add check for wikipedia importance data

Adds a new check level WARNING because missing wikipedia importances
are not necessarily an error. If the database is run for reverse
requests only, then it is fine to go without them.

nominatim/tools/check_database.py

@@ -23,6 +23,7 @@ class CheckState(Enum):
     FAIL = 1
     FATAL = 2
     NOT_APPLICABLE = 3
+    WARN = 4
 
 def _check(hint=None):
     """ Decorator for checks. It adds the function to the list of
@@ -40,6 +41,11 @@ def _check(hint=None):
                 params = {}
             if ret == CheckState.OK:
                 print('\033[92mOK\033[0m')
+            elif ret == CheckState.WARN:
+                print('\033[93mWARNING\033[0m')
+                if hint:
+                    print('')
+                    print(dedent(hint.format(**params)))
             elif ret == CheckState.NOT_APPLICABLE:
                 print('not applicable')
             else:
@@ -180,6 +186,20 @@ def check_tokenizer(_, config):
     return CheckState.FAIL, dict(msg=result)
 
 
+@_check(hint="""\
+             Wikipedia/Wikidata importance tables missing.
+             Quality of search results may be degraded. Reverse geocoding is unaffected.
+             See https://nominatim.org/release-docs/latest/admin/Import/#wikipediawikidata-rankings
+             """)
+def check_existance_wikipedia(conn, _):
+    """ Checking for wikipedia/wikidata data
+    """
+    with conn.cursor() as cur:
+        cnt = cur.scalar('SELECT count(*) FROM wikipedia_article')
+
+        return CheckState.WARN if cnt == 0 else CheckState.OK
+
+
 @_check(hint="""\
              The indexing didn't finish. {count} entries are not yet indexed.