Re: [PATCH v5] git-apply: allow simultaneous --cached and --3way options

[Elijah Newren <newren@gmail.com>]

On Wed, Apr 7, 2021 at 7:13 PM Jerry Zhang <jerry@skydio.com> wrote:
>
> "git apply" does not allow "--cached" and
> "--3way" to be used together, since "--3way"
> writes conflict markers into the working tree.
>
> Allow "git apply" to accept "--cached" and
> "--3way" at the same time.  When a single file
> auto-resolves cleanly, the result is placed in the
> index at stage #0 and the command exits with 0
> status.

Should this instead read:
  "...placed in the index at stage #0.  If all files auto-resolve
cleanly, the command exits with 0 status."
or something like that?

>  For a file that has a conflict which
> cannot be cleanly auto-resolved, the original
> contents from common ancestor (stage #1), our
> version (stage #2) and the contents from the
> patch (stage #3) are left at separate stages.
> No attempt is made to resolve the conflict at
> the content level, and the command exists with

s/exists/exits/

> non-zero status, because there is no place
> (like the working tree) to leave a half-resolved
> merge for the user to resolve.
>
> The user can use `git diff` to view the contents
> of the conflict, or `git checkout -m -- .` to
> regenerate the conflict markers in the working
> directory.
>
> Don't attempt rerere in this case since it depends
> on conflict markers written to file for its database
> storage and lookup. There would be two main changes
> required to get rerere working:
> 1. Allow the rerere api to accept in memory object
> rather than files, which would allow us to pass in
> the conflict markers contained in the result from
> ll_merge().
> 2. Rerere can't write to the working directory, so
> it would have to apply the result to cache stage #0
> directly. A flag would be needed to control this.
>
> Signed-off-by: Jerry Zhang <jerry@skydio.com>
> ---
> Patch applies on top of
> "[PATCH v2] git-apply: try threeway first when "--3way""
> Main merge conflict is the addition of multiple
> tests at the bottom of the file.
>
> v4->v5:
>
> Updated in file comment about rerere
> Added test for cleanly applying patch (should return 0)
> Previous test captured case where patch fails to apply
> due to 1 conflicting file and 1 cleanly applying file
> (returns 1).
>
>  Documentation/git-apply.txt |  6 +++--
>  apply.c                     |  9 ++++---
>  t/t4108-apply-threeway.sh   | 50 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 59 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/git-apply.txt b/Documentation/git-apply.txt
> index 9144575299c264dd299b542b7b5948eef35f211c..aa1ae56a25e0428cabcfa2539900ef2a09abcb7c 100644
> --- a/Documentation/git-apply.txt
> +++ b/Documentation/git-apply.txt
> @@ -87,8 +87,10 @@ OPTIONS
>         Attempt 3-way merge if the patch records the identity of blobs it is supposed
>         to apply to and we have those blobs available locally, possibly leaving the
>         conflict markers in the files in the working tree for the user to
> -       resolve.  This option implies the `--index` option, and is incompatible
> -       with the `--reject` and the `--cached` options.
> +       resolve.  This option implies the `--index` option unless the
> +       `--cached` option is used, and is incompatible with the `--reject` option.
> +       When used with the `--cached` option, any conflicts are left at higher stages
> +       in the cache.
>
>  --build-fake-ancestor=<file>::
>         Newer 'git diff' output has embedded 'index information'
> diff --git a/apply.c b/apply.c
> index 9bd4efcbced842d2c5c030a0f2178ddb36114600..dadab80ec967357b031657d4e3d0ae52fac11411 100644
> --- a/apply.c
> +++ b/apply.c
> @@ -133,8 +133,6 @@ int check_apply_state(struct apply_state *state, int force_apply)
>
>         if (state->apply_with_reject && state->threeway)
>                 return error(_("--reject and --3way cannot be used together."));
> -       if (state->cached && state->threeway)
> -               return error(_("--cached and --3way cannot be used together."));
>         if (state->threeway) {
>                 if (is_not_gitdir)
>                         return error(_("--3way outside a repository"));
> @@ -4644,8 +4642,11 @@ static int write_out_results(struct apply_state *state, struct patch *list)
>                                 fprintf(stderr, "U %s\n", item->string);
>                 }
>                 string_list_clear(&cpath, 0);
> -
> -               repo_rerere(state->repo, 0);
> +               /* Rerere relies on the partially merged result being in the working tree
> +                * with conflict markers, but that isn't written with --cached.
> +                */
> +               if (!state->cached)
> +                       repo_rerere(state->repo, 0);
>         }
>
>         return errs;
> diff --git a/t/t4108-apply-threeway.sh b/t/t4108-apply-threeway.sh
> index 9ff313f976422f9c12dc8032d14567b54cfe3765..65147efdea9a00e30d156e6f4d5d72a3987f230d 100755
> --- a/t/t4108-apply-threeway.sh
> +++ b/t/t4108-apply-threeway.sh
> @@ -180,4 +180,54 @@ test_expect_success 'apply -3 with ambiguous repeating file' '
>         test_cmp expect one_two_repeat
>  '
>
> +test_expect_success 'apply with --3way --cached clean apply' '
> +       # Merging side should be similar to applying this patch
> +       git diff ...side >P.diff &&
> +
> +       # The corresponding cleanly applied merge
> +       git reset --hard &&
> +       git checkout main~ &&
> +       git merge --no-commit side &&
> +       git ls-files -s >expect.ls &&
> +
> +       # should succeed
> +       git reset --hard &&
> +       git checkout main~ &&
> +       git apply --cached --3way P.diff &&
> +       git ls-files -s >actual.ls &&
> +       print_sanitized_conflicted_diff >actual.diff &&
> +
> +       # The cache should resemble the corresponding merge
> +       # (both files at stage #0)
> +       test_cmp expect.ls actual.ls &&
> +       # However the working directory should not change
> +       >expect.diff &&
> +       test_cmp expect.diff actual.diff
> +'
> +
> +test_expect_success 'apply with --3way --cached and conflicts' '
> +       # Merging side should be similar to applying this patch
> +       git diff ...side >P.diff &&
> +
> +       # The corresponding conflicted merge
> +       git reset --hard &&
> +       git checkout main^0 &&
> +       test_must_fail git merge --no-commit side &&
> +       git ls-files -s >expect.ls &&
> +
> +       # should fail to apply
> +       git reset --hard &&
> +       git checkout main^0 &&
> +       test_must_fail git apply --cached --3way P.diff &&
> +       git ls-files -s >actual.ls &&
> +       print_sanitized_conflicted_diff >actual.diff &&
> +
> +       # The cache should resemble the corresponding merge
> +       # (one file at stage #0, one file at stages #1 #2 #3)
> +       test_cmp expect.ls actual.ls &&
> +       # However the working directory should not change
> +       >expect.diff &&
> +       test_cmp expect.diff actual.diff
> +'
> +
>  test_done
> --
> 2.29.0

Otherwise, looks good to me.