Re: [PATCH 1/1] Introduce "precious" file concept

[Duy Nguyen <pclouds@gmail.com>]

On Wed, Feb 20, 2019 at 6:11 PM Clemens Buchacher <drizzd@gmx.net> wrote:
> >And requiring to mark trashable files manually duplicates a
> >lot of ignore patterns. Have a look at any .gitignore file, the
> >majority of them is for discardable files because "ignored" class was
> >created with those in mind (*.o and friends). So now you would need to
> >add more or less the same set of ignore rules in .gitattributes to
> >mark them trashable, and gitignore/gitattributes rules are not exactly
> >compatible, you can't just blindly copy them over. Every time you add
> >one more .gitignore rule, there's a good chance you need to add a
> >similar rule for trashable attribute.
>
> I agree that ignored precious files are typically a small subset of the ignore files. Maintaining separate rules for ignored files and for trashable files would result in a lot of duplication.
>
> On the other hand, how frequently do we really have to trash ignored files? Trashing a file should only be necessary if a tracked file overwrites an ignored file. When does this happen? I don't think it will happen for *.o files. So in most cases, there is simply no need to specify which files are precious. The default could simply be that all files are precious.
>
> To support more complex use cases, we could specify precious files in addition to ignored files. Only if we specify precious files (and/or enable the ignored-are-trashable config option on a repository level), all other files become trashable.
>
> Functionally this is equivalent the newbie option which you suggest, but I think it is not an issue of newbie vs experienced users but an issue of common vs special use cases.

So far the two conflicting cases are "git checkout/merge" and "git
clean". Ignored files are valuable by default in the former, while
it's expendable by default in the latter.

So if you add this ignored-are-trashable config key (defaults to
false), git-clean -if will not do anything anymore. We _could_ advice
the user to turn the config on (with all the consequences). I don't
know if we have any other use cases that deserve the same advice.

Another option is simply leave the expendable/precious nature of
ignored files undefined like it is now and handle case by case:

 - git-clean learns to use a new attribute "clean". Undefined
attribute is seen as +clean. To keep some files "precious" you update
.gitattributes and add -clean rules.
 - git merge/checkout learns another attribute,
checkout-overwrite-ignore? Undefined attribute is seen as
-checkout-overwrite-ignore (i.e. abort the operation).

We stay away from any generic attribute name in this direction to make
clear it's only applicable to specific use cases.
-- 
Duy