Andrew's git / gitweb.git / sha1_name.c
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sha1_name.con commit describe: Break annotated tag ties by tagger date (03e8b54)
   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
   9static 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
  56static 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
  71static 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
 133static 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
 157static 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
 193const 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
 216static 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 */
 245static char *substitute_branch_name(const char **string, int *len)
 246{
 247        struct strbuf buf = STRBUF_INIT;
 248        int ret = interpret_branch_name(*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
 260int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
 261{
 262        char *last_branch = substitute_branch_name(&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                int flag;
 272
 273                this_result = refs_found ? sha1_from_ref : sha1;
 274                mksnpath(fullref, sizeof(fullref), *p, len, str);
 275                r = resolve_ref(fullref, this_result, 1, &flag);
 276                if (r) {
 277                        if (!refs_found++)
 278                                *ref = xstrdup(r);
 279                        if (!warn_ambiguous_refs)
 280                                break;
 281                } else if ((flag & REF_ISSYMREF) && strcmp(fullref, "HEAD"))
 282                        warning("ignoring dangling symref %s.", fullref);
 283        }
 284        free(last_branch);
 285        return refs_found;
 286}
 287
 288int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
 289{
 290        char *last_branch = substitute_branch_name(&str, &len);
 291        const char **p;
 292        int logs_found = 0;
 293
 294        *log = NULL;
 295        for (p = ref_rev_parse_rules; *p; p++) {
 296                struct stat st;
 297                unsigned char hash[20];
 298                char path[PATH_MAX];
 299                const char *ref, *it;
 300
 301                mksnpath(path, sizeof(path), *p, len, str);
 302                ref = resolve_ref(path, hash, 1, NULL);
 303                if (!ref)
 304                        continue;
 305                if (!stat(git_path("logs/%s", path), &st) &&
 306                    S_ISREG(st.st_mode))
 307                        it = path;
 308                else if (strcmp(ref, path) &&
 309                         !stat(git_path("logs/%s", ref), &st) &&
 310                         S_ISREG(st.st_mode))
 311                        it = ref;
 312                else
 313                        continue;
 314                if (!logs_found++) {
 315                        *log = xstrdup(it);
 316                        hashcpy(sha1, hash);
 317                }
 318                if (!warn_ambiguous_refs)
 319                        break;
 320        }
 321        free(last_branch);
 322        return logs_found;
 323}
 324
 325static int get_sha1_1(const char *name, int len, unsigned char *sha1);
 326
 327static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 328{
 329        static const char *warning = "warning: refname '%.*s' is ambiguous.\n";
 330        char *real_ref = NULL;
 331        int refs_found = 0;
 332        int at, reflog_len;
 333
 334        if (len == 40 && !get_sha1_hex(str, sha1))
 335                return 0;
 336
 337        /* basic@{time or number or -number} format to query ref-log */
 338        reflog_len = at = 0;
 339        if (len && str[len-1] == '}') {
 340                for (at = len-2; at >= 0; at--) {
 341                        if (str[at] == '@' && str[at+1] == '{') {
 342                                reflog_len = (len-1) - (at+2);
 343                                len = at;
 344                                break;
 345                        }
 346                }
 347        }
 348
 349        /* Accept only unambiguous ref paths. */
 350        if (len && ambiguous_path(str, len))
 351                return -1;
 352
 353        if (!len && reflog_len) {
 354                struct strbuf buf = STRBUF_INIT;
 355                int ret;
 356                /* try the @{-N} syntax for n-th checkout */
 357                ret = interpret_branch_name(str+at, &buf);
 358                if (ret > 0) {
 359                        /* substitute this branch name and restart */
 360                        return get_sha1_1(buf.buf, buf.len, sha1);
 361                } else if (ret == 0) {
 362                        return -1;
 363                }
 364                /* allow "@{...}" to mean the current branch reflog */
 365                refs_found = dwim_ref("HEAD", 4, sha1, &real_ref);
 366        } else if (reflog_len)
 367                refs_found = dwim_log(str, len, sha1, &real_ref);
 368        else
 369                refs_found = dwim_ref(str, len, sha1, &real_ref);
 370
 371        if (!refs_found)
 372                return -1;
 373
 374        if (warn_ambiguous_refs && refs_found > 1)
 375                fprintf(stderr, warning, len, str);
 376
 377        if (reflog_len) {
 378                int nth, i;
 379                unsigned long at_time;
 380                unsigned long co_time;
 381                int co_tz, co_cnt;
 382
 383                /* Is it asking for N-th entry, or approxidate? */
 384                for (i = nth = 0; 0 <= nth && i < reflog_len; i++) {
 385                        char ch = str[at+2+i];
 386                        if ('0' <= ch && ch <= '9')
 387                                nth = nth * 10 + ch - '0';
 388                        else
 389                                nth = -1;
 390                }
 391                if (100000000 <= nth) {
 392                        at_time = nth;
 393                        nth = -1;
 394                } else if (0 <= nth)
 395                        at_time = 0;
 396                else {
 397                        int errors = 0;
 398                        char *tmp = xstrndup(str + at + 2, reflog_len);
 399                        at_time = approxidate_careful(tmp, &errors);
 400                        free(tmp);
 401                        if (errors)
 402                                return -1;
 403                }
 404                if (read_ref_at(real_ref, at_time, nth, sha1, NULL,
 405                                &co_time, &co_tz, &co_cnt)) {
 406                        if (at_time)
 407                                fprintf(stderr,
 408                                        "warning: Log for '%.*s' only goes "
 409                                        "back to %s.\n", len, str,
 410                                        show_date(co_time, co_tz, DATE_RFC2822));
 411                        else
 412                                fprintf(stderr,
 413                                        "warning: Log for '%.*s' only has "
 414                                        "%d entries.\n", len, str, co_cnt);
 415                }
 416        }
 417
 418        free(real_ref);
 419        return 0;
 420}
 421
 422static int get_parent(const char *name, int len,
 423                      unsigned char *result, int idx)
 424{
 425        unsigned char sha1[20];
 426        int ret = get_sha1_1(name, len, sha1);
 427        struct commit *commit;
 428        struct commit_list *p;
 429
 430        if (ret)
 431                return ret;
 432        commit = lookup_commit_reference(sha1);
 433        if (!commit)
 434                return -1;
 435        if (parse_commit(commit))
 436                return -1;
 437        if (!idx) {
 438                hashcpy(result, commit->object.sha1);
 439                return 0;
 440        }
 441        p = commit->parents;
 442        while (p) {
 443                if (!--idx) {
 444                        hashcpy(result, p->item->object.sha1);
 445                        return 0;
 446                }
 447                p = p->next;
 448        }
 449        return -1;
 450}
 451
 452static int get_nth_ancestor(const char *name, int len,
 453                            unsigned char *result, int generation)
 454{
 455        unsigned char sha1[20];
 456        struct commit *commit;
 457        int ret;
 458
 459        ret = get_sha1_1(name, len, sha1);
 460        if (ret)
 461                return ret;
 462        commit = lookup_commit_reference(sha1);
 463        if (!commit)
 464                return -1;
 465
 466        while (generation--) {
 467                if (parse_commit(commit) || !commit->parents)
 468                        return -1;
 469                commit = commit->parents->item;
 470        }
 471        hashcpy(result, commit->object.sha1);
 472        return 0;
 473}
 474
 475struct object *peel_to_type(const char *name, int namelen,
 476                            struct object *o, enum object_type expected_type)
 477{
 478        if (name && !namelen)
 479                namelen = strlen(name);
 480        if (!o) {
 481                unsigned char sha1[20];
 482                if (get_sha1_1(name, namelen, sha1))
 483                        return NULL;
 484                o = parse_object(sha1);
 485        }
 486        while (1) {
 487                if (!o || (!o->parsed && !parse_object(o->sha1)))
 488                        return NULL;
 489                if (o->type == expected_type)
 490                        return o;
 491                if (o->type == OBJ_TAG)
 492                        o = ((struct tag*) o)->tagged;
 493                else if (o->type == OBJ_COMMIT)
 494                        o = &(((struct commit *) o)->tree->object);
 495                else {
 496                        if (name)
 497                                error("%.*s: expected %s type, but the object "
 498                                      "dereferences to %s type",
 499                                      namelen, name, typename(expected_type),
 500                                      typename(o->type));
 501                        return NULL;
 502                }
 503        }
 504}
 505
 506static int peel_onion(const char *name, int len, unsigned char *sha1)
 507{
 508        unsigned char outer[20];
 509        const char *sp;
 510        unsigned int expected_type = 0;
 511        struct object *o;
 512
 513        /*
 514         * "ref^{type}" dereferences ref repeatedly until you cannot
 515         * dereference anymore, or you get an object of given type,
 516         * whichever comes first.  "ref^{}" means just dereference
 517         * tags until you get a non-tag.  "ref^0" is a shorthand for
 518         * "ref^{commit}".  "commit^{tree}" could be used to find the
 519         * top-level tree of the given commit.
 520         */
 521        if (len < 4 || name[len-1] != '}')
 522                return -1;
 523
 524        for (sp = name + len - 1; name <= sp; sp--) {
 525                int ch = *sp;
 526                if (ch == '{' && name < sp && sp[-1] == '^')
 527                        break;
 528        }
 529        if (sp <= name)
 530                return -1;
 531
 532        sp++; /* beginning of type name, or closing brace for empty */
 533        if (!strncmp(commit_type, sp, 6) && sp[6] == '}')
 534                expected_type = OBJ_COMMIT;
 535        else if (!strncmp(tree_type, sp, 4) && sp[4] == '}')
 536                expected_type = OBJ_TREE;
 537        else if (!strncmp(blob_type, sp, 4) && sp[4] == '}')
 538                expected_type = OBJ_BLOB;
 539        else if (sp[0] == '}')
 540                expected_type = OBJ_NONE;
 541        else
 542                return -1;
 543
 544        if (get_sha1_1(name, sp - name - 2, outer))
 545                return -1;
 546
 547        o = parse_object(outer);
 548        if (!o)
 549                return -1;
 550        if (!expected_type) {
 551                o = deref_tag(o, name, sp - name - 2);
 552                if (!o || (!o->parsed && !parse_object(o->sha1)))
 553                        return -1;
 554                hashcpy(sha1, o->sha1);
 555        }
 556        else {
 557                /*
 558                 * At this point, the syntax look correct, so
 559                 * if we do not get the needed object, we should
 560                 * barf.
 561                 */
 562                o = peel_to_type(name, len, o, expected_type);
 563                if (o) {
 564                        hashcpy(sha1, o->sha1);
 565                        return 0;
 566                }
 567                return -1;
 568        }
 569        return 0;
 570}
 571
 572static int get_describe_name(const char *name, int len, unsigned char *sha1)
 573{
 574        const char *cp;
 575
 576        for (cp = name + len - 1; name + 2 <= cp; cp--) {
 577                char ch = *cp;
 578                if (hexval(ch) & ~0377) {
 579                        /* We must be looking at g in "SOMETHING-g"
 580                         * for it to be describe output.
 581                         */
 582                        if (ch == 'g' && cp[-1] == '-') {
 583                                cp++;
 584                                len -= cp - name;
 585                                return get_short_sha1(cp, len, sha1, 1);
 586                        }
 587                }
 588        }
 589        return -1;
 590}
 591
 592static int get_sha1_1(const char *name, int len, unsigned char *sha1)
 593{
 594        int ret, has_suffix;
 595        const char *cp;
 596
 597        /*
 598         * "name~3" is "name^^^", "name~" is "name~1", and "name^" is "name^1".
 599         */
 600        has_suffix = 0;
 601        for (cp = name + len - 1; name <= cp; cp--) {
 602                int ch = *cp;
 603                if ('0' <= ch && ch <= '9')
 604                        continue;
 605                if (ch == '~' || ch == '^')
 606                        has_suffix = ch;
 607                break;
 608        }
 609
 610        if (has_suffix) {
 611                int num = 0;
 612                int len1 = cp - name;
 613                cp++;
 614                while (cp < name + len)
 615                        num = num * 10 + *cp++ - '0';
 616                if (!num && len1 == len - 1)
 617                        num = 1;
 618                if (has_suffix == '^')
 619                        return get_parent(name, len1, sha1, num);
 620                /* else if (has_suffix == '~') -- goes without saying */
 621                return get_nth_ancestor(name, len1, sha1, num);
 622        }
 623
 624        ret = peel_onion(name, len, sha1);
 625        if (!ret)
 626                return 0;
 627
 628        ret = get_sha1_basic(name, len, sha1);
 629        if (!ret)
 630                return 0;
 631
 632        /* It could be describe output that is "SOMETHING-gXXXX" */
 633        ret = get_describe_name(name, len, sha1);
 634        if (!ret)
 635                return 0;
 636
 637        return get_short_sha1(name, len, sha1, 0);
 638}
 639
 640static int handle_one_ref(const char *path,
 641                const unsigned char *sha1, int flag, void *cb_data)
 642{
 643        struct commit_list **list = cb_data;
 644        struct object *object = parse_object(sha1);
 645        if (!object)
 646                return 0;
 647        if (object->type == OBJ_TAG) {
 648                object = deref_tag(object, path, strlen(path));
 649                if (!object)
 650                        return 0;
 651        }
 652        if (object->type != OBJ_COMMIT)
 653                return 0;
 654        insert_by_date((struct commit *)object, list);
 655        return 0;
 656}
 657
 658/*
 659 * This interprets names like ':/Initial revision of "git"' by searching
 660 * through history and returning the first commit whose message starts
 661 * with the given string.
 662 *
 663 * For future extension, ':/!' is reserved. If you want to match a message
 664 * beginning with a '!', you have to repeat the exclamation mark.
 665 */
 666
 667#define ONELINE_SEEN (1u<<20)
 668static int get_sha1_oneline(const char *prefix, unsigned char *sha1)
 669{
 670        struct commit_list *list = NULL, *backup = NULL, *l;
 671        int retval = -1;
 672        char *temp_commit_buffer = NULL;
 673
 674        if (prefix[0] == '!') {
 675                if (prefix[1] != '!')
 676                        die ("Invalid search pattern: %s", prefix);
 677                prefix++;
 678        }
 679        for_each_ref(handle_one_ref, &list);
 680        for (l = list; l; l = l->next)
 681                commit_list_insert(l->item, &backup);
 682        while (list) {
 683                char *p;
 684                struct commit *commit;
 685                enum object_type type;
 686                unsigned long size;
 687
 688                commit = pop_most_recent_commit(&list, ONELINE_SEEN);
 689                if (!parse_object(commit->object.sha1))
 690                        continue;
 691                free(temp_commit_buffer);
 692                if (commit->buffer)
 693                        p = commit->buffer;
 694                else {
 695                        p = read_sha1_file(commit->object.sha1, &type, &size);
 696                        if (!p)
 697                                continue;
 698                        temp_commit_buffer = p;
 699                }
 700                if (!(p = strstr(p, "\n\n")))
 701                        continue;
 702                if (!prefixcmp(p + 2, prefix)) {
 703                        hashcpy(sha1, commit->object.sha1);
 704                        retval = 0;
 705                        break;
 706                }
 707        }
 708        free(temp_commit_buffer);
 709        free_commit_list(list);
 710        for (l = backup; l; l = l->next)
 711                clear_commit_marks(l->item, ONELINE_SEEN);
 712        return retval;
 713}
 714
 715struct grab_nth_branch_switch_cbdata {
 716        long cnt, alloc;
 717        struct strbuf *buf;
 718};
 719
 720static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
 721                                  const char *email, unsigned long timestamp, int tz,
 722                                  const char *message, void *cb_data)
 723{
 724        struct grab_nth_branch_switch_cbdata *cb = cb_data;
 725        const char *match = NULL, *target = NULL;
 726        size_t len;
 727        int nth;
 728
 729        if (!prefixcmp(message, "checkout: moving from ")) {
 730                match = message + strlen("checkout: moving from ");
 731                target = strstr(match, " to ");
 732        }
 733
 734        if (!match || !target)
 735                return 0;
 736
 737        len = target - match;
 738        nth = cb->cnt++ % cb->alloc;
 739        strbuf_reset(&cb->buf[nth]);
 740        strbuf_add(&cb->buf[nth], match, len);
 741        return 0;
 742}
 743
 744/*
 745 * This reads "@{-N}" syntax, finds the name of the Nth previous
 746 * branch we were on, and places the name of the branch in the given
 747 * buf and returns the number of characters parsed if successful.
 748 *
 749 * If the input is not of the accepted format, it returns a negative
 750 * number to signal an error.
 751 *
 752 * If the input was ok but there are not N branch switches in the
 753 * reflog, it returns 0.
 754 */
 755int interpret_branch_name(const char *name, struct strbuf *buf)
 756{
 757        long nth;
 758        int i, retval;
 759        struct grab_nth_branch_switch_cbdata cb;
 760        const char *brace;
 761        char *num_end;
 762
 763        if (name[0] != '@' || name[1] != '{' || name[2] != '-')
 764                return -1;
 765        brace = strchr(name, '}');
 766        if (!brace)
 767                return -1;
 768        nth = strtol(name+3, &num_end, 10);
 769        if (num_end != brace)
 770                return -1;
 771        if (nth <= 0)
 772                return -1;
 773        cb.alloc = nth;
 774        cb.buf = xmalloc(nth * sizeof(struct strbuf));
 775        for (i = 0; i < nth; i++)
 776                strbuf_init(&cb.buf[i], 20);
 777        cb.cnt = 0;
 778        retval = 0;
 779        for_each_recent_reflog_ent("HEAD", grab_nth_branch_switch, 40960, &cb);
 780        if (cb.cnt < nth) {
 781                cb.cnt = 0;
 782                for_each_reflog_ent("HEAD", grab_nth_branch_switch, &cb);
 783        }
 784        if (cb.cnt < nth)
 785                goto release_return;
 786        i = cb.cnt % nth;
 787        strbuf_reset(buf);
 788        strbuf_add(buf, cb.buf[i].buf, cb.buf[i].len);
 789        retval = brace-name+1;
 790
 791release_return:
 792        for (i = 0; i < nth; i++)
 793                strbuf_release(&cb.buf[i]);
 794        free(cb.buf);
 795
 796        return retval;
 797}
 798
 799/*
 800 * This is like "get_sha1_basic()", except it allows "sha1 expressions",
 801 * notably "xyz^" for "parent of xyz"
 802 */
 803int get_sha1(const char *name, unsigned char *sha1)
 804{
 805        unsigned unused;
 806        return get_sha1_with_mode(name, sha1, &unused);
 807}
 808
 809int get_sha1_with_mode(const char *name, unsigned char *sha1, unsigned *mode)
 810{
 811        int ret, bracket_depth;
 812        int namelen = strlen(name);
 813        const char *cp;
 814
 815        *mode = S_IFINVALID;
 816        ret = get_sha1_1(name, namelen, sha1);
 817        if (!ret)
 818                return ret;
 819        /* sha1:path --> object name of path in ent sha1
 820         * :path -> object name of path in index
 821         * :[0-3]:path -> object name of path in index at stage
 822         */
 823        if (name[0] == ':') {
 824                int stage = 0;
 825                struct cache_entry *ce;
 826                int pos;
 827                if (namelen > 2 && name[1] == '/')
 828                        return get_sha1_oneline(name + 2, sha1);
 829                if (namelen < 3 ||
 830                    name[2] != ':' ||
 831                    name[1] < '0' || '3' < name[1])
 832                        cp = name + 1;
 833                else {
 834                        stage = name[1] - '0';
 835                        cp = name + 3;
 836                }
 837                namelen = namelen - (cp - name);
 838                if (!active_cache)
 839                        read_cache();
 840                pos = cache_name_pos(cp, namelen);
 841                if (pos < 0)
 842                        pos = -pos - 1;
 843                while (pos < active_nr) {
 844                        ce = active_cache[pos];
 845                        if (ce_namelen(ce) != namelen ||
 846                            memcmp(ce->name, cp, namelen))
 847                                break;
 848                        if (ce_stage(ce) == stage) {
 849                                hashcpy(sha1, ce->sha1);
 850                                *mode = ce->ce_mode;
 851                                return 0;
 852                        }
 853                        pos++;
 854                }
 855                return -1;
 856        }
 857        for (cp = name, bracket_depth = 0; *cp; cp++) {
 858                if (*cp == '{')
 859                        bracket_depth++;
 860                else if (bracket_depth && *cp == '}')
 861                        bracket_depth--;
 862                else if (!bracket_depth && *cp == ':')
 863                        break;
 864        }
 865        if (*cp == ':') {
 866                unsigned char tree_sha1[20];
 867                if (!get_sha1_1(name, cp-name, tree_sha1))
 868                        return get_tree_entry(tree_sha1, cp+1, sha1,
 869                                              mode);
 870        }
 871        return ret;
 872}