Incorporate SolveMeta into LockDiff

[carolynvs]

Currently LockDiff only compares the memo. but now that #584 has added new metadata fields, the LockDiff should be updated to include them as well. Also we should print "Inputs Digest" instead of "Memo" now that the field has been renamed.

For example:

Old Gopkg.lock

[solve-meta]
  analyzer-name = "dep"
  analyzer-version = 1
  inputs-digest = "abc123"
  solver-name = "gps-cdcl"
  solver-version = 1

New Gopkg.lock

[solve-meta]
  analyzer-name = "dep+imports"
  analyzer-version = 4
  inputs-digest = "def456"
  solver-name = "gps-cdcl"
  solver-version = 2

Running dep ensure -n would print:

Would have written the following changes to Gopkg.lock:
Analyzer Name: dep -> dep imports
Analyzer Version: 1 -> 4
Solver Version: 1 -> 2
Inputs Digest: abc123 -> def456

[mikijov]

Hi. I will take a stab at this.

[mikijov]

Hi @carolynvs. I took a look around the code and I think I understand what is being asked. It's not as simple as adding serialization. The biggest work is around gps.Lock interface having no idea about the new SolveMeta data which is in root namespace. I will probably refactor SolveMeta or an interface resembling it into gps, and then I would have to add at least getter for it into gps.Lock. Before I start on this not so trivial refactoring, I would like little guidance from you, @sdboyer or someone else on the project if I am on the right track.

[carolynvs]

@mikijov Sorry, I didn't realize that SolveMeta isn't in gps and shouldn't have flagged this as a good first PR... 😞

I'll let @sdboyer say if he'd like this refactored.

[sdboyer]

Yeah, this'd be a little more involved, as SolveMeta is a layer that dep adds itself. gps is aware of all the constituent parts, but they aren't consolidated in a way where it'd be easy to produce the diff.

Hmm...I think, maybe, we should actually go the opposite direction, and drop the input hash from the diff, so that we're ignoring all the solve meta. That's information people can see in a git diff, but it's not really actionable information in the way that actual project changes are.