checkout: fix bug with --to and relative HEAD

Given "git checkout --to <path> HEAD~1", the new worktree's HEAD should
begin life at the current branch's HEAD~1, however, it actually ends up
at HEAD~2. This happens because:

    1. git-checkout resolves HEAD~1

    2. to satisfy is_git_directory(), prepare_linked_worktree() creates
       a HEAD for the new worktree with the value of the resolved HEAD~1

    3. git-checkout re-invokes itself with the same arguments within the
       new worktree to populate the worktree

    4. the sub git-checkout resolves HEAD~1 relative to its own HEAD,
       which is the resolved HEAD~1 from the original invocation,
       resulting unexpectedly and incorrectly in HEAD~2 (relative to the
       original)

Fix this by unconditionally assigning the current worktree's HEAD as the
value of the new worktree's HEAD.

As a side-effect, this change also eliminates a dependence within
prepare_linked_checkout() upon 'struct branch_info'. The plan is to
eventually relocate "git checkout --to" functionality to "git worktree
add", and worktree.c won't have knowledge of 'struct branch_info', so
removal of this dependency is a step toward that goal.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 2079aa417076201dd6bafe832393eb27aaa83ec9..5ada22a39084f3a301115e7091100a51965ae51c 100644 (file)
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -863,6 +863,7 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
        struct stat st;
        struct child_process cp;
        int counter = 0, len, ret;
+       unsigned char rev[20];
 
        if (!new->commit)
                die(_("no branch specified"));
@@ -920,13 +921,20 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
                   real_path(get_git_common_dir()), name);
        /*
         * This is to keep resolve_ref() happy. We need a valid HEAD
-        * or is_git_directory() will reject the directory. Any valid
-        * value would do because this value will be ignored and
-        * replaced at the next (real) checkout.
+        * or is_git_directory() will reject the directory. Moreover, HEAD
+        * in the new worktree must resolve to the same value as HEAD in
+        * the current tree since the command invoked to populate the new
+        * worktree will be handed the branch/ref specified by the user.
+        * For instance, if the user asks for the new worktree to be based
+        * at HEAD~5, then the resolved HEAD~5 in the new worktree must
+        * match the resolved HEAD~5 in the current tree in order to match
+        * the user's expectation.
         */
+       if (!resolve_ref_unsafe("HEAD", 0, rev, NULL))
+               die(_("unable to resolve HEAD"));
        strbuf_reset(&sb);
        strbuf_addf(&sb, "%s/HEAD", sb_repo.buf);
-       write_file(sb.buf, 1, "%s\n", sha1_to_hex(new->commit->object.sha1));
+       write_file(sb.buf, 1, "%s\n", sha1_to_hex(rev));
        strbuf_reset(&sb);
        strbuf_addf(&sb, "%s/commondir", sb_repo.buf);
        write_file(sb.buf, 1, "../..\n");

diff --git a/t/t2025-checkout-to.sh b/t/t2025-checkout-to.sh
index a8d93366f6bff23ec8edab5227f4931215a6dd3d..0fd731b4bc5d53fe63a7dd8a73457a6e916b7b98 100755 (executable)
--- a/t/t2025-checkout-to.sh
+++ b/t/t2025-checkout-to.sh
@@ -134,4 +134,14 @@ test_expect_success 'checkout with grafts' '
        test_cmp expected actual
 '
 
+test_expect_success 'checkout --to from relative HEAD' '
+       test_commit a &&
+       test_commit b &&
+       test_commit c &&
+       git rev-parse HEAD~1 >expected &&
+       git checkout --to relhead HEAD~1 &&
+       git -C relhead rev-parse HEAD >actual &&
+       test_cmp expected actual
+'
+
 test_done