Re: A project-files implementation for Git projects

[Dmitry Gutov]

On 14.09.2019 19:43, Tassilo Horn wrote:

> > Why exclude unregistered? I don't imagine they would slow anything
> > down.
>
> Because IMHO they are not interesting except if they were just created
> by myself and not yet added which seemed like a minor edge case (and at
> least git ls-files lists files which are not yet committed but staged).

Why else would they be there if not created by yourself? 
Machine-generated files are usually in gitignore.

And every new file goes through this status. It would be an omission if 
project-find-file could find the file you just created (and probably 
working on).

> And because it seems to me that git is more an exception in being able
> to list unregistered files.

If some VC backends just can't provide the full functionality, we should 
disable using them by default (and only leave 'Git in the defcustom you 
added, with some explanation).

> > Speaking of ignores format, maybe they should just be whatever the
> > backend in question understands, e.g. the contents of gitignore
> > verbatim.
>
> I don't see how that would work except by modifying (or moving back and
> forth) the existing .{git,hg,bzr}ignore to include project-vc-ignores.

It's an option, although not a very fail-proof one.

Git has helpful options like --exclude and --exclude-from, although it 
seems they don't affect the already tracked files. For which there are 
different things we can do:

* Use negative patterns (https://stackoverflow.com/a/53083343/615245), 
this approach seems to recommend we use a separate argument like 
extra-ignores for the backend command. --exclude-from should help with 
whitelisting entries, though.

* Grep the output, or process it in Emacs programmatically.

* Idea from https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=556584#10, 
though using it might not be the fastest option. Someone should 
benchmark it.

With the first option, the command line would look like:

  git ls-files -c -o --exclude=!whitelisted-dir1 
--exclude=!whitelisted-dir2 --exclude-standard ":!:extra-ignore1" 
":!:extra-ignore2"