feat(switch): accept revset arguments, and explicitly support - shorthand

[claytonrcarter]

This updated git switch to accept a revset as it's argument, and also to support - (to checkout previously checked out branch/commit) by passing it through to git.

The revset parameter must evaluate to a set with a single head, and I've found this handy in cases like current(...) to move to the latest version of a commit if I had an old smartlog or SHA still on screen or such, and also switch foo: for when I have a branch ref handy but I really want to checkout the latest detached commit in that stack.

But with revset support added, switch - broke because it looked a poorly formed revset:

Message:  A fatal error occurred:
   0: parse error in "-": parse error: Unrecognized token `-` found at 0:1
      Expected one of "(", "..", ":", "::", a commit/branch/tag or a string literal
   1: parse error: Unrecognized token `-` found at 0:1
      Expected one of "(", "..", ":", "::", a commit/branch/tag or a string literal

The last commit in this stack adds an explicit check for - so that this support is restored.

Apparently, revparse_single() in libgit2 doesn't support this. ~~I didn't patch - support into repo.revparse_single_commit() but I'm thinking as I write this that perhaps that may be better? There is already a special case in that function to work around another libgit2 issue, and I suppose we could detect if the passed spec is - and then pass @{-1} to revparse_single() instead. 🤔 ~~ edit I made this change and it seems to be working.

[arxanas]

Thanks! Both of these issues have bothered me personally as well.

[claytonrcarter]

Thanks! Both of these issues have bothered me personally as well.

Thanks for the review! I've updated my change, and I'll park this here for a few days while I continue using it locally in case I missed anything.

[claytonrcarter]

This has been working fine for me. Let's see what everyone else thinks of it. 😄