Better error message on license check

[DougBurke]

After today's Hackage update, I get

% cabal upload dist/swish-0.9.2.1.tar.gz 
Hackage username: NotMyUserName
Hackage password: DefinitelyNotMyPassword
Uploading dist/swish-0.9.2.1.tar.gz...
Error uploading dist/swish-0.9.2.1.tar.gz: http code 400
Error: Invalid package

This server does not accept packages with 'license' field set to e.g.
AllRightsReserved. See https://hackage.haskell.org/upload for more information
about accepted licenses.

which I don't understand since

% grep -i license swish.cabal
License:            LGPL
License-file:       LICENSE 

and Hackage was perfectly fine with this license on March 8th when I last uploaded a version (https://hackage.haskell.org/package/swish-0.9.2.0).

For reference the cabal file used when attempting the upload is https://bitbucket.org/doug_burke/swish/src/6d1b4d4fad760b64904dff6230a1612464cf9b24/swish.cabal?at=default&fileviewer=file-view-default

and

% cabal --version
cabal-install version 1.24.0.2
compiled using version 1.24.2.0 of the Cabal library 

[gbaz]

I think I figured it out, but we really should catch this error and document it better. In part of the translation to SPDX now, we call the following logic: https://hackage.haskell.org/package/Cabal-2.2.0.0/docs/src/Distribution.License.html#licenseToSPDX

Note that it falls through on LPGL if it does not have a proper version. So we are stricter than before. You need LGPL-3 or LGPL-2.1.

(but yes, that error message is not helpful at all!)

[gbaz]

cc @phadej -- maybe we can update some docs here too. the upload page currently points to Distribution.License, which doesn't explain that the version fields are mandatory. So we should update the docs there in Cabal? Also maybe create a better place to give recommended licenses and syntax? In the cabal manual? (On the other hand, cabal init does the right thing, so this is really an issue with old legacy packages...)

[DougBurke]

Thanks for the pointer - I was able to upload after changing LGPL to LGPL-2.1.