Re: [PATCH v5 3/4] builtin/stash: provide a way to export stashes to a ref

[Phillip Wood <phillip.wood123@gmail.com>]

Hi brian

On 09/05/2025 00:44, brian m. carlson wrote:
> A common user problem is how to sync in-progress work to another
> machine.  Users currently must use some sort of transfer of the working
> tree, which poses security risks and also necessarily causes the index
> to become dirty.  The experience is suboptimal and frustrating for
> users.
> 
> A reasonable idea is to use the stash for this purpose, but the stash is
> stored in the reflog, not in a ref, and as such it cannot be pushed or
> pulled. 

I think the commit message would be more convincing if it concentrated
on the need to import / export chains of stashes and the convenience of
having a dedicated command to import a stash as one can export a single
stash with

     git push <remote> refs/stash@{<n>}:refs/exported-stash

and then import it with

     git pull <remote> refs/exported-stash
     git update-ref refs/stash FETCH_HEAD

Having said that I do agree that adding these new commands is a good
idea.

> @@ -154,6 +155,12 @@ store::
>   	reflog.  This is intended to be useful for scripts.  It is
>   	probably not the command you want to use; see "push" above.
>   
> +export ( --print | --to-ref <ref> ) [<stash>...]::

I was surprised to see that --to-ref does not take an argument. I think
that is confusing and it would be better to use OPT_STRING() rather than
OPT_CMDMODE() and manually check that only one of "--print" or
"--to-ref" is given. In the end it is no more work because now you have
to manually check that we have a ref when "--to-ref" is given.

I was also surprised to find that "git stash export HEAD" did not error
out. I was looking for a function that checked the topology of a stash
commit and could not find one so I thought I see how difficult it was to
add that. The fixup commit below adds a new function to check that a
commit looks like a stash and refuses to export anything else. The patch
adds a new function rather than using assert_stash_like() because
despite its name that function is pretty lax (any merge commit will
satisfy it) and is more concerned about filling out a stash_info struct.

Best Wishes

Phillip

---- >8 ----
From: Phillip Wood <phillip.wood@dunelm.org.uk>
Subject: [PATCH] fixup! builtin/stash: provide a way to export stashes to a
  ref

Reject commits that do not look like stashes.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
  builtin/stash.c | 42 ++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 42 insertions(+)

diff --git a/builtin/stash.c b/builtin/stash.c
index d8332af4017..02cf344ed96 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -180,6 +180,33 @@ static void free_stash_info(struct stash_info *info)
  	strbuf_release(&info->revision);
  }

+static int check_stash_topology(struct repository *r, struct commit *stash)
+{
+	struct commit *p1, *p2, *p3 = NULL;
+
+	/* stash must have two or three parents */
+	if (!stash->parents || !stash->parents->next ||
+	    (stash->parents->next->next && stash->parents->next->next->next))
+		return -1;
+	p1 = stash->parents->item;
+	p2 = stash->parents->next->item;
+	if (stash->parents->next->next)
+		p3 = stash->parents->next->next->item;
+	if (repo_parse_commit(r, p1) || repo_parse_commit(r, p2) ||
+	    (p3 && repo_parse_commit(r, p3)))
+		return -1;
+	/* p2 must have a single parent, p3 must have no parents */
+	if (!p2->parents || p2->parents->next || (p3 && p3->parents))
+		return -1;
+	if (repo_parse_commit(r, p2->parents->item))
+		return -1;
+	/* p2^1 must equal p1 */
+	if (!oideq(&p1->object.oid, &p2->parents->item->object.oid))
+		return -1;
+
+	return 0;
+}
+
  static void assert_stash_like(struct stash_info *info, const char *revision)
  {
  	if (get_oidf(&info->b_commit, "%s^1", revision) ||
@@ -2101,13 +2128,21 @@ static int do_export_stash(struct repository *r,
  		 */
  		for (i = 0; i < argc; i++) {
  			struct object_id oid;
+			struct commit *stash;
+
  			if (parse_revision(&revision, argv[i], 1) ||
  			    get_oid_with_context(r, revision.buf,
  						 GET_OID_QUIETLY | GET_OID_GENTLY,
  						 &oid, &unused)) {
  				res = error(_("unable to find stash entry %s"), argv[i]);
  				goto out;
  			}
+			stash = lookup_commit_reference(r, &oid);
+			if (!stash || check_stash_topology(r, stash)) {
+				res = error(_("%s does not look like a stash commit"),
+					    argv[i]);
+				goto out;
+			}
  			oid_array_append(&items, &oid);
  		}
  	} else {
@@ -2118,13 +2153,20 @@ static int do_export_stash(struct repository *r,
  		for (i = 0;; i++) {
  			char buf[32];
  			struct object_id oid;
+			struct commit *stash;

  			snprintf(buf, sizeof(buf), "%d", i);
  			if (parse_revision(&revision, buf, 1) ||
  			    get_oid_with_context(r, revision.buf,
  						 GET_OID_QUIETLY | GET_OID_GENTLY,
  						 &oid, &unused))
  				break;
+			stash = lookup_commit_reference(r, &oid);
+			if (!stash || check_stash_topology(r, stash)) {
+				res = error(_("%s does not look like a stash commit"),
+					    revision.buf);
+				goto out;
+			}
  			oid_array_append(&items, &oid);
  		}
  	}
-- 
2.49.0.300.g813f75aecee