Change license :: License to Either SPDX.License License

[phadej]

WIP: [ci skip] Have to fix cabal-tests and check that we don't break
older (i.e all) ghc-pkgs

Resolves #2547

I introduce SimpleLicenseExpression to make "OrAnyLater LicenseRef"
unrepresentable. That also simplifies types.

license field is parsed as old License when cabal-version <2.2,
and as SPDX expression otherwise. NONE is recognised.

There are also IPI changes, there both old and SPDX license expressions
are accepted, as both can occur in package database.

Please include the following checklist in your PR:

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
• The documentation has been updated, if necessary.
• If the change is docs-only, [ci skip] is used to avoid triggering the build bots.

Please also shortly describe how you tested your change. Bonus points for added tests!

[phadej]

I probably end up introducing spdx field into IPI, so license field can be left intact, and new field used for SPDX stuff. I have to run cabal-tests to see how badly things are broken right now.

[phadej]

I made Register write license as SPDX in IPI with GHC >= 8.4 only. That will do it. Simple.

[phadej]

This choice converts everything to SPDX, so in GHC-8.4 package databases will only contain SPDX expressions.
Alternatively we can let licenseRaw to go though unmodified, or convert only "sure" things (e.g. MIT, BSD3, GPL-3, not PublicDomain or OtherLicense)

[hvr]

Sounds good to me :-)

[phadej]

How it's possible that in GHC-7.8.4 output https://travis-ci.org/haskell/cabal/jobs/330116951#L2091 I see

Linked component graph:
    unit my-0
        include base-4.11.0.0

ping @ezyang, any ideas?

[phadej]

ping @ezyang , any ideas why tests fail on older GHC? For example https://travis-ci.org/haskell/cabal/jobs/330116951

[phadej]

Ah I see, it actually tests with ghc-head! I have to skip that tests before GHC-head is updated :)

[23Skidoo]

You can change the GHC version check to 8.4.0.2018MMDD: make this a month or two in the future now and update later once you know the correct snapshot date.

[phadej]

@23Skidoo head is 8.5 so that won't work, I'll just temporarily skip the test for 8.4+ and unskip it when Cabal is updated in GHC-tree.

[23Skidoo]

Looks all right from a quick glance.

[phadej]

@23Skidoo do you want to take a closer look, or should I merge? (when travis is green, at least mostly)

[23Skidoo]

I'll try to later today, feel free to merge if I won't.

[phadej]

I merged this now, any comments are still welcome