Re: [RFC] Define "precious" attribute and support it in `git clean`

From: Phillip Wood <phillip.wood123@gmail.com>
Date: Oct 13, 2023, 10:06 UTC
Message-ID: <0deee2bc-1775-4459-906d-1d44b3103499@gmail.com>
In-Reply-To: <xmqqttqvg4lw.fsf@gitster.g>

On 12/10/2023 17:58, Junio C Hamano wrote:

> Sebastian Thiel <sebastian.thiel@icloud.com> writes:

Sebastian - thanks for raising this again, it would be really good to get a solution for handling "ignored but not expendable" files

Show 18 quoted lines

> I have been regretting that I did not make the quoting syntax not
> obviously extensible in f87f9497 (git-ls-files: --exclude mechanism
> updates., 2005-07-24), which technically was a breaking change (as a
> relative pathname that began with '!' were not special, but after
> the change, it became necessary to '\'-quote it).  A relative
> pathname that begins with '$' would be now broken the same way, but
> hopefully the fallout would be minor.  I presume you picked '$'
> exactly because of this reason?
> 
> I do not think it will be the end of the world if we don't do so,
> but it would be really really nice if we at least explored a way (or
> two) to make a big enough hole in the syntax to not just add
> "precious", but leave room to later add other traits, without having
> to worry about breaking the backward compatibility again.  A
> simplest and suboptimal way may be to declare that a path that
> begins with '$' now needs '\'-quoting (just like your proposal),
> reserve '$$' as the precious prefix, and '$' followed by any other
> byte reserved for future use, but there may be better ideas.

One thought I had was that we could abuse the comment syntax to annotate paths something like

#(keep) /my-precious-file

would prevent /my-precious-file from being deleted by git clean (and hopefully unpack-trees()[1]). It means that older versions of git would treat the file as ignored. If we ever want more than one annotation per path we could separate them with commas

#(keep,something-else) /my-file

Strictly speaking it is a backward incompatible change but I doubt there are many people using comments like that. I also wondered about some kind of suffix on the file

/my-precious-file #(keep)

but that means that older versions of git would not ignore the file.

Best Wishes

Phillip

[1] Of the cases listed in [2] it is "git checkout" and friends overwriting ignored files that I worry about more. At least "git clean" defaults to a dry-run and has in interactive mode to select what gets deleted.

[2] https://lore.kernel.org/git/xmqqttqytnqb.fsf@gitster.g