pyrsistent "transitive dep" is problematic

[gdt]

Background

As discussed in the Synapse Package Maintainers room,

pyproject.toml declares synapse's dependencies. In addition to what synapse actually depends on there are "transitive dependencies". These are a least-bad approach for avoiding user problems (and bug reports!) because A that Synapse depends on is a version which is good enough, except that it depends on B, and the B installed was good enough for what A said at release, except that it actually isn't good enough for correct behavior. Synapse therefore adds a dependency on new-enough B. This is all merely background.

Description

One of the "transitive dependencies" is pyrsistent, said to be for jsonschema. However, jsonschema dropped pyrsistent as a dependency in 4.18.0, summer of 2023. People who are up to date then won't need pyrsistent. But Synapse only requires jsonschema > 3, and people with ancient jsonschema might have problems.

My suggestion is to require jsonschema >= 4.18.0, and drop the pyrsistent transitive dependency. (I realize that wades into the supporting LTS question, but I don't understand wanting new synapse and old everything else.)

Steps to reproduce

Read the source code and then go read lots of other repo history.

Homeserver

reading.the.code

Synapse Version

1.148.0

Installation Method

Other (please mention below)

Database

none

Workers

I don't know

Platform

Discovered during packaging by code reading.

Configuration

No response

Relevant log output

N/A

Anything else that would be useful to know?

No response