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 #include "remote.h"
   9
  10 static int get_sha1_oneline(const char *, unsigned char *, struct commit_list *);
  11
  12 static int find_short_object_filename(int len, const char *name, unsigned char *sha1)
  13 {
  14         struct alternate_object_database *alt;
  15         char hex[40];
  16         int found = 0;
  17         static struct alternate_object_database *fakeent;
  18
  19         if (!fakeent) {
  20                 const char *objdir = get_object_directory();
  21                 int objdir_len = strlen(objdir);
  22                 int entlen = objdir_len + 43;
  23                 fakeent = xmalloc(sizeof(*fakeent) + entlen);
  24                 memcpy(fakeent->base, objdir, objdir_len);
  25                 fakeent->name = fakeent->base + objdir_len + 1;
  26                 fakeent->name[-1] = '/';
  27         }
  28         fakeent->next = alt_odb_list;
  29
  30         sprintf(hex, "%.2s", name);
  31         for (alt = fakeent; alt && found < 2; alt = alt->next) {
  32                 struct dirent *de;
  33                 DIR *dir;
  34                 sprintf(alt->name, "%.2s/", name);
  35                 dir = opendir(alt->base);
  36                 if (!dir)
  37                         continue;
  38                 while ((de = readdir(dir)) != NULL) {
  39                         if (strlen(de->d_name) != 38)
  40                                 continue;
  41                         if (memcmp(de->d_name, name + 2, len - 2))
  42                                 continue;
  43                         if (!found) {
  44                                 memcpy(hex + 2, de->d_name, 38);
  45                                 found++;
  46                         }
  47                         else if (memcmp(hex + 2, de->d_name, 38)) {
  48                                 found = 2;
  49                                 break;
  50                         }
  51                 }
  52                 closedir(dir);
  53         }
  54         if (found == 1)
  55                 return get_sha1_hex(hex, sha1) == 0;
  56         return found;
  57 }
  58
  59 static int match_sha(unsigned len, const unsigned char *a, const unsigned char *b)
  60 {
  61         do {
  62                 if (*a != *b)
  63                         return 0;
  64                 a++;
  65                 b++;
  66                 len -= 2;
  67         } while (len > 1);
  68         if (len)
  69                 if ((*a ^ *b) & 0xf0)
  70                         return 0;
  71         return 1;
  72 }
  73
  74 static int find_short_packed_object(int len, const unsigned char *match, unsigned char *sha1)
  75 {
  76         struct packed_git *p;
  77         const unsigned char *found_sha1 = NULL;
  78         int found = 0;
  79
  80         prepare_packed_git();
  81         for (p = packed_git; p && found < 2; p = p->next) {
  82                 uint32_t num, last;
  83                 uint32_t first = 0;
  84                 open_pack_index(p);
  85                 num = p->num_objects;
  86                 last = num;
  87                 while (first < last) {
  88                         uint32_t mid = (first + last) / 2;
  89                         const unsigned char *now;
  90                         int cmp;
  91
  92                         now = nth_packed_object_sha1(p, mid);
  93                         cmp = hashcmp(match, now);
  94                         if (!cmp) {
  95                                 first = mid;
  96                                 break;
  97                         }
  98                         if (cmp > 0) {
  99                                 first = mid+1;
 100                                 continue;
 101                         }
 102                         last = mid;
 103                 }
 104                 if (first < num) {
 105                         const unsigned char *now, *next;
 106                        now = nth_packed_object_sha1(p, first);
 107                         if (match_sha(len, match, now)) {
 108                                 next = nth_packed_object_sha1(p, first+1);
 109                                if (!next|| !match_sha(len, match, next)) {
 110                                         /* unique within this pack */
 111                                         if (!found) {
 112                                                 found_sha1 = now;
 113                                                 found++;
 114                                         }
 115                                         else if (hashcmp(found_sha1, now)) {
 116                                                 found = 2;
 117                                                 break;
 118                                         }
 119                                 }
 120                                 else {
 121                                         /* not even unique within this pack */
 122                                         found = 2;
 123                                         break;
 124                                 }
 125                         }
 126                 }
 127         }
 128         if (found == 1)
 129                 hashcpy(sha1, found_sha1);
 130         return found;
 131 }
 132
 133 #define SHORT_NAME_NOT_FOUND (-1)
 134 #define SHORT_NAME_AMBIGUOUS (-2)
 135
 136 static int find_unique_short_object(int len, char *canonical,
 137                                     unsigned char *res, unsigned char *sha1)
 138 {
 139         int has_unpacked, has_packed;
 140         unsigned char unpacked_sha1[20], packed_sha1[20];
 141
 142         prepare_alt_odb();
 143         has_unpacked = find_short_object_filename(len, canonical, unpacked_sha1);
 144         has_packed = find_short_packed_object(len, res, packed_sha1);
 145         if (!has_unpacked && !has_packed)
 146                 return SHORT_NAME_NOT_FOUND;
 147         if (1 < has_unpacked || 1 < has_packed)
 148                 return SHORT_NAME_AMBIGUOUS;
 149         if (has_unpacked != has_packed) {
 150                 hashcpy(sha1, (has_packed ? packed_sha1 : unpacked_sha1));
 151                 return 0;
 152         }
 153         /* Both have unique ones -- do they match? */
 154         if (hashcmp(packed_sha1, unpacked_sha1))
 155                 return SHORT_NAME_AMBIGUOUS;
 156         hashcpy(sha1, packed_sha1);
 157         return 0;
 158 }
 159
 160 static int get_short_sha1(const char *name, int len, unsigned char *sha1,
 161                           int quietly)
 162 {
 163         int i, status;
 164         char canonical[40];
 165         unsigned char res[20];
 166
 167         if (len < MINIMUM_ABBREV || len > 40)
 168                 return -1;
 169         hashclr(res);
 170         memset(canonical, 'x', 40);
 171         for (i = 0; i < len ;i++) {
 172                 unsigned char c = name[i];
 173                 unsigned char val;
 174                 if (c >= '0' && c <= '9')
 175                         val = c - '0';
 176                 else if (c >= 'a' && c <= 'f')
 177                         val = c - 'a' + 10;
 178                 else if (c >= 'A' && c <='F') {
 179                         val = c - 'A' + 10;
 180                         c -= 'A' - 'a';
 181                 }
 182                 else
 183                         return -1;
 184                 canonical[i] = c;
 185                 if (!(i & 1))
 186                         val <<= 4;
 187                 res[i >> 1] |= val;
 188         }
 189
 190         status = find_unique_short_object(i, canonical, res, sha1);
 191         if (!quietly && (status == SHORT_NAME_AMBIGUOUS))
 192                 return error("short SHA1 %.*s is ambiguous.", len, canonical);
 193         return status;
 194 }
 195
 196 const char *find_unique_abbrev(const unsigned char *sha1, int len)
 197 {
 198         int status, exists;
 199         static char hex[41];
 200
 201         exists = has_sha1_file(sha1);
 202         memcpy(hex, sha1_to_hex(sha1), 40);
 203         if (len == 40 || !len)
 204                 return hex;
 205         while (len < 40) {
 206                 unsigned char sha1_ret[20];
 207                 status = get_short_sha1(hex, len, sha1_ret, 1);
 208                 if (exists
 209                     ? !status
 210                     : status == SHORT_NAME_NOT_FOUND) {
 211                         hex[len] = 0;
 212                         return hex;
 213                 }
 214                 len++;
 215         }
 216         return hex;
 217 }
 218
 219 static int ambiguous_path(const char *path, int len)
 220 {
 221         int slash = 1;
 222         int cnt;
 223
 224         for (cnt = 0; cnt < len; cnt++) {
 225                 switch (*path++) {
 226                 case '\0':
 227                         break;
 228                 case '/':
 229                         if (slash)
 230                                 break;
 231                         slash = 1;
 232                         continue;
 233                 case '.':
 234                         continue;
 235                 default:
 236                         slash = 0;
 237                         continue;
 238                 }
 239                 break;
 240         }
 241         return slash;
 242 }
 243
 244 static inline int upstream_mark(const char *string, int len)
 245 {
 246         const char *suffix[] = { "@{upstream}", "@{u}" };
 247         int i;
 248
 249         for (i = 0; i < ARRAY_SIZE(suffix); i++) {
 250                 int suffix_len = strlen(suffix[i]);
 251                 if (suffix_len <= len
 252                     && !memcmp(string, suffix[i], suffix_len))
 253                         return suffix_len;
 254         }
 255         return 0;
 256 }
 257
 258 static int get_sha1_1(const char *name, int len, unsigned char *sha1);
 259
 260 static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 261 {
 262         static const char *warn_msg = "refname '%.*s' is ambiguous.";
 263         char *real_ref = NULL;
 264         int refs_found = 0;
 265         int at, reflog_len;
 266
 267         if (len == 40 && !get_sha1_hex(str, sha1))
 268                 return 0;
 269
 270         /* basic@{time or number or -number} format to query ref-log */
 271         reflog_len = at = 0;
 272         if (len && str[len-1] == '}') {
 273                 for (at = len-2; at >= 0; at--) {
 274                         if (str[at] == '@' && str[at+1] == '{') {
 275                                 if (!upstream_mark(str + at, len - at)) {
 276                                         reflog_len = (len-1) - (at+2);
 277                                         len = at;
 278                                 }
 279                                 break;
 280                         }
 281                 }
 282         }
 283
 284         /* Accept only unambiguous ref paths. */
 285         if (len && ambiguous_path(str, len))
 286                 return -1;
 287
 288         if (!len && reflog_len) {
 289                 struct strbuf buf = STRBUF_INIT;
 290                 int ret;
 291                 /* try the @{-N} syntax for n-th checkout */
 292                 ret = interpret_branch_name(str+at, &buf);
 293                 if (ret > 0) {
 294                         /* substitute this branch name and restart */
 295                         return get_sha1_1(buf.buf, buf.len, sha1);
 296                 } else if (ret == 0) {
 297                         return -1;
 298                 }
 299                 /* allow "@{...}" to mean the current branch reflog */
 300                 refs_found = dwim_ref("HEAD", 4, sha1, &real_ref);
 301         } else if (reflog_len)
 302                 refs_found = dwim_log(str, len, sha1, &real_ref);
 303         else
 304                 refs_found = dwim_ref(str, len, sha1, &real_ref);
 305
 306         if (!refs_found)
 307                 return -1;
 308
 309         if (warn_ambiguous_refs && refs_found > 1)
 310                 warning(warn_msg, len, str);
 311
 312         if (reflog_len) {
 313                 int nth, i;
 314                 unsigned long at_time;
 315                 unsigned long co_time;
 316                 int co_tz, co_cnt;
 317
 318                 /* a @{-N} placed anywhere except the start is an error */
 319                 if (str[at+2] == '-')
 320                         return -1;
 321
 322                 /* Is it asking for N-th entry, or approxidate? */
 323                 for (i = nth = 0; 0 <= nth && i < reflog_len; i++) {
 324                         char ch = str[at+2+i];
 325                         if ('0' <= ch && ch <= '9')
 326                                 nth = nth * 10 + ch - '0';
 327                         else
 328                                 nth = -1;
 329                 }
 330                 if (100000000 <= nth) {
 331                         at_time = nth;
 332                         nth = -1;
 333                 } else if (0 <= nth)
 334                         at_time = 0;
 335                 else {
 336                         int errors = 0;
 337                         char *tmp = xstrndup(str + at + 2, reflog_len);
 338                         at_time = approxidate_careful(tmp, &errors);
 339                         free(tmp);
 340                         if (errors)
 341                                 return -1;
 342                 }
 343                 if (read_ref_at(real_ref, at_time, nth, sha1, NULL,
 344                                 &co_time, &co_tz, &co_cnt)) {
 345                         if (at_time)
 346                                 warning("Log for '%.*s' only goes "
 347                                         "back to %s.", len, str,
 348                                         show_date(co_time, co_tz, DATE_RFC2822));
 349                         else {
 350                                 free(real_ref);
 351                                 die("Log for '%.*s' only has %d entries.",
 352                                     len, str, co_cnt);
 353                         }
 354                 }
 355         }
 356
 357         free(real_ref);
 358         return 0;
 359 }
 360
 361 static int get_parent(const char *name, int len,
 362                       unsigned char *result, int idx)
 363 {
 364         unsigned char sha1[20];
 365         int ret = get_sha1_1(name, len, sha1);
 366         struct commit *commit;
 367         struct commit_list *p;
 368
 369         if (ret)
 370                 return ret;
 371         commit = lookup_commit_reference(sha1);
 372         if (!commit)
 373                 return -1;
 374         if (parse_commit(commit))
 375                 return -1;
 376         if (!idx) {
 377                 hashcpy(result, commit->object.sha1);
 378                 return 0;
 379         }
 380         p = commit->parents;
 381         while (p) {
 382                 if (!--idx) {
 383                         hashcpy(result, p->item->object.sha1);
 384                         return 0;
 385                 }
 386                 p = p->next;
 387         }
 388         return -1;
 389 }
 390
 391 static int get_nth_ancestor(const char *name, int len,
 392                             unsigned char *result, int generation)
 393 {
 394         unsigned char sha1[20];
 395         struct commit *commit;
 396         int ret;
 397
 398         ret = get_sha1_1(name, len, sha1);
 399         if (ret)
 400                 return ret;
 401         commit = lookup_commit_reference(sha1);
 402         if (!commit)
 403                 return -1;
 404
 405         while (generation--) {
 406                 if (parse_commit(commit) || !commit->parents)
 407                         return -1;
 408                 commit = commit->parents->item;
 409         }
 410         hashcpy(result, commit->object.sha1);
 411         return 0;
 412 }
 413
 414 struct object *peel_to_type(const char *name, int namelen,
 415                             struct object *o, enum object_type expected_type)
 416 {
 417         if (name && !namelen)
 418                 namelen = strlen(name);
 419         while (1) {
 420                 if (!o || (!o->parsed && !parse_object(o->sha1)))
 421                         return NULL;
 422                 if (o->type == expected_type)
 423                         return o;
 424                 if (o->type == OBJ_TAG)
 425                         o = ((struct tag*) o)->tagged;
 426                 else if (o->type == OBJ_COMMIT)
 427                         o = &(((struct commit *) o)->tree->object);
 428                 else {
 429                         if (name)
 430                                 error("%.*s: expected %s type, but the object "
 431                                       "dereferences to %s type",
 432                                       namelen, name, typename(expected_type),
 433                                       typename(o->type));
 434                         return NULL;
 435                 }
 436         }
 437 }
 438
 439 static int peel_onion(const char *name, int len, unsigned char *sha1)
 440 {
 441         unsigned char outer[20];
 442         const char *sp;
 443         unsigned int expected_type = 0;
 444         struct object *o;
 445
 446         /*
 447          * "ref^{type}" dereferences ref repeatedly until you cannot
 448          * dereference anymore, or you get an object of given type,
 449          * whichever comes first.  "ref^{}" means just dereference
 450          * tags until you get a non-tag.  "ref^0" is a shorthand for
 451          * "ref^{commit}".  "commit^{tree}" could be used to find the
 452          * top-level tree of the given commit.
 453          */
 454         if (len < 4 || name[len-1] != '}')
 455                 return -1;
 456
 457         for (sp = name + len - 1; name <= sp; sp--) {
 458                 int ch = *sp;
 459                 if (ch == '{' && name < sp && sp[-1] == '^')
 460                         break;
 461         }
 462         if (sp <= name)
 463                 return -1;
 464
 465         sp++; /* beginning of type name, or closing brace for empty */
 466         if (!strncmp(commit_type, sp, 6) && sp[6] == '}')
 467                 expected_type = OBJ_COMMIT;
 468         else if (!strncmp(tree_type, sp, 4) && sp[4] == '}')
 469                 expected_type = OBJ_TREE;
 470         else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')
 471                 expected_type = OBJ_BLOB;
 472         else if (sp[0] == '}')
 473                 expected_type = OBJ_NONE;
 474         else if (sp[0] == '/')
 475                 expected_type = OBJ_COMMIT;
 476         else
 477                 return -1;
 478
 479         if (get_sha1_1(name, sp - name - 2, outer))
 480                 return -1;
 481
 482         o = parse_object(outer);
 483         if (!o)
 484                 return -1;
 485         if (!expected_type) {
 486                 o = deref_tag(o, name, sp - name - 2);
 487                 if (!o || (!o->parsed && !parse_object(o->sha1)))
 488                         return -1;
 489                 hashcpy(sha1, o->sha1);
 490                 return 0;
 491         }
 492
 493         /*
 494          * At this point, the syntax look correct, so
 495          * if we do not get the needed object, we should
 496          * barf.
 497          */
 498         o = peel_to_type(name, len, o, expected_type);
 499         if (!o)
 500                 return -1;
 501
 502         hashcpy(sha1, o->sha1);
 503         if (sp[0] == '/') {
 504                 /* "$commit^{/foo}" */
 505                 char *prefix;
 506                 int ret;
 507                 struct commit_list *list = NULL;
 508
 509                 /*
 510                  * $commit^{/}. Some regex implementation may reject.
 511                  * We don't need regex anyway. '' pattern always matches.
 512                  */
 513                 if (sp[1] == '}')
 514                         return 0;
 515
 516                 prefix = xstrndup(sp + 1, name + len - 1 - (sp + 1));
 517                 commit_list_insert((struct commit *)o, &list);
 518                 ret = get_sha1_oneline(prefix, sha1, list);
 519                 free(prefix);
 520                 return ret;
 521         }
 522         return 0;
 523 }
 524
 525 static int get_describe_name(const char *name, int len, unsigned char *sha1)
 526 {
 527         const char *cp;
 528
 529         for (cp = name + len - 1; name + 2 <= cp; cp--) {
 530                 char ch = *cp;
 531                 if (hexval(ch) & ~0377) {
 532                         /* We must be looking at g in "SOMETHING-g"
 533                          * for it to be describe output.
 534                          */
 535                         if (ch == 'g' && cp[-1] == '-') {
 536                                 cp++;
 537                                 len -= cp - name;
 538                                 return get_short_sha1(cp, len, sha1, 1);
 539                         }
 540                 }
 541         }
 542         return -1;
 543 }
 544
 545 static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 546 {
 547         int ret, has_suffix;
 548         const char *cp;
 549
 550         /*
 551          * "name~3" is "name^^^", "name~" is "name~1", and "name^" is "name^1".
 552          */
 553         has_suffix = 0;
 554         for (cp = name + len - 1; name <= cp; cp--) {
 555                 int ch = *cp;
 556                 if ('0' <= ch && ch <= '9')
 557                         continue;
 558                 if (ch == '~' || ch == '^')
 559                         has_suffix = ch;
 560                 break;
 561         }
 562
 563         if (has_suffix) {
 564                 int num = 0;
 565                 int len1 = cp - name;
 566                 cp++;
 567                 while (cp < name + len)
 568                         num = num * 10 + *cp++ - '0';
 569                 if (!num && len1 == len - 1)
 570                         num = 1;
 571                 if (has_suffix == '^')
 572                         return get_parent(name, len1, sha1, num);
 573                 /* else if (has_suffix == '~') -- goes without saying */
 574                 return get_nth_ancestor(name, len1, sha1, num);
 575         }
 576
 577         ret = peel_onion(name, len, sha1);
 578         if (!ret)
 579                 return 0;
 580
 581         ret = get_sha1_basic(name, len, sha1);
 582         if (!ret)
 583                 return 0;
 584
 585         /* It could be describe output that is "SOMETHING-gXXXX" */
 586         ret = get_describe_name(name, len, sha1);
 587         if (!ret)
 588                 return 0;
 589
 590         return get_short_sha1(name, len, sha1, 0);
 591 }
 592
 593 /*
 594  * This interprets names like ':/Initial revision of "git"' by searching
 595  * through history and returning the first commit whose message starts
 596  * the given regular expression.
 597  *
 598  * For future extension, ':/!' is reserved. If you want to match a message
 599  * beginning with a '!', you have to repeat the exclamation mark.
 600  */
 601 #define ONELINE_SEEN (1u<<20)
 602
 603 static int handle_one_ref(const char *path,
 604                 const unsigned char *sha1, int flag, void *cb_data)
 605 {
 606         struct commit_list **list = cb_data;
 607         struct object *object = parse_object(sha1);
 608         if (!object)
 609                 return 0;
 610         if (object->type == OBJ_TAG) {
 611                 object = deref_tag(object, path, strlen(path));
 612                 if (!object)
 613                         return 0;
 614         }
 615         if (object->type != OBJ_COMMIT)
 616                 return 0;
 617         commit_list_insert_by_date((struct commit *)object, list);
 618         return 0;
 619 }
 620
 621 static int get_sha1_oneline(const char *prefix, unsigned char *sha1,
 622                             struct commit_list *list)
 623 {
 624         struct commit_list *backup = NULL, *l;
 625         int found = 0;
 626         regex_t regex;
 627
 628         if (prefix[0] == '!') {
 629                 if (prefix[1] != '!')
 630                         die ("Invalid search pattern: %s", prefix);
 631                 prefix++;
 632         }
 633
 634         if (regcomp(&regex, prefix, REG_EXTENDED))
 635                 die("Invalid search pattern: %s", prefix);
 636
 637         for (l = list; l; l = l->next) {
 638                 l->item->object.flags |= ONELINE_SEEN;
 639                 commit_list_insert(l->item, &backup);
 640         }
 641         while (list) {
 642                 char *p, *to_free = NULL;
 643                 struct commit *commit;
 644                 enum object_type type;
 645                 unsigned long size;
 646                 int matches;
 647
 648                 commit = pop_most_recent_commit(&list, ONELINE_SEEN);
 649                 if (!parse_object(commit->object.sha1))
 650                         continue;
 651                 if (commit->buffer)
 652                         p = commit->buffer;
 653                 else {
 654                         p = read_sha1_file(commit->object.sha1, &type, &size);
 655                         if (!p)
 656                                 continue;
 657                         to_free = p;
 658                 }
 659
 660                 p = strstr(p, "\n\n");
 661                 matches = p && !regexec(&regex, p + 2, 0, NULL, 0);
 662                 free(to_free);
 663
 664                 if (matches) {
 665                         hashcpy(sha1, commit->object.sha1);
 666                         found = 1;
 667                         break;
 668                 }
 669         }
 670         regfree(&regex);
 671         free_commit_list(list);
 672         for (l = backup; l; l = l->next)
 673                 clear_commit_marks(l->item, ONELINE_SEEN);
 674         free_commit_list(backup);
 675         return found ? 0 : -1;
 676 }
 677
 678 struct grab_nth_branch_switch_cbdata {
 679         long cnt, alloc;
 680         struct strbuf *buf;
 681 };
 682
 683 static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
 684                                   const char *email, unsigned long timestamp, int tz,
 685                                   const char *message, void *cb_data)
 686 {
 687         struct grab_nth_branch_switch_cbdata *cb = cb_data;
 688         const char *match = NULL, *target = NULL;
 689         size_t len;
 690         int nth;
 691
 692         if (!prefixcmp(message, "checkout: moving from ")) {
 693                 match = message + strlen("checkout: moving from ");
 694                 target = strstr(match, " to ");
 695         }
 696
 697         if (!match || !target)
 698                 return 0;
 699
 700         len = target - match;
 701         nth = cb->cnt++ % cb->alloc;
 702         strbuf_reset(&cb->buf[nth]);
 703         strbuf_add(&cb->buf[nth], match, len);
 704         return 0;
 705 }
 706
 707 /*
 708  * Parse @{-N} syntax, return the number of characters parsed
 709  * if successful; otherwise signal an error with negative value.
 710  */
 711 static int interpret_nth_prior_checkout(const char *name, struct strbuf *buf)
 712 {
 713         long nth;
 714         int i, retval;
 715         struct grab_nth_branch_switch_cbdata cb;
 716         const char *brace;
 717         char *num_end;
 718
 719         if (name[0] != '@' || name[1] != '{' || name[2] != '-')
 720                 return -1;
 721         brace = strchr(name, '}');
 722         if (!brace)
 723                 return -1;
 724         nth = strtol(name+3, &num_end, 10);
 725         if (num_end != brace)
 726                 return -1;
 727         if (nth <= 0)
 728                 return -1;
 729         cb.alloc = nth;
 730         cb.buf = xmalloc(nth * sizeof(struct strbuf));
 731         for (i = 0; i < nth; i++)
 732                 strbuf_init(&cb.buf[i], 20);
 733         cb.cnt = 0;
 734         retval = 0;
 735         for_each_recent_reflog_ent("HEAD", grab_nth_branch_switch, 40960, &cb);
 736         if (cb.cnt < nth) {
 737                 cb.cnt = 0;
 738                 for_each_reflog_ent("HEAD", grab_nth_branch_switch, &cb);
 739         }
 740         if (cb.cnt < nth)
 741                 goto release_return;
 742         i = cb.cnt % nth;
 743         strbuf_reset(buf);
 744         strbuf_add(buf, cb.buf[i].buf, cb.buf[i].len);
 745         retval = brace-name+1;
 746
 747 release_return:
 748         for (i = 0; i < nth; i++)
 749                 strbuf_release(&cb.buf[i]);
 750         free(cb.buf);
 751
 752         return retval;
 753 }
 754
 755 int get_sha1_mb(const char *name, unsigned char *sha1)
 756 {
 757         struct commit *one, *two;
 758         struct commit_list *mbs;
 759         unsigned char sha1_tmp[20];
 760         const char *dots;
 761         int st;
 762
 763         dots = strstr(name, "...");
 764         if (!dots)
 765                 return get_sha1(name, sha1);
 766         if (dots == name)
 767                 st = get_sha1("HEAD", sha1_tmp);
 768         else {
 769                 struct strbuf sb;
 770                 strbuf_init(&sb, dots - name);
 771                 strbuf_add(&sb, name, dots - name);
 772                 st = get_sha1(sb.buf, sha1_tmp);
 773                 strbuf_release(&sb);
 774         }
 775         if (st)
 776                 return st;
 777         one = lookup_commit_reference_gently(sha1_tmp, 0);
 778         if (!one)
 779                 return -1;
 780
 781         if (get_sha1(dots[3] ? (dots + 3) : "HEAD", sha1_tmp))
 782                 return -1;
 783         two = lookup_commit_reference_gently(sha1_tmp, 0);
 784         if (!two)
 785                 return -1;
 786         mbs = get_merge_bases(one, two, 1);
 787         if (!mbs || mbs->next)
 788                 st = -1;
 789         else {
 790                 st = 0;
 791                 hashcpy(sha1, mbs->item->object.sha1);
 792         }
 793         free_commit_list(mbs);
 794         return st;
 795 }
 796
 797 /*
 798  * This reads short-hand syntax that not only evaluates to a commit
 799  * object name, but also can act as if the end user spelled the name
 800  * of the branch from the command line.
 801  *
 802  * - "@{-N}" finds the name of the Nth previous branch we were on, and
 803  *   places the name of the branch in the given buf and returns the
 804  *   number of characters parsed if successful.
 805  *
 806  * - "<branch>@{upstream}" finds the name of the other ref that
 807  *   <branch> is configured to merge with (missing <branch> defaults
 808  *   to the current branch), and places the name of the branch in the
 809  *   given buf and returns the number of characters parsed if
 810  *   successful.
 811  *
 812  * If the input is not of the accepted format, it returns a negative
 813  * number to signal an error.
 814  *
 815  * If the input was ok but there are not N branch switches in the
 816  * reflog, it returns 0.
 817  */
 818 int interpret_branch_name(const char *name, struct strbuf *buf)
 819 {
 820         char *cp;
 821         struct branch *upstream;
 822         int namelen = strlen(name);
 823         int len = interpret_nth_prior_checkout(name, buf);
 824         int tmp_len;
 825
 826         if (!len)
 827                 return len; /* syntax Ok, not enough switches */
 828         if (0 < len && len == namelen)
 829                 return len; /* consumed all */
 830         else if (0 < len) {
 831                 /* we have extra data, which might need further processing */
 832                 struct strbuf tmp = STRBUF_INIT;
 833                 int used = buf->len;
 834                 int ret;
 835
 836                 strbuf_add(buf, name + len, namelen - len);
 837                 ret = interpret_branch_name(buf->buf, &tmp);
 838                 /* that data was not interpreted, remove our cruft */
 839                 if (ret < 0) {
 840                         strbuf_setlen(buf, used);
 841                         return len;
 842                 }
 843                 strbuf_reset(buf);
 844                 strbuf_addbuf(buf, &tmp);
 845                 strbuf_release(&tmp);
 846                 /* tweak for size of {-N} versus expanded ref name */
 847                 return ret - used + len;
 848         }
 849
 850         cp = strchr(name, '@');
 851         if (!cp)
 852                 return -1;
 853         tmp_len = upstream_mark(cp, namelen - (cp - name));
 854         if (!tmp_len)
 855                 return -1;
 856         len = cp + tmp_len - name;
 857         cp = xstrndup(name, cp - name);
 858         upstream = branch_get(*cp ? cp : NULL);
 859         if (!upstream
 860             || !upstream->merge
 861             || !upstream->merge[0]->dst)
 862                 return error("No upstream branch found for '%s'", cp);
 863         free(cp);
 864         cp = shorten_unambiguous_ref(upstream->merge[0]->dst, 0);
 865         strbuf_reset(buf);
 866         strbuf_addstr(buf, cp);
 867         free(cp);
 868         return len;
 869 }
 870
 871 int strbuf_branchname(struct strbuf *sb, const char *name)
 872 {
 873         int len = strlen(name);
 874         if (interpret_branch_name(name, sb) == len)
 875                 return 0;
 876         strbuf_add(sb, name, len);
 877         return len;
 878 }
 879
 880 int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
 881 {
 882         strbuf_branchname(sb, name);
 883         if (name[0] == '-')
 884                 return -1;
 885         strbuf_splice(sb, 0, 0, "refs/heads/", 11);
 886         return check_refname_format(sb->buf, 0);
 887 }
 888
 889 /*
 890  * This is like "get_sha1_basic()", except it allows "sha1 expressions",
 891  * notably "xyz^" for "parent of xyz"
 892  */
 893 int get_sha1(const char *name, unsigned char *sha1)
 894 {
 895         struct object_context unused;
 896         return get_sha1_with_context(name, sha1, &unused);
 897 }
 898
 899 /* Must be called only when object_name:filename doesn't exist. */
 900 static void diagnose_invalid_sha1_path(const char *prefix,
 901                                        const char *filename,
 902                                        const unsigned char *tree_sha1,
 903                                        const char *object_name)
 904 {
 905         struct stat st;
 906         unsigned char sha1[20];
 907         unsigned mode;
 908
 909         if (!prefix)
 910                 prefix = "";
 911
 912         if (!lstat(filename, &st))
 913                 die("Path '%s' exists on disk, but not in '%s'.",
 914                     filename, object_name);
 915         if (errno == ENOENT || errno == ENOTDIR) {
 916                 char *fullname = xmalloc(strlen(filename)
 917                                              + strlen(prefix) + 1);
 918                 strcpy(fullname, prefix);
 919                 strcat(fullname, filename);
 920
 921                 if (!get_tree_entry(tree_sha1, fullname,
 922                                     sha1, &mode)) {
 923                         die("Path '%s' exists, but not '%s'.\n"
 924                             "Did you mean '%s:%s' aka '%s:./%s'?",
 925                             fullname,
 926                             filename,
 927                             object_name,
 928                             fullname,
 929                             object_name,
 930                             filename);
 931                 }
 932                 die("Path '%s' does not exist in '%s'",
 933                     filename, object_name);
 934         }
 935 }
 936
 937 /* Must be called only when :stage:filename doesn't exist. */
 938 static void diagnose_invalid_index_path(int stage,
 939                                         const char *prefix,
 940                                         const char *filename)
 941 {
 942         struct stat st;
 943         struct cache_entry *ce;
 944         int pos;
 945         unsigned namelen = strlen(filename);
 946         unsigned fullnamelen;
 947         char *fullname;
 948
 949         if (!prefix)
 950                 prefix = "";
 951
 952         /* Wrong stage number? */
 953         pos = cache_name_pos(filename, namelen);
 954         if (pos < 0)
 955                 pos = -pos - 1;
 956         if (pos < active_nr) {
 957                 ce = active_cache[pos];
 958                 if (ce_namelen(ce) == namelen &&
 959                     !memcmp(ce->name, filename, namelen))
 960                         die("Path '%s' is in the index, but not at stage %d.\n"
 961                             "Did you mean ':%d:%s'?",
 962                             filename, stage,
 963                             ce_stage(ce), filename);
 964         }
 965
 966         /* Confusion between relative and absolute filenames? */
 967         fullnamelen = namelen + strlen(prefix);
 968         fullname = xmalloc(fullnamelen + 1);
 969         strcpy(fullname, prefix);
 970         strcat(fullname, filename);
 971         pos = cache_name_pos(fullname, fullnamelen);
 972         if (pos < 0)
 973                 pos = -pos - 1;
 974         if (pos < active_nr) {
 975                 ce = active_cache[pos];
 976                 if (ce_namelen(ce) == fullnamelen &&
 977                     !memcmp(ce->name, fullname, fullnamelen))
 978                         die("Path '%s' is in the index, but not '%s'.\n"
 979                             "Did you mean ':%d:%s' aka ':%d:./%s'?",
 980                             fullname, filename,
 981                             ce_stage(ce), fullname,
 982                             ce_stage(ce), filename);
 983         }
 984
 985         if (!lstat(filename, &st))
 986                 die("Path '%s' exists on disk, but not in the index.", filename);
 987         if (errno == ENOENT || errno == ENOTDIR)
 988                 die("Path '%s' does not exist (neither on disk nor in the index).",
 989                     filename);
 990
 991         free(fullname);
 992 }
 993
 994
 995 int get_sha1_with_mode_1(const char *name, unsigned char *sha1, unsigned *mode,
 996                          int only_to_die, const char *prefix)
 997 {
 998         struct object_context oc;
 999         int ret;
1000         ret = get_sha1_with_context_1(name, sha1, &oc, only_to_die, prefix);
1001         *mode = oc.mode;
1002         return ret;
1003 }
1004
1005 static char *resolve_relative_path(const char *rel)
1006 {
1007         if (prefixcmp(rel, "./") && prefixcmp(rel, "../"))
1008                 return NULL;
1009
1010         if (!startup_info)
1011                 die("BUG: startup_info struct is not initialized.");
1012
1013         if (!is_inside_work_tree())
1014                 die("relative path syntax can't be used outside working tree.");
1015
1016         /* die() inside prefix_path() if resolved path is outside worktree */
1017         return prefix_path(startup_info->prefix,
1018                            startup_info->prefix ? strlen(startup_info->prefix) : 0,
1019                            rel);
1020 }
1021
1022 int get_sha1_with_context_1(const char *name, unsigned char *sha1,
1023                             struct object_context *oc,
1024                             int only_to_die, const char *prefix)
1025 {
1026         int ret, bracket_depth;
1027         int namelen = strlen(name);
1028         const char *cp;
1029
1030         memset(oc, 0, sizeof(*oc));
1031         oc->mode = S_IFINVALID;
1032         ret = get_sha1_1(name, namelen, sha1);
1033         if (!ret)
1034                 return ret;
1035         /* sha1:path --> object name of path in ent sha1
1036          * :path -> object name of absolute path in index
1037          * :./path -> object name of path relative to cwd in index
1038          * :[0-3]:path -> object name of path in index at stage
1039          * :/foo -> recent commit matching foo
1040          */
1041         if (name[0] == ':') {
1042                 int stage = 0;
1043                 struct cache_entry *ce;
1044                 char *new_path = NULL;
1045                 int pos;
1046                 if (!only_to_die && namelen > 2 && name[1] == '/') {
1047                         struct commit_list *list = NULL;
1048                         for_each_ref(handle_one_ref, &list);
1049                         return get_sha1_oneline(name + 2, sha1, list);
1050                 }
1051                 if (namelen < 3 ||
1052                     name[2] != ':' ||
1053                     name[1] < '0' || '3' < name[1])
1054                         cp = name + 1;
1055                 else {
1056                         stage = name[1] - '0';
1057                         cp = name + 3;
1058                 }
1059                 new_path = resolve_relative_path(cp);
1060                 if (!new_path) {
1061                         namelen = namelen - (cp - name);
1062                 } else {
1063                         cp = new_path;
1064                         namelen = strlen(cp);
1065                 }
1066
1067                 strncpy(oc->path, cp,
1068                         sizeof(oc->path));
1069                 oc->path[sizeof(oc->path)-1] = '\0';
1070
1071                 if (!active_cache)
1072                         read_cache();
1073                 pos = cache_name_pos(cp, namelen);
1074                 if (pos < 0)
1075                         pos = -pos - 1;
1076                 while (pos < active_nr) {
1077                         ce = active_cache[pos];
1078                         if (ce_namelen(ce) != namelen ||
1079                             memcmp(ce->name, cp, namelen))
1080                                 break;
1081                         if (ce_stage(ce) == stage) {
1082                                 hashcpy(sha1, ce->sha1);
1083                                 oc->mode = ce->ce_mode;
1084                                 free(new_path);
1085                                 return 0;
1086                         }
1087                         pos++;
1088                 }
1089                 if (only_to_die && name[1] && name[1] != '/')
1090                         diagnose_invalid_index_path(stage, prefix, cp);
1091                 free(new_path);
1092                 return -1;
1093         }
1094         for (cp = name, bracket_depth = 0; *cp; cp++) {
1095                 if (*cp == '{')
1096                         bracket_depth++;
1097                 else if (bracket_depth && *cp == '}')
1098                         bracket_depth--;
1099                 else if (!bracket_depth && *cp == ':')
1100                         break;
1101         }
1102         if (*cp == ':') {
1103                 unsigned char tree_sha1[20];
1104                 char *object_name = NULL;
1105                 if (only_to_die) {
1106                         object_name = xmalloc(cp-name+1);
1107                         strncpy(object_name, name, cp-name);
1108                         object_name[cp-name] = '\0';
1109                 }
1110                 if (!get_sha1_1(name, cp-name, tree_sha1)) {
1111                         const char *filename = cp+1;
1112                         char *new_filename = NULL;
1113
1114                         new_filename = resolve_relative_path(filename);
1115                         if (new_filename)
1116                                 filename = new_filename;
1117                         ret = get_tree_entry(tree_sha1, filename, sha1, &oc->mode);
1118                         if (only_to_die) {
1119                                 diagnose_invalid_sha1_path(prefix, filename,
1120                                                            tree_sha1, object_name);
1121                                 free(object_name);
1122                         }
1123                         hashcpy(oc->tree, tree_sha1);
1124                         strncpy(oc->path, filename,
1125                                 sizeof(oc->path));
1126                         oc->path[sizeof(oc->path)-1] = '\0';
1127
1128                         free(new_filename);
1129                         return ret;
1130                 } else {
1131                         if (only_to_die)
1132                                 die("Invalid object name '%s'.", object_name);
1133                 }
1134         }
1135         return ret;
1136 }