builtin/stash: fix `--keep-index --include-untracked` with empty HEAD

It was reported that creating a stash with `--keep-index
--include-untracked` causes an error when HEAD points to a commit whose
tree is empty:

    $ git stash push --keep-index --include-untracked
    error: pathspec ':/' did not match any file(s) known to git

This error comes from `git checkout --no-overlay $i_tree -- :/`, which
we execute to reset the working tree to the state in our index. As the
tree generated from the index is empty in our case, ':/' does not match
any files and thus causes git-checkout(1) to error out.

Fix the issue by skipping the checkout when the index tree is empty. As
explained in the in-code comment, this should be the correct thing to do
as there is nothing that we'd have to reset in the first place.

Reported-by: Piotr Siupa <piotrsiupa@gmail.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/stash.c b/builtin/stash.c
index 3a4f9fd566d27cfea7039f9c92f7a9730f37f912..d2b701ef88f755c6e29fc0d95de11ccd37ca7c1c 100644 (file)
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -1647,7 +1647,28 @@ static int do_push_stash(const struct pathspec *ps, const char *stash_msg, int q
                        }
                }
 
-               if (keep_index == 1 && !is_null_oid(&info.i_tree)) {
+               /*
+                * When keeping staged entries, we need to reset the working
+                * directory to match the state of our index. This can be
+                * skipped when the index is the empty tree, because there is
+                * nothing to reset in that case:
+                *
+                *   - When the index has any file, regardless of whether
+                *     staged or not, the tree cannot be empty by definition
+                *     and thus we enter the condition.
+                *
+                *   - When the index has no files, the only thing we need to
+                *     care about is untracked files when `--include-untracked`
+                *     is given. But as we already execute git-clean(1) further
+                *     up to delete such untracked files we don't have to do
+                *     anything here, either.
+                *
+                * We thus skip calling git-checkout(1) in this case, also
+                * because running it on an empty tree will cause it to fail
+                * due to the pathspec not matching anything.
+                */
+               if (keep_index == 1 && !is_null_oid(&info.i_tree) &&
+                   !is_empty_tree_oid(&info.i_tree, the_repository->hash_algo)) {
                        struct child_process cp = CHILD_PROCESS_INIT;
 
                        cp.git_cmd = 1;

diff --git a/t/t3903-stash.sh b/t/t3903-stash.sh
index 376cc8f4ab8429b0488ad23b0f9731c9af237124..38906785e2a76207cc507f7960a7cef61c210ad8 100755 (executable)
--- a/t/t3903-stash.sh
+++ b/t/t3903-stash.sh
@@ -1384,6 +1384,21 @@ test_expect_success 'stash --keep-index with file deleted in index does not resu
        test_path_is_missing to-remove
 '
 
+test_expect_success 'stash --keep-index --include-untracked with empty tree' '
+       test_when_finished "rm -rf empty" &&
+       git init empty &&
+       (
+               cd empty &&
+               git commit --allow-empty --message "empty" &&
+               echo content >file &&
+               git stash push --keep-index --include-untracked &&
+               test_path_is_missing file &&
+               git stash pop &&
+               echo content >expect &&
+               test_cmp expect file
+       )
+'
+
 test_expect_success 'stash apply should succeed with unmodified file' '
        echo base >file &&
        git add file &&