git.oblomov.eu Git - git/blob - bisect.c

   1 #include "cache.h"
   2 #include "commit.h"
   3 #include "diff.h"
   4 #include "revision.h"
   5 #include "refs.h"
   6 #include "list-objects.h"
   7 #include "quote.h"
   8 #include "sha1-lookup.h"
   9 #include "run-command.h"
  10 #include "log-tree.h"
  11 #include "bisect.h"
  12 #include "sha1-array.h"
  13 #include "argv-array.h"
  14
  15 static struct sha1_array good_revs;
  16 static struct sha1_array skipped_revs;
  17
  18 static struct object_id *current_bad_oid;
  19
  20 static const char *argv_checkout[] = {"checkout", "-q", NULL, "--", NULL};
  21 static const char *argv_show_branch[] = {"show-branch", NULL, NULL};
  22
  23 static const char *term_bad;
  24 static const char *term_good;
  25
  26 /* Remember to update object flag allocation in object.h */
  27 #define COUNTED         (1u<<16)
  28
  29 /*
  30  * This is a truly stupid algorithm, but it's only
  31  * used for bisection, and we just don't care enough.
  32  *
  33  * We care just barely enough to avoid recursing for
  34  * non-merge entries.
  35  */
  36 static int count_distance(struct commit_list *entry)
  37 {
  38         int nr = 0;
  39
  40         while (entry) {
  41                 struct commit *commit = entry->item;
  42                 struct commit_list *p;
  43
  44                 if (commit->object.flags & (UNINTERESTING | COUNTED))
  45                         break;
  46                 if (!(commit->object.flags & TREESAME))
  47                         nr++;
  48                 commit->object.flags |= COUNTED;
  49                 p = commit->parents;
  50                 entry = p;
  51                 if (p) {
  52                         p = p->next;
  53                         while (p) {
  54                                 nr += count_distance(p);
  55                                 p = p->next;
  56                         }
  57                 }
  58         }
  59
  60         return nr;
  61 }
  62
  63 static void clear_distance(struct commit_list *list)
  64 {
  65         while (list) {
  66                 struct commit *commit = list->item;
  67                 commit->object.flags &= ~COUNTED;
  68                 list = list->next;
  69         }
  70 }
  71
  72 #define DEBUG_BISECT 0
  73
  74 static inline int weight(struct commit_list *elem)
  75 {
  76         return *((int*)(elem->item->util));
  77 }
  78
  79 static inline void weight_set(struct commit_list *elem, int weight)
  80 {
  81         *((int*)(elem->item->util)) = weight;
  82 }
  83
  84 static int count_interesting_parents(struct commit *commit)
  85 {
  86         struct commit_list *p;
  87         int count;
  88
  89         for (count = 0, p = commit->parents; p; p = p->next) {
  90                 if (p->item->object.flags & UNINTERESTING)
  91                         continue;
  92                 count++;
  93         }
  94         return count;
  95 }
  96
  97 static inline int halfway(struct commit_list *p, int nr)
  98 {
  99         /*
 100          * Don't short-cut something we are not going to return!
 101          */
 102         if (p->item->object.flags & TREESAME)
 103                 return 0;
 104         if (DEBUG_BISECT)
 105                 return 0;
 106         /*
 107          * 2 and 3 are halfway of 5.
 108          * 3 is halfway of 6 but 2 and 4 are not.
 109          */
 110         switch (2 * weight(p) - nr) {
 111         case -1: case 0: case 1:
 112                 return 1;
 113         default:
 114                 return 0;
 115         }
 116 }
 117
 118 #if !DEBUG_BISECT
 119 #define show_list(a,b,c,d) do { ; } while (0)
 120 #else
 121 static void show_list(const char *debug, int counted, int nr,
 122                       struct commit_list *list)
 123 {
 124         struct commit_list *p;
 125
 126         fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
 127
 128         for (p = list; p; p = p->next) {
 129                 struct commit_list *pp;
 130                 struct commit *commit = p->item;
 131                 unsigned flags = commit->object.flags;
 132                 enum object_type type;
 133                 unsigned long size;
 134                 char *buf = read_sha1_file(commit->object.sha1, &type, &size);
 135                 const char *subject_start;
 136                 int subject_len;
 137
 138                 fprintf(stderr, "%c%c%c ",
 139                         (flags & TREESAME) ? ' ' : 'T',
 140                         (flags & UNINTERESTING) ? 'U' : ' ',
 141                         (flags & COUNTED) ? 'C' : ' ');
 142                 if (commit->util)
 143                         fprintf(stderr, "%3d", weight(p));
 144                 else
 145                         fprintf(stderr, "---");
 146                 fprintf(stderr, " %.*s", 8, sha1_to_hex(commit->object.sha1));
 147                 for (pp = commit->parents; pp; pp = pp->next)
 148                         fprintf(stderr, " %.*s", 8,
 149                                 sha1_to_hex(pp->item->object.sha1));
 150
 151                 subject_len = find_commit_subject(buf, &subject_start);
 152                 if (subject_len)
 153                         fprintf(stderr, " %.*s", subject_len, subject_start);
 154                 fprintf(stderr, "\n");
 155         }
 156 }
 157 #endif /* DEBUG_BISECT */
 158
 159 static struct commit_list *best_bisection(struct commit_list *list, int nr)
 160 {
 161         struct commit_list *p, *best;
 162         int best_distance = -1;
 163
 164         best = list;
 165         for (p = list; p; p = p->next) {
 166                 int distance;
 167                 unsigned flags = p->item->object.flags;
 168
 169                 if (flags & TREESAME)
 170                         continue;
 171                 distance = weight(p);
 172                 if (nr - distance < distance)
 173                         distance = nr - distance;
 174                 if (distance > best_distance) {
 175                         best = p;
 176                         best_distance = distance;
 177                 }
 178         }
 179
 180         return best;
 181 }
 182
 183 struct commit_dist {
 184         struct commit *commit;
 185         int distance;
 186 };
 187
 188 static int compare_commit_dist(const void *a_, const void *b_)
 189 {
 190         struct commit_dist *a, *b;
 191
 192         a = (struct commit_dist *)a_;
 193         b = (struct commit_dist *)b_;
 194         if (a->distance != b->distance)
 195                 return b->distance - a->distance; /* desc sort */
 196         return oidcmp(&a->commit->object.oid, &b->commit->object.oid);
 197 }
 198
 199 static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
 200 {
 201         struct commit_list *p;
 202         struct commit_dist *array = xcalloc(nr, sizeof(*array));
 203         int cnt, i;
 204
 205         for (p = list, cnt = 0; p; p = p->next) {
 206                 int distance;
 207                 unsigned flags = p->item->object.flags;
 208
 209                 if (flags & TREESAME)
 210                         continue;
 211                 distance = weight(p);
 212                 if (nr - distance < distance)
 213                         distance = nr - distance;
 214                 array[cnt].commit = p->item;
 215                 array[cnt].distance = distance;
 216                 cnt++;
 217         }
 218         qsort(array, cnt, sizeof(*array), compare_commit_dist);
 219         for (p = list, i = 0; i < cnt; i++) {
 220                 char buf[100]; /* enough for dist=%d */
 221                 struct object *obj = &(array[i].commit->object);
 222
 223                 snprintf(buf, sizeof(buf), "dist=%d", array[i].distance);
 224                 add_name_decoration(DECORATION_NONE, buf, obj);
 225
 226                 p->item = array[i].commit;
 227                 p = p->next;
 228         }
 229         if (p)
 230                 p->next = NULL;
 231         free(array);
 232         return list;
 233 }
 234
 235 /*
 236  * zero or positive weight is the number of interesting commits it can
 237  * reach, including itself.  Especially, weight = 0 means it does not
 238  * reach any tree-changing commits (e.g. just above uninteresting one
 239  * but traversal is with pathspec).
 240  *
 241  * weight = -1 means it has one parent and its distance is yet to
 242  * be computed.
 243  *
 244  * weight = -2 means it has more than one parent and its distance is
 245  * unknown.  After running count_distance() first, they will get zero
 246  * or positive distance.
 247  */
 248 static struct commit_list *do_find_bisection(struct commit_list *list,
 249                                              int nr, int *weights,
 250                                              int find_all)
 251 {
 252         int n, counted;
 253         struct commit_list *p;
 254
 255         counted = 0;
 256
 257         for (n = 0, p = list; p; p = p->next) {
 258                 struct commit *commit = p->item;
 259                 unsigned flags = commit->object.flags;
 260
 261                 p->item->util = &weights[n++];
 262                 switch (count_interesting_parents(commit)) {
 263                 case 0:
 264                         if (!(flags & TREESAME)) {
 265                                 weight_set(p, 1);
 266                                 counted++;
 267                                 show_list("bisection 2 count one",
 268                                           counted, nr, list);
 269                         }
 270                         /*
 271                          * otherwise, it is known not to reach any
 272                          * tree-changing commit and gets weight 0.
 273                          */
 274                         break;
 275                 case 1:
 276                         weight_set(p, -1);
 277                         break;
 278                 default:
 279                         weight_set(p, -2);
 280                         break;
 281                 }
 282         }
 283
 284         show_list("bisection 2 initialize", counted, nr, list);
 285
 286         /*
 287          * If you have only one parent in the resulting set
 288          * then you can reach one commit more than that parent
 289          * can reach.  So we do not have to run the expensive
 290          * count_distance() for single strand of pearls.
 291          *
 292          * However, if you have more than one parents, you cannot
 293          * just add their distance and one for yourself, since
 294          * they usually reach the same ancestor and you would
 295          * end up counting them twice that way.
 296          *
 297          * So we will first count distance of merges the usual
 298          * way, and then fill the blanks using cheaper algorithm.
 299          */
 300         for (p = list; p; p = p->next) {
 301                 if (p->item->object.flags & UNINTERESTING)
 302                         continue;
 303                 if (weight(p) != -2)
 304                         continue;
 305                 weight_set(p, count_distance(p));
 306                 clear_distance(list);
 307
 308                 /* Does it happen to be at exactly half-way? */
 309                 if (!find_all && halfway(p, nr))
 310                         return p;
 311                 counted++;
 312         }
 313
 314         show_list("bisection 2 count_distance", counted, nr, list);
 315
 316         while (counted < nr) {
 317                 for (p = list; p; p = p->next) {
 318                         struct commit_list *q;
 319                         unsigned flags = p->item->object.flags;
 320
 321                         if (0 <= weight(p))
 322                                 continue;
 323                         for (q = p->item->parents; q; q = q->next) {
 324                                 if (q->item->object.flags & UNINTERESTING)
 325                                         continue;
 326                                 if (0 <= weight(q))
 327                                         break;
 328                         }
 329                         if (!q)
 330                                 continue;
 331
 332                         /*
 333                          * weight for p is unknown but q is known.
 334                          * add one for p itself if p is to be counted,
 335                          * otherwise inherit it from q directly.
 336                          */
 337                         if (!(flags & TREESAME)) {
 338                                 weight_set(p, weight(q)+1);
 339                                 counted++;
 340                                 show_list("bisection 2 count one",
 341                                           counted, nr, list);
 342                         }
 343                         else
 344                                 weight_set(p, weight(q));
 345
 346                         /* Does it happen to be at exactly half-way? */
 347                         if (!find_all && halfway(p, nr))
 348                                 return p;
 349                 }
 350         }
 351
 352         show_list("bisection 2 counted all", counted, nr, list);
 353
 354         if (!find_all)
 355                 return best_bisection(list, nr);
 356         else
 357                 return best_bisection_sorted(list, nr);
 358 }
 359
 360 struct commit_list *find_bisection(struct commit_list *list,
 361                                           int *reaches, int *all,
 362                                           int find_all)
 363 {
 364         int nr, on_list;
 365         struct commit_list *p, *best, *next, *last;
 366         int *weights;
 367
 368         show_list("bisection 2 entry", 0, 0, list);
 369
 370         /*
 371          * Count the number of total and tree-changing items on the
 372          * list, while reversing the list.
 373          */
 374         for (nr = on_list = 0, last = NULL, p = list;
 375              p;
 376              p = next) {
 377                 unsigned flags = p->item->object.flags;
 378
 379                 next = p->next;
 380                 if (flags & UNINTERESTING)
 381                         continue;
 382                 p->next = last;
 383                 last = p;
 384                 if (!(flags & TREESAME))
 385                         nr++;
 386                 on_list++;
 387         }
 388         list = last;
 389         show_list("bisection 2 sorted", 0, nr, list);
 390
 391         *all = nr;
 392         weights = xcalloc(on_list, sizeof(*weights));
 393
 394         /* Do the real work of finding bisection commit. */
 395         best = do_find_bisection(list, nr, weights, find_all);
 396         if (best) {
 397                 if (!find_all)
 398                         best->next = NULL;
 399                 *reaches = weight(best);
 400         }
 401         free(weights);
 402         return best;
 403 }
 404
 405 static int register_ref(const char *refname, const struct object_id *oid,
 406                         int flags, void *cb_data)
 407 {
 408         struct strbuf good_prefix = STRBUF_INIT;
 409         strbuf_addstr(&good_prefix, term_good);
 410         strbuf_addstr(&good_prefix, "-");
 411
 412         if (!strcmp(refname, term_bad)) {
 413                 current_bad_oid = xmalloc(sizeof(*current_bad_oid));
 414                 oidcpy(current_bad_oid, oid);
 415         } else if (starts_with(refname, good_prefix.buf)) {
 416                 sha1_array_append(&good_revs, oid->hash);
 417         } else if (starts_with(refname, "skip-")) {
 418                 sha1_array_append(&skipped_revs, oid->hash);
 419         }
 420
 421         strbuf_release(&good_prefix);
 422
 423         return 0;
 424 }
 425
 426 static int read_bisect_refs(void)
 427 {
 428         return for_each_ref_in("refs/bisect/", register_ref, NULL);
 429 }
 430
 431 static GIT_PATH_FUNC(git_path_bisect_names, "BISECT_NAMES")
 432 static GIT_PATH_FUNC(git_path_bisect_expected_rev, "BISECT_EXPECTED_REV")
 433
 434 static void read_bisect_paths(struct argv_array *array)
 435 {
 436         struct strbuf str = STRBUF_INIT;
 437         const char *filename = git_path_bisect_names();
 438         FILE *fp = fopen(filename, "r");
 439
 440         if (!fp)
 441                 die_errno("Could not open file '%s'", filename);
 442
 443         while (strbuf_getline(&str, fp, '\n') != EOF) {
 444                 strbuf_trim(&str);
 445                 if (sq_dequote_to_argv_array(str.buf, array))
 446                         die("Badly quoted content in file '%s': %s",
 447                             filename, str.buf);
 448         }
 449
 450         strbuf_release(&str);
 451         fclose(fp);
 452 }
 453
 454 static char *join_sha1_array_hex(struct sha1_array *array, char delim)
 455 {
 456         struct strbuf joined_hexs = STRBUF_INIT;
 457         int i;
 458
 459         for (i = 0; i < array->nr; i++) {
 460                 strbuf_addstr(&joined_hexs, sha1_to_hex(array->sha1[i]));
 461                 if (i + 1 < array->nr)
 462                         strbuf_addch(&joined_hexs, delim);
 463         }
 464
 465         return strbuf_detach(&joined_hexs, NULL);
 466 }
 467
 468 /*
 469  * In this function, passing a not NULL skipped_first is very special.
 470  * It means that we want to know if the first commit in the list is
 471  * skipped because we will want to test a commit away from it if it is
 472  * indeed skipped.
 473  * So if the first commit is skipped, we cannot take the shortcut to
 474  * just "return list" when we find the first non skipped commit, we
 475  * have to return a fully filtered list.
 476  *
 477  * We use (*skipped_first == -1) to mean "it has been found that the
 478  * first commit is not skipped". In this case *skipped_first is set back
 479  * to 0 just before the function returns.
 480  */
 481 struct commit_list *filter_skipped(struct commit_list *list,
 482                                    struct commit_list **tried,
 483                                    int show_all,
 484                                    int *count,
 485                                    int *skipped_first)
 486 {
 487         struct commit_list *filtered = NULL, **f = &filtered;
 488
 489         *tried = NULL;
 490
 491         if (skipped_first)
 492                 *skipped_first = 0;
 493         if (count)
 494                 *count = 0;
 495
 496         if (!skipped_revs.nr)
 497                 return list;
 498
 499         while (list) {
 500                 struct commit_list *next = list->next;
 501                 list->next = NULL;
 502                 if (0 <= sha1_array_lookup(&skipped_revs,
 503                                            list->item->object.oid.hash)) {
 504                         if (skipped_first && !*skipped_first)
 505                                 *skipped_first = 1;
 506                         /* Move current to tried list */
 507                         *tried = list;
 508                         tried = &list->next;
 509                 } else {
 510                         if (!show_all) {
 511                                 if (!skipped_first || !*skipped_first)
 512                                         return list;
 513                         } else if (skipped_first && !*skipped_first) {
 514                                 /* This means we know it's not skipped */
 515                                 *skipped_first = -1;
 516                         }
 517                         /* Move current to filtered list */
 518                         *f = list;
 519                         f = &list->next;
 520                         if (count)
 521                                 (*count)++;
 522                 }
 523                 list = next;
 524         }
 525
 526         if (skipped_first && *skipped_first == -1)
 527                 *skipped_first = 0;
 528
 529         return filtered;
 530 }
 531
 532 #define PRN_MODULO 32768
 533
 534 /*
 535  * This is a pseudo random number generator based on "man 3 rand".
 536  * It is not used properly because the seed is the argument and it
 537  * is increased by one between each call, but that should not matter
 538  * for this application.
 539  */
 540 static unsigned get_prn(unsigned count) {
 541         count = count * 1103515245 + 12345;
 542         return (count/65536) % PRN_MODULO;
 543 }
 544
 545 /*
 546  * Custom integer square root from
 547  * http://en.wikipedia.org/wiki/Integer_square_root
 548  */
 549 static int sqrti(int val)
 550 {
 551         float d, x = val;
 552
 553         if (val == 0)
 554                 return 0;
 555
 556         do {
 557                 float y = (x + (float)val / x) / 2;
 558                 d = (y > x) ? y - x : x - y;
 559                 x = y;
 560         } while (d >= 0.5);
 561
 562         return (int)x;
 563 }
 564
 565 static struct commit_list *skip_away(struct commit_list *list, int count)
 566 {
 567         struct commit_list *cur, *previous;
 568         int prn, index, i;
 569
 570         prn = get_prn(count);
 571         index = (count * prn / PRN_MODULO) * sqrti(prn) / sqrti(PRN_MODULO);
 572
 573         cur = list;
 574         previous = NULL;
 575
 576         for (i = 0; cur; cur = cur->next, i++) {
 577                 if (i == index) {
 578                         if (oidcmp(&cur->item->object.oid, current_bad_oid))
 579                                 return cur;
 580                         if (previous)
 581                                 return previous;
 582                         return list;
 583                 }
 584                 previous = cur;
 585         }
 586
 587         return list;
 588 }
 589
 590 static struct commit_list *managed_skipped(struct commit_list *list,
 591                                            struct commit_list **tried)
 592 {
 593         int count, skipped_first;
 594
 595         *tried = NULL;
 596
 597         if (!skipped_revs.nr)
 598                 return list;
 599
 600         list = filter_skipped(list, tried, 0, &count, &skipped_first);
 601
 602         if (!skipped_first)
 603                 return list;
 604
 605         return skip_away(list, count);
 606 }
 607
 608 static void bisect_rev_setup(struct rev_info *revs, const char *prefix,
 609                              const char *bad_format, const char *good_format,
 610                              int read_paths)
 611 {
 612         struct argv_array rev_argv = ARGV_ARRAY_INIT;
 613         int i;
 614
 615         init_revisions(revs, prefix);
 616         revs->abbrev = 0;
 617         revs->commit_format = CMIT_FMT_UNSPECIFIED;
 618
 619         /* rev_argv.argv[0] will be ignored by setup_revisions */
 620         argv_array_push(&rev_argv, "bisect_rev_setup");
 621         argv_array_pushf(&rev_argv, bad_format, oid_to_hex(current_bad_oid));
 622         for (i = 0; i < good_revs.nr; i++)
 623                 argv_array_pushf(&rev_argv, good_format,
 624                                  sha1_to_hex(good_revs.sha1[i]));
 625         argv_array_push(&rev_argv, "--");
 626         if (read_paths)
 627                 read_bisect_paths(&rev_argv);
 628
 629         setup_revisions(rev_argv.argc, rev_argv.argv, revs, NULL);
 630         /* XXX leak rev_argv, as "revs" may still be pointing to it */
 631 }
 632
 633 static void bisect_common(struct rev_info *revs)
 634 {
 635         if (prepare_revision_walk(revs))
 636                 die("revision walk setup failed");
 637         if (revs->tree_objects)
 638                 mark_edges_uninteresting(revs, NULL);
 639 }
 640
 641 static void exit_if_skipped_commits(struct commit_list *tried,
 642                                     const struct object_id *bad)
 643 {
 644         if (!tried)
 645                 return;
 646
 647         printf("There are only 'skip'ped commits left to test.\n"
 648                "The first %s commit could be any of:\n", term_bad);
 649         print_commit_list(tried, "%s\n", "%s\n");
 650         if (bad)
 651                 printf("%s\n", oid_to_hex(bad));
 652         printf("We cannot bisect more!\n");
 653         exit(2);
 654 }
 655
 656 static int is_expected_rev(const struct object_id *oid)
 657 {
 658         const char *filename = git_path_bisect_expected_rev();
 659         struct stat st;
 660         struct strbuf str = STRBUF_INIT;
 661         FILE *fp;
 662         int res = 0;
 663
 664         if (stat(filename, &st) || !S_ISREG(st.st_mode))
 665                 return 0;
 666
 667         fp = fopen(filename, "r");
 668         if (!fp)
 669                 return 0;
 670
 671         if (strbuf_getline(&str, fp, '\n') != EOF)
 672                 res = !strcmp(str.buf, oid_to_hex(oid));
 673
 674         strbuf_release(&str);
 675         fclose(fp);
 676
 677         return res;
 678 }
 679
 680 static int bisect_checkout(const unsigned char *bisect_rev, int no_checkout)
 681 {
 682         char bisect_rev_hex[GIT_SHA1_HEXSZ + 1];
 683
 684         memcpy(bisect_rev_hex, sha1_to_hex(bisect_rev), GIT_SHA1_HEXSZ + 1);
 685         update_ref(NULL, "BISECT_EXPECTED_REV", bisect_rev, NULL, 0, UPDATE_REFS_DIE_ON_ERR);
 686
 687         argv_checkout[2] = bisect_rev_hex;
 688         if (no_checkout) {
 689                 update_ref(NULL, "BISECT_HEAD", bisect_rev, NULL, 0, UPDATE_REFS_DIE_ON_ERR);
 690         } else {
 691                 int res;
 692                 res = run_command_v_opt(argv_checkout, RUN_GIT_CMD);
 693                 if (res)
 694                         exit(res);
 695         }
 696
 697         argv_show_branch[1] = bisect_rev_hex;
 698         return run_command_v_opt(argv_show_branch, RUN_GIT_CMD);
 699 }
 700
 701 static struct commit *get_commit_reference(const unsigned char *sha1)
 702 {
 703         struct commit *r = lookup_commit_reference(sha1);
 704         if (!r)
 705                 die("Not a valid commit name %s", sha1_to_hex(sha1));
 706         return r;
 707 }
 708
 709 static struct commit **get_bad_and_good_commits(int *rev_nr)
 710 {
 711         int len = 1 + good_revs.nr;
 712         struct commit **rev = xmalloc(len * sizeof(*rev));
 713         int i, n = 0;
 714
 715         rev[n++] = get_commit_reference(current_bad_oid->hash);
 716         for (i = 0; i < good_revs.nr; i++)
 717                 rev[n++] = get_commit_reference(good_revs.sha1[i]);
 718         *rev_nr = n;
 719
 720         return rev;
 721 }
 722
 723 static void handle_bad_merge_base(void)
 724 {
 725         if (is_expected_rev(current_bad_oid)) {
 726                 char *bad_hex = oid_to_hex(current_bad_oid);
 727                 char *good_hex = join_sha1_array_hex(&good_revs, ' ');
 728                 if (!strcmp(term_bad, "bad") && !strcmp(term_good, "good")) {
 729                         fprintf(stderr, "The merge base %s is bad.\n"
 730                                 "This means the bug has been fixed "
 731                                 "between %s and [%s].\n",
 732                                 bad_hex, bad_hex, good_hex);
 733                 } else if (!strcmp(term_bad, "new") && !strcmp(term_good, "old")) {
 734                         fprintf(stderr, "The merge base %s is new.\n"
 735                                 "The property has changed "
 736                                 "between %s and [%s].\n",
 737                                 bad_hex, bad_hex, good_hex);
 738                 } else {
 739                         fprintf(stderr, "The merge base %s is %s.\n"
 740                                 "This means the first '%s' commit is "
 741                                 "between %s and [%s].\n",
 742                                 bad_hex, term_bad, term_good, bad_hex, good_hex);
 743                 }
 744                 exit(3);
 745         }
 746
 747         fprintf(stderr, "Some %s revs are not ancestor of the %s rev.\n"
 748                 "git bisect cannot work properly in this case.\n"
 749                 "Maybe you mistook %s and %s revs?\n",
 750                 term_good, term_bad, term_good, term_bad);
 751         exit(1);
 752 }
 753
 754 static void handle_skipped_merge_base(const unsigned char *mb)
 755 {
 756         char *mb_hex = sha1_to_hex(mb);
 757         char *bad_hex = sha1_to_hex(current_bad_oid->hash);
 758         char *good_hex = join_sha1_array_hex(&good_revs, ' ');
 759
 760         warning("the merge base between %s and [%s] "
 761                 "must be skipped.\n"
 762                 "So we cannot be sure the first %s commit is "
 763                 "between %s and %s.\n"
 764                 "We continue anyway.",
 765                 bad_hex, good_hex, term_bad, mb_hex, bad_hex);
 766         free(good_hex);
 767 }
 768
 769 /*
 770  * "check_merge_bases" checks that merge bases are not "bad" (or "new").
 771  *
 772  * - If one is "bad" (or "new"), it means the user assumed something wrong
 773  * and we must exit with a non 0 error code.
 774  * - If one is "good" (or "old"), that's good, we have nothing to do.
 775  * - If one is "skipped", we can't know but we should warn.
 776  * - If we don't know, we should check it out and ask the user to test.
 777  */
 778 static void check_merge_bases(int no_checkout)
 779 {
 780         struct commit_list *result;
 781         int rev_nr;
 782         struct commit **rev = get_bad_and_good_commits(&rev_nr);
 783
 784         result = get_merge_bases_many(rev[0], rev_nr - 1, rev + 1);
 785
 786         for (; result; result = result->next) {
 787                 const unsigned char *mb = result->item->object.oid.hash;
 788                 if (!hashcmp(mb, current_bad_oid->hash)) {
 789                         handle_bad_merge_base();
 790                 } else if (0 <= sha1_array_lookup(&good_revs, mb)) {
 791                         continue;
 792                 } else if (0 <= sha1_array_lookup(&skipped_revs, mb)) {
 793                         handle_skipped_merge_base(mb);
 794                 } else {
 795                         printf("Bisecting: a merge base must be tested\n");
 796                         exit(bisect_checkout(mb, no_checkout));
 797                 }
 798         }
 799
 800         free(rev);
 801         free_commit_list(result);
 802 }
 803
 804 static int check_ancestors(const char *prefix)
 805 {
 806         struct rev_info revs;
 807         struct object_array pending_copy;
 808         int res;
 809
 810         bisect_rev_setup(&revs, prefix, "^%s", "%s", 0);
 811
 812         /* Save pending objects, so they can be cleaned up later. */
 813         pending_copy = revs.pending;
 814         revs.leak_pending = 1;
 815
 816         /*
 817          * bisect_common calls prepare_revision_walk right away, which
 818          * (together with .leak_pending = 1) makes us the sole owner of
 819          * the list of pending objects.
 820          */
 821         bisect_common(&revs);
 822         res = (revs.commits != NULL);
 823
 824         /* Clean up objects used, as they will be reused. */
 825         clear_commit_marks_for_object_array(&pending_copy, ALL_REV_FLAGS);
 826         free(pending_copy.objects);
 827
 828         return res;
 829 }
 830
 831 /*
 832  * "check_good_are_ancestors_of_bad" checks that all "good" revs are
 833  * ancestor of the "bad" rev.
 834  *
 835  * If that's not the case, we need to check the merge bases.
 836  * If a merge base must be tested by the user, its source code will be
 837  * checked out to be tested by the user and we will exit.
 838  */
 839 static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
 840 {
 841         char *filename = git_pathdup("BISECT_ANCESTORS_OK");
 842         struct stat st;
 843         int fd;
 844
 845         if (!current_bad_oid)
 846                 die("a %s revision is needed", term_bad);
 847
 848         /* Check if file BISECT_ANCESTORS_OK exists. */
 849         if (!stat(filename, &st) && S_ISREG(st.st_mode))
 850                 goto done;
 851
 852         /* Bisecting with no good rev is ok. */
 853         if (good_revs.nr == 0)
 854                 goto done;
 855
 856         /* Check if all good revs are ancestor of the bad rev. */
 857         if (check_ancestors(prefix))
 858                 check_merge_bases(no_checkout);
 859
 860         /* Create file BISECT_ANCESTORS_OK. */
 861         fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
 862         if (fd < 0)
 863                 warning("could not create file '%s': %s",
 864                         filename, strerror(errno));
 865         else
 866                 close(fd);
 867  done:
 868         free(filename);
 869 }
 870
 871 /*
 872  * This does "git diff-tree --pretty COMMIT" without one fork+exec.
 873  */
 874 static void show_diff_tree(const char *prefix, struct commit *commit)
 875 {
 876         struct rev_info opt;
 877
 878         /* diff-tree init */
 879         init_revisions(&opt, prefix);
 880         git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
 881         opt.abbrev = 0;
 882         opt.diff = 1;
 883
 884         /* This is what "--pretty" does */
 885         opt.verbose_header = 1;
 886         opt.use_terminator = 0;
 887         opt.commit_format = CMIT_FMT_DEFAULT;
 888
 889         /* diff-tree init */
 890         if (!opt.diffopt.output_format)
 891                 opt.diffopt.output_format = DIFF_FORMAT_RAW;
 892
 893         log_tree_commit(&opt, commit);
 894 }
 895
 896 /*
 897  * The terms used for this bisect session are stored in BISECT_TERMS.
 898  * We read them and store them to adapt the messages accordingly.
 899  * Default is bad/good.
 900  */
 901 void read_bisect_terms(const char **read_bad, const char **read_good)
 902 {
 903         struct strbuf str = STRBUF_INIT;
 904         const char *filename = git_path("BISECT_TERMS");
 905         FILE *fp = fopen(filename, "r");
 906
 907         if (!fp) {
 908                 if (errno == ENOENT) {
 909                         *read_bad = "bad";
 910                         *read_good = "good";
 911                         return;
 912                 } else {
 913                         die("could not read file '%s': %s", filename,
 914                                 strerror(errno));
 915                 }
 916         } else {
 917                 strbuf_getline(&str, fp, '\n');
 918                 *read_bad = strbuf_detach(&str, NULL);
 919                 strbuf_getline(&str, fp, '\n');
 920                 *read_good = strbuf_detach(&str, NULL);
 921         }
 922         strbuf_release(&str);
 923         fclose(fp);
 924 }
 925
 926 /*
 927  * We use the convention that exiting with an exit code 10 means that
 928  * the bisection process finished successfully.
 929  * In this case the calling shell script should exit 0.
 930  *
 931  * If no_checkout is non-zero, the bisection process does not
 932  * checkout the trial commit but instead simply updates BISECT_HEAD.
 933  */
 934 int bisect_next_all(const char *prefix, int no_checkout)
 935 {
 936         struct rev_info revs;
 937         struct commit_list *tried;
 938         int reaches = 0, all = 0, nr, steps;
 939         const unsigned char *bisect_rev;
 940
 941         read_bisect_terms(&term_bad, &term_good);
 942         if (read_bisect_refs())
 943                 die("reading bisect refs failed");
 944
 945         check_good_are_ancestors_of_bad(prefix, no_checkout);
 946
 947         bisect_rev_setup(&revs, prefix, "%s", "^%s", 1);
 948         revs.limited = 1;
 949
 950         bisect_common(&revs);
 951
 952         revs.commits = find_bisection(revs.commits, &reaches, &all,
 953                                        !!skipped_revs.nr);
 954         revs.commits = managed_skipped(revs.commits, &tried);
 955
 956         if (!revs.commits) {
 957                 /*
 958                  * We should exit here only if the "bad"
 959                  * commit is also a "skip" commit.
 960                  */
 961                 exit_if_skipped_commits(tried, NULL);
 962
 963                 printf("%s was both %s and %s\n",
 964                        oid_to_hex(current_bad_oid),
 965                        term_good,
 966                        term_bad);
 967                 exit(1);
 968         }
 969
 970         if (!all) {
 971                 fprintf(stderr, "No testable commit found.\n"
 972                         "Maybe you started with bad path parameters?\n");
 973                 exit(4);
 974         }
 975
 976         bisect_rev = revs.commits->item->object.oid.hash;
 977
 978         if (!hashcmp(bisect_rev, current_bad_oid->hash)) {
 979                 exit_if_skipped_commits(tried, current_bad_oid);
 980                 printf("%s is the first %s commit\n", sha1_to_hex(bisect_rev),
 981                         term_bad);
 982                 show_diff_tree(prefix, revs.commits->item);
 983                 /* This means the bisection process succeeded. */
 984                 exit(10);
 985         }
 986
 987         nr = all - reaches - 1;
 988         steps = estimate_bisect_steps(all);
 989         printf("Bisecting: %d revision%s left to test after this "
 990                "(roughly %d step%s)\n", nr, (nr == 1 ? "" : "s"),
 991                steps, (steps == 1 ? "" : "s"));
 992
 993         return bisect_checkout(bisect_rev, no_checkout);
 994 }
 995
 996 static inline int log2i(int n)
 997 {
 998         int log2 = 0;
 999
1000         for (; n > 1; n >>= 1)
1001                 log2++;
1002
1003         return log2;
1004 }
1005
1006 static inline int exp2i(int n)
1007 {
1008         return 1 << n;
1009 }
1010
1011 /*
1012  * Estimate the number of bisect steps left (after the current step)
1013  *
1014  * For any x between 0 included and 2^n excluded, the probability for
1015  * n - 1 steps left looks like:
1016  *
1017  * P(2^n + x) == (2^n - x) / (2^n + x)
1018  *
1019  * and P(2^n + x) < 0.5 means 2^n < 3x
1020  */
1021 int estimate_bisect_steps(int all)
1022 {
1023         int n, x, e;
1024
1025         if (all < 3)
1026                 return 0;
1027
1028         n = log2i(all);
1029         e = exp2i(n);
1030         x = all - e;
1031
1032         return (e < 3 * x) ? n : n - 1;
1033 }