Re: [PATCH v3 0/2] merge-tree: add new --dry-run option

["Kristoffer Haugsbakk" <kristofferhaugsbakk@fastmail.com>]

On Wed, May 14, 2025, at 02:24, Elijah Newren via GitGitGadget wrote:
> Changes since v2:
>
>  * Converted locations missed in v1 in changing --mergeability-only ->
>    --dry-run
>
> Changes since v1:
>
>  * Renamed --mergeability-only flag to --dry-run, as per suggestion from
>    Junio
>  * added some commit message clarifications
>
> This adds a new flag, --dry-run, to git merge-tree, which suppresses all
> output and leaves only the exit status (reflecting successful merge or
> conflict). This is useful for Git Forges in cases where they are only
> interested in whether two branches can be merged, without needing the actual
> merge result or conflict details.
>
> The advantage of the flag is two fold:
>
>  * The merge machinery can exit once it detects a conflict, instead of
>    continuing to compute merge result information
>  * The merge machinery can avoid writing merged blobs and trees to the
>    object store when in the outer layer of the merging process (more details
>    in the first commit message).
>
> Elijah Newren (2):
>   merge-ort: add a new mergeability_only option
>   merge-tree: add a new --dry-run flag

All I can say is that this looks good considering the comments on v2.

Interdiff:

```
diff --git a/Documentation/git-merge-tree.adoc b/Documentation/git-merge-tree.adoc
index 7dcc1780619..74716b91019 100644
--- a/Documentation/git-merge-tree.adoc
+++ b/Documentation/git-merge-tree.adoc
@@ -65,11 +65,11 @@ OPTIONS
 	default is to include these messages if there are merge
 	conflicts, and to omit them otherwise.

---mergeability-only::
+--dry-run::
 	Disable all output from the program.  Useful when you are only
 	interested in the exit status.  Allows merge-tree to exit
-	early on the first conflict it finds, and allows it to avoid
-	writing most objects created by merges.
+	early when it finds a conflict, and allows it to avoid writing
+	most objects created by merges.

 --allow-unrelated-histories::
 	merge-tree will by default error out if the two branches specified
diff --git a/builtin/merge-tree.c b/builtin/merge-tree.c
index 579e81d5184..273ec171e98 100644
--- a/builtin/merge-tree.c
+++ b/builtin/merge-tree.c
@@ -596,13 +596,13 @@ int cmd_merge_tree(int argc,
 	if (dry_run && o.show_messages == -1)
 		o.show_messages = 0;
 	o.merge_options.mergeability_only = dry_run;
-	die_for_incompatible_opt2(dry_run, "--mergeability-only",
+	die_for_incompatible_opt2(dry_run, "--dry-run",
 				  o.show_messages, "--messages");
-	die_for_incompatible_opt2(dry_run, "--mergeability-only",
+	die_for_incompatible_opt2(dry_run, "--dry-run",
 				  o.name_only, "--name-only");
-	die_for_incompatible_opt2(dry_run, "--mergeability-only",
+	die_for_incompatible_opt2(dry_run, "--dry-run",
 				  o.use_stdin, "--stdin");
-	die_for_incompatible_opt2(dry_run, "--mergeability-only",
+	die_for_incompatible_opt2(dry_run, "--dry-run",
 				  !line_termination, "-z");

 	if (xopts.nr && o.mode == MODE_TRIVIAL)
```