checkout: fix bug with --to and relative HEAD

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");