git/builtin-describe.c
Shawn O. Pearce 1b600e659a Compute accurate distances in git-describe before output.
My prior change to git-describe attempts to print the distance
between the input commit and the best matching tag, but this distance
was usually only an estimate as we always aborted revision walking
as soon as we overflowed the configured limit on the number of
possible tags (as set by --candidates).

Displaying an estimated distance is not very useful and can just be
downright confusing.  Most users (heck, most Git developers) don't
immediately understand why this distance differs from the output
of common tools such as `git rev-list | wc -l`.  Even worse, the
estimated distance could change in the future (including decreasing
despite no rebase occuring) if we find more possible tags earlier
on during traversal.  (This could happen if more tags are merged
into the branch between queries.)  These factors basically make an
estimated distance useless.

Fortunately we are usually most of the way through an accurate
distance computation by the time we abort (due to reaching the
current --candidates limit).  This means we can simply finish
counting out the revisions still in our commit queue to present
the accurate distance at the end.  The number of commits remaining
in the commit queue is probably less than the number of commits
already traversed, so finishing out the count is not likely to take
very long.  This final distance will then always match the output of
`git rev-list | wc -l`.

We can easily reduce the total number of commits that need to be
walked at the end by stopping as soon as all of the commits in the
commit queue are flagged as being merged into the already selected
best possible tag.  If that's true then there are no remaining
unseen commits which can contribute to our best possible tag's
depth counter, so further traversal is useless.

Basic testing on my Mac OS X system shows there is no noticable
performance difference between this accurate distance counting
version of git-describe and the prior version of git-describe,
at least when run on git.git.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
2007-01-28 02:08:51 -08:00

285 lines
6.6 KiB
C

#include "cache.h"
#include "commit.h"
#include "tag.h"
#include "refs.h"
#include "builtin.h"
#define SEEN (1u<<0)
#define MAX_TAGS (FLAG_BITS - 1)
static const char describe_usage[] =
"git-describe [--all] [--tags] [--abbrev=<n>] <committish>*";
static int debug; /* Display lots of verbose info */
static int all; /* Default to annotated tags only */
static int tags; /* But allow any tags if --tags is specified */
static int abbrev = DEFAULT_ABBREV;
static int max_candidates = 10;
struct commit_name {
int prio; /* annotated tag = 2, tag = 1, head = 0 */
char path[FLEX_ARRAY]; /* more */
};
static const char *prio_names[] = {
"head", "lightweight", "annotated",
};
static void add_to_known_names(const char *path,
struct commit *commit,
int prio)
{
struct commit_name *e = commit->util;
if (!e || e->prio < prio) {
size_t len = strlen(path)+1;
free(e);
e = xmalloc(sizeof(struct commit_name) + len);
e->prio = prio;
memcpy(e->path, path, len);
commit->util = e;
}
}
static int get_name(const char *path, const unsigned char *sha1, int flag, void *cb_data)
{
struct commit *commit = lookup_commit_reference_gently(sha1, 1);
struct object *object;
int prio;
if (!commit)
return 0;
object = parse_object(sha1);
/* If --all, then any refs are used.
* If --tags, then any tags are used.
* Otherwise only annotated tags are used.
*/
if (!strncmp(path, "refs/tags/", 10)) {
if (object->type == OBJ_TAG)
prio = 2;
else
prio = 1;
}
else
prio = 0;
if (!all) {
if (!prio)
return 0;
if (!tags && prio < 2)
return 0;
}
add_to_known_names(all ? path + 5 : path + 10, commit, prio);
return 0;
}
struct possible_tag {
struct commit_name *name;
int depth;
int found_order;
unsigned flag_within;
};
static int compare_pt(const void *a_, const void *b_)
{
struct possible_tag *a = (struct possible_tag *)a_;
struct possible_tag *b = (struct possible_tag *)b_;
if (a->name->prio != b->name->prio)
return b->name->prio - a->name->prio;
if (a->depth != b->depth)
return a->depth - b->depth;
if (a->found_order != b->found_order)
return a->found_order - b->found_order;
return 0;
}
static unsigned long finish_depth_computation(
struct commit_list **list,
struct possible_tag *best)
{
unsigned long seen_commits = 0;
while (*list) {
struct commit *c = pop_commit(list);
struct commit_list *parents = c->parents;
seen_commits++;
if (c->object.flags & best->flag_within) {
struct commit_list *a = *list;
while (a) {
struct commit *i = a->item;
if (!(i->object.flags & best->flag_within))
break;
a = a->next;
}
if (!a)
break;
} else
best->depth++;
while (parents) {
struct commit *p = parents->item;
parse_commit(p);
if (!(p->object.flags & SEEN))
insert_by_date(p, list);
p->object.flags |= c->object.flags;
parents = parents->next;
}
}
return seen_commits;
}
static void describe(const char *arg, int last_one)
{
unsigned char sha1[20];
struct commit *cmit, *gave_up_on = NULL;
struct commit_list *list;
static int initialized = 0;
struct commit_name *n;
struct possible_tag all_matches[MAX_TAGS];
unsigned int match_cnt = 0, annotated_cnt = 0, cur_match;
unsigned long seen_commits = 0;
if (get_sha1(arg, sha1))
die("Not a valid object name %s", arg);
cmit = lookup_commit_reference(sha1);
if (!cmit)
die("%s is not a valid '%s' object", arg, commit_type);
if (!initialized) {
initialized = 1;
for_each_ref(get_name, NULL);
}
n = cmit->util;
if (n) {
printf("%s\n", n->path);
return;
}
if (debug)
fprintf(stderr, "searching to describe %s\n", arg);
list = NULL;
cmit->object.flags = SEEN;
commit_list_insert(cmit, &list);
while (list) {
struct commit *c = pop_commit(&list);
struct commit_list *parents = c->parents;
seen_commits++;
n = c->util;
if (n) {
if (match_cnt < max_candidates) {
struct possible_tag *t = &all_matches[match_cnt++];
t->name = n;
t->depth = seen_commits - 1;
t->flag_within = 1u << match_cnt;
t->found_order = match_cnt;
c->object.flags |= t->flag_within;
if (n->prio == 2)
annotated_cnt++;
}
else {
gave_up_on = c;
break;
}
}
for (cur_match = 0; cur_match < match_cnt; cur_match++) {
struct possible_tag *t = &all_matches[cur_match];
if (!(c->object.flags & t->flag_within))
t->depth++;
}
if (annotated_cnt && !list) {
if (debug)
fprintf(stderr, "finished search at %s\n",
sha1_to_hex(c->object.sha1));
break;
}
while (parents) {
struct commit *p = parents->item;
parse_commit(p);
if (!(p->object.flags & SEEN))
insert_by_date(p, &list);
p->object.flags |= c->object.flags;
parents = parents->next;
}
}
if (!match_cnt)
die("cannot describe '%s'", sha1_to_hex(cmit->object.sha1));
qsort(all_matches, match_cnt, sizeof(all_matches[0]), compare_pt);
if (gave_up_on) {
insert_by_date(gave_up_on, &list);
seen_commits--;
}
seen_commits += finish_depth_computation(&list, &all_matches[0]);
free_commit_list(list);
if (debug) {
for (cur_match = 0; cur_match < match_cnt; cur_match++) {
struct possible_tag *t = &all_matches[cur_match];
fprintf(stderr, " %-11s %8d %s\n",
prio_names[t->name->prio],
t->depth, t->name->path);
}
fprintf(stderr, "traversed %lu commits\n", seen_commits);
if (gave_up_on) {
fprintf(stderr,
"more than %i tags found; listed %i most recent\n"
"gave up search at %s\n",
max_candidates, max_candidates,
sha1_to_hex(gave_up_on->object.sha1));
}
}
if (abbrev == 0)
printf("%s\n", all_matches[0].name->path );
else
printf("%s-%d-g%s\n", all_matches[0].name->path,
all_matches[0].depth,
find_unique_abbrev(cmit->object.sha1, abbrev));
if (!last_one)
clear_commit_marks(cmit, -1);
}
int cmd_describe(int argc, const char **argv, const char *prefix)
{
int i;
for (i = 1; i < argc; i++) {
const char *arg = argv[i];
if (*arg != '-')
break;
else if (!strcmp(arg, "--debug"))
debug = 1;
else if (!strcmp(arg, "--all"))
all = 1;
else if (!strcmp(arg, "--tags"))
tags = 1;
else if (!strncmp(arg, "--abbrev=", 9)) {
abbrev = strtoul(arg + 9, NULL, 10);
if (abbrev != 0 && (abbrev < MINIMUM_ABBREV || 40 < abbrev))
abbrev = DEFAULT_ABBREV;
}
else if (!strncmp(arg, "--candidates=", 13)) {
max_candidates = strtoul(arg + 13, NULL, 10);
if (max_candidates < 1)
max_candidates = 1;
else if (max_candidates > MAX_TAGS)
max_candidates = MAX_TAGS;
}
else
usage(describe_usage);
}
save_commit_buffer = 0;
if (argc <= i)
describe("HEAD", 1);
else
while (i < argc) {
describe(argv[i], (i == argc - 1));
i++;
}
return 0;
}