Re: [PATCH v2 03/30] object-names: support input of oids in any supported hash

From: Linus Arver <linusa@google.com>
Date: Feb 13, 2024, 09:33 UTC
Message-ID: <owly7cj8d7y6.fsf@fine.c.googlers.com>
In-Reply-To: <20231002024034.2611-3-ebiederm@gmail.com>

"Eric W. Biederman" <ebiederm@gmail.com> writes:

Show 57 quoted lines

> From: "Eric W. Biederman" <ebiederm@xmission.com>
>
> Support short oids encoded in any algorithm, while ensuring enough of
> the oid is specified to disambiguate between all of the oids in the
> repository encoded in any algorithm.
>
> By default have the code continue to only accept oids specified in the
> storage hash algorithm of the repository, but when something is
> ambiguous display all of the possible oids from any accepted oid
> encoding.
>
> A new flag is added GET_OID_HASH_ANY that when supplied causes the
> code to accept oids specified in any hash algorithm, and to return the
> oids that were resolved.
>
> This implements the functionality that allows both SHA-1 and SHA-256
> object names, from the "Object names on the command line" section of
> the hash function transition document.
>
> Care is taken in get_short_oid so that when the result is ambiguous
> the output remains the same if GIT_OID_HASH_ANY was not supplied.  If
> GET_OID_HASH_ANY was supplied objects of any hash algorithm that match
> the prefix are displayed.
>
> This required updating repo_for_each_abbrev to give it a parameter so
> that it knows to look at all hash algorithms.
>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
> ---
>  builtin/rev-parse.c |  2 +-
>  hash-ll.h           |  1 +
>  object-name.c       | 46 ++++++++++++++++++++++++++++++++++-----------
>  object-name.h       |  3 ++-
>  4 files changed, 39 insertions(+), 13 deletions(-)
>
> diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
> index fde8861ca4e0..43e96765400c 100644
> --- a/builtin/rev-parse.c
> +++ b/builtin/rev-parse.c
> @@ -882,7 +882,7 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
>  				continue;
>  			}
>  			if (skip_prefix(arg, "--disambiguate=", &arg)) {
> -				repo_for_each_abbrev(the_repository, arg,
> +				repo_for_each_abbrev(the_repository, arg, the_hash_algo,
>  						     show_abbrev, NULL);
>  				continue;
>  			}
> diff --git a/hash-ll.h b/hash-ll.h
> index 10d84cc20888..2cfde63ae1cf 100644
> --- a/hash-ll.h
> +++ b/hash-ll.h
> @@ -145,6 +145,7 @@ struct object_id {
>  #define GET_OID_RECORD_PATH     0200
>  #define GET_OID_ONLY_TO_DIE    04000
>  #define GET_OID_REQUIRE_PATH  010000
> +#define GET_OID_HASH_ANY      020000

So far the "GET_OID_*" flags sound like the "GET_OID" is the prefix and the remaining text describes the behavior. So in this sense, the behavior here would be "HASH_ANY" and I think "ANY_HASH" is better. But also, going by the description of this flag in the commit message, I think "ACCEPT_ANY_HASH" is still better.

Show 20 quoted lines

>
>  #define GET_OID_DISAMBIGUATORS \
>  	(GET_OID_COMMIT | GET_OID_COMMITTISH | \
> diff --git a/object-name.c b/object-name.c
> index 0bfa29dbbfe9..7dd6e5e47566 100644
> --- a/object-name.c
> +++ b/object-name.c
> @@ -25,6 +25,7 @@
>  #include "midx.h"
>  #include "commit-reach.h"
>  #include "date.h"
> +#include "object-file-convert.h"
>
>  static int get_oid_oneline(struct repository *r, const char *, struct object_id *, struct commit_list *);
>
> @@ -49,6 +50,7 @@ struct disambiguate_state {
>
>  static void update_candidates(struct disambiguate_state *ds, const struct object_id *current)
>  {
> +	/* The hash algorithm of current has already been filtered */

Is this new comment describing existing behavior before this patch or after?

Show 9 quoted lines

>  	if (ds->always_call_fn) {
>  		ds->ambiguous = ds->fn(ds->repo, current, ds->cb_data) ? 1 : 0;
>  		return;
> @@ -134,6 +136,8 @@ static void unique_in_midx(struct multi_pack_index *m,
>  {
>  	uint32_t num, i, first = 0;
>  	const struct object_id *current = NULL;
> +	int len = ds->len > ds->repo->hash_algo->hexsz ?
> +		ds->repo->hash_algo->hexsz : ds->len;

Nit: So this is just trying to use the shorter length between ds->len
and hexsz. Would it be good to encode this information into the variable
name, such as "len_short" or similar? And if so, flipping the ">" to
"<" would be more natural, like

    int shorter_len = ds->len < ds->repo->hash_algo->hexsz ?
                      ds->len : ds->repo->hash_algo->hexsz;

because it reads "if ds->len is shorter, use it; otherwise use hexsz".

Show 18 quoted lines

>  	num = m->num_objects;
>
>  	if (!num)
> @@ -149,7 +153,7 @@ static void unique_in_midx(struct multi_pack_index *m,
>  	for (i = first; i < num && !ds->ambiguous; i++) {
>  		struct object_id oid;
>  		current = nth_midxed_object_oid(&oid, m, i);
> -		if (!match_hash(ds->len, ds->bin_pfx.hash, current->hash))
> +		if (!match_hash(len, ds->bin_pfx.hash, current->hash))
>  			break;
>  		update_candidates(ds, current);
>  	}
> @@ -159,6 +163,8 @@ static void unique_in_pack(struct packed_git *p,
>  			   struct disambiguate_state *ds)
>  {
>  	uint32_t num, i, first = 0;
> +	int len = ds->len > ds->repo->hash_algo->hexsz ?
> +		ds->repo->hash_algo->hexsz : ds->len;

Ditto.

Show 17 quoted lines

>
>  	if (p->multi_pack_index)
>  		return;
> @@ -177,7 +183,7 @@ static void unique_in_pack(struct packed_git *p,
>  	for (i = first; i < num && !ds->ambiguous; i++) {
>  		struct object_id oid;
>  		nth_packed_object_id(&oid, p, i);
> -		if (!match_hash(ds->len, ds->bin_pfx.hash, oid.hash))
> +		if (!match_hash(len, ds->bin_pfx.hash, oid.hash))
>  			break;
>  		update_candidates(ds, &oid);
>  	}
> @@ -188,6 +194,10 @@ static void find_short_packed_object(struct disambiguate_state *ds)
>  	struct multi_pack_index *m;
>  	struct packed_git *p;
>
> +	/* Skip, unless oids from the storage hash algorithm are wanted */

Perhaps a simpler phrasing would be

    /* Only accept oids specified in the storage hash algorithm of the repository. */

which is closer to the wording of the commit message?

Show 52 quoted lines

> +	if (ds->bin_pfx.algo && (&hash_algos[ds->bin_pfx.algo] != ds->repo->hash_algo))
> +		return;
> +
>  	for (m = get_multi_pack_index(ds->repo); m && !ds->ambiguous;
>  	     m = m->next)
>  		unique_in_midx(m, ds);
> @@ -326,11 +336,12 @@ int set_disambiguate_hint_config(const char *var, const char *value)
>
>  static int init_object_disambiguation(struct repository *r,
>  				      const char *name, int len,
> +				      const struct git_hash_algo *algo,
>  				      struct disambiguate_state *ds)
>  {
>  	int i;
>
> -	if (len < MINIMUM_ABBREV || len > the_hash_algo->hexsz)
> +	if (len < MINIMUM_ABBREV || len > GIT_MAX_HEXSZ)
>  		return -1;
>
>  	memset(ds, 0, sizeof(*ds));
> @@ -357,6 +368,7 @@ static int init_object_disambiguation(struct repository *r,
>  	ds->len = len;
>  	ds->hex_pfx[len] = '\0';
>  	ds->repo = r;
> +	ds->bin_pfx.algo = algo ? hash_algo_by_ptr(algo) : GIT_HASH_UNKNOWN;
>  	prepare_alt_odb(r);
>  	return 0;
>  }
> @@ -491,9 +503,10 @@ static int repo_collect_ambiguous(struct repository *r UNUSED,
>  	return collect_ambiguous(oid, data);
>  }
>
> -static int sort_ambiguous(const void *a, const void *b, void *ctx)
> +static int sort_ambiguous(const void *va, const void *vb, void *ctx)
>  {
>  	struct repository *sort_ambiguous_repo = ctx;
> +	const struct object_id *a = va, *b = vb;
>  	int a_type = oid_object_info(sort_ambiguous_repo, a, NULL);
>  	int b_type = oid_object_info(sort_ambiguous_repo, b, NULL);
>  	int a_type_sort;
> @@ -503,8 +516,12 @@ static int sort_ambiguous(const void *a, const void *b, void *ctx)
>  	 * Sorts by hash within the same object type, just as
>  	 * oid_array_for_each_unique() would do.
>  	 */
> -	if (a_type == b_type)
> -		return oidcmp(a, b);
> +	if (a_type == b_type) {
> +		if (a->algo == b->algo)
> +			return oidcmp(a, b);
> +		else
> +			return a->algo > b->algo ? 1 : -1;
> +	}

This is duplicated from the previous patch (void_hashcmp). Do we want to avoid a performance penalty from calling out to a common function?

Show 7 quoted lines

>  	/*
>  	 * Between object types show tags, then commits, and finally
> @@ -533,8 +550,12 @@ static enum get_oid_result get_short_oid(struct repository *r,
>  	int status;
>  	struct disambiguate_state ds;
>  	int quietly = !!(flags & GET_OID_QUIETLY);
> +	const struct git_hash_algo *algo = r->hash_algo;

I see some existing uses of the name "algop" (presumably to mean pointer-to-algorithm) and wonder if we should do the same here, for consistency.

> +
> +	if (flags & GET_OID_HASH_ANY)
> +		algo = NULL;

If we look at the change to init_object_disambiguation() above, it looks like the "algo" here is only used to find a GIT_HASH_* constant. So it seems a bit roundabout to use a NULL here, then inside init_object_disambiguation() do

    ds->bin_pfx.algo = algo ? hash_algo_by_ptr(algo) : GIT_HASH_UNKNOWN;

to convert the NULL to GIT_HASH_UNKNOWN when we could probably just pass in the GIT_HASH_* constant directly from the caller.

Show 36 quoted lines

> -	if (init_object_disambiguation(r, name, len, &ds) < 0)
> +	if (init_object_disambiguation(r, name, len, algo, &ds) < 0)
>  		return -1;
>
>  	if (HAS_MULTI_BITS(flags & GET_OID_DISAMBIGUATORS))
> @@ -588,7 +609,7 @@ static enum get_oid_result get_short_oid(struct repository *r,
>  		if (!ds.ambiguous)
>  			ds.fn = NULL;
>
> -		repo_for_each_abbrev(r, ds.hex_pfx, collect_ambiguous, &collect);
> +		repo_for_each_abbrev(r, ds.hex_pfx, algo, collect_ambiguous, &collect);
>  		sort_ambiguous_oid_array(r, &collect);
>
>  		if (oid_array_for_each(&collect, show_ambiguous_object, &out))
> @@ -610,13 +631,14 @@ static enum get_oid_result get_short_oid(struct repository *r,
>  }
>
>  int repo_for_each_abbrev(struct repository *r, const char *prefix,
> +			 const struct git_hash_algo *algo,
>  			 each_abbrev_fn fn, void *cb_data)
>  {
>  	struct oid_array collect = OID_ARRAY_INIT;
>  	struct disambiguate_state ds;
>  	int ret;
>
> -	if (init_object_disambiguation(r, prefix, strlen(prefix), &ds) < 0)
> +	if (init_object_disambiguation(r, prefix, strlen(prefix), algo, &ds) < 0)
>  		return -1;
>
>  	ds.always_call_fn = 1;
> @@ -787,10 +809,12 @@ void strbuf_add_unique_abbrev(struct strbuf *sb, const struct object_id *oid,
>  int repo_find_unique_abbrev_r(struct repository *r, char *hex,
>  			      const struct object_id *oid, int len)
>  {
> +	const struct git_hash_algo *algo =
> +		oid->algo ? &hash_algos[oid->algo] : r->hash_algo;

It would be nice to have symmetry with the style in get_short_oid() and instead do

   const struct git_hash_algo *algo = r->hash_algo;

   if (oid->algo)
       algo = &hash_algos[oid->algo];

Show 33 quoted lines

>  	struct disambiguate_state ds;
>  	struct min_abbrev_data mad;
>  	struct object_id oid_ret;
> -	const unsigned hexsz = r->hash_algo->hexsz;
> +	const unsigned hexsz = algo->hexsz;
>
>  	if (len < 0) {
>  		unsigned long count = repo_approximate_object_count(r);
> @@ -826,7 +850,7 @@ int repo_find_unique_abbrev_r(struct repository *r, char *hex,
>
>  	find_abbrev_len_packed(&mad);
>
> -	if (init_object_disambiguation(r, hex, mad.cur_len, &ds) < 0)
> +	if (init_object_disambiguation(r, hex, mad.cur_len, algo, &ds) < 0)
>  		return -1;
>
>  	ds.fn = repo_extend_abbrev_len;
> diff --git a/object-name.h b/object-name.h
> index 9ae522307148..064ddc97d1fe 100644
> --- a/object-name.h
> +++ b/object-name.h
> @@ -67,7 +67,8 @@ enum get_oid_result get_oid_with_context(struct repository *repo, const char *st
>
>
>  typedef int each_abbrev_fn(const struct object_id *oid, void *);
> -int repo_for_each_abbrev(struct repository *r, const char *prefix, each_abbrev_fn, void *);
> +int repo_for_each_abbrev(struct repository *r, const char *prefix,
> +			 const struct git_hash_algo *algo, each_abbrev_fn, void *);
>
>  int set_disambiguate_hint_config(const char *var, const char *value);
>
> --
> 2.41.0