Re: [PATCH v3 2/3] shallow: offer to prune only non-existing entries

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Junio & Jonathan,

On Wed, 24 Oct 2018, Junio C Hamano wrote:

> Jonathan, do you see any issues with the use of lookup_commit() in
> this change wrt lazy clone?  I am wondering what happens when the
> commit in question is at, an immediate parent of, or an immediate
> child of a promisor object.  I _think_ this change won't make it
> worse for two features in playing together, but thought that it
> would be better to double check.

Good point.

Instinctively, I would say that no promised object can be a shallow
commit. The entire idea of a shallow commit is that it *is* present, but
none of its parents.

Also, I would claim that the shallow feature does not make sense with lazy
clones, as lazy clones offer a superset of shallow clone's functionality.

However, I am curious whether there is a better way to check for the
presence of a local commit? Do we have an API function for that, that I
missed? (I do not really want to parse the commit, after all, just verify
that it is not pruned.)

Thanks,
Dscho

> 
> "Johannes Schindelin via GitGitGadget" <gitgitgadget@gmail.com>
> writes:
> 
> > From: Johannes Schindelin <johannes.schindelin@gmx.de>
> >
> > The `prune_shallow()` function wants a full reachability check to be
> > completed before it goes to work, to ensure that all unreachable entries
> > are removed from the shallow file.
> >
> > However, in the upcoming patch we do not even want to go that far. We
> > really only need to remove entries corresponding to pruned commits, i.e.
> > to commits that no longer exist.
> >
> > Let's support that use case.
> >
> > Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
> > ---
> >  builtin/prune.c |  2 +-
> >  commit.h        |  2 +-
> >  shallow.c       | 22 +++++++++++++++++-----
> >  3 files changed, 19 insertions(+), 7 deletions(-)
> >
> > diff --git a/builtin/prune.c b/builtin/prune.c
> > index 41230f821..6d6ab6cf1 100644
> > --- a/builtin/prune.c
> > +++ b/builtin/prune.c
> > @@ -161,7 +161,7 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
> >  	free(s);
> >  
> >  	if (is_repository_shallow(the_repository))
> > -		prune_shallow(show_only);
> > +		prune_shallow(show_only, 0);
> >  
> >  	return 0;
> >  }
> > diff --git a/commit.h b/commit.h
> > index 1d260d62f..ff34447ab 100644
> > --- a/commit.h
> > +++ b/commit.h
> > @@ -249,7 +249,7 @@ extern void assign_shallow_commits_to_refs(struct shallow_info *info,
> >  					   uint32_t **used,
> >  					   int *ref_status);
> >  extern int delayed_reachability_test(struct shallow_info *si, int c);
> > -extern void prune_shallow(int show_only);
> > +extern void prune_shallow(int show_only, int quick_prune);
> >  extern struct trace_key trace_shallow;
> >  
> >  extern int interactive_add(int argc, const char **argv, const char *prefix, int patch);
> > diff --git a/shallow.c b/shallow.c
> > index 732e18d54..0a2671bc2 100644
> > --- a/shallow.c
> > +++ b/shallow.c
> > @@ -247,6 +247,7 @@ static void check_shallow_file_for_update(struct repository *r)
> >  
> >  #define SEEN_ONLY 1
> >  #define VERBOSE   2
> > +#define QUICK_PRUNE 4
> >  
> >  struct write_shallow_data {
> >  	struct strbuf *out;
> > @@ -261,7 +262,11 @@ static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
> >  	const char *hex = oid_to_hex(&graft->oid);
> >  	if (graft->nr_parent != -1)
> >  		return 0;
> > -	if (data->flags & SEEN_ONLY) {
> > +	if (data->flags & QUICK_PRUNE) {
> > +		struct commit *c = lookup_commit(the_repository, &graft->oid);
> > +		if (!c || parse_commit(c))
> > +			return 0;
> > +	} else if (data->flags & SEEN_ONLY) {
> >  		struct commit *c = lookup_commit(the_repository, &graft->oid);
> >  		if (!c || !(c->object.flags & SEEN)) {
> >  			if (data->flags & VERBOSE)
> > @@ -371,16 +376,23 @@ void advertise_shallow_grafts(int fd)
> >  
> >  /*
> >   * mark_reachable_objects() should have been run prior to this and all
> > - * reachable commits marked as "SEEN".
> > + * reachable commits marked as "SEEN", except when quick_prune is non-zero,
> > + * in which case lines are excised from the shallow file if they refer to
> > + * commits that do not exist (any longer).
> >   */
> > -void prune_shallow(int show_only)
> > +void prune_shallow(int show_only, int quick_prune)
> >  {
> >  	struct lock_file shallow_lock = LOCK_INIT;
> >  	struct strbuf sb = STRBUF_INIT;
> > +	unsigned flags = SEEN_ONLY;
> >  	int fd;
> >  
> > +	if (quick_prune)
> > +		flags |= QUICK_PRUNE;
> > +
> >  	if (show_only) {
> > -		write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY | VERBOSE);
> > +		flags |= VERBOSE;
> > +		write_shallow_commits_1(&sb, 0, NULL, flags);
> >  		strbuf_release(&sb);
> >  		return;
> >  	}
> > @@ -388,7 +400,7 @@ void prune_shallow(int show_only)
> >  				       git_path_shallow(the_repository),
> >  				       LOCK_DIE_ON_ERROR);
> >  	check_shallow_file_for_update(the_repository);
> > -	if (write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY)) {
> > +	if (write_shallow_commits_1(&sb, 0, NULL, flags)) {
> >  		if (write_in_full(fd, sb.buf, sb.len) < 0)
> >  			die_errno("failed to write to %s",
> >  				  get_lock_file_path(&shallow_lock));
>