Fix implicit permission resolution for Thread

Fix #9153

discord/abc.py

@@ -755,6 +755,20 @@ class GuildChannel:
         category = self.guild.get_channel(self.category_id)
         return bool(category and category.overwrites == self.overwrites)
 
+    def _apply_implicit_permissions(self, base: Permissions) -> None:
+        # if you can't send a message in a channel then you can't have certain
+        # permissions as well
+        if not base.send_messages:
+            base.send_tts_messages = False
+            base.mention_everyone = False
+            base.embed_links = False
+            base.attach_files = False
+
+        # if you can't read a channel then you have no permissions there
+        if not base.read_messages:
+            denied = Permissions.all_channel()
+            base.value &= ~denied.value
+
     def permissions_for(self, obj: Union[Member, Role], /) -> Permissions:
         """Handles permission resolution for the :class:`~discord.Member`
         or :class:`~discord.Role`.
@@ -765,6 +779,7 @@ class GuildChannel:
         - Guild roles
         - Channel overrides
         - Member overrides
+        - Implicit permissions
         - Member timeout
 
         If a :class:`~discord.Role` is passed, then it checks the permissions
@@ -880,19 +895,6 @@ class GuildChannel:
                 base.handle_overwrite(allow=overwrite.allow, deny=overwrite.deny)
                 break
 
-        # if you can't send a message in a channel then you can't have certain
-        # permissions as well
-        if not base.send_messages:
-            base.send_tts_messages = False
-            base.mention_everyone = False
-            base.embed_links = False
-            base.attach_files = False
-
-        # if you can't read a channel then you have no permissions there
-        if not base.read_messages:
-            denied = Permissions.all_channel()
-            base.value &= ~denied.value
-
         if obj.is_timed_out():
             # Timeout leads to every permission except VIEW_CHANNEL and READ_MESSAGE_HISTORY
             # being explicitly denied

discord/channel.py

@@ -226,6 +226,7 @@ class TextChannel(discord.abc.Messageable, discord.abc.GuildChannel, Hashable):
     @utils.copy_doc(discord.abc.GuildChannel.permissions_for)
     def permissions_for(self, obj: Union[Member, Role], /) -> Permissions:
         base = super().permissions_for(obj)
+        self._apply_implicit_permissions(base)
 
         # text channels do not have voice related permissions
         denied = Permissions.voice()
@@ -947,6 +948,7 @@ class VocalGuildChannel(discord.abc.Connectable, discord.abc.GuildChannel, Hasha
     @utils.copy_doc(discord.abc.GuildChannel.permissions_for)
     def permissions_for(self, obj: Union[Member, Role], /) -> Permissions:
         base = super().permissions_for(obj)
+        self._apply_implicit_permissions(base)
 
         # voice channels cannot be edited by people who can't connect to them
         # It also implicitly denies all other voice perms
@@ -2151,6 +2153,7 @@ class ForumChannel(discord.abc.GuildChannel, Hashable):
     @utils.copy_doc(discord.abc.GuildChannel.permissions_for)
     def permissions_for(self, obj: Union[Member, Role], /) -> Permissions:
         base = super().permissions_for(obj)
+        self._apply_implicit_permissions(base)
 
         # text channels do not have voice related permissions
         denied = Permissions.voice()

discord/threads.py

@@ -31,10 +31,11 @@ import array
 import copy
 
 from .mixins import Hashable
-from .abc import Messageable, _purge_helper
+from .abc import Messageable, GuildChannel, _purge_helper
 from .enums import ChannelType, try_enum
 from .errors import ClientException, InvalidData
 from .flags import ChannelFlags
+from .permissions import Permissions
 from .utils import MISSING, parse_time, snowflake_time, _get_as_snowflake, _unique
 
 __all__ = (
@@ -58,7 +59,6 @@ if TYPE_CHECKING:
     from .message import Message, PartialMessage
     from .abc import Snowflake, SnowflakeTime
     from .role import Role
-    from .permissions import Permissions
     from .state import ConnectionState
 
 
@@ -411,10 +411,9 @@ class Thread(Messageable, Hashable):
         """Handles permission resolution for the :class:`~discord.Member`
         or :class:`~discord.Role`.
 
-        Since threads do not have their own permissions, they inherit them
-        from the parent channel. This is a convenience method for
-        calling :meth:`~discord.TextChannel.permissions_for` on the
-        parent channel.
+        Since threads do not have their own permissions, they mostly
+        inherit them from the parent channel with some implicit
+        permissions changed.
 
         Parameters
         ----------
@@ -437,7 +436,23 @@ class Thread(Messageable, Hashable):
         parent = self.parent
         if parent is None:
             raise ClientException('Parent channel not found')
-        return parent.permissions_for(obj)
+
+        base = GuildChannel.permissions_for(parent, obj)
+
+        # if you can't send a message in a channel then you can't have certain
+        # permissions as well
+        if not base.send_messages_in_threads:
+            base.send_tts_messages = False
+            base.mention_everyone = False
+            base.embed_links = False
+            base.attach_files = False
+
+        # if you can't read a channel then you have no permissions there
+        if not base.read_messages:
+            denied = Permissions.all_channel()
+            base.value &= ~denied.value
+
+        return base
 
     async def delete_messages(self, messages: Iterable[Snowflake], /, *, reason: Optional[str] = None) -> None:
         """|coro|