NoUsernameError, 'User not logged in'):
+            query_object.select(query, full_data=False)
+
+
 class Shared:
     """Shared test placeholder."""
 

