ext_encryption_disabler_patch_power_levels incompatibilities with Rooms v12

[Mauricio-Bernuy]

Describe the bug

Having matrix_synapse_ext_encryption_disabler_patch_power_levels set to true with the latest matrix spec updates for Rooms v12 causes an error while creating direct message rooms with other users in the homeserver.

Users attempting to start a direct message with another local user of the homeserver results in the following error displayed at the client level:

POST /_matrix/client/v3/createRoom response using DevTools returns the following error message:

{
    "errcode": "M_UNKNOWN",
    "error": "Creator user @current_user:matrix.example.com must not appear in content.users"
}

To Reproduce Ran just update and ensured having the latest build of synapse installed.

This behavior presents itself when enabling the encryption disabler plugin in conjunction with the power level patcher mechanism. Disabling the patch_power_levels setting by itself fixes the issue completely.

# Doesn't seem to affect createRoom behavior
matrix_synapse_ext_encryption_disabler_enabled: true

# Causes createRoom to fail
matrix_synapse_ext_encryption_disabler_patch_power_levels: true

Expected behavior Private rooms should be created as expected.

Matrix Server:

• OS: [Debian 11]
• Architecture [amd64]

Additional context This issue might be explained by the following new behavior stated in the documentation:

[spantaleev]

Sounds like the default setup (power-level-patching being disabled) still works OK, which is good!

This issue should probably also be raised (and hopefully fixed) here: https://github.com/digitalentity/matrix_encryption_disabler