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

> 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));