Fix new flake8 errors (#7489)

This is a cherry-pick of 1a1da60ad2c9172fe487cd38a164b39df60f4cb5 (#7470)
to the release-v1.13.0 branch.

7 files changed, 19 insertions, 12 deletions

diff --git a/changelog.d/7470.misc b/changelog.d/7470.misc
new file mode 100644
index 0000000000..45e66ecf48
--- /dev/null
+++ b/changelog.d/7470.misc
@@ -0,0 +1 @@
+Fix linting errors in new version of Flake8.
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index 628292b890..dedff81af3 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -22,6 +22,7 @@ import sys
 import traceback
 
 from daemonize import Daemonize
+from typing_extensions import NoReturn
 
 from twisted.internet import defer, error, reactor
 from twisted.protocols.tls import TLSMemoryBIOFactory
@@ -139,9 +140,9 @@ def start_reactor(
             run()
 
 
-def quit_with_error(error_string):
+def quit_with_error(error_string: str) -> NoReturn:
     message_lines = error_string.split("\n")
-    line_length = max(len(l) for l in message_lines if len(l) < 80) + 2
+    line_length = max(len(line) for line in message_lines if len(line) < 80) + 2
     sys.stderr.write("*" * line_length + "\n")
     for line in message_lines:
         sys.stderr.write(" %s\n" % (line.rstrip(),))
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 6d88231843..ed28da3deb 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -522,7 +522,7 @@ class ServerConfig(Config):
         )
 
     def has_tls_listener(self) -> bool:
-        return any(l["tls"] for l in self.listeners)
+        return any(listener["tls"] for listener in self.listeners)
 
     def generate_config_section(
         self, server_name, data_dir_path, open_private_ports, listeners, **kwargs
diff --git a/synapse/notifier.py b/synapse/notifier.py
index 71d9ed62b0..87c120a59c 100644
--- a/synapse/notifier.py
+++ b/synapse/notifier.py
@@ -15,7 +15,7 @@
 
 import logging
 from collections import namedtuple
-from typing import Callable, List
+from typing import Callable, Iterable, List, TypeVar
 
 from prometheus_client import Counter
 
@@ -42,12 +42,14 @@ users_woken_by_stream_counter = Counter(
     "synapse_notifier_users_woken_by_stream", "", ["stream"]
 )
 
+T = TypeVar("T")
+
 
 # TODO(paul): Should be shared somewhere
-def count(func, l):
-    """Return the number of items in l for which func returns true."""
+def count(func: Callable[[T], bool], it: Iterable[T]) -> int:
+    """Return the number of items in it for which func returns true."""
     n = 0
-    for x in l:
+    for x in it:
         if func(x):
             n += 1
     return n
diff --git a/synapse/push/mailer.py b/synapse/push/mailer.py
index 73580c1c6c..ab33abbeed 100644
--- a/synapse/push/mailer.py
+++ b/synapse/push/mailer.py
@@ -19,6 +19,7 @@ import logging
 import time
 from email.mime.multipart import MIMEMultipart
 from email.mime.text import MIMEText
+from typing import Iterable, List, TypeVar
 
 from six.moves import urllib
 
@@ -41,6 +42,8 @@ from synapse.visibility import filter_events_for_client
 
 logger = logging.getLogger(__name__)
 
+T = TypeVar("T")
+
 
 MESSAGE_FROM_PERSON_IN_ROOM = (
     "You have a message on %(app)s from %(person)s in the %(room)s room..."
@@ -638,10 +641,10 @@ def safe_text(raw_text):
     )
 
 
-def deduped_ordered_list(l):
+def deduped_ordered_list(it: Iterable[T]) -> List[T]:
     seen = set()
     ret = []
-    for item in l:
+    for item in it:
         if item not in seen:
             seen.add(item)
             ret.append(item)
diff --git a/synapse/storage/database.py b/synapse/storage/database.py
index a7cd97b0b0..50f475bfd3 100644
--- a/synapse/storage/database.py
+++ b/synapse/storage/database.py
@@ -212,9 +212,9 @@ class LoggingTransaction:
     def executemany(self, sql: str, *args: Any):
         self._do_execute(self.txn.executemany, sql, *args)
 
-    def _make_sql_one_line(self, sql):
+    def _make_sql_one_line(self, sql: str) -> str:
         "Strip newlines out of SQL so that the loggers in the DB are on one line"
-        return " ".join(l.strip() for l in sql.splitlines() if l.strip())
+        return " ".join(line.strip() for line in sql.splitlines() if line.strip())
 
     def _do_execute(self, func, sql, *args):
         sql = self._make_sql_one_line(sql)
diff --git a/tests/config/test_load.py b/tests/config/test_load.py
index b3e557bd6a..734a9983e8 100644
--- a/tests/config/test_load.py
+++ b/tests/config/test_load.py
@@ -122,7 +122,7 @@ class ConfigLoadingTestCase(unittest.TestCase):
 
         with open(self.file, "r") as f:
             contents = f.readlines()
-        contents = [l for l in contents if needle not in l]
+        contents = [line for line in contents if needle not in line]
         with open(self.file, "w") as f:
             f.write("".join(contents))