Re: [RFC/PATCH] worktree: replace "checkout --to" with "worktree new"

[Duy Nguyen <pclouds@gmail.com>]

On Thu, Jul 2, 2015 at 9:52 AM, Eric Sunshine <sunshine@sunshineco.com> wrote:
> On Wed, Jul 1, 2015 at 9:07 PM, Duy Nguyen <pclouds@gmail.com> wrote:
>> On Thu, Jul 2, 2015 at 12:13 AM, Eric Sunshine <sunshine@sunshineco.com> wrote:
>>>>    I noticed GIT_CHECKOUT_NEW_WORKTREE environment variabl that does
>>>>    not seem to be documented.  Is this something we still need?
>>>>    The log message of 529fef20 (checkout: support checking out into
>>>>    a new working directory, 2014-11-30) does not tell us much.
>>>
>>> Yes, it's still used for the same purpose as before the conversion: as
>>> a private signal to the sub git-checkout invocation that it's
>>> operating on a new worktree. When defined, it sets the
>>> 'new_worktree_mode' flag in checkout.c, and there are still a few bits
>>> of code which apparently need to know about it. It would be nice to
>>> eliminate this special knowledge from checkout.c, however, I'm not yet
>>> familiar enough with the checkout code to determine if doing so is
>>> viable.
>>
>> I think it can go away. When "--to" is used, I have to re-execute "git
>> checkout" command again after creating the new worktree. I could
>> process the command line arguments from the first execution, delete
>> "--to", then use the remaining options to run checkout the second
>> time. But I chose to pass the entire command line to the second
>> execution. The env is used to let the second run know it should ignore
>> "--to" (or we get infinite recursion). With "git worktree add" this
>> recursion disappears and this env var has no reason to exist.
>
> The recursion protection is indeed no longer needed and gets removed
> by the "worktree add" patch. However, there are still a few bits of
> code which want to know that the checkout is happening in a new
> worktree. I haven't examined them closely yet to diagnose if this
> specialized knowledge can be eliminated. Perhaps you can weight in. In
> particular:
>
> checkout_paths:
>     if (opts->new_worktree)
>         die(_("'%s' cannot be used with updating paths"), "--to");

This one is easy, as "--to" is gone, no reason to report anything about "--to"

> merge_working_tree:
>     tree = parse_tree_indirect(old->commit &&
>         !opts->new_worktree_mode ?
>             old->commit->object.sha1 :
>             EMPTY_TREE_SHA1_BIN);

I think it's to make sure empty sha-1 is used with --to. If
old->commit->object.sha1 is used and it's something, a real two way
merge may happen probably with not-so-fun consequences. If it's empty
sha1, the effect is like "reset --hard", silent and reliable..

> switch_branches:
>     if (!opts->quiet && !old.path && old.commit &&
>         new->commit != old.commit && !opts->new_worktree_mode)
>             orphaned_commit_warning(old.commit, new->commit);

to suppress misleading warning if old.commit happens to be something.
-- 
Duy