Updates for recent Hy changes

[brandonwillard]

Beyond simple syntax and function signature updates, the biggest changes are in the handling/use of—the now missing—cons.

Also, some rules have been added that reflect the Hy language changes made in this commit. Those additions still need tests.

A great test/demo of hydiomatic would be to use itself to apply the changes in this commit! Only a subset of changes could currently be performed with the ruleset additions; the other changes (e.g. the "lifting"/pulling out of conses from quoted forms and additional condes for the strict list type returned by the cons helper function) haven't been added, yet. We might be able to add them, though, and/or use them as an opportunity to demonstrate user-level modifications/additions to hydiomatic rules.

[brandonwillard]

One test isn't passing and requires the fix from brandonwillard/loghyc#7.

Otherwise, the let/when macro pairing/unpacking rules are causing problems because of changes in the acceptable patterns for let bindings (e.g. from (let [[[a b] [c d]] e] ...) to (let [a c b d e] ...)). As a result, simple bindings like (let [x 1] ...) are mistakenly converted to (let [x None 1 None] ...).

We need a more sophisticated handling that can cover the old and the new patterns. We might get away with separating the old and the new style as configurable options (e.g. source and target version) and let the user pick up the slack. (That sounds lame, though.)
For now, I could simply disable those specific rules so that this PR, and all the language updates, can go through.
@algernon, tell me if you have a preference for one or the other (or even something else).

Also, I'm trying to find a way to automatically add the requires and imports implied by the let and cons changes (i.e. move and removal, respectively). I started putting in rules that would prepend those imports and requires to the relevant uses of let and cons, but that's clearly overkill, so I disabled them for now and made it simply emit a warning in the log.

[algernon]

There are already rules which aren't enabled by default, adding some more, behind a new flag does not sound wrong. To be honest, I quite like the idea of being able to specify a source and a target version.

(Agree about the require/import stuff, its overkill to add them to every let and cons. The good option would be to treat the whole file as one big, implicit do, and have a rule that finds let/cons anywhere, and adds that to the beginning. And in the end, we unwrap the do and voila.)

[brandonwillard]

(Agree about the require/import stuff, its overkill to add them to every let and cons. The good option would be to treat the whole file as one big, implicit do, and have a rule that finds let/cons anywhere, and adds that to the beginning. And in the end, we unwrap the do and voila.)

Exactly! I just wasn't sure if we would want/need some awareness of scope, but I suppose top-level could do the trick (except for macros, at least until hylang/hy#1682 goes through).

[brandonwillard]

By the way, I think I'll just disable the problematic stuff, let this PR fix the Hy language changes in the core library, and start another for the source, target parameter/flag and new rules.