feat: make pull call new merge instead of old merge

[mitchellwrosen]

Overview

This PR makes pull perform a new merge instead of an old merge.old.

Implementation notes

pull now has a more restricted type: you can only target a project branch. So, this syntax no longer works

> pull @unison/base/releases/latest lib.base

that people will be familiar with from our docs. So, we'll probably want to have a better error message than the current one, which just prints the help pull output.

Test coverage

No new tests, but I tested the command manually

[aryairani]

👍

[aryairani]

Nice!

Could you fix up (or link a new ticket up to fix up) the error message, maybe just in the InputPattern, so that if someone tries to pull @<x..> lib.<z>, it will suggest lib.install @<x..> instead.

Could you comment on the new help message that talks about "remote namespace" but "destination branch"; remind us why namespace in one case and branch in the other; is that purely a concession to Share loose code?

The PR description tells us the variation that no longer works, but could you remind us of the variations that do work, as of this PR? If it ends up only needing to be short then that's good enough; if it ends up being needing to be long, then maybe a manual transcript to demo the pull command?

[mitchellwrosen]

Could you fix up (or link a new ticket up to fix up) the error message, maybe just in the InputPattern, so that if someone tries to pull @<x..> lib., it will suggest lib.install @<x..> instead.

Sure.

Could you comment on the new help message that talks about "remote namespace" but "destination branch"; remind us why namespace in one case and branch in the other; is that purely a concession to Share loose code?

Just that the source can be a project branch ("branch") or arbitrary path into loose code ("namespace"), but the target can only be a project branch ("branch").

The PR description tells us the variation that no longer works, but could you remind us of the variations that do work, as of this PR?

This: "pull now has a more restricted type: you can only target a project branch"
means: you can pass a project/branch, /branch or branch (equivalent to /branch)

[mitchellwrosen]

I updated the pull error message to recommend lib.install if you try to pull into lib, and show more info about the parse error in other cases (in addition to showing help as before)