Re: [PATCH v3] stash: make sure we have a valid index before writing it

> Subject: [PATCH v3] stash: make sure we have a valid index before writing it
>
> In 'do_apply_stash()' we refresh the index in the end.  Since
> 34933d0eff ("stash: make sure to write refreshed cache", 2019-09-11),
> we also write that refreshed index when --quiet is given to 'git stash
> apply'.
>
> However if '--index' is not given to 'git stash apply', we also
> discard the index in the else clause just before.  We need to do so
> because we use an external 'git update-index --add --stdin', which
> leads to an out of date in-core index.
>
> Later we call 'refresh_and_write_cache', which now leads to writing
> the discarded index, which means we essentially write an empty index
> file.  This is obviously not correct, or the behaviour the user
> wanted.  We should not modify the users index without being asked to
> do so.
>
> Make sure to re-read the index after discarding the current in-core
> index, to avoid dealing with outdated information.  Instead we could
> also drop the 'discard_cache()' + 'read_cache()', however that would
> make it easy to fall into the same trap as 34933d0eff did, so it's
> better to avoid that.
>
> We can also drop the 'refresh_and_write_cache' completely in the quiet
> case.  Previously in legacy stash we relied on 'git status' to refresh
> the index after calling 'git read-tree' when '--index' was passed to
> 'git apply'.  However the 'reset_tree()' call that replaced 'git
> read-tree' always passes options that are equivalent to '-m', making
> the refresh of the index unnecessary.
>
> Reported-by: Grzegorz Rajchman <rayman17@gmail.com>
> Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
> ---

>  builtin/stash.c  | 7 +++----
>  t/t3903-stash.sh | 7 ++++++-
>  2 files changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/builtin/stash.c b/builtin/stash.c
> index ab30d1e920..372fbdb7ac 100644
> --- a/builtin/stash.c
> +++ b/builtin/stash.c
> @@ -481,13 +481,12 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
>  		if (ret)
>  			return -1;
>  
> +		/* read back the result of update_index() back from the disk */
>  		discard_cache();
> +		read_cache();
>  	}
>  
> -	if (quiet) {
> -		if (refresh_and_write_cache(REFRESH_QUIET, 0, 0))
> -			warning("could not refresh index");
> -	} else {
> +	if (!quiet) {
>  		struct child_process cp = CHILD_PROCESS_INIT;
>  
>  		/*
> diff --git a/t/t3903-stash.sh b/t/t3903-stash.sh
> index 392954d6dd..9de1c3616a 100755
> --- a/t/t3903-stash.sh
> +++ b/t/t3903-stash.sh
> @@ -232,8 +232,11 @@ test_expect_success 'save -q is quiet' '
>  	test_must_be_empty output.out
>  '
>  
> -test_expect_success 'pop -q is quiet' '
> +test_expect_success 'pop -q works and is quiet' '
>  	git stash pop -q >output.out 2>&1 &&
> +	echo bar >expect &&
> +	git show :file >actual &&
> +	test_cmp expect actual &&
>  	test_must_be_empty output.out
>  '
>  
> @@ -242,6 +245,8 @@ test_expect_success 'pop -q --index works and is quiet' '
>  	git add file &&
>  	git stash save --quiet &&
>  	git stash pop -q --index >output.out 2>&1 &&
> +	git diff-files file2 >file2.diff &&
> +	test_must_be_empty file2.diff &&
>  	test foo = "$(git show :file)" &&
>  	test_must_be_empty output.out
>  '