Bump mypy from 1.8.0 to 1.9.0 (#17297)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

changelog.d/17297.misc

@@ -0,0 +1 @@
+Bump `mypy` from 1.8.0 to 1.9.0.

tests/push/test_email.py

@@ -205,8 +205,24 @@ def test_unsubscribe(self, use_post: bool) -> None:
 
         # Multipart: plain text, base 64 encoded; html, base 64 encoded
         multipart_msg = email.message_from_bytes(msg)
-        txt = multipart_msg.get_payload()[0].get_payload(decode=True).decode()
-        html = multipart_msg.get_payload()[1].get_payload(decode=True).decode()
+
+        # Extract the text (non-HTML) portion of the multipart Message,
+        # as a Message.
+        txt_message = multipart_msg.get_payload(i=0)
+        assert isinstance(txt_message, email.message.Message)
+
+        # Extract the actual bytes from the Message object, and decode them to a `str`.
+        txt_bytes = txt_message.get_payload(decode=True)
+        assert isinstance(txt_bytes, bytes)
+        txt = txt_bytes.decode()
+
+        # Do the same for the HTML portion of the multipart Message.
+        html_message = multipart_msg.get_payload(i=1)
+        assert isinstance(html_message, email.message.Message)
+        html_bytes = html_message.get_payload(decode=True)
+        assert isinstance(html_bytes, bytes)
+        html = html_bytes.decode()
+
         self.assertIn("/_synapse/client/unsubscribe", txt)
         self.assertIn("/_synapse/client/unsubscribe", html)
 
@@ -347,12 +363,17 @@ def test_room_notifications_include_avatar(self) -> None:
         # That email should contain the room's avatar
         msg: bytes = args[5]
         # Multipart: plain text, base 64 encoded; html, base 64 encoded
-        html = (
-            email.message_from_bytes(msg)
-            .get_payload()[1]
-            .get_payload(decode=True)
-            .decode()
-        )
+
+        # Extract the html Message object from the Multipart Message.
+        # We need the asserts to convince mypy that this is OK.
+        html_message = email.message_from_bytes(msg).get_payload(i=1)
+        assert isinstance(html_message, email.message.Message)
+
+        # Extract the `bytes` from the html Message object, and decode to a `str`.
+        html = html_message.get_payload(decode=True)
+        assert isinstance(html, bytes)
+        html = html.decode()
+
         self.assertIn("_matrix/media/v1/thumbnail/DUMMY_MEDIA_ID", html)
 
     def test_empty_room(self) -> None:

tests/rest/client/test_account.py

@@ -427,13 +427,23 @@ def _get_link_from_email(self) -> str:
         text = None
         for part in mail.walk():
             if part.get_content_type() == "text/plain":
-                text = part.get_payload(decode=True).decode("UTF-8")
+                text = part.get_payload(decode=True)
+                if text is not None:
+                    # According to the logic table in `get_payload`, we know that
+                    # the result of `get_payload` will be `bytes`, but mypy doesn't
+                    # know this and complains. Thus, we assert the type.
+                    assert isinstance(text, bytes)
+                    text = text.decode("UTF-8")
+
                 break
 
         if not text:
             self.fail("Could not find text portion of email to parse")
 
-        assert text is not None
+        # `text` must be a `str`, after being decoded and determined just above
+        # to not be `None` or an empty `str`.
+        assert isinstance(text, str)
+
         match = re.search(r"https://example.com\S+", text)
         assert match, "Could not find link in email"
 
@@ -1209,13 +1219,23 @@ def _get_link_from_email(self) -> str:
         text = None
         for part in mail.walk():
             if part.get_content_type() == "text/plain":
-                text = part.get_payload(decode=True).decode("UTF-8")
+                text = part.get_payload(decode=True)
+                if text is not None:
+                    # According to the logic table in `get_payload`, we know that
+                    # the result of `get_payload` will be `bytes`, but mypy doesn't
+                    # know this and complains. Thus, we assert the type.
+                    assert isinstance(text, bytes)
+                    text = text.decode("UTF-8")
+
                 break
 
         if not text:
             self.fail("Could not find text portion of email to parse")
 
-        assert text is not None
+        # `text` must be a `str`, after being decoded and determined just above
+        # to not be `None` or an empty `str`.
+        assert isinstance(text, str)
+
         match = re.search(r"https://example.com\S+", text)
         assert match, "Could not find link in email"