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 /*
 242  * *string and *len will only be substituted, and *string returned (for
 243  * later free()ing) if the string passed in is of the form @{-<n>}.
 244  */
 245 static char *substitute_nth_last_branch(const char **string, int *len)
 246 {
 247         struct strbuf buf = STRBUF_INIT;
 248         int ret = interpret_nth_last_branch(*string, &buf);
 249
 250         if (ret == *len) {
 251                 size_t size;
 252                 *string = strbuf_detach(&buf, &size);
 253                 *len = size;
 254                 return (char *)*string;
 255         }
 256
 257         return NULL;
 258 }
 259
 260 int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
 261 {
 262         char *last_branch = substitute_nth_last_branch(&str, &len);
 263         const char **p, *r;
 264         int refs_found = 0;
 265
 266         *ref = NULL;
 267         for (p = ref_rev_parse_rules; *p; p++) {
 268                 char fullref[PATH_MAX];
 269                 unsigned char sha1_from_ref[20];
 270                 unsigned char *this_result;
 271
 272                 this_result = refs_found ? sha1_from_ref : sha1;
 273                 mksnpath(fullref, sizeof(fullref), *p, len, str);
 274                 r = resolve_ref(fullref, this_result, 1, NULL);
 275                 if (r) {
 276                         if (!refs_found++)
 277                                 *ref = xstrdup(r);
 278                         if (!warn_ambiguous_refs)
 279                                 break;
 280                 }
 281         }
 282         free(last_branch);
 283         return refs_found;
 284 }
 285
 286 int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
 287 {
 288         char *last_branch = substitute_nth_last_branch(&str, &len);
 289         const char **p;
 290         int logs_found = 0;
 291
 292         *log = NULL;
 293         for (p = ref_rev_parse_rules; *p; p++) {
 294                 struct stat st;
 295                 unsigned char hash[20];
 296                 char path[PATH_MAX];
 297                 const char *ref, *it;
 298
 299                 mksnpath(path, sizeof(path), *p, len, str);
 300                 ref = resolve_ref(path, hash, 1, NULL);
 301                 if (!ref)
 302                         continue;
 303                 if (!stat(git_path("logs/%s", path), &st) &&
 304                     S_ISREG(st.st_mode))
 305                         it = path;
 306                 else if (strcmp(ref, path) &&
 307                          !stat(git_path("logs/%s", ref), &st) &&
 308                          S_ISREG(st.st_mode))
 309                         it = ref;
 310                 else
 311                         continue;
 312                 if (!logs_found++) {
 313                         *log = xstrdup(it);
 314                         hashcpy(sha1, hash);
 315                 }
 316                 if (!warn_ambiguous_refs)
 317                         break;
 318         }
 319         free(last_branch);
 320         return logs_found;
 321 }
 322
 323 static int get_sha1_1(const char *name, int len, unsigned char *sha1);
 324
 325 static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 326 {
 327         static const char *warning = "warning: refname '%.*s' is ambiguous.\n";
 328         char *real_ref = NULL;
 329         int refs_found = 0;
 330         int at, reflog_len;
 331
 332         if (len == 40 && !get_sha1_hex(str, sha1))
 333                 return 0;
 334
 335         /* basic@{time or number or -number} format to query ref-log */
 336         reflog_len = at = 0;
 337         if (str[len-1] == '}') {
 338                 for (at = len-2; at >= 0; at--) {
 339                         if (str[at] == '@' && str[at+1] == '{') {
 340                                 reflog_len = (len-1) - (at+2);
 341                                 len = at;
 342                                 break;
 343                         }
 344                 }
 345         }
 346
 347         /* Accept only unambiguous ref paths. */
 348         if (len && ambiguous_path(str, len))
 349                 return -1;
 350
 351         if (!len && reflog_len) {
 352                 struct strbuf buf = STRBUF_INIT;
 353                 int ret;
 354                 /* try the @{-N} syntax for n-th checkout */
 355                 ret = interpret_nth_last_branch(str+at, &buf);
 356                 if (ret > 0) {
 357                         /* substitute this branch name and restart */
 358                         return get_sha1_1(buf.buf, buf.len, sha1);
 359                 } else if (ret == 0) {
 360                         return -1;
 361                 }
 362                 /* allow "@{...}" to mean the current branch reflog */
 363                 refs_found = dwim_ref("HEAD", 4, sha1, &real_ref);
 364         } else if (reflog_len)
 365                 refs_found = dwim_log(str, len, sha1, &real_ref);
 366         else
 367                 refs_found = dwim_ref(str, len, sha1, &real_ref);
 368
 369         if (!refs_found)
 370                 return -1;
 371
 372         if (warn_ambiguous_refs && refs_found > 1)
 373                 fprintf(stderr, warning, len, str);
 374
 375         if (reflog_len) {
 376                 int nth, i;
 377                 unsigned long at_time;
 378                 unsigned long co_time;
 379                 int co_tz, co_cnt;
 380
 381                 /* Is it asking for N-th entry, or approxidate? */
 382                 for (i = nth = 0; 0 <= nth && i < reflog_len; i++) {
 383                         char ch = str[at+2+i];
 384                         if ('0' <= ch && ch <= '9')
 385                                 nth = nth * 10 + ch - '0';
 386                         else
 387                                 nth = -1;
 388                 }
 389                 if (100000000 <= nth) {
 390                         at_time = nth;
 391                         nth = -1;
 392                 } else if (0 <= nth)
 393                         at_time = 0;
 394                 else {
 395                         char *tmp = xstrndup(str + at + 2, reflog_len);
 396                         at_time = approxidate(tmp);
 397                         free(tmp);
 398                 }
 399                 if (read_ref_at(real_ref, at_time, nth, sha1, NULL,
 400                                 &co_time, &co_tz, &co_cnt)) {
 401                         if (at_time)
 402                                 fprintf(stderr,
 403                                         "warning: Log for '%.*s' only goes "
 404                                         "back to %s.\n", len, str,
 405                                         show_date(co_time, co_tz, DATE_RFC2822));
 406                         else
 407                                 fprintf(stderr,
 408                                         "warning: Log for '%.*s' only has "
 409                                         "%d entries.\n", len, str, co_cnt);
 410                 }
 411         }
 412
 413         free(real_ref);
 414         return 0;
 415 }
 416
 417 static int get_parent(const char *name, int len,
 418                       unsigned char *result, int idx)
 419 {
 420         unsigned char sha1[20];
 421         int ret = get_sha1_1(name, len, sha1);
 422         struct commit *commit;
 423         struct commit_list *p;
 424
 425         if (ret)
 426                 return ret;
 427         commit = lookup_commit_reference(sha1);
 428         if (!commit)
 429                 return -1;
 430         if (parse_commit(commit))
 431                 return -1;
 432         if (!idx) {
 433                 hashcpy(result, commit->object.sha1);
 434                 return 0;
 435         }
 436         p = commit->parents;
 437         while (p) {
 438                 if (!--idx) {
 439                         hashcpy(result, p->item->object.sha1);
 440                         return 0;
 441                 }
 442                 p = p->next;
 443         }
 444         return -1;
 445 }
 446
 447 static int get_nth_ancestor(const char *name, int len,
 448                             unsigned char *result, int generation)
 449 {
 450         unsigned char sha1[20];
 451         struct commit *commit;
 452         int ret;
 453
 454         ret = get_sha1_1(name, len, sha1);
 455         if (ret)
 456                 return ret;
 457         commit = lookup_commit_reference(sha1);
 458         if (!commit)
 459                 return -1;
 460
 461         while (generation--) {
 462                 if (parse_commit(commit) || !commit->parents)
 463                         return -1;
 464                 commit = commit->parents->item;
 465         }
 466         hashcpy(result, commit->object.sha1);
 467         return 0;
 468 }
 469
 470 struct object *peel_to_type(const char *name, int namelen,
 471                             struct object *o, enum object_type expected_type)
 472 {
 473         if (name && !namelen)
 474                 namelen = strlen(name);
 475         if (!o) {
 476                 unsigned char sha1[20];
 477                 if (get_sha1_1(name, namelen, sha1))
 478                         return NULL;
 479                 o = parse_object(sha1);
 480         }
 481         while (1) {
 482                 if (!o || (!o->parsed && !parse_object(o->sha1)))
 483                         return NULL;
 484                 if (o->type == expected_type)
 485                         return o;
 486                 if (o->type == OBJ_TAG)
 487                         o = ((struct tag*) o)->tagged;
 488                 else if (o->type == OBJ_COMMIT)
 489                         o = &(((struct commit *) o)->tree->object);
 490                 else {
 491                         if (name)
 492                                 error("%.*s: expected %s type, but the object "
 493                                       "dereferences to %s type",
 494                                       namelen, name, typename(expected_type),
 495                                       typename(o->type));
 496                         return NULL;
 497                 }
 498         }
 499 }
 500
 501 static int peel_onion(const char *name, int len, unsigned char *sha1)
 502 {
 503         unsigned char outer[20];
 504         const char *sp;
 505         unsigned int expected_type = 0;
 506         struct object *o;
 507
 508         /*
 509          * "ref^{type}" dereferences ref repeatedly until you cannot
 510          * dereference anymore, or you get an object of given type,
 511          * whichever comes first.  "ref^{}" means just dereference
 512          * tags until you get a non-tag.  "ref^0" is a shorthand for
 513          * "ref^{commit}".  "commit^{tree}" could be used to find the
 514          * top-level tree of the given commit.
 515          */
 516         if (len < 4 || name[len-1] != '}')
 517                 return -1;
 518
 519         for (sp = name + len - 1; name <= sp; sp--) {
 520                 int ch = *sp;
 521                 if (ch == '{' && name < sp && sp[-1] == '^')
 522                         break;
 523         }
 524         if (sp <= name)
 525                 return -1;
 526
 527         sp++; /* beginning of type name, or closing brace for empty */
 528         if (!strncmp(commit_type, sp, 6) && sp[6] == '}')
 529                 expected_type = OBJ_COMMIT;
 530         else if (!strncmp(tree_type, sp, 4) && sp[4] == '}')
 531                 expected_type = OBJ_TREE;
 532         else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')
 533                 expected_type = OBJ_BLOB;
 534         else if (sp[0] == '}')
 535                 expected_type = OBJ_NONE;
 536         else
 537                 return -1;
 538
 539         if (get_sha1_1(name, sp - name - 2, outer))
 540                 return -1;
 541
 542         o = parse_object(outer);
 543         if (!o)
 544                 return -1;
 545         if (!expected_type) {
 546                 o = deref_tag(o, name, sp - name - 2);
 547                 if (!o || (!o->parsed && !parse_object(o->sha1)))
 548                         return -1;
 549                 hashcpy(sha1, o->sha1);
 550         }
 551         else {
 552                 /*
 553                  * At this point, the syntax look correct, so
 554                  * if we do not get the needed object, we should
 555                  * barf.
 556                  */
 557                 o = peel_to_type(name, len, o, expected_type);
 558                 if (o) {
 559                         hashcpy(sha1, o->sha1);
 560                         return 0;
 561                 }
 562                 return -1;
 563         }
 564         return 0;
 565 }
 566
 567 static int get_describe_name(const char *name, int len, unsigned char *sha1)
 568 {
 569         const char *cp;
 570
 571         for (cp = name + len - 1; name + 2 <= cp; cp--) {
 572                 char ch = *cp;
 573                 if (hexval(ch) & ~0377) {
 574                         /* We must be looking at g in "SOMETHING-g"
 575                          * for it to be describe output.
 576                          */
 577                         if (ch == 'g' && cp[-1] == '-') {
 578                                 cp++;
 579                                 len -= cp - name;
 580                                 return get_short_sha1(cp, len, sha1, 1);
 581                         }
 582                 }
 583         }
 584         return -1;
 585 }
 586
 587 static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 588 {
 589         int ret, has_suffix;
 590         const char *cp;
 591
 592         /*
 593          * "name~3" is "name^^^", "name~" is "name~1", and "name^" is "name^1".
 594          */
 595         has_suffix = 0;
 596         for (cp = name + len - 1; name <= cp; cp--) {
 597                 int ch = *cp;
 598                 if ('0' <= ch && ch <= '9')
 599                         continue;
 600                 if (ch == '~' || ch == '^')
 601                         has_suffix = ch;
 602                 break;
 603         }
 604
 605         if (has_suffix) {
 606                 int num = 0;
 607                 int len1 = cp - name;
 608                 cp++;
 609                 while (cp < name + len)
 610                         num = num * 10 + *cp++ - '0';
 611                 if (!num && len1 == len - 1)
 612                         num = 1;
 613                 if (has_suffix == '^')
 614                         return get_parent(name, len1, sha1, num);
 615                 /* else if (has_suffix == '~') -- goes without saying */
 616                 return get_nth_ancestor(name, len1, sha1, num);
 617         }
 618
 619         ret = peel_onion(name, len, sha1);
 620         if (!ret)
 621                 return 0;
 622
 623         ret = get_sha1_basic(name, len, sha1);
 624         if (!ret)
 625                 return 0;
 626
 627         /* It could be describe output that is "SOMETHING-gXXXX" */
 628         ret = get_describe_name(name, len, sha1);
 629         if (!ret)
 630                 return 0;
 631
 632         return get_short_sha1(name, len, sha1, 0);
 633 }
 634
 635 static int handle_one_ref(const char *path,
 636                 const unsigned char *sha1, int flag, void *cb_data)
 637 {
 638         struct commit_list **list = cb_data;
 639         struct object *object = parse_object(sha1);
 640         if (!object)
 641                 return 0;
 642         if (object->type == OBJ_TAG) {
 643                 object = deref_tag(object, path, strlen(path));
 644                 if (!object)
 645                         return 0;
 646         }
 647         if (object->type != OBJ_COMMIT)
 648                 return 0;
 649         insert_by_date((struct commit *)object, list);
 650         return 0;
 651 }
 652
 653 /*
 654  * This interprets names like ':/Initial revision of "git"' by searching
 655  * through history and returning the first commit whose message starts
 656  * with the given string.
 657  *
 658  * For future extension, ':/!' is reserved. If you want to match a message
 659  * beginning with a '!', you have to repeat the exclamation mark.
 660  */
 661
 662 #define ONELINE_SEEN (1u<<20)
 663 static int get_sha1_oneline(const char *prefix, unsigned char *sha1)
 664 {
 665         struct commit_list *list = NULL, *backup = NULL, *l;
 666         int retval = -1;
 667         char *temp_commit_buffer = NULL;
 668
 669         if (prefix[0] == '!') {
 670                 if (prefix[1] != '!')
 671                         die ("Invalid search pattern: %s", prefix);
 672                 prefix++;
 673         }
 674         for_each_ref(handle_one_ref, &list);
 675         for (l = list; l; l = l->next)
 676                 commit_list_insert(l->item, &backup);
 677         while (list) {
 678                 char *p;
 679                 struct commit *commit;
 680                 enum object_type type;
 681                 unsigned long size;
 682
 683                 commit = pop_most_recent_commit(&list, ONELINE_SEEN);
 684                 if (!parse_object(commit->object.sha1))
 685                         continue;
 686                 free(temp_commit_buffer);
 687                 if (commit->buffer)
 688                         p = commit->buffer;
 689                 else {
 690                         p = read_sha1_file(commit->object.sha1, &type, &size);
 691                         if (!p)
 692                                 continue;
 693                         temp_commit_buffer = p;
 694                 }
 695                 if (!(p = strstr(p, "\n\n")))
 696                         continue;
 697                 if (!prefixcmp(p + 2, prefix)) {
 698                         hashcpy(sha1, commit->object.sha1);
 699                         retval = 0;
 700                         break;
 701                 }
 702         }
 703         free(temp_commit_buffer);
 704         free_commit_list(list);
 705         for (l = backup; l; l = l->next)
 706                 clear_commit_marks(l->item, ONELINE_SEEN);
 707         return retval;
 708 }
 709
 710 struct grab_nth_branch_switch_cbdata {
 711         long cnt, alloc;
 712         struct strbuf *buf;
 713 };
 714
 715 static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
 716                                   const char *email, unsigned long timestamp, int tz,
 717                                   const char *message, void *cb_data)
 718 {
 719         struct grab_nth_branch_switch_cbdata *cb = cb_data;
 720         const char *match = NULL, *target = NULL;
 721         size_t len;
 722         int nth;
 723
 724         if (!prefixcmp(message, "checkout: moving from ")) {
 725                 match = message + strlen("checkout: moving from ");
 726                 if ((target = strstr(match, " to ")) != NULL)
 727                         target += 4;
 728         }
 729
 730         if (!match)
 731                 return 0;
 732
 733         len = target - match - 4;
 734         if (target[len] == '\n' && !strncmp(match, target, len))
 735                 return 0;
 736
 737         nth = cb->cnt++ % cb->alloc;
 738         strbuf_reset(&cb->buf[nth]);
 739         strbuf_add(&cb->buf[nth], match, len);
 740         return 0;
 741 }
 742
 743 /*
 744  * This reads "@{-N}" syntax, finds the name of the Nth previous
 745  * branch we were on, and places the name of the branch in the given
 746  * buf and returns the number of characters parsed if successful.
 747  *
 748  * If the input is not of the accepted format, it returns a negative
 749  * number to signal an error.
 750  *
 751  * If the input was ok but there are not N branch switches in the
 752  * reflog, it returns 0.
 753  */
 754 int interpret_nth_last_branch(const char *name, struct strbuf *buf)
 755 {
 756         long nth;
 757         int i;
 758         struct grab_nth_branch_switch_cbdata cb;
 759         const char *brace;
 760         char *num_end;
 761
 762         if (name[0] != '@' || name[1] != '{' || name[2] != '-')
 763                 return -1;
 764         brace = strchr(name, '}');
 765         if (!brace)
 766                 return -1;
 767         nth = strtol(name+3, &num_end, 10);
 768         if (num_end != brace)
 769                 return -1;
 770         if (nth <= 0)
 771                 return -1;
 772         cb.alloc = nth;
 773         cb.buf = xmalloc(nth * sizeof(struct strbuf));
 774         for (i = 0; i < nth; i++)
 775                 strbuf_init(&cb.buf[i], 20);
 776         cb.cnt = 0;
 777         for_each_reflog_ent("HEAD", grab_nth_branch_switch, &cb);
 778         if (cb.cnt < nth)
 779                 return 0;
 780         i = cb.cnt % nth;
 781         strbuf_reset(buf);
 782         strbuf_add(buf, cb.buf[i].buf, cb.buf[i].len);
 783         for (i = 0; i < nth; i++)
 784                 strbuf_release(&cb.buf[i]);
 785         free(cb.buf);
 786
 787         return brace-name+1;
 788 }
 789
 790 /*
 791  * This is like "get_sha1_basic()", except it allows "sha1 expressions",
 792  * notably "xyz^" for "parent of xyz"
 793  */
 794 int get_sha1(const char *name, unsigned char *sha1)
 795 {
 796         unsigned unused;
 797         return get_sha1_with_mode(name, sha1, &unused);
 798 }
 799
 800 int get_sha1_with_mode(const char *name, unsigned char *sha1, unsigned *mode)
 801 {
 802         int ret, bracket_depth;
 803         int namelen = strlen(name);
 804         const char *cp;
 805
 806         *mode = S_IFINVALID;
 807         ret = get_sha1_1(name, namelen, sha1);
 808         if (!ret)
 809                 return ret;
 810         /* sha1:path --> object name of path in ent sha1
 811          * :path -> object name of path in index
 812          * :[0-3]:path -> object name of path in index at stage
 813          */
 814         if (name[0] == ':') {
 815                 int stage = 0;
 816                 struct cache_entry *ce;
 817                 int pos;
 818                 if (namelen > 2 && name[1] == '/')
 819                         return get_sha1_oneline(name + 2, sha1);
 820                 if (namelen < 3 ||
 821                     name[2] != ':' ||
 822                     name[1] < '0' || '3' < name[1])
 823                         cp = name + 1;
 824                 else {
 825                         stage = name[1] - '0';
 826                         cp = name + 3;
 827                 }
 828                 namelen = namelen - (cp - name);
 829                 if (!active_cache)
 830                         read_cache();
 831                 pos = cache_name_pos(cp, namelen);
 832                 if (pos < 0)
 833                         pos = -pos - 1;
 834                 while (pos < active_nr) {
 835                         ce = active_cache[pos];
 836                         if (ce_namelen(ce) != namelen ||
 837                             memcmp(ce->name, cp, namelen))
 838                                 break;
 839                         if (ce_stage(ce) == stage) {
 840                                 hashcpy(sha1, ce->sha1);
 841                                 *mode = ce->ce_mode;
 842                                 return 0;
 843                         }
 844                         pos++;
 845                 }
 846                 return -1;
 847         }
 848         for (cp = name, bracket_depth = 0; *cp; cp++) {
 849                 if (*cp == '{')
 850                         bracket_depth++;
 851                 else if (bracket_depth && *cp == '}')
 852                         bracket_depth--;
 853                 else if (!bracket_depth && *cp == ':')
 854                         break;
 855         }
 856         if (*cp == ':') {
 857                 unsigned char tree_sha1[20];
 858                 if (!get_sha1_1(name, cp-name, tree_sha1))
 859                         return get_tree_entry(tree_sha1, cp+1, sha1,
 860                                               mode);
 861         }
 862         return ret;
 863 }