Re: [PATCH] notes: handle multiple worktrees

[Eric Sunshine <sunshine@sunshineco.com>]

On Tue, Jul 28, 2015 at 5:23 PM, David Turner <dturner@twopensource.com> wrote:
> Prevent merges to the same notes branch from different worktrees.
> Before creating NOTES_MERGE_REF, check NOTES_MERGE_REF using the same
> code we use to check that two HEADs in different worktrees don't point
> to the same branch.  Modify that code, die_if_checked_out, to take a
> "head" ref to examine; previously, it just looked at HEAD.

die_if_checked_out() seems to be grossly misnamed following this
change since a branch (or detached head) can be "checked out", but
asking it if a HEAD or NOTES_MERGE_REF is "checked out" sounds weird.
Perhaps rename it to die_if_symref_shared() or something?

The new argument order, die_if_checked_out("HEAD", "branchname"), also
seems backward to me, at least with the current function name
(die_if_checked_out). With a better function name, maybe it wouldn't
be so bad.

I could also see die_if_checked_out() being refactored to move the
underlying logic to a new (better named) function for checking the
value of a particular file (HEAD, NOTES_MERGE_REF) in each linked
worktree. And then die_if_checked_out() would be a thin wrapper over
that new function. A reason for preferring this approach and keeping
die_if_checked_out() as a convenience wrapper is that it's likely that
it's going to be needed in more places in the future.

> Reported-by: Junio C Hamano <gitster@pobox.com>
> Signed-off-by: David Turner <dturner@twopensource.com>
> ---
> diff --git a/branch.c b/branch.c
> index c85be07..60eadc6 100644
> --- a/branch.c
> +++ b/branch.c
> @@ -311,21 +311,22 @@ void remove_branch_state(void)
>         unlink(git_path("SQUASH_MSG"));
>  }
>
> -static void check_linked_checkout(const char *branch, const char *id)
> +static void check_linked_checkout(const char *head, const char *branch,
> +                                 const char *id)
>  {
>         struct strbuf sb = STRBUF_INIT;
>         struct strbuf path = STRBUF_INIT;
>         struct strbuf gitdir = STRBUF_INIT;
>
>         /*
> -        * $GIT_COMMON_DIR/HEAD is practically outside
> +        * $GIT_COMMON_DIR/$head is practically outside
>          * $GIT_DIR so resolve_ref_unsafe() won't work (it
>          * uses git_path). Parse the ref ourselves.
>          */
>         if (id)
> -               strbuf_addf(&path, "%s/worktrees/%s/HEAD", get_git_common_dir(), id);
> +               strbuf_addf(&path, "%s/worktrees/%s/%s", get_git_common_dir(), id, head);
>         else
> -               strbuf_addf(&path, "%s/HEAD", get_git_common_dir());
> +               strbuf_addf(&path, "%s/%s", get_git_common_dir(), head);
>
>         if (!strbuf_readlink(&sb, path.buf, 0)) {
>                 if (!starts_with(sb.buf, "refs/") ||
> @@ -356,13 +357,13 @@ done:
>         strbuf_release(&gitdir);
>  }
>
> -void die_if_checked_out(const char *branch)
> +void die_if_checked_out(const char *head, const char *branch)
>  {
>         struct strbuf path = STRBUF_INIT;
>         DIR *dir;
>         struct dirent *d;
>
> -       check_linked_checkout(branch, NULL);
> +       check_linked_checkout(head, branch, NULL);
>
>         strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
>         dir = opendir(path.buf);
> @@ -373,7 +374,7 @@ void die_if_checked_out(const char *branch)
>         while ((d = readdir(dir)) != NULL) {
>                 if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
>                         continue;
> -               check_linked_checkout(branch, d->d_name);
> +               check_linked_checkout(head, branch, d->d_name);
>         }
>         closedir(dir);
>  }
> diff --git a/branch.h b/branch.h
> index 58aa45f..3577fe5 100644
> --- a/branch.h
> +++ b/branch.h
> @@ -57,6 +57,6 @@ extern int read_branch_desc(struct strbuf *, const char *branch_name);
>   * worktree and die (with a message describing its checkout location) if
>   * it is.
>   */
> -extern void die_if_checked_out(const char *branch);
> +extern void die_if_checked_out(const char *head, const char *branch);
>
>  #endif