Re: what should "git clean -n -f [-d] [-x] <pattern>" do?

[Sergey Organov <sorganov@gmail.com>]

Junio C Hamano <gitster@pobox.com> writes:

> Sergey Organov <sorganov@gmail.com> writes:
>
>> Whereas obsoleting second -f in favor of new --nested-repo might be a
>> good idea indeed, I believe it's still a mistake for "dry run" to
>> somehow interfere with -f, sorry.
>
> No need to be sorry ;-)
>
> I actually think the true culprit of making this an odd-man-out is
> that the use of "-f" in "git clean", especially with its use of the
> configuration variable clean.requireForce that defaults to true, is
> utterly non-standard.
>
> The usual pattern of defining what "-f" does is that the "git foo"
> command without any options does its common thing but refuses to
> perform undesirable operations (e.g. "git add ."  adds everything
> but refrains from adding ignored paths). And "git foo -f" is a way
> to also perform what it commonly skips.
>
> In contrast, with clean.requireForce that defaults to true, "git
> clean" does not do anything useful by default.  Without such a
> safety, "git clean" would be a way to clean expendable paths, and
> "git clean -f" might be to also clean precious paths.  But it does
> not work that way.  It always requires "-f" to do anything.  Worse
> yet, it is not even "by default it acts as if -n is given and -f is
> a way to countermand that implicit -n".  It is "you must give me
> either -f (i.e. please do work) or -n (i.e. please show what you
> would do) before I do anything".
>
>   $ git clean
>   fatal: clean.requireForce defaults to true and neither -i, -n, nor -f given; refusing to clean
>
> Given that, it is hard to argue that it would be a natural end-user
> expectation that the command does something useful (i.e. show what
> would be done) when it is given "-f" and "-n" at the same time.
> What makes this a rather nonsense UI is the fact that "-f" does not
> work the way we would expect for this command.

I think we all agree that current UI is a kind of nonsense, but have
different views of the optimal target interface. My points are as
following:

1. The fact that bare "git clean" only produces error by default is
probably a good thing, as removal of untracked files is unrecoverable
operation in Git domain, so requiring -f by default is probably a good
thing as well, provided the *only* operation that "git clean" performs
is dangerous enough.

2. The "-n" behavior is pure nonsense.

So, how do we fix (2)? Let's try mental experiment. Suppose there is no
"-n" option for "git clean" and we are going to implement it. We start
from:

  $ git clean
  fatal: clean.requireForce defaults to true and neither -i nor -f given; refusing to clean
  $ git clean -f
  removing "a"
  removing "b"
  $

Please notice that there is no "-n" in the error message as there is no
such option yet in our experiment.

Now we are going to introduce "dry run" option "-n". Most simple and
obvious way to do it is to set internal flag "dry_run" and then at every
invocation of "remove(file_name)" put an if(dry_run) that will just
print(file_name) instead or removing it. Let's suppose we did just that.
We get this behavior:

  $ git clean -n
  fatal: clean.requireForce defaults to true and neither -i nor -f given; refusing to clean
  $ git clean -f -n
  would remove "a"
  would remove "b"
  $ git clean -f -f -n
  would remove "a"
  would remove "b"
  would remove "sub/a"
  $

I see this as logical, clean, and straightforward behavior, meeting user
expectations for "dry run" option, so I suggest to do just that.

Thanks,
-- Sergey Organov.