pip show displays License metadata field - switch to License-Expression?

[befeleme]

What's the problem this feature will solve?

With PEP 639 accepted, there is a new metadata field to get the license information from: License-Expression.

pip show currently shows the License field contents:

pip/src/pip/_internal/commands/show.py

Line 163 in 947917b

license=metadata.get("License", ""),

Describe the solution you'd like

I think should add the display of License-Expression field and in the long run maybe switch to it entirely. Initially there will be a few packages produced with the new metadata, but in the long run only the License-Expression will remain.
Hence, I'd propose to try to obtain the license information from License-Expression - standardized and validated and fall back to the deprecated unstructured License in case License-Expression isn't found.

Alternative Solutions

What else is possible:

• do nothing - the deprecated License will be less used in time
• switch to License-Expression entirely - for majority of existing packages this would mean producing an empty field for months/years to come
• add License-Expression as a separate field displayed with the package data - this feels redundant, but if that's deemed a better approach, I'm not against.

Additional context

Once agreed upon solution, I can send a patch.

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[pfmoore]

I agree, in principle. I would suggest we only show License-Expression if metadata version is 2.4 or greater. So the logic should be:

1. If metadata version >= 2.4 and License-Expression is present: Display License-Expression.
2. Otherwise, display License.