Re: [PATCH] git-new-workdir: Don't fail if the target directory is empty

From: Junio C Hamano <gitster@pobox.com>
Date: Nov 19, 2014, 17:32 UTC
Message-ID: <xmqqd28jt7tb.fsf@gitster.dls.corp.google.com>
In-Reply-To: <1416339408.3899.22.camel@mad-scientist.net>

Paul Smith <paul@mad-scientist.net> writes:

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> Allow new workdirs to be created in an empty directory (similar to "git
> clone").  Provide more error checking and clean up on failure.
>
> Signed-off-by: Paul Smith <paul@mad-scientist.net>
> ---
>
> Getting rid of ls/wc was not as simple as I'd hoped, due to glob
> pathname expansion (can't rely on nullglob e.g.)  If you want this let
> me know; it will require some yucky code to do the whole thing in native
> shell.  Since new-workdir only works on systems with "ln -s" I think we
> can feel confident requiring "ls" and "wc" as well.
>
>  contrib/workdir/git-new-workdir | 55 +++++++++++++++++++++++++++--------------
>  1 file changed, 36 insertions(+), 19 deletions(-)

I took a look at this again, and I do not agree with one design decision it makes, namely:

>> I split the creation of the directories from the symlinks: see the new
>> loop above.  This allows us to avoid the icky dirname stuff.

which forces those who maintain the script to make sure that these two loops

	for dir in log
        do
        	make leading directory $dir
	done
	for path in refs logs/refs objects ...
	do
        	make symlink, assuming the leading directory exists
	done

kept consistent with each other. If you forget to add frotz to the upper loop when adding frotz/nitfol to the latter, you are breaking it.

I find it much more icky than computing what is necessary on the fly.

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> +# don't recreate a workdir over an existing directory, unless it's empty
> +if test -d "$new_workdir"
>  then
> -	die "destination directory '$new_workdir' already exists."
> +	if test $(ls -a1 "$new_workdir/." | wc -l) -ne 2

I wondered if -gt instead of -ne is safer just in case what the description of "-A" alludes to, i.e. "ls -a" may not have ".." in its output, happens.

But that would not matter. If you are on such a filesystem and have a directory with a single file, you will see two entries in "ls -a" (one "." and the other the sole file) and mistake it as an empty directory whether you use -ne or -gt anyway, so -gt is not making it safer anyway. So let's go with this version.

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> +	then
> +		die "destination directory '$new_workdir' is not empty."
> +	fi
> +	cleandir="$new_workdir"/.git
> +else
> +	mkdir -p "$new_workdir" || failed
> +	cleandir="$new_workdir"
>  fi
>  
> -# make sure the links use full paths
> -git_dir=$(cd "$git_dir"; pwd)
> +cleanup () {
> +	rm -rf "$cleandir"
> +}

Aversion to turning $cleandir to an absolute path?  Why?

You may have avoided a problem by removing "cd" below in the current code, but I do not think it is a good future-proofing. If you make sure $cleandir is absolute, then you would not have to be even worried about other people breaking that assumption "this script will never let the trap hit while it cd to other places".

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> -# now setup the workdir
> -cd "$new_workdir"
>  # copy the HEAD from the original repository as a default branch
> -cp "$git_dir/HEAD" .git/HEAD
> -# checkout the branch (either the same as HEAD from the original repository, or
> -# the one that was asked for)
> -git checkout -f $branch
> +cp "$git_dir/HEAD" "$new_workdir"/.git/HEAD || failed
> +
> +# the workdir is set up.  if the checkout fails, the user can fix it.
> +trap - $siglist
> +
> +# checkout the branch (either the same as HEAD from the original repository,
> +# or the one that was asked for)
> +git --git-dir="$new_workdir"/.git --work-tree="$new_workdir" checkout -f $branch

These uses of --git-dir/--work-tree look somewhat funny. You want to say "I want to run checkout in that $new_workdir", so say it in a more direct way, i.e.

    git -C "$new_workdir" checkout -f "$branch"

perhaps?

Thanks.