patchcheckout.c: unstage empty deleted ita files

>
> It is possible to delete a committed file from the index and then add it
> as intent-to-add. After `git checkout HEAD` or `git restore --staged`,
> the file should be identical in the index and HEAD. This patch provides
> the desired behavior even when the file is empty in the index.
>
> Signed-off-by: Varun Naik <vcnaik94@gmail.com>
> ---
> CC Jeff because you wrote the code that I am changing now.
>
> checkout.c:update_some() discards the newly created cache entry when its
> mode and oid match those of the old entry. Since an ita file has the
> same oid as an empty file, an empty deleted ita file passes both of
> these checks, and the new entry is discarded. In this case, the file
> should be added to the cache instead.
>
> This change should not affect newly added ita files. For those, inside
> tree.c:read_tree_1(), tree_entry_interesting() returns
> entry_not_interesting, so fn (which points to update_some()) is never
> called.
>
> To the best of my understanding, the only other command that makes
> changes to the index differently for nonempty vs empty deleted ita files
> is "reset", which I am fixing in [0]. I am separating the two changes
> because this change affects "restore", which has not reached maint yet.
>
> [0]: https://public-inbox.org/git/20190726044806.2216-1-vcnaik94@gmail.com/
>
>  builtin/checkout.c        |  1 +
>  t/t2022-checkout-paths.sh | 11 +++++++++++
>  t/t2070-restore.sh        | 11 +++++++++++
>  3 files changed, 23 insertions(+)
>
> diff --git a/builtin/checkout.c b/builtin/checkout.c
> index 91f8509f85..27daa09c3c 100644
> --- a/builtin/checkout.c
> +++ b/builtin/checkout.c
> @@ -126,6 +126,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
>         if (pos >= 0) {
>                 struct cache_entry *old = active_cache[pos];
>                 if (ce->ce_mode == old->ce_mode &&
> +                   !ce_intent_to_add(old) &&
>                     oideq(&ce->oid, &old->oid)) {
>                         old->ce_flags |= CE_UPDATE;
>                         discard_cache_entry(ce);
> diff --git a/t/t2022-checkout-paths.sh b/t/t2022-checkout-paths.sh
> index fc3eb43b89..74add853fd 100755
> --- a/t/t2022-checkout-paths.sh
> +++ b/t/t2022-checkout-paths.sh
> @@ -78,4 +78,15 @@ test_expect_success 'do not touch files that are already up-to-date' '
>         test_cmp expect actual
>  '
>
> +test_expect_success 'checkout HEAD adds deleted intent-to-add file back to index' '
> +       echo "nonempty" >nonempty &&
> +       >empty &&
> +       git add nonempty empty &&
> +       git commit -m "create files to be deleted" &&
> +       git rm --cached nonempty empty &&
> +       git add -N nonempty empty &&
> +       git checkout HEAD nonempty empty &&
> +       git diff --staged --exit-code
> +'
> +
>  test_done
> diff --git a/t/t2070-restore.sh b/t/t2070-restore.sh
> index 2650df1966..09b1543a5b 100755
> --- a/t/t2070-restore.sh
> +++ b/t/t2070-restore.sh
> @@ -95,4 +95,15 @@ test_expect_success 'restore --ignore-unmerged ignores unmerged entries' '
>         )
>  '
>
> +test_expect_success 'restore --staged adds deleted intent-to-add file back to index' '
> +       echo "nonempty" >nonempty &&
> +       >empty &&
> +       git add nonempty empty &&
> +       git commit -m "create files to be deleted" &&
> +       git rm --cached nonempty empty &&
> +       git add -N nonempty empty &&
> +       git restore --staged nonempty empty &&
> +       git diff --staged --exit-code
> +'
> +
>  test_done
> --
> 2.22.0
>

> ---
> CC Jeff because you wrote the code that I am changing now.
> 
> checkout.c:update_some() discards the newly created cache entry when its
> mode and oid match those of the old entry. Since an ita file has the
> same oid as an empty file, an empty deleted ita file passes both of
> these checks, and the new entry is discarded. In this case, the file
> should be added to the cache instead.
> 
> This change should not affect newly added ita files. For those, inside
> tree.c:read_tree_1(), tree_entry_interesting() returns
> entry_not_interesting, so fn (which points to update_some()) is never
> called.

> diff --git a/builtin/checkout.c b/builtin/checkout.c
> index 91f8509f85..27daa09c3c 100644
> --- a/builtin/checkout.c
> +++ b/builtin/checkout.c
> @@ -126,6 +126,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
>  	if (pos >= 0) {
>  		struct cache_entry *old = active_cache[pos];
>  		if (ce->ce_mode == old->ce_mode &&
> +		    !ce_intent_to_add(old) &&
>  		    oideq(&ce->oid, &old->oid)) {
>  			old->ce_flags |= CE_UPDATE;
>  			discard_cache_entry(ce);

> +test_expect_success 'checkout HEAD adds deleted intent-to-add file back to index' '
> +	echo "nonempty" >nonempty &&
> +	>empty &&
> +	git add nonempty empty &&
> +	git commit -m "create files to be deleted" &&
> +	git rm --cached nonempty empty &&
> +	git add -N nonempty empty &&
> +	git checkout HEAD nonempty empty &&
> +	git diff --staged --exit-code
> +'

> +test_expect_success 'restore --staged adds deleted intent-to-add file back to index' '
> +	echo "nonempty" >nonempty &&
> +	>empty &&
> +	git add nonempty empty &&
> +	git commit -m "create files to be deleted" &&
> +	git rm --cached nonempty empty &&
> +	git add -N nonempty empty &&
> +	git restore --staged nonempty empty &&
> +	git diff --staged --exit-code
> +'

>
> On Thu, Jul 25, 2019 at 09:56:45PM -0700, Varun Naik wrote:
>
> > It is possible to delete a committed file from the index and then add it
> > as intent-to-add. After `git checkout HEAD` or `git restore --staged`,
> > the file should be identical in the index and HEAD. This patch provides
> > the desired behavior even when the file is empty in the index.
>
> OK, so the issue is that ITA entries have an empty-file sha1, so they
> confuse the logic to decide if we can use the old entry. Your fix makes
> sense.
>
> > ---
> > CC Jeff because you wrote the code that I am changing now.
> >
> > checkout.c:update_some() discards the newly created cache entry when its
> > mode and oid match those of the old entry. Since an ita file has the
> > same oid as an empty file, an empty deleted ita file passes both of
> > these checks, and the new entry is discarded. In this case, the file
> > should be added to the cache instead.
> >
> > This change should not affect newly added ita files. For those, inside
> > tree.c:read_tree_1(), tree_entry_interesting() returns
> > entry_not_interesting, so fn (which points to update_some()) is never
> > called.
>
> These two paragraphs would be a nice addition to the actual commit
> message.
>

> > diff --git a/builtin/checkout.c b/builtin/checkout.c
> > index 91f8509f85..27daa09c3c 100644
> > --- a/builtin/checkout.c
> > +++ b/builtin/checkout.c
> > @@ -126,6 +126,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
> >       if (pos >= 0) {
> >               struct cache_entry *old = active_cache[pos];
> >               if (ce->ce_mode == old->ce_mode &&
> > +                 !ce_intent_to_add(old) &&
> >                   oideq(&ce->oid, &old->oid)) {
> >                       old->ce_flags |= CE_UPDATE;
> >                       discard_cache_entry(ce);
>
> My first thought here was that we could skip ITA entries here only when
> the HEAD hash is also the empty blob, which would let us retain index
> results in more cases. But it doesn't help. If the HEAD entry isn't the
> empty blob, then we'll have !oideq() and we'll skip anyway, because an
> ITA entry must be the empty blob (if we `git add` some other content,
> then it ceases to be ITA).
>
> So it makes sense to just always skip this "retain the old index entry"
> block for any ITA entry.
>
> > +test_expect_success 'checkout HEAD adds deleted intent-to-add file back to index' '
> > +     echo "nonempty" >nonempty &&
> > +     >empty &&
> > +     git add nonempty empty &&
> > +     git commit -m "create files to be deleted" &&
> > +     git rm --cached nonempty empty &&
> > +     git add -N nonempty empty &&
> > +     git checkout HEAD nonempty empty &&
> > +     git diff --staged --exit-code
> > +'
>
> This clearly demonstrates the problem. Nice.
>
> > +test_expect_success 'restore --staged adds deleted intent-to-add file back to index' '
> > +     echo "nonempty" >nonempty &&
> > +     >empty &&
> > +     git add nonempty empty &&
> > +     git commit -m "create files to be deleted" &&
> > +     git rm --cached nonempty empty &&
> > +     git add -N nonempty empty &&
> > +     git restore --staged nonempty empty &&
> > +     git diff --staged --exit-code
> > +'
>
> Hmm. This git-restore test means we don't apply to maint. But wouldn't
> we want the fix for "checkout" there?
>
> I.e., I'd expect a patch to fix and test git-checkout, and then an
> additional patch to be added on the merge of that plus master to test
> git-restore.
>

> > Hmm. This git-restore test means we don't apply to maint. But wouldn't
> > we want the fix for "checkout" there?
> >
> > I.e., I'd expect a patch to fix and test git-checkout, and then an
> > additional patch to be added on the merge of that plus master to test
> > git-restore.
> >
> 
> To make sure I understand, do you mean that I should omit the test
> case for "restore" right now, wait for the patch to reach master, and
> then create another patch for the "restore" test case?

> `git checkout HEAD` calls tree.c:read_tree_1(), with fn pointing to
> checkout.c:update_some(). update_some() creates a new cache entry but
> discards it when its mode and oid match those of the old entry. A cache
> entry for an ita file and a cache entry for an empty file have the same
> oid. Therefore, an empty deleted ita file previously passed both of
> these checks, and the new entry was discarded, so the file remained
> unchanged in the index. After this fix, if the file is marked as ita in
> the cache, then we avoid discarding the new entry and add the new entry
> to the cache instead.

> It is possible to delete a committed file from the index and then add it
> as intent-to-add. After `git checkout HEAD`, the file should be
> identical in the index and HEAD. The command already works correctly if
> the file has contents in HEAD. This patch provides the desired behavior
> even when the file is empty in HEAD.
> 
> `git checkout HEAD` calls tree.c:read_tree_1(), with fn pointing to
> checkout.c:update_some(). update_some() creates a new cache entry but
> discards it when its mode and oid match those of the old entry. A cache
> entry for an ita file and a cache entry for an empty file have the same
> oid. Therefore, an empty deleted ita file previously passed both of
> these checks, and the new entry was discarded, so the file remained
> unchanged in the index. After this fix, if the file is marked as ita in
> the cache, then we avoid discarding the new entry and add the new entry
> to the cache instead.
> 
> This change should not affect newly added ita files. For those, inside
> tree.c:read_tree_1(), tree_entry_interesting() returns
> entry_not_interesting, so fn is never called.
> 
> Helped-by: Jeff King <peff@peff.net>
> Signed-off-by: Varun Naik <vcnaik94@gmail.com>
> ---
> This patch fixes and tests only "checkout", because "restore" has not
> reached maint yet. A second patch on the merge of this patch into master
> with a test case for "restore" is coming.

> `git restore --staged` uses the same machinery as `git checkout HEAD`,
> so there should be a similar test case for "restore" as the existing
> test case for "checkout" with deleted ita files.
>
> Helped-by: Jeff King <peff@peff.net>
> Signed-off-by: Varun Naik <vcnaik94@gmail.com>
> ---
> This is the "restore" patch based on the merge of the "checkout" patch
> into master.