For some legacy plugins, mostly those based on https://github.com/singer-io/singer-python, users may start getting an installation error on Python 3.12+:

setuptools.errors.InvalidConfigError: Invalid dash-separated key 'description-file' in 'metadata' (setup.cfg), please use the underscore name 'description_file' instead.

This is caused by a breaking change introduced by setuptools 78:

• Disallow deprecated dash-separated and uppercase options in setup.cfg pypa/setuptools#4870
• [BUG] Version 78.0.1 breaks install of ansible-vault package pypa/setuptools#4910

In the meantime, the easiest workaround for this is

1. create a constraints file

   # build_constraints.txt
   setuptools<78
   

2. configure Meltano to use the uv build backend if you haven't already

   meltano config meltano set venv.backend uv
   

3. set this env var in your shell, or add it to your project's .env

   UV_BUILD_CONSTRAINT=build_constraints.txt