Re: [PATCH v3 5/6] stash: apply stash using 'merge_ort_nonrecursive()'

>
> From: Victoria Dye <vdye@github.com>
>
> Update 'stash' to use 'merge_ort_nonrecursive()' to apply a stash to the
> current working tree. When 'git stash apply' was converted from its shell
> script implementation to a builtin in 8a0fc8d19d (stash: convert apply to
> builtin, 2019-02-25), 'merge_recursive_generic()' was used to merge a stash
> into the working tree as part of 'git stash (apply|pop)'. However, with the
> single merge base used in 'do_apply_stash()', the commit wrapping done by
> 'merge_recursive_generic()' is not only unnecessary, but misleading (the
> *real* merge base is labeled "constructed merge base"). Therefore, a
> non-recursive merge of the working tree, stashed tree, and stash base tree
> is more appropriate.
>
> There are two options for a non-recursive merge-then-update-worktree
> function: 'merge_trees()' and 'merge_ort_nonrecursive()'. Use
> 'merge_ort_nonrecursive()' to align with the default merge strategy used by
> 'git merge' (6a5fb96672 (Change default merge backend from recursive to ort,
> 2021-08-04)) and, because merge-ort does not operate in-place on the index,
> avoid unnecessary index expansion. Update tests in 't1092' verifying index
> expansion for 'git stash' accordingly.
>
> Signed-off-by: Victoria Dye <vdye@github.com>
> ---
>  builtin/stash.c                          | 30 +++++++++++++++++++-----
>  t/t1092-sparse-checkout-compatibility.sh |  4 ++--
>  2 files changed, 26 insertions(+), 8 deletions(-)
>
> diff --git a/builtin/stash.c b/builtin/stash.c
> index 1bfba532044..3fe549f7d3c 100644
> --- a/builtin/stash.c
> +++ b/builtin/stash.c
> @@ -7,6 +7,7 @@
>  #include "cache-tree.h"
>  #include "unpack-trees.h"
>  #include "merge-recursive.h"
> +#include "merge-ort-wrappers.h"
>  #include "strvec.h"
>  #include "run-command.h"
>  #include "dir.h"
> @@ -492,13 +493,13 @@ static void unstage_changes_unless_new(struct object_id *orig_tree)
>  static int do_apply_stash(const char *prefix, struct stash_info *info,
>                           int index, int quiet)
>  {
> -       int ret;
> +       int clean, ret;
>         int has_index = index;
>         struct merge_options o;
>         struct object_id c_tree;
>         struct object_id index_tree;
> -       struct commit *result;
> -       const struct object_id *bases[1];
> +       struct tree *head, *merge, *merge_base;
> +       struct lock_file lock = LOCK_INIT;
>
>         read_cache_preload(NULL);
>         if (refresh_and_write_cache(REFRESH_QUIET, 0, 0))
> @@ -541,6 +542,7 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
>
>         o.branch1 = "Updated upstream";
>         o.branch2 = "Stashed changes";
> +       o.ancestor = "Stash base";
>
>         if (oideq(&info->b_tree, &c_tree))
>                 o.branch1 = "Version stash was based on";
> @@ -551,10 +553,26 @@ static int do_apply_stash(const char *prefix, struct stash_info *info,
>         if (o.verbosity >= 3)
>                 printf_ln(_("Merging %s with %s"), o.branch1, o.branch2);
>
> -       bases[0] = &info->b_tree;
> +       head = lookup_tree(o.repo, &c_tree);
> +       merge = lookup_tree(o.repo, &info->w_tree);
> +       merge_base = lookup_tree(o.repo, &info->b_tree);
> +
> +       repo_hold_locked_index(o.repo, &lock, LOCK_DIE_ON_ERROR);
> +       clean = merge_ort_nonrecursive(&o, head, merge, merge_base);