Re: [PATCH v4 3/4] sequencer: refactor the code to detach HEAD to checkout.c

[Pratik Karki <predatoramigo@gmail.com>]

Hi,
On Mon, Jul 9, 2018 at 3:16 AM Johannes Schindelin
<Johannes.Schindelin@gmx.de> wrote:
>
> Hi Pratik,
>
> On Sun, 8 Jul 2018, Pratik Karki wrote:
>
> > diff --git a/checkout.c b/checkout.c
> > index bdefc888ba..da68915fd7 100644
> > --- a/checkout.c
> > +++ b/checkout.c
> > @@ -2,6 +2,11 @@
> >  #include "remote.h"
> >  #include "refspec.h"
> >  #include "checkout.h"
> > +#include "unpack-trees.h"
> > +#include "lockfile.h"
> > +#include "refs.h"
> > +#include "tree.h"
> > +#include "cache-tree.h"
> >
> >  struct tracking_name_data {
> >       /* const */ char *src_ref;
> > @@ -42,3 +47,62 @@ const char *unique_tracking_name(const char *name, struct object_id *oid)
> >       free(cb_data.dst_ref);
> >       return NULL;
> >  }
> > +
> > +int detach_head_to(struct object_id *oid, const char *action,
> > +                const char *reflog_message)
> > +{
> > +     struct strbuf ref_name = STRBUF_INIT;
> > +     struct tree_desc desc;
> > +     struct lock_file lock = LOCK_INIT;
> > +     struct unpack_trees_options unpack_tree_opts;
> > +     struct tree *tree;
> > +     int ret = 0;
> > +
> > +     if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0)
> > +             return -1;
> > +
> > +     memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));
> > +     setup_unpack_trees_porcelain(&unpack_tree_opts, action);
> > +     unpack_tree_opts.head_idx = 1;
> > +     unpack_tree_opts.src_index = &the_index;
> > +     unpack_tree_opts.dst_index = &the_index;
> > +     unpack_tree_opts.fn = oneway_merge;
> > +     unpack_tree_opts.merge = 1;
> > +     unpack_tree_opts.update = 1;
> > +
> > +     if (read_cache_unmerged()) {
> > +             rollback_lock_file(&lock);
> > +             strbuf_release(&ref_name);
> > +             return error_resolve_conflict(_(action));
> > +     }
> > +
> > +     if (!fill_tree_descriptor(&desc, oid)) {
> > +             error(_("failed to find tree of %s"), oid_to_hex(oid));
> > +             rollback_lock_file(&lock);
> > +             free((void *)desc.buffer);
> > +             strbuf_release(&ref_name);
> > +             return -1;
> > +     }
> > +
> > +     if (unpack_trees(1, &desc, &unpack_tree_opts)) {
> > +             rollback_lock_file(&lock);
> > +             free((void *)desc.buffer);
> > +             strbuf_release(&ref_name);
> > +             return -1;
> > +     }
> > +
> > +     tree = parse_tree_indirect(oid);
> > +     prime_cache_tree(&the_index, tree);
> > +
> > +     if (write_locked_index(&the_index, &lock, COMMIT_LOCK) < 0)
> > +             ret = error(_("could not write index"));
> > +     free((void *)desc.buffer);
> > +
> > +     if (!ret)
> > +             ret = update_ref(reflog_message, "HEAD", oid,
> > +                              NULL, 0, UPDATE_REFS_MSG_ON_ERR);
>
> I noticed that this does not actually detach the HEAD. That is my fault,
> of course, as I should have not only suggested refactoring the
> `do_reset()` function from `sequencer.c`, but I should also have
> remembered that that function has the benefit of *always* acting on a
> detached HEAD (because it runs during an interactive rebase), and
> therefore does not need to detach it explicitly.
>
> In light of the `reset_hard()` function that you added in a `wip` (see
> https://github.com/git/git/pull/505/files#diff-c7361e406139e8cd3a300b80b8f8cc8dR296),
> I could imagine that it might be better, after all, to leave `do_reset()`
> alone and implement a `reset_hard()` function that also optionally
> detaches the `HEAD` (I *think* that the flag `REF_NO_DEREF` would do that
> for you).

Yes. I think this will be better. Thanks.

> Alternatively, just update the code in `do_reset()` to use that flag
> first, and only *then* extract the code to `checkout.c`.
>
> (I could not resist, and made this quick change on top of your
> `wip-rebase`, and together with a couple more, obvious fixups, this lets
> t3403 pass. It still needs some things that you have not yet sent to the
> mailing list, such as support for `--skip`.)

Thank you for taking the time to review.