sha1_name.c

   1 #include "cache.h"
   2 #include "tag.h"
   3 #include "commit.h"
   4 #include "tree.h"
   5 #include "blob.h"
   6 #include "tree-walk.h"
   7 #include "refs.h"
   8
   9 static int find_short_object_filename(int len, const char *name, unsigned char *sha1)
  10 {
  11         struct alternate_object_database *alt;
  12         char hex[40];
  13         int found = 0;
  14         static struct alternate_object_database *fakeent;
  15
  16         if (!fakeent) {
  17                 const char *objdir = get_object_directory();
  18                 int objdir_len = strlen(objdir);
  19                 int entlen = objdir_len + 43;
  20                 fakeent = xmalloc(sizeof(*fakeent) + entlen);
  21                 memcpy(fakeent->base, objdir, objdir_len);
  22                 fakeent->name = fakeent->base + objdir_len + 1;
  23                 fakeent->name[-1] = '/';
  24         }
  25         fakeent->next = alt_odb_list;
  26
  27         sprintf(hex, "%.2s", name);
  28         for (alt = fakeent; alt && found < 2; alt = alt->next) {
  29                 struct dirent *de;
  30                 DIR *dir;
  31                 sprintf(alt->name, "%.2s/", name);
  32                 dir = opendir(alt->base);
  33                 if (!dir)
  34                         continue;
  35                 while ((de = readdir(dir)) != NULL) {
  36                         if (strlen(de->d_name) != 38)
  37                                 continue;
  38                         if (memcmp(de->d_name, name + 2, len - 2))
  39                                 continue;
  40                         if (!found) {
  41                                 memcpy(hex + 2, de->d_name, 38);
  42                                 found++;
  43                         }
  44                         else if (memcmp(hex + 2, de->d_name, 38)) {
  45                                 found = 2;
  46                                 break;
  47                         }
  48                 }
  49                 closedir(dir);
  50         }
  51         if (found == 1)
  52                 return get_sha1_hex(hex, sha1) == 0;
  53         return found;
  54 }
  55
  56 static int match_sha(unsigned len, const unsigned char *a, const unsigned char *b)
  57 {
  58         do {
  59                 if (*a != *b)
  60                         return 0;
  61                 a++;
  62                 b++;
  63                 len -= 2;
  64         } while (len > 1);
  65         if (len)
  66                 if ((*a ^ *b) & 0xf0)
  67                         return 0;
  68         return 1;
  69 }
  70
  71 static int find_short_packed_object(int len, const unsigned char *match, unsigned char *sha1)
  72 {
  73         struct packed_git *p;
  74         const unsigned char *found_sha1 = NULL;
  75         int found = 0;
  76
  77         prepare_packed_git();
  78         for (p = packed_git; p && found < 2; p = p->next) {
  79                 uint32_t num, last;
  80                 uint32_t first = 0;
  81                 open_pack_index(p);
  82                 num = p->num_objects;
  83                 last = num;
  84                 while (first < last) {
  85                         uint32_t mid = (first + last) / 2;
  86                         const unsigned char *now;
  87                         int cmp;
  88
  89                         now = nth_packed_object_sha1(p, mid);
  90                         cmp = hashcmp(match, now);
  91                         if (!cmp) {
  92                                 first = mid;
  93                                 break;
  94                         }
  95                         if (cmp > 0) {
  96                                 first = mid+1;
  97                                 continue;
  98                         }
  99                         last = mid;
 100                 }
 101                 if (first < num) {
 102                         const unsigned char *now, *next;
 103                        now = nth_packed_object_sha1(p, first);
 104                         if (match_sha(len, match, now)) {
 105                                 next = nth_packed_object_sha1(p, first+1);
 106                                if (!next|| !match_sha(len, match, next)) {
 107                                         /* unique within this pack */
 108                                         if (!found) {
 109                                                 found_sha1 = now;
 110                                                 found++;
 111                                         }
 112                                         else if (hashcmp(found_sha1, now)) {
 113                                                 found = 2;
 114                                                 break;
 115                                         }
 116                                 }
 117                                 else {
 118                                         /* not even unique within this pack */
 119                                         found = 2;
 120                                         break;
 121                                 }
 122                         }
 123                 }
 124         }
 125         if (found == 1)
 126                 hashcpy(sha1, found_sha1);
 127         return found;
 128 }
 129
 130 #define SHORT_NAME_NOT_FOUND (-1)
 131 #define SHORT_NAME_AMBIGUOUS (-2)
 132
 133 static int find_unique_short_object(int len, char *canonical,
 134                                     unsigned char *res, unsigned char *sha1)
 135 {
 136         int has_unpacked, has_packed;
 137         unsigned char unpacked_sha1[20], packed_sha1[20];
 138
 139         prepare_alt_odb();
 140         has_unpacked = find_short_object_filename(len, canonical, unpacked_sha1);
 141         has_packed = find_short_packed_object(len, res, packed_sha1);
 142         if (!has_unpacked && !has_packed)
 143                 return SHORT_NAME_NOT_FOUND;
 144         if (1 < has_unpacked || 1 < has_packed)
 145                 return SHORT_NAME_AMBIGUOUS;
 146         if (has_unpacked != has_packed) {
 147                 hashcpy(sha1, (has_packed ? packed_sha1 : unpacked_sha1));
 148                 return 0;
 149         }
 150         /* Both have unique ones -- do they match? */
 151         if (hashcmp(packed_sha1, unpacked_sha1))
 152                 return SHORT_NAME_AMBIGUOUS;
 153         hashcpy(sha1, packed_sha1);
 154         return 0;
 155 }
 156
 157 static int get_short_sha1(const char *name, int len, unsigned char *sha1,
 158                           int quietly)
 159 {
 160         int i, status;
 161         char canonical[40];
 162         unsigned char res[20];
 163
 164         if (len < MINIMUM_ABBREV || len > 40)
 165                 return -1;
 166         hashclr(res);
 167         memset(canonical, 'x', 40);
 168         for (i = 0; i < len ;i++) {
 169                 unsigned char c = name[i];
 170                 unsigned char val;
 171                 if (c >= '0' && c <= '9')
 172                         val = c - '0';
 173                 else if (c >= 'a' && c <= 'f')
 174                         val = c - 'a' + 10;
 175                 else if (c >= 'A' && c <='F') {
 176                         val = c - 'A' + 10;
 177                         c -= 'A' - 'a';
 178                 }
 179                 else
 180                         return -1;
 181                 canonical[i] = c;
 182                 if (!(i & 1))
 183                         val <<= 4;
 184                 res[i >> 1] |= val;
 185         }
 186
 187         status = find_unique_short_object(i, canonical, res, sha1);
 188         if (!quietly && (status == SHORT_NAME_AMBIGUOUS))
 189                 return error("short SHA1 %.*s is ambiguous.", len, canonical);
 190         return status;
 191 }
 192
 193 const char *find_unique_abbrev(const unsigned char *sha1, int len)
 194 {
 195         int status, exists;
 196         static char hex[41];
 197
 198         exists = has_sha1_file(sha1);
 199         memcpy(hex, sha1_to_hex(sha1), 40);
 200         if (len == 40 || !len)
 201                 return hex;
 202         while (len < 40) {
 203                 unsigned char sha1_ret[20];
 204                 status = get_short_sha1(hex, len, sha1_ret, 1);
 205                 if (exists
 206                     ? !status
 207                     : status == SHORT_NAME_NOT_FOUND) {
 208                         hex[len] = 0;
 209                         return hex;
 210                 }
 211                 len++;
 212         }
 213         return hex;
 214 }
 215
 216 static int ambiguous_path(const char *path, int len)
 217 {
 218         int slash = 1;
 219         int cnt;
 220
 221         for (cnt = 0; cnt < len; cnt++) {
 222                 switch (*path++) {
 223                 case '\0':
 224                         break;
 225                 case '/':
 226                         if (slash)
 227                                 break;
 228                         slash = 1;
 229                         continue;
 230                 case '.':
 231                         continue;
 232                 default:
 233                         slash = 0;
 234                         continue;
 235                 }
 236                 break;
 237         }
 238         return slash;
 239 }
 240
 241 int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
 242 {
 243         const char **p, *r;
 244         int refs_found = 0;
 245
 246         *ref = NULL;
 247         for (p = ref_rev_parse_rules; *p; p++) {
 248                 char fullref[PATH_MAX];
 249                 unsigned char sha1_from_ref[20];
 250                 unsigned char *this_result;
 251
 252                 this_result = refs_found ? sha1_from_ref : sha1;
 253                 mksnpath(fullref, sizeof(fullref), *p, len, str);
 254                 r = resolve_ref(fullref, this_result, 1, NULL);
 255                 if (r) {
 256                         if (!refs_found++)
 257                                 *ref = xstrdup(r);
 258                         if (!warn_ambiguous_refs)
 259                                 break;
 260                 }
 261         }
 262         return refs_found;
 263 }
 264
 265 int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
 266 {
 267         const char **p;
 268         int logs_found = 0;
 269
 270         *log = NULL;
 271         for (p = ref_rev_parse_rules; *p; p++) {
 272                 struct stat st;
 273                 unsigned char hash[20];
 274                 char path[PATH_MAX];
 275                 const char *ref, *it;
 276
 277                 mksnpath(path, sizeof(path), *p, len, str);
 278                 ref = resolve_ref(path, hash, 1, NULL);
 279                 if (!ref)
 280                         continue;
 281                 if (!stat(git_path("logs/%s", path), &st) &&
 282                     S_ISREG(st.st_mode))
 283                         it = path;
 284                 else if (strcmp(ref, path) &&
 285                          !stat(git_path("logs/%s", ref), &st) &&
 286                          S_ISREG(st.st_mode))
 287                         it = ref;
 288                 else
 289                         continue;
 290                 if (!logs_found++) {
 291                         *log = xstrdup(it);
 292                         hashcpy(sha1, hash);
 293                 }
 294                 if (!warn_ambiguous_refs)
 295                         break;
 296         }
 297         return logs_found;
 298 }
 299
 300 static int get_sha1_1(const char *name, int len, unsigned char *sha1);
 301
 302 static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 303 {
 304         static const char *warning = "warning: refname '%.*s' is ambiguous.\n";
 305         char *real_ref = NULL;
 306         int refs_found = 0;
 307         int at, reflog_len;
 308
 309         if (len == 40 && !get_sha1_hex(str, sha1))
 310                 return 0;
 311
 312         /* basic@{time or number or -number} format to query ref-log */
 313         reflog_len = at = 0;
 314         if (str[len-1] == '}') {
 315                 for (at = 0; at < len - 1; at++) {
 316                         if (str[at] == '@' && str[at+1] == '{') {
 317                                 reflog_len = (len-1) - (at+2);
 318                                 len = at;
 319                                 break;
 320                         }
 321                 }
 322         }
 323
 324         /* Accept only unambiguous ref paths. */
 325         if (len && ambiguous_path(str, len))
 326                 return -1;
 327
 328         if (!len && reflog_len) {
 329                 struct strbuf buf = STRBUF_INIT;
 330                 int ret;
 331                 /* try the @{-N} syntax for n-th checkout */
 332                 ret = interpret_nth_last_branch(str+at, &buf);
 333                 if (ret > 0) {
 334                         /* substitute this branch name and restart */
 335                         return get_sha1_1(buf.buf, buf.len, sha1);
 336                 } else if (ret == 0) {
 337                         return -1;
 338                 }
 339                 /* allow "@{...}" to mean the current branch reflog */
 340                 refs_found = dwim_ref("HEAD", 4, sha1, &real_ref);
 341         } else if (reflog_len)
 342                 refs_found = dwim_log(str, len, sha1, &real_ref);
 343         else
 344                 refs_found = dwim_ref(str, len, sha1, &real_ref);
 345
 346         if (!refs_found)
 347                 return -1;
 348
 349         if (warn_ambiguous_refs && refs_found > 1)
 350                 fprintf(stderr, warning, len, str);
 351
 352         if (reflog_len) {
 353                 int nth, i;
 354                 unsigned long at_time;
 355                 unsigned long co_time;
 356                 int co_tz, co_cnt;
 357
 358                 /* Is it asking for N-th entry, or approxidate? */
 359                 for (i = nth = 0; 0 <= nth && i < reflog_len; i++) {
 360                         char ch = str[at+2+i];
 361                         if ('0' <= ch && ch <= '9')
 362                                 nth = nth * 10 + ch - '0';
 363                         else
 364                                 nth = -1;
 365                 }
 366                 if (100000000 <= nth) {
 367                         at_time = nth;
 368                         nth = -1;
 369                 } else if (0 <= nth)
 370                         at_time = 0;
 371                 else {
 372                         char *tmp = xstrndup(str + at + 2, reflog_len);
 373                         at_time = approxidate(tmp);
 374                         free(tmp);
 375                 }
 376                 if (read_ref_at(real_ref, at_time, nth, sha1, NULL,
 377                                 &co_time, &co_tz, &co_cnt)) {
 378                         if (at_time)
 379                                 fprintf(stderr,
 380                                         "warning: Log for '%.*s' only goes "
 381                                         "back to %s.\n", len, str,
 382                                         show_date(co_time, co_tz, DATE_RFC2822));
 383                         else
 384                                 fprintf(stderr,
 385                                         "warning: Log for '%.*s' only has "
 386                                         "%d entries.\n", len, str, co_cnt);
 387                 }
 388         }
 389
 390         free(real_ref);
 391         return 0;
 392 }
 393
 394 static int get_parent(const char *name, int len,
 395                       unsigned char *result, int idx)
 396 {
 397         unsigned char sha1[20];
 398         int ret = get_sha1_1(name, len, sha1);
 399         struct commit *commit;
 400         struct commit_list *p;
 401
 402         if (ret)
 403                 return ret;
 404         commit = lookup_commit_reference(sha1);
 405         if (!commit)
 406                 return -1;
 407         if (parse_commit(commit))
 408                 return -1;
 409         if (!idx) {
 410                 hashcpy(result, commit->object.sha1);
 411                 return 0;
 412         }
 413         p = commit->parents;
 414         while (p) {
 415                 if (!--idx) {
 416                         hashcpy(result, p->item->object.sha1);
 417                         return 0;
 418                 }
 419                 p = p->next;
 420         }
 421         return -1;
 422 }
 423
 424 static int get_nth_ancestor(const char *name, int len,
 425                             unsigned char *result, int generation)
 426 {
 427         unsigned char sha1[20];
 428         struct commit *commit;
 429         int ret;
 430
 431         ret = get_sha1_1(name, len, sha1);
 432         if (ret)
 433                 return ret;
 434         commit = lookup_commit_reference(sha1);
 435         if (!commit)
 436                 return -1;
 437
 438         while (generation--) {
 439                 if (parse_commit(commit) || !commit->parents)
 440                         return -1;
 441                 commit = commit->parents->item;
 442         }
 443         hashcpy(result, commit->object.sha1);
 444         return 0;
 445 }
 446
 447 struct object *peel_to_type(const char *name, int namelen,
 448                             struct object *o, enum object_type expected_type)
 449 {
 450         if (name && !namelen)
 451                 namelen = strlen(name);
 452         if (!o) {
 453                 unsigned char sha1[20];
 454                 if (get_sha1_1(name, namelen, sha1))
 455                         return NULL;
 456                 o = parse_object(sha1);
 457         }
 458         while (1) {
 459                 if (!o || (!o->parsed && !parse_object(o->sha1)))
 460                         return NULL;
 461                 if (o->type == expected_type)
 462                         return o;
 463                 if (o->type == OBJ_TAG)
 464                         o = ((struct tag*) o)->tagged;
 465                 else if (o->type == OBJ_COMMIT)
 466                         o = &(((struct commit *) o)->tree->object);
 467                 else {
 468                         if (name)
 469                                 error("%.*s: expected %s type, but the object "
 470                                       "dereferences to %s type",
 471                                       namelen, name, typename(expected_type),
 472                                       typename(o->type));
 473                         return NULL;
 474                 }
 475         }
 476 }
 477
 478 static int peel_onion(const char *name, int len, unsigned char *sha1)
 479 {
 480         unsigned char outer[20];
 481         const char *sp;
 482         unsigned int expected_type = 0;
 483         struct object *o;
 484
 485         /*
 486          * "ref^{type}" dereferences ref repeatedly until you cannot
 487          * dereference anymore, or you get an object of given type,
 488          * whichever comes first.  "ref^{}" means just dereference
 489          * tags until you get a non-tag.  "ref^0" is a shorthand for
 490          * "ref^{commit}".  "commit^{tree}" could be used to find the
 491          * top-level tree of the given commit.
 492          */
 493         if (len < 4 || name[len-1] != '}')
 494                 return -1;
 495
 496         for (sp = name + len - 1; name <= sp; sp--) {
 497                 int ch = *sp;
 498                 if (ch == '{' && name < sp && sp[-1] == '^')
 499                         break;
 500         }
 501         if (sp <= name)
 502                 return -1;
 503
 504         sp++; /* beginning of type name, or closing brace for empty */
 505         if (!strncmp(commit_type, sp, 6) && sp[6] == '}')
 506                 expected_type = OBJ_COMMIT;
 507         else if (!strncmp(tree_type, sp, 4) && sp[4] == '}')
 508                 expected_type = OBJ_TREE;
 509         else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')
 510                 expected_type = OBJ_BLOB;
 511         else if (sp[0] == '}')
 512                 expected_type = OBJ_NONE;
 513         else
 514                 return -1;
 515
 516         if (get_sha1_1(name, sp - name - 2, outer))
 517                 return -1;
 518
 519         o = parse_object(outer);
 520         if (!o)
 521                 return -1;
 522         if (!expected_type) {
 523                 o = deref_tag(o, name, sp - name - 2);
 524                 if (!o || (!o->parsed && !parse_object(o->sha1)))
 525                         return -1;
 526                 hashcpy(sha1, o->sha1);
 527         }
 528         else {
 529                 /*
 530                  * At this point, the syntax look correct, so
 531                  * if we do not get the needed object, we should
 532                  * barf.
 533                  */
 534                 o = peel_to_type(name, len, o, expected_type);
 535                 if (o) {
 536                         hashcpy(sha1, o->sha1);
 537                         return 0;
 538                 }
 539                 return -1;
 540         }
 541         return 0;
 542 }
 543
 544 static int get_describe_name(const char *name, int len, unsigned char *sha1)
 545 {
 546         const char *cp;
 547
 548         for (cp = name + len - 1; name + 2 <= cp; cp--) {
 549                 char ch = *cp;
 550                 if (hexval(ch) & ~0377) {
 551                         /* We must be looking at g in "SOMETHING-g"
 552                          * for it to be describe output.
 553                          */
 554                         if (ch == 'g' && cp[-1] == '-') {
 555                                 cp++;
 556                                 len -= cp - name;
 557                                 return get_short_sha1(cp, len, sha1, 1);
 558                         }
 559                 }
 560         }
 561         return -1;
 562 }
 563
 564 static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 565 {
 566         int ret, has_suffix;
 567         const char *cp;
 568
 569         /*
 570          * "name~3" is "name^^^", "name~" is "name~1", and "name^" is "name^1".
 571          */
 572         has_suffix = 0;
 573         for (cp = name + len - 1; name <= cp; cp--) {
 574                 int ch = *cp;
 575                 if ('0' <= ch && ch <= '9')
 576                         continue;
 577                 if (ch == '~' || ch == '^')
 578                         has_suffix = ch;
 579                 break;
 580         }
 581
 582         if (has_suffix) {
 583                 int num = 0;
 584                 int len1 = cp - name;
 585                 cp++;
 586                 while (cp < name + len)
 587                         num = num * 10 + *cp++ - '0';
 588                 if (!num && len1 == len - 1)
 589                         num = 1;
 590                 if (has_suffix == '^')
 591                         return get_parent(name, len1, sha1, num);
 592                 /* else if (has_suffix == '~') -- goes without saying */
 593                 return get_nth_ancestor(name, len1, sha1, num);
 594         }
 595
 596         ret = peel_onion(name, len, sha1);
 597         if (!ret)
 598                 return 0;
 599
 600         ret = get_sha1_basic(name, len, sha1);
 601         if (!ret)
 602                 return 0;
 603
 604         /* It could be describe output that is "SOMETHING-gXXXX" */
 605         ret = get_describe_name(name, len, sha1);
 606         if (!ret)
 607                 return 0;
 608
 609         return get_short_sha1(name, len, sha1, 0);
 610 }
 611
 612 static int handle_one_ref(const char *path,
 613                 const unsigned char *sha1, int flag, void *cb_data)
 614 {
 615         struct commit_list **list = cb_data;
 616         struct object *object = parse_object(sha1);
 617         if (!object)
 618                 return 0;
 619         if (object->type == OBJ_TAG) {
 620                 object = deref_tag(object, path, strlen(path));
 621                 if (!object)
 622                         return 0;
 623         }
 624         if (object->type != OBJ_COMMIT)
 625                 return 0;
 626         insert_by_date((struct commit *)object, list);
 627         return 0;
 628 }
 629
 630 /*
 631  * This interprets names like ':/Initial revision of "git"' by searching
 632  * through history and returning the first commit whose message starts
 633  * with the given string.
 634  *
 635  * For future extension, ':/!' is reserved. If you want to match a message
 636  * beginning with a '!', you have to repeat the exclamation mark.
 637  */
 638
 639 #define ONELINE_SEEN (1u<<20)
 640 static int get_sha1_oneline(const char *prefix, unsigned char *sha1)
 641 {
 642         struct commit_list *list = NULL, *backup = NULL, *l;
 643         int retval = -1;
 644         char *temp_commit_buffer = NULL;
 645
 646         if (prefix[0] == '!') {
 647                 if (prefix[1] != '!')
 648                         die ("Invalid search pattern: %s", prefix);
 649                 prefix++;
 650         }
 651         for_each_ref(handle_one_ref, &list);
 652         for (l = list; l; l = l->next)
 653                 commit_list_insert(l->item, &backup);
 654         while (list) {
 655                 char *p;
 656                 struct commit *commit;
 657                 enum object_type type;
 658                 unsigned long size;
 659
 660                 commit = pop_most_recent_commit(&list, ONELINE_SEEN);
 661                 if (!parse_object(commit->object.sha1))
 662                         continue;
 663                 free(temp_commit_buffer);
 664                 if (commit->buffer)
 665                         p = commit->buffer;
 666                 else {
 667                         p = read_sha1_file(commit->object.sha1, &type, &size);
 668                         if (!p)
 669                                 continue;
 670                         temp_commit_buffer = p;
 671                 }
 672                 if (!(p = strstr(p, "\n\n")))
 673                         continue;
 674                 if (!prefixcmp(p + 2, prefix)) {
 675                         hashcpy(sha1, commit->object.sha1);
 676                         retval = 0;
 677                         break;
 678                 }
 679         }
 680         free(temp_commit_buffer);
 681         free_commit_list(list);
 682         for (l = backup; l; l = l->next)
 683                 clear_commit_marks(l->item, ONELINE_SEEN);
 684         return retval;
 685 }
 686
 687 struct grab_nth_branch_switch_cbdata {
 688         long cnt, alloc;
 689         struct strbuf *buf;
 690 };
 691
 692 static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
 693                                   const char *email, unsigned long timestamp, int tz,
 694                                   const char *message, void *cb_data)
 695 {
 696         struct grab_nth_branch_switch_cbdata *cb = cb_data;
 697         const char *match = NULL, *target = NULL;
 698         size_t len;
 699         int nth;
 700
 701         if (!prefixcmp(message, "checkout: moving from ")) {
 702                 match = message + strlen("checkout: moving from ");
 703                 if ((target = strstr(match, " to ")) != NULL)
 704                         target += 4;
 705         }
 706
 707         if (!match)
 708                 return 0;
 709
 710         len = target - match - 4;
 711         if (target[len] == '\n' && !strncmp(match, target, len))
 712                 return 0;
 713
 714         nth = cb->cnt++ % cb->alloc;
 715         strbuf_reset(&cb->buf[nth]);
 716         strbuf_add(&cb->buf[nth], match, len);
 717         return 0;
 718 }
 719
 720 /*
 721  * This reads "@{-N}" syntax, finds the name of the Nth previous
 722  * branch we were on, and places the name of the branch in the given
 723  * buf and returns the number of characters parsed if successful.
 724  *
 725  * If the input is not of the accepted format, it returns a negative
 726  * number to signal an error.
 727  *
 728  * If the input was ok but there are not N branch switches in the
 729  * reflog, it returns 0.
 730  */
 731 int interpret_nth_last_branch(const char *name, struct strbuf *buf)
 732 {
 733         long nth;
 734         int i;
 735         struct grab_nth_branch_switch_cbdata cb;
 736         const char *brace;
 737         char *num_end;
 738
 739         if (name[0] != '@' || name[1] != '{' || name[2] != '-')
 740                 return -1;
 741         brace = strchr(name, '}');
 742         if (!brace)
 743                 return -1;
 744         nth = strtol(name+3, &num_end, 10);
 745         if (num_end != brace)
 746                 return -1;
 747         if (nth <= 0)
 748                 return -1;
 749         cb.alloc = nth;
 750         cb.buf = xmalloc(nth * sizeof(struct strbuf));
 751         for (i = 0; i < nth; i++)
 752                 strbuf_init(&cb.buf[i], 20);
 753         cb.cnt = 0;
 754         for_each_reflog_ent("HEAD", grab_nth_branch_switch, &cb);
 755         if (cb.cnt < nth)
 756                 return 0;
 757         i = cb.cnt % nth;
 758         strbuf_reset(buf);
 759         strbuf_add(buf, cb.buf[i].buf, cb.buf[i].len);
 760         for (i = 0; i < nth; i++)
 761                 strbuf_release(&cb.buf[i]);
 762         free(cb.buf);
 763
 764         return brace-name+1;
 765 }
 766
 767 /*
 768  * This is like "get_sha1_basic()", except it allows "sha1 expressions",
 769  * notably "xyz^" for "parent of xyz"
 770  */
 771 int get_sha1(const char *name, unsigned char *sha1)
 772 {
 773         unsigned unused;
 774         return get_sha1_with_mode(name, sha1, &unused);
 775 }
 776
 777 int get_sha1_with_mode(const char *name, unsigned char *sha1, unsigned *mode)
 778 {
 779         int ret, bracket_depth;
 780         int namelen = strlen(name);
 781         const char *cp;
 782
 783         *mode = S_IFINVALID;
 784         ret = get_sha1_1(name, namelen, sha1);
 785         if (!ret)
 786                 return ret;
 787         /* sha1:path --> object name of path in ent sha1
 788          * :path -> object name of path in index
 789          * :[0-3]:path -> object name of path in index at stage
 790          */
 791         if (name[0] == ':') {
 792                 int stage = 0;
 793                 struct cache_entry *ce;
 794                 int pos;
 795                 if (namelen > 2 && name[1] == '/')
 796                         return get_sha1_oneline(name + 2, sha1);
 797                 if (namelen < 3 ||
 798                     name[2] != ':' ||
 799                     name[1] < '0' || '3' < name[1])
 800                         cp = name + 1;
 801                 else {
 802                         stage = name[1] - '0';
 803                         cp = name + 3;
 804                 }
 805                 namelen = namelen - (cp - name);
 806                 if (!active_cache)
 807                         read_cache();
 808                 pos = cache_name_pos(cp, namelen);
 809                 if (pos < 0)
 810                         pos = -pos - 1;
 811                 while (pos < active_nr) {
 812                         ce = active_cache[pos];
 813                         if (ce_namelen(ce) != namelen ||
 814                             memcmp(ce->name, cp, namelen))
 815                                 break;
 816                         if (ce_stage(ce) == stage) {
 817                                 hashcpy(sha1, ce->sha1);
 818                                 *mode = ce->ce_mode;
 819                                 return 0;
 820                         }
 821                         pos++;
 822                 }
 823                 return -1;
 824         }
 825         for (cp = name, bracket_depth = 0; *cp; cp++) {
 826                 if (*cp == '{')
 827                         bracket_depth++;
 828                 else if (bracket_depth && *cp == '}')
 829                         bracket_depth--;
 830                 else if (!bracket_depth && *cp == ':')
 831                         break;
 832         }
 833         if (*cp == ':') {
 834                 unsigned char tree_sha1[20];
 835                 if (!get_sha1_1(name, cp-name, tree_sha1))
 836                         return get_tree_entry(tree_sha1, cp+1, sha1,
 837                                               mode);
 838         }
 839         return ret;
 840 }