Re: [RFC PATCH 1/2] merge-ort: add new merge-tree-ort command

[Elijah Newren <newren@gmail.com>]

On Wed, Jan 5, 2022 at 8:33 AM Christian Couder
<christian.couder@gmail.com> wrote:
>
> This new command is similar as merge-tree, but uses
> merge-ort code and features, especially
> merge_incore_nonrecursive(), instead of those from
> resursive merge, to perform the merge.

s/resursive/recursive/

> The output from this new command is very different from
> merge-tree's custom output, as we are only using code and
> features from diff.{h,c}, especially diff_tree_oid(). This
> should make it easy to customize and standardize the output
> using regular diff options in the future.
>
> This command will be extended to support new features
> with the long-term goal of enabling merges and rebases
> without a worktree.

And cherry-picks?  And reverts?

I think the cherry-pick/rebase replacement actually deserves a
separate command from what merges should use.  Replaying a sequence of
commits just has a number of UI differences and abilities that I think
pull it in a different direction.  And I don't want replaying of a
sequence of commits via a script like the old days (even if one that
calls something that doesn't update the working tree and index would
be better than the old rebases built on top of `git merge-recursive`
and `git cherry-pick`).  I'm working on such a thing, though it's
still kind of early.

>
> Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
> ---
>  .gitignore               |  1 +
>  Makefile                 |  1 +
>  builtin.h                |  1 +
>  builtin/merge-tree-ort.c | 93 ++++++++++++++++++++++++++++++++++++++++
>  git.c                    |  1 +
>  5 files changed, 97 insertions(+)
>  create mode 100644 builtin/merge-tree-ort.c
>
> diff --git a/.gitignore b/.gitignore
> index 054249b20a..2dfcb1a589 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -98,6 +98,7 @@
>  /git-merge-index
>  /git-merge-file
>  /git-merge-tree
> +/git-merge-tree-ort
>  /git-merge-octopus
>  /git-merge-one-file
>  /git-merge-ours
> diff --git a/Makefile b/Makefile
> index 75ed168adb..915e500b06 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1124,6 +1124,7 @@ BUILTIN_OBJS += builtin/merge-index.o
>  BUILTIN_OBJS += builtin/merge-ours.o
>  BUILTIN_OBJS += builtin/merge-recursive.o
>  BUILTIN_OBJS += builtin/merge-tree.o
> +BUILTIN_OBJS += builtin/merge-tree-ort.o
>  BUILTIN_OBJS += builtin/merge.o
>  BUILTIN_OBJS += builtin/mktag.o
>  BUILTIN_OBJS += builtin/mktree.o
> diff --git a/builtin.h b/builtin.h
> index 8a58743ed6..c68f46b118 100644
> --- a/builtin.h
> +++ b/builtin.h
> @@ -182,6 +182,7 @@ int cmd_merge_ours(int argc, const char **argv, const char *prefix);
>  int cmd_merge_file(int argc, const char **argv, const char *prefix);
>  int cmd_merge_recursive(int argc, const char **argv, const char *prefix);
>  int cmd_merge_tree(int argc, const char **argv, const char *prefix);
> +int cmd_merge_tree_ort(int argc, const char **argv, const char *prefix);
>  int cmd_mktag(int argc, const char **argv, const char *prefix);
>  int cmd_mktree(int argc, const char **argv, const char *prefix);
>  int cmd_multi_pack_index(int argc, const char **argv, const char *prefix);
> diff --git a/builtin/merge-tree-ort.c b/builtin/merge-tree-ort.c
> new file mode 100644
> index 0000000000..1c8ecd16ec
> --- /dev/null
> +++ b/builtin/merge-tree-ort.c
> @@ -0,0 +1,93 @@
> +#include "builtin.h"
> +#include "merge-ort.h"
> +#include "diff.h"
> +
> +static const char merge_tree_ort_usage[] = "git merge-tree-ort <base-tree> <branch1> <branch2>";

I think this is somewhat limiting to use for merges in general; it'll
generate trees that do not match what users get from `git merge ...`
at the command line, because specifying a single base-tree is
different than having the algorithm determine the merge base,
particularly when it needs to construct a virtual merge base.

> +
> +static void show_result(struct tree *base_tree,
> +                       struct tree *head_tree,
> +                       struct tree *merge_tree,
> +                       struct merge_result *result)
> +{
> +       const struct object_id *base_oid = &(base_tree->object.oid);
> +       const struct object_id *head_oid = &(head_tree->object.oid);
> +       const struct object_id *merge_oid = &(merge_tree->object.oid);
> +       const struct object_id *result_oid = &(result->tree->object.oid);
> +       struct diff_options opts;
> +
> +       repo_diff_setup(the_repository, &opts);
> +       opts.stat_width = -1; /* use full terminal width */
> +       opts.output_format |= DIFF_FORMAT_RAW | DIFF_FORMAT_PATCH;
> +       opts.detect_rename = DIFF_DETECT_RENAME;
> +       diff_setup_done(&opts);
> +
> +       printf("result tree: %s\n", oid_to_hex(result_oid));
> +       printf("clean: %d\n", result->clean);
> +
> +       printf("diff with branch1:\n");
> +       diff_tree_oid(head_oid, result_oid, "", &opts);
> +       diffcore_std(&opts);
> +       diff_flush(&opts);
> +
> +       printf("diff with branch2:\n");
> +       diff_tree_oid(merge_oid, result_oid, "", &opts);
> +       diffcore_std(&opts);
> +       diff_flush(&opts);
> +
> +       printf("diff with base:\n");
> +       diff_tree_oid(base_oid, result_oid, "", &opts);
> +       diffcore_std(&opts);
> +       diff_flush(&opts);

I commented on the diffs in my response on the cover letter.

> +}
> +
> +static struct commit *get_commit_by_name_or_die(const char *name)
> +{
> +       struct commit *c = lookup_commit_reference_by_name(name);
> +       if (!c)
> +               die(_("not a valid commit name '%s'"), name);
> +       return c;
> +}
> +
> +static void merge_trees_ort(const char *base_name,
> +                           const char *branch1,
> +                           const char *branch2)
> +{
> +       struct merge_result result;
> +       struct merge_options merge_opt;
> +
> +       struct commit *base = get_commit_by_name_or_die(base_name);
> +       struct commit *head = get_commit_by_name_or_die(branch1);
> +       struct commit *merge = get_commit_by_name_or_die(branch2);
> +
> +       struct tree *base_tree = get_commit_tree(base);
> +       struct tree *head_tree = get_commit_tree(head);
> +       struct tree *merge_tree = get_commit_tree(merge);
> +
> +       memset(&result, 0, sizeof(result));
> +       init_merge_options(&merge_opt, the_repository);
> +
> +       merge_opt.show_rename_progress = 1;
> +       merge_opt.branch1 = branch1;
> +       merge_opt.branch2 = branch2;
> +       merge_opt.ancestor = base_name;
> +
> +       result.tree = head_tree;
> +
> +       merge_incore_nonrecursive(&merge_opt,
> +                                 base_tree,
> +                                 result.tree,
> +                                 merge_tree,
> +                                 &result);

I think for server side merges, merge_incore_recursive() should be
used, so that they match what a `git merge ...` would provide.  I
think merge_incore_nonrecursive() is better used for replaying a
sequence of commits.

So, I view this as more suitable for usage with the server side
rebase, except that it seems to be serving as a building block and
expecting the rebase to be some script on top.  I think server-side
rebase/cherry-pick should be a builtin of some form.

> +
> +       show_result(base_tree, head_tree, merge_tree, &result);

As noted in the cover letter, this current form doesn't provide 2
things that users can't get some other way: (1) a list of conflicted
paths, and (2) the various conflict and warning messages generated
during the merge.  I agree that many usecases might not want those,
but since they can't be obtained another way I think it'd be prudent
to provide them.

And this show_result provides 3 things that users could generate on
their own with the information already provided -- namely the three
diffs that you do.  I'm curious what the usecase is for those diffs.

> +}
> +
> +int cmd_merge_tree_ort(int argc, const char **argv, const char *prefix)
> +{
> +       if (argc != 4)
> +               usage(merge_tree_ort_usage);
> +
> +       merge_trees_ort(argv[1], argv[2], argv[3]);
> +
> +       return 0;
> +}
> diff --git a/git.c b/git.c
> index 7edafd8ecf..90b8a4984c 100644
> --- a/git.c
> +++ b/git.c
> @@ -562,6 +562,7 @@ static struct cmd_struct commands[] = {
>         { "merge-recursive-theirs", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE | NO_PARSEOPT },
>         { "merge-subtree", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE | NO_PARSEOPT },
>         { "merge-tree", cmd_merge_tree, RUN_SETUP | NO_PARSEOPT },
> +       { "merge-tree-ort", cmd_merge_tree_ort, RUN_SETUP | NO_PARSEOPT },
>         { "mktag", cmd_mktag, RUN_SETUP | NO_PARSEOPT },
>         { "mktree", cmd_mktree, RUN_SETUP },
>         { "multi-pack-index", cmd_multi_pack_index, RUN_SETUP },
> --
> 2.34.1.433.g7bc349372a.dirty