/createRoom API behaviour does not match spec

[t3chguy]

Background information

• Dendrite version or git SHA: docker main
• SQLite3 or Postgres?: sqlite3
• Running in Docker?: yes
• go version: docker main
• Client used (if applicable): matrix-js-sdk

Description

• What is the problem: /createRoom API uses join_rule=invite if preset is unspecified even if visibility is specified
• Who is affected: Unclear
• How is this bug manifesting: Creating rooms unlike the intent of the creator
• When did this first appear: Unclear

#3123 (comment) for more context

The spec does say to use visibility if preset is unspecified.

If unspecified, the server should use the visibility to determine which preset to use. A visibility of public equates to a preset of public_chat and private visibility equates to a preset of private_chat.

https://spec.matrix.org/v1.13/client-server-api/#post_matrixclientv3createroom

Steps to reproduce

• call /createRoom API with visibility=public
• receive a room via /sync which has join_rule=invite instead of join_rule=public