Subject: Re: [PATCH 1/2] update-index: optionally leave skip-worktree entries alone

From: Junio C Hamano <[email-masked]>
Date: Mon, 28 Oct 2019 13:38:23 +0900

"Johannes Schindelin via GitGitGadget" <[email-masked]>
writes:

> From: Johannes Schindelin <[email-masked]>
>
> While `git update-index` mostly ignores paths referring to index entries
> whose skip-worktree bit is set, in b4d1690df11 (Teach Git to respect
> skip-worktree bit (reading part), 2009-08-20), for reasons that are not
> entirely obvious, the `--remove` option was made special: it _does_
> remove index entries even if their skip-worktree bit is set.

I think that made sense to notice removal of the path, because
skip-worktree bit was not "apply --cached semantics instead of
looking at the working tree files".  In other words, it was only
about contents inside the files, and not existence of paths.

I am not offhand sure if it still makes sense; if I were being asked
to review that commit today, I suspect that I may be tempted to say
that we should ignore both contents change and presence change for
entries that have skip-worktree bit set.

> However, in preparation for fixing a bug in `git stash` where it
> pretends that skip-worktree entries have actually been removed, we need
> a mode where `git update-index` leaves all skip-worktree entries alone,
> even if the `--remove` option was passed.

We might want to make this the default eventually (is there a known
use case where the current behaviour makes sense, I wonder?), but
I agree that this is a safe thing to do at least for now.

> Signed-off-by: Johannes Schindelin <[email-masked]>
> ---
>  Documentation/git-update-index.txt | 6 ++++++
>  builtin/update-index.c             | 6 +++++-
>  2 files changed, 11 insertions(+), 1 deletion(-)

Isn't this something reasonably easy to guard against regression with
a test or two?

>
> diff --git a/Documentation/git-update-index.txt b/Documentation/git-update-index.txt
> index 1c4d146a41..08393445e7 100644
> --- a/Documentation/git-update-index.txt
> +++ b/Documentation/git-update-index.txt
> @@ -16,6 +16,7 @@ SYNOPSIS
>  	     [--chmod=(+|-)x]
>  	     [--[no-]assume-unchanged]
>  	     [--[no-]skip-worktree]
> +	     [--[no-]ignore-skip-worktree-entries]
>  	     [--[no-]fsmonitor-valid]
>  	     [--ignore-submodules]
>  	     [--[no-]split-index]
> @@ -113,6 +114,11 @@ you will need to handle the situation manually.
>  	set and unset the "skip-worktree" bit for the paths. See
>  	section "Skip-worktree bit" below for more information.
>  
> +
> +--[no-]ignore-skip-worktree-entries::
> +	Do not remove skip-worktree (AKA "index-only") entries even when
> +	the `--remove` option was specified.
> +
>  --[no-]fsmonitor-valid::
>  	When one of these flags is specified, the object name recorded
>  	for the paths are not updated. Instead, these options
> diff --git a/builtin/update-index.c b/builtin/update-index.c
> index dff2f4b837..074d563df0 100644
> --- a/builtin/update-index.c
> +++ b/builtin/update-index.c
> @@ -35,6 +35,7 @@ static int verbose;
>  static int mark_valid_only;
>  static int mark_skip_worktree_only;
>  static int mark_fsmonitor_only;
> +static int ignore_skip_worktree_entries;
>  #define MARK_FLAG 1
>  #define UNMARK_FLAG 2
>  static struct strbuf mtime_dir = STRBUF_INIT;
> @@ -381,7 +382,8 @@ static int process_path(const char *path, struct stat *st, int stat_errno)
>  		 * so updating it does not make sense.
>  		 * On the other hand, removing it from index should work
>  		 */
> -		if (allow_remove && remove_file_from_cache(path))
> +		if (!ignore_skip_worktree_entries && allow_remove &&
> +		    remove_file_from_cache(path))
>  			return error("%s: cannot remove from the index", path);
>  		return 0;
>  	}
> @@ -1013,6 +1015,8 @@ int cmd_update_index(int argc, const char **argv, const char *prefix)
>  		{OPTION_SET_INT, 0, "no-skip-worktree", &mark_skip_worktree_only, NULL,
>  			N_("clear skip-worktree bit"),
>  			PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, UNMARK_FLAG},
> +		OPT_BOOL(0, "ignore-skip-worktree-entries", &ignore_skip_worktree_entries,
> +			 N_("do not touch index-only entries")),
>  		OPT_SET_INT(0, "info-only", &info_only,
>  			N_("add to index only; do not add content to object database"), 1),
>  		OPT_SET_INT(0, "force-remove", &force_remove,