Opt for simpler Literal[...] type

I would like to see a StrEnum but I am somewhat anxious of making that
change right now. I think we should get validation in place first and
then look at propagating better types into the application.

synapse/rest/client/account.py

@@ -19,6 +19,7 @@
 from urllib.parse import urlparse
 
 from pydantic import StrictBool, StrictStr, constr
+from typing_extensions import Literal
 
 from twisted.web.server import Request
 
@@ -46,7 +47,6 @@
     ClientSecretType,
     EmailRequestTokenBody,
     MsisdnRequestTokenBody,
-    ThreepidMedium,
 )
 from synapse.rest.models import RequestBodyModel
 from synapse.types import JsonDict
@@ -710,7 +710,7 @@ def __init__(self, hs: "HomeServer"):
     class PostBody(RequestBodyModel):
         address: StrictStr
         id_server: Optional[StrictStr] = None
-        medium: ThreepidMedium
+        medium: Literal["email", "msisdn"]
 
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
         """Unbind the given 3pid from a specific identity server, or identity servers that are
@@ -744,7 +744,7 @@ def __init__(self, hs: "HomeServer"):
     class PostBody(RequestBodyModel):
         address: StrictStr
         id_server: Optional[StrictStr] = None
-        medium: ThreepidMedium
+        medium: Literal["email", "msisdn"]
 
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
         if not self.hs.config.registration.enable_3pid_changes:

synapse/rest/client/models.py

@@ -11,7 +11,6 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from enum import Enum
 from typing import TYPE_CHECKING, Dict, Optional
 
 from pydantic import Extra, StrictInt, StrictStr, constr, validator
@@ -20,12 +19,6 @@
 from synapse.util.threepids import validate_email
 
 
-class ThreepidMedium(str, Enum):
-    # Per advice at https://pydantic-docs.helpmanual.io/usage/types/#enums-and-choices
-    email = "email"
-    msisdn = "msisdn"
-
-
 class AuthenticationData(RequestBodyModel):
     """
     Data used during user-interactive authentication.

tests/rest/client/test_models.py

@@ -14,13 +14,14 @@
 import unittest as stdlib_unittest
 
 from pydantic import BaseModel, ValidationError
+from typing_extensions import Literal
 
-from synapse.rest.client.models import EmailRequestTokenBody, ThreepidMedium
+from synapse.rest.client.models import EmailRequestTokenBody
 
 
 class ThreepidMediumEnumTestCase(stdlib_unittest.TestCase):
     class Model(BaseModel):
-        medium: ThreepidMedium
+        medium: Literal["email", "msisdn"]
 
     def test_accepts_valid_medium_string(self) -> None:
         """Sanity check that Pydantic behaves sensibly with an enum-of-str
@@ -29,18 +30,7 @@ def test_accepts_valid_medium_string(self) -> None:
         simultaneously.
         """
         model = self.Model.parse_obj({"medium": "email"})
-        self.assertIsInstance(model.medium, str)
         self.assertEqual(model.medium, "email")
-        self.assertEqual(model.medium, ThreepidMedium.email)
-        self.assertIs(model.medium, ThreepidMedium.email)
-
-        self.assertNotEqual(model.medium, "msisdn")
-        self.assertNotEqual(model.medium, ThreepidMedium.msisdn)
-        self.assertIsNot(model.medium, ThreepidMedium.msisdn)
-
-    def test_accepts_valid_medium_enum(self) -> None:
-        model = self.Model.parse_obj({"medium": ThreepidMedium.email})
-        self.assertIs(model.medium, ThreepidMedium.email)
 
     def test_rejects_invalid_medium_value(self) -> None:
         with self.assertRaises(ValidationError):