Standards-first detections sequence

[Philipp A.]

You should search for the specified build tool first and fall back to legacy stuff then:

1. Parse PEP 621 static metadata
2. If no PEP 621 metadata exists, read pyproject.toml’s build-system.build-backend (PEP 517) and parse tool specific metadata
3. If no standard metadata exists at all, fall back to setup.py or requirements.txt