Switch user permissions to use an enum

Previously, there wasn't any defined list of which permissions were
valid or not. You basically had to look through each model's __acl__
method to see what the possibilities were.

Using an enum will be less convenient when adding new permissions or
changing existing ones (since it will require a database migration), but
it makes it much easier to see what the valid options are, and will
prevent invalid permissions from being set up in the database.

tildes/alembic/versions/28d7ce2c4825_use_enum_for_user_permissions.py

@@ -0,0 +1,49 @@
+"""Use enum for user permissions
+
+Revision ID: 28d7ce2c4825
+Revises: 82e9801eb2d6
+Create Date: 2020-08-05 20:32:51.047215
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = "28d7ce2c4825"
+down_revision = "82e9801eb2d6"
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.execute(
+        """
+        create type userpermission as enum(
+            'comment.remove',
+            'comment.view_labels',
+            'topic.edit_by_generic_user',
+            'topic.edit_link',
+            'topic.edit_title',
+            'topic.lock',
+            'topic.move',
+            'topic.post',
+            'topic.remove',
+            'topic.tag',
+            'user.ban',
+            'user.view_removed_posts',
+            'wiki.edit'
+        )
+        """
+    )
+    op.execute(
+        """
+        alter table user_permissions
+        alter column permission type userpermission using permission::userpermission
+        """
+    )
+
+
+def downgrade():
+    op.execute("alter table user_permissions alter column permission type text")
+    op.execute("drop type userpermission")

tildes/tildes/enums.py

@@ -290,6 +290,28 @@ class HTMLSanitizationContext(enum.Enum):
     USER_BIO = enum.auto()
 
 
+# Enum for the possible user permissions
+# (Using functional API for this one because the values aren't valid Python names)
+UserPermission = enum.Enum(
+    "UserPermission",
+    [
+        "comment.remove",
+        "comment.view_labels",
+        "topic.edit_by_generic_user",
+        "topic.edit_link",
+        "topic.edit_title",
+        "topic.lock",
+        "topic.move",
+        "topic.post",
+        "topic.remove",
+        "topic.tag",
+        "user.ban",
+        "user.view_removed_posts",
+        "wiki.edit",
+    ],
+)
+
+
 class UserPermissionType(enum.Enum):
     """Enum for the types of user permissions."""
 

tildes/tildes/models/user/user_permissions.py

@@ -3,11 +3,11 @@
 
 """Contains the UserPermissions class."""
 
-from sqlalchemy import Column, ForeignKey, Integer, Text
+from sqlalchemy import Column, ForeignKey, Integer
 from sqlalchemy.dialects.postgresql import ENUM
 from sqlalchemy.orm import relationship
 
-from tildes.enums import UserPermissionType
+from tildes.enums import UserPermission, UserPermissionType
 from tildes.models import DatabaseModel
 from tildes.models.group import Group
 from tildes.models.user import User
@@ -21,7 +21,7 @@ class UserPermissions(DatabaseModel):
     permission_id: int = Column(Integer, primary_key=True)
     user_id: int = Column(Integer, ForeignKey("users.user_id"), nullable=False)
     group_id: int = Column(Integer, ForeignKey("groups.group_id"), nullable=True)
-    permission: str = Column(Text, nullable=False)
+    permission: UserPermission = Column(ENUM(UserPermission), nullable=False)
     permission_type: UserPermissionType = Column(
         ENUM(UserPermissionType), nullable=False, server_default="ALLOW"
     )
@@ -50,6 +50,6 @@ class UserPermissions(DatabaseModel):
         if self.permission_type == UserPermissionType.DENY:
             principal += "!"
 
-        principal += self.permission
+        principal += str(self.permission.name)
 
         return principal