Parameterize SourcePackage and ConfiguredPackage on package location

[BardurArantsson]

This is a step towards breaking the dependency from the modular
solver on cabal-install.

[BardurArantsson]

I should say: The reason we want to break the "PackageLocation" dependency is that it brings in a lot of unnecessary baggage, namely URI (i.e. the network package), etc. I can't recall all the details, but ISTR it also brings in other parts of cabal-install which aren't needed for the solver.

[BardurArantsson]

Most of the remainder of splitting out the solver into its own library "between" Cabal and cabal-install is just moving files around and splitting up Distribution.Client.Types appropriately.

I think we can hold off on that for a bit if we still want to keep master close to 1.24.x for a while. This bit is the most code-edit heavy bit.

[BardurArantsson]

/cc @kosmikus @hvr

[23Skidoo]

Looks harmless enough, the only complaint is bikeshedding: the PackageLocation' type name is pretty uninformative. Maybe we could have something like UnresolvedPackageLocation = PackageLocation (Maybe FilePath) and ResolvedPackageLocation = PackageLocation FilePath instead? Better naming suggestions welcome, of course.

[BardurArantsson]

That's a good point. I'll have a look at it tomorrow.

[BardurArantsson]

Looking over the other code, we have three variants:

• PackageLocation (Maybe FilePath)
• PackageLocation FilePath
• PackageLocation ()

I'm not sure what that last one really represents.

My only concern about doing what you suggest is really that the names are a bit long... though obviously not as long as spelling out the full types. Would UnresolvedPkgLoc and ResolvedPkgLoc be acceptable? (Or maybe spell out Location in full?)

EDIT: I mean UnresolvedPackageLocation is 25 characters which is ~30% of the 80-column budget!

(BTW, if we're going to be systematic about it, this does involve changes in a few further places that this patch doesn't currently touch. It's not too bad, but worth mentioning.)

[BardurArantsson]

OK, so I've changed this to two commits:

• The first commit was amended thus: Renamed PackageLocation' to UnresolvedPkgLoc and replaced stray instances of PackageLocation (Maybe FilePath) with the UnresolvedPkgLoc alias.
• The second commit adds ResolvedPkgLoc and replaces instances of PackageLocation FilePath with a reference to the alias.

Hopefully that should be it.

Let me know if you'd like the longer names -- it's pretty trivial to do a global search/replace.

[ezyang]

Sorry for ALL THE BIKESHEDS, but I'd be keen for an alias on SourcePackage UnresolvedPkgLoc too.

[BardurArantsson]

Can we please do that in a follow-up? I'd really like to get this merged ASAP since it's pretty prone to conflicts with other stuff.

[BardurArantsson]

@23Skidoo OK to merge?

[23Skidoo]

@BardurArantsson

PackageLocation ()

I think we can leave this one as it is.

[23Skidoo]

Merged, thanks!