PEP 639, Round 3: Improving license clarity with better package metadata

I agree with that… That is a very strong requirement to be tackled by build tools.

Build tools already have the restriction that is not trivial to add dependencies, and every dependency added comes with a cost. Unless there is support for parsing and validating licenses in a library that is already used and vendored commonly in build tools (yes that would be packaging), I disagree with enforcing any form of validation/normalisation/processing of license expressions in build time.