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

   1 #include "cache.h"
   2 #include "config.h"
   3 #include "commit.h"
   4 #include "diff.h"
   5 #include "revision.h"
   6 #include "refs.h"
   7 #include "list-objects.h"
   8 #include "quote.h"
   9 #include "sha1-lookup.h"
  10 #include "run-command.h"
  11 #include "log-tree.h"
  12 #include "bisect.h"
  13 #include "sha1-array.h"
  14 #include "argv-array.h"
  15
  16 static struct oid_array good_revs;
  17 static struct oid_array skipped_revs;
  18
  19 static struct object_id *current_bad_oid;
  20
  21 static const char *argv_checkout[] = {"checkout", "-q", NULL, "--", NULL};
  22 static const char *argv_show_branch[] = {"show-branch", NULL, NULL};
  23
  24 static const char *term_bad;
  25 static const char *term_good;
  26
  27 /* Remember to update object flag allocation in object.h */
  28 #define COUNTED         (1u<<16)
  29
  30 /*
  31  * This is a truly stupid algorithm, but it's only
  32  * used for bisection, and we just don't care enough.
  33  *
  34  * We care just barely enough to avoid recursing for
  35  * non-merge entries.
  36  */
  37 static int count_distance(struct commit_list *entry)
  38 {
  39         int nr = 0;
  40
  41         while (entry) {
  42                 struct commit *commit = entry->item;
  43                 struct commit_list *p;
  44
  45                 if (commit->object.flags & (UNINTERESTING | COUNTED))
  46                         break;
  47                 if (!(commit->object.flags & TREESAME))
  48                         nr++;
  49                 commit->object.flags |= COUNTED;
  50                 p = commit->parents;
  51                 entry = p;
  52                 if (p) {
  53                         p = p->next;
  54                         while (p) {
  55                                 nr += count_distance(p);
  56                                 p = p->next;
  57                         }
  58                 }
  59         }
  60
  61         return nr;
  62 }
  63
  64 static void clear_distance(struct commit_list *list)
  65 {
  66         while (list) {
  67                 struct commit *commit = list->item;
  68                 commit->object.flags &= ~COUNTED;
  69                 list = list->next;
  70         }
  71 }
  72
  73 #define DEBUG_BISECT 0
  74
  75 static inline int weight(struct commit_list *elem)
  76 {
  77         return *((int*)(elem->item->util));
  78 }
  79
  80 static inline void weight_set(struct commit_list *elem, int weight)
  81 {
  82         *((int*)(elem->item->util)) = weight;
  83 }
  84
  85 static int count_interesting_parents(struct commit *commit)
  86 {
  87         struct commit_list *p;
  88         int count;
  89
  90         for (count = 0, p = commit->parents; p; p = p->next) {
  91                 if (p->item->object.flags & UNINTERESTING)
  92                         continue;
  93                 count++;
  94         }
  95         return count;
  96 }
  97
  98 static inline int halfway(struct commit_list *p, int nr)
  99 {
 100         /*
 101          * Don't short-cut something we are not going to return!
 102          */
 103         if (p->item->object.flags & TREESAME)
 104                 return 0;
 105         if (DEBUG_BISECT)
 106                 return 0;
 107         /*
 108          * 2 and 3 are halfway of 5.
 109          * 3 is halfway of 6 but 2 and 4 are not.
 110          */
 111         switch (2 * weight(p) - nr) {
 112         case -1: case 0: case 1:
 113                 return 1;
 114         default:
 115                 return 0;
 116         }
 117 }
 118
 119 #if !DEBUG_BISECT
 120 #define show_list(a,b,c,d) do { ; } while (0)
 121 #else
 122 static void show_list(const char *debug, int counted, int nr,
 123                       struct commit_list *list)
 124 {
 125         struct commit_list *p;
 126
 127         fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
 128
 129         for (p = list; p; p = p->next) {
 130                 struct commit_list *pp;
 131                 struct commit *commit = p->item;
 132                 unsigned flags = commit->object.flags;
 133                 enum object_type type;
 134                 unsigned long size;
 135                 char *buf = read_sha1_file(commit->object.sha1, &type, &size);
 136                 const char *subject_start;
 137                 int subject_len;
 138
 139                 fprintf(stderr, "%c%c%c ",
 140                         (flags & TREESAME) ? ' ' : 'T',
 141                         (flags & UNINTERESTING) ? 'U' : ' ',
 142                         (flags & COUNTED) ? 'C' : ' ');
 143                 if (commit->util)
 144                         fprintf(stderr, "%3d", weight(p));
 145                 else
 146                         fprintf(stderr, "---");
 147                 fprintf(stderr, " %.*s", 8, sha1_to_hex(commit->object.sha1));
 148                 for (pp = commit->parents; pp; pp = pp->next)
 149                         fprintf(stderr, " %.*s", 8,
 150                                 sha1_to_hex(pp->item->object.sha1));
 151
 152                 subject_len = find_commit_subject(buf, &subject_start);
 153                 if (subject_len)
 154                         fprintf(stderr, " %.*s", subject_len, subject_start);
 155                 fprintf(stderr, "\n");
 156         }
 157 }
 158 #endif /* DEBUG_BISECT */
 159
 160 static struct commit_list *best_bisection(struct commit_list *list, int nr)
 161 {
 162         struct commit_list *p, *best;
 163         int best_distance = -1;
 164
 165         best = list;
 166         for (p = list; p; p = p->next) {
 167                 int distance;
 168                 unsigned flags = p->item->object.flags;
 169
 170                 if (flags & TREESAME)
 171                         continue;
 172                 distance = weight(p);
 173                 if (nr - distance < distance)
 174                         distance = nr - distance;
 175                 if (distance > best_distance) {
 176                         best = p;
 177                         best_distance = distance;
 178                 }
 179         }
 180
 181         return best;
 182 }
 183
 184 struct commit_dist {
 185         struct commit *commit;
 186         int distance;
 187 };
 188
 189 static int compare_commit_dist(const void *a_, const void *b_)
 190 {
 191         struct commit_dist *a, *b;
 192
 193         a = (struct commit_dist *)a_;
 194         b = (struct commit_dist *)b_;
 195         if (a->distance != b->distance)
 196                 return b->distance - a->distance; /* desc sort */
 197         return oidcmp(&a->commit->object.oid, &b->commit->object.oid);
 198 }
 199
 200 static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
 201 {
 202         struct commit_list *p;
 203         struct commit_dist *array = xcalloc(nr, sizeof(*array));
 204         struct strbuf buf = STRBUF_INIT;
 205         int cnt, i;
 206
 207         for (p = list, cnt = 0; p; p = p->next) {
 208                 int distance;
 209                 unsigned flags = p->item->object.flags;
 210
 211                 if (flags & TREESAME)
 212                         continue;
 213                 distance = weight(p);
 214                 if (nr - distance < distance)
 215                         distance = nr - distance;
 216                 array[cnt].commit = p->item;
 217                 array[cnt].distance = distance;
 218                 cnt++;
 219         }
 220         QSORT(array, cnt, compare_commit_dist);
 221         for (p = list, i = 0; i < cnt; i++) {
 222                 struct object *obj = &(array[i].commit->object);
 223
 224                 strbuf_reset(&buf);
 225                 strbuf_addf(&buf, "dist=%d", array[i].distance);
 226                 add_name_decoration(DECORATION_NONE, buf.buf, obj);
 227
 228                 p->item = array[i].commit;
 229                 p = p->next;
 230         }
 231         if (p)
 232                 p->next = NULL;
 233         strbuf_release(&buf);
 234         free(array);
 235         return list;
 236 }
 237
 238 /*
 239  * zero or positive weight is the number of interesting commits it can
 240  * reach, including itself.  Especially, weight = 0 means it does not
 241  * reach any tree-changing commits (e.g. just above uninteresting one
 242  * but traversal is with pathspec).
 243  *
 244  * weight = -1 means it has one parent and its distance is yet to
 245  * be computed.
 246  *
 247  * weight = -2 means it has more than one parent and its distance is
 248  * unknown.  After running count_distance() first, they will get zero
 249  * or positive distance.
 250  */
 251 static struct commit_list *do_find_bisection(struct commit_list *list,
 252                                              int nr, int *weights,
 253                                              int find_all)
 254 {
 255         int n, counted;
 256         struct commit_list *p;
 257
 258         counted = 0;
 259
 260         for (n = 0, p = list; p; p = p->next) {
 261                 struct commit *commit = p->item;
 262                 unsigned flags = commit->object.flags;
 263
 264                 p->item->util = &weights[n++];
 265                 switch (count_interesting_parents(commit)) {
 266                 case 0:
 267                         if (!(flags & TREESAME)) {
 268                                 weight_set(p, 1);
 269                                 counted++;
 270                                 show_list("bisection 2 count one",
 271                                           counted, nr, list);
 272                         }
 273                         /*
 274                          * otherwise, it is known not to reach any
 275                          * tree-changing commit and gets weight 0.
 276                          */
 277                         break;
 278                 case 1:
 279                         weight_set(p, -1);
 280                         break;
 281                 default:
 282                         weight_set(p, -2);
 283                         break;
 284                 }
 285         }
 286
 287         show_list("bisection 2 initialize", counted, nr, list);
 288
 289         /*
 290          * If you have only one parent in the resulting set
 291          * then you can reach one commit more than that parent
 292          * can reach.  So we do not have to run the expensive
 293          * count_distance() for single strand of pearls.
 294          *
 295          * However, if you have more than one parents, you cannot
 296          * just add their distance and one for yourself, since
 297          * they usually reach the same ancestor and you would
 298          * end up counting them twice that way.
 299          *
 300          * So we will first count distance of merges the usual
 301          * way, and then fill the blanks using cheaper algorithm.
 302          */
 303         for (p = list; p; p = p->next) {
 304                 if (p->item->object.flags & UNINTERESTING)
 305                         continue;
 306                 if (weight(p) != -2)
 307                         continue;
 308                 weight_set(p, count_distance(p));
 309                 clear_distance(list);
 310
 311                 /* Does it happen to be at exactly half-way? */
 312                 if (!find_all && halfway(p, nr))
 313                         return p;
 314                 counted++;
 315         }
 316
 317         show_list("bisection 2 count_distance", counted, nr, list);
 318
 319         while (counted < nr) {
 320                 for (p = list; p; p = p->next) {
 321                         struct commit_list *q;
 322                         unsigned flags = p->item->object.flags;
 323
 324                         if (0 <= weight(p))
 325                                 continue;
 326                         for (q = p->item->parents; q; q = q->next) {
 327                                 if (q->item->object.flags & UNINTERESTING)
 328                                         continue;
 329                                 if (0 <= weight(q))
 330                                         break;
 331                         }
 332                         if (!q)
 333                                 continue;
 334
 335                         /*
 336                          * weight for p is unknown but q is known.
 337                          * add one for p itself if p is to be counted,
 338                          * otherwise inherit it from q directly.
 339                          */
 340                         if (!(flags & TREESAME)) {
 341                                 weight_set(p, weight(q)+1);
 342                                 counted++;
 343                                 show_list("bisection 2 count one",
 344                                           counted, nr, list);
 345                         }
 346                         else
 347                                 weight_set(p, weight(q));
 348
 349                         /* Does it happen to be at exactly half-way? */
 350                         if (!find_all && halfway(p, nr))
 351                                 return p;
 352                 }
 353         }
 354
 355         show_list("bisection 2 counted all", counted, nr, list);
 356
 357         if (!find_all)
 358                 return best_bisection(list, nr);
 359         else
 360                 return best_bisection_sorted(list, nr);
 361 }
 362
 363 struct commit_list *find_bisection(struct commit_list *list,
 364                                           int *reaches, int *all,
 365                                           int find_all)
 366 {
 367         int nr, on_list;
 368         struct commit_list *p, *best, *next, *last;
 369         int *weights;
 370
 371         show_list("bisection 2 entry", 0, 0, list);
 372
 373         /*
 374          * Count the number of total and tree-changing items on the
 375          * list, while reversing the list.
 376          */
 377         for (nr = on_list = 0, last = NULL, p = list;
 378              p;
 379              p = next) {
 380                 unsigned flags = p->item->object.flags;
 381
 382                 next = p->next;
 383                 if (flags & UNINTERESTING)
 384                         continue;
 385                 p->next = last;
 386                 last = p;
 387                 if (!(flags & TREESAME))
 388                         nr++;
 389                 on_list++;
 390         }
 391         list = last;
 392         show_list("bisection 2 sorted", 0, nr, list);
 393
 394         *all = nr;
 395         weights = xcalloc(on_list, sizeof(*weights));
 396
 397         /* Do the real work of finding bisection commit. */
 398         best = do_find_bisection(list, nr, weights, find_all);
 399         if (best) {
 400                 if (!find_all)
 401                         best->next = NULL;
 402                 *reaches = weight(best);
 403         }
 404         free(weights);
 405         return best;
 406 }
 407
 408 static int register_ref(const char *refname, const struct object_id *oid,
 409                         int flags, void *cb_data)
 410 {
 411         struct strbuf good_prefix = STRBUF_INIT;
 412         strbuf_addstr(&good_prefix, term_good);
 413         strbuf_addstr(&good_prefix, "-");
 414
 415         if (!strcmp(refname, term_bad)) {
 416                 current_bad_oid = xmalloc(sizeof(*current_bad_oid));
 417                 oidcpy(current_bad_oid, oid);
 418         } else if (starts_with(refname, good_prefix.buf)) {
 419                 oid_array_append(&good_revs, oid);
 420         } else if (starts_with(refname, "skip-")) {
 421                 oid_array_append(&skipped_revs, oid);
 422         }
 423
 424         strbuf_release(&good_prefix);
 425
 426         return 0;
 427 }
 428
 429 static int read_bisect_refs(void)
 430 {
 431         return for_each_ref_in("refs/bisect/", register_ref, NULL);
 432 }
 433
 434 static GIT_PATH_FUNC(git_path_bisect_names, "BISECT_NAMES")
 435 static GIT_PATH_FUNC(git_path_bisect_expected_rev, "BISECT_EXPECTED_REV")
 436 static GIT_PATH_FUNC(git_path_bisect_terms, "BISECT_TERMS")
 437
 438 static void read_bisect_paths(struct argv_array *array)
 439 {
 440         struct strbuf str = STRBUF_INIT;
 441         const char *filename = git_path_bisect_names();
 442         FILE *fp = xfopen(filename, "r");
 443
 444         while (strbuf_getline_lf(&str, fp) != EOF) {
 445                 strbuf_trim(&str);
 446                 if (sq_dequote_to_argv_array(str.buf, array))
 447                         die(_("Badly quoted content in file '%s': %s"),
 448                             filename, str.buf);
 449         }
 450
 451         strbuf_release(&str);
 452         fclose(fp);
 453 }
 454
 455 static char *join_sha1_array_hex(struct oid_array *array, char delim)
 456 {
 457         struct strbuf joined_hexs = STRBUF_INIT;
 458         int i;
 459
 460         for (i = 0; i < array->nr; i++) {
 461                 strbuf_addstr(&joined_hexs, oid_to_hex(array->oid + i));
 462                 if (i + 1 < array->nr)
 463                         strbuf_addch(&joined_hexs, delim);
 464         }
 465
 466         return strbuf_detach(&joined_hexs, NULL);
 467 }
 468
 469 /*
 470  * In this function, passing a not NULL skipped_first is very special.
 471  * It means that we want to know if the first commit in the list is
 472  * skipped because we will want to test a commit away from it if it is
 473  * indeed skipped.
 474  * So if the first commit is skipped, we cannot take the shortcut to
 475  * just "return list" when we find the first non skipped commit, we
 476  * have to return a fully filtered list.
 477  *
 478  * We use (*skipped_first == -1) to mean "it has been found that the
 479  * first commit is not skipped". In this case *skipped_first is set back
 480  * to 0 just before the function returns.
 481  */
 482 struct commit_list *filter_skipped(struct commit_list *list,
 483                                    struct commit_list **tried,
 484                                    int show_all,
 485                                    int *count,
 486                                    int *skipped_first)
 487 {
 488         struct commit_list *filtered = NULL, **f = &filtered;
 489
 490         *tried = NULL;
 491
 492         if (skipped_first)
 493                 *skipped_first = 0;
 494         if (count)
 495                 *count = 0;
 496
 497         if (!skipped_revs.nr)
 498                 return list;
 499
 500         while (list) {
 501                 struct commit_list *next = list->next;
 502                 list->next = NULL;
 503                 if (0 <= oid_array_lookup(&skipped_revs, &list->item->object.oid)) {
 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  * https://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                                  oid_to_hex(good_revs.oid + 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
 650         for ( ; tried; tried = tried->next)
 651                 printf("%s\n", oid_to_hex(&tried->item->object.oid));
 652
 653         if (bad)
 654                 printf("%s\n", oid_to_hex(bad));
 655         printf(_("We cannot bisect more!\n"));
 656         exit(2);
 657 }
 658
 659 static int is_expected_rev(const struct object_id *oid)
 660 {
 661         const char *filename = git_path_bisect_expected_rev();
 662         struct stat st;
 663         struct strbuf str = STRBUF_INIT;
 664         FILE *fp;
 665         int res = 0;
 666
 667         if (stat(filename, &st) || !S_ISREG(st.st_mode))
 668                 return 0;
 669
 670         fp = fopen_or_warn(filename, "r");
 671         if (!fp)
 672                 return 0;
 673
 674         if (strbuf_getline_lf(&str, fp) != EOF)
 675                 res = !strcmp(str.buf, oid_to_hex(oid));
 676
 677         strbuf_release(&str);
 678         fclose(fp);
 679
 680         return res;
 681 }
 682
 683 static int bisect_checkout(const struct object_id *bisect_rev, int no_checkout)
 684 {
 685         char bisect_rev_hex[GIT_MAX_HEXSZ + 1];
 686
 687         memcpy(bisect_rev_hex, oid_to_hex(bisect_rev), GIT_SHA1_HEXSZ + 1);
 688         update_ref(NULL, "BISECT_EXPECTED_REV", bisect_rev->hash, NULL, 0, UPDATE_REFS_DIE_ON_ERR);
 689
 690         argv_checkout[2] = bisect_rev_hex;
 691         if (no_checkout) {
 692                 update_ref(NULL, "BISECT_HEAD", bisect_rev->hash, NULL, 0, UPDATE_REFS_DIE_ON_ERR);
 693         } else {
 694                 int res;
 695                 res = run_command_v_opt(argv_checkout, RUN_GIT_CMD);
 696                 if (res)
 697                         exit(res);
 698         }
 699
 700         argv_show_branch[1] = bisect_rev_hex;
 701         return run_command_v_opt(argv_show_branch, RUN_GIT_CMD);
 702 }
 703
 704 static struct commit *get_commit_reference(const struct object_id *oid)
 705 {
 706         struct commit *r = lookup_commit_reference(oid);
 707         if (!r)
 708                 die(_("Not a valid commit name %s"), oid_to_hex(oid));
 709         return r;
 710 }
 711
 712 static struct commit **get_bad_and_good_commits(int *rev_nr)
 713 {
 714         struct commit **rev;
 715         int i, n = 0;
 716
 717         ALLOC_ARRAY(rev, 1 + good_revs.nr);
 718         rev[n++] = get_commit_reference(current_bad_oid);
 719         for (i = 0; i < good_revs.nr; i++)
 720                 rev[n++] = get_commit_reference(good_revs.oid + i);
 721         *rev_nr = n;
 722
 723         return rev;
 724 }
 725
 726 static void handle_bad_merge_base(void)
 727 {
 728         if (is_expected_rev(current_bad_oid)) {
 729                 char *bad_hex = oid_to_hex(current_bad_oid);
 730                 char *good_hex = join_sha1_array_hex(&good_revs, ' ');
 731                 if (!strcmp(term_bad, "bad") && !strcmp(term_good, "good")) {
 732                         fprintf(stderr, _("The merge base %s is bad.\n"
 733                                 "This means the bug has been fixed "
 734                                 "between %s and [%s].\n"),
 735                                 bad_hex, bad_hex, good_hex);
 736                 } else if (!strcmp(term_bad, "new") && !strcmp(term_good, "old")) {
 737                         fprintf(stderr, _("The merge base %s is new.\n"
 738                                 "The property has changed "
 739                                 "between %s and [%s].\n"),
 740                                 bad_hex, bad_hex, good_hex);
 741                 } else {
 742                         fprintf(stderr, _("The merge base %s is %s.\n"
 743                                 "This means the first '%s' commit is "
 744                                 "between %s and [%s].\n"),
 745                                 bad_hex, term_bad, term_good, bad_hex, good_hex);
 746                 }
 747                 exit(3);
 748         }
 749
 750         fprintf(stderr, _("Some %s revs are not ancestors of the %s rev.\n"
 751                 "git bisect cannot work properly in this case.\n"
 752                 "Maybe you mistook %s and %s revs?\n"),
 753                 term_good, term_bad, term_good, term_bad);
 754         exit(1);
 755 }
 756
 757 static void handle_skipped_merge_base(const struct object_id *mb)
 758 {
 759         char *mb_hex = oid_to_hex(mb);
 760         char *bad_hex = oid_to_hex(current_bad_oid);
 761         char *good_hex = join_sha1_array_hex(&good_revs, ' ');
 762
 763         warning(_("the merge base between %s and [%s] "
 764                 "must be skipped.\n"
 765                 "So we cannot be sure the first %s commit is "
 766                 "between %s and %s.\n"
 767                 "We continue anyway."),
 768                 bad_hex, good_hex, term_bad, mb_hex, bad_hex);
 769         free(good_hex);
 770 }
 771
 772 /*
 773  * "check_merge_bases" checks that merge bases are not "bad" (or "new").
 774  *
 775  * - If one is "bad" (or "new"), it means the user assumed something wrong
 776  * and we must exit with a non 0 error code.
 777  * - If one is "good" (or "old"), that's good, we have nothing to do.
 778  * - If one is "skipped", we can't know but we should warn.
 779  * - If we don't know, we should check it out and ask the user to test.
 780  */
 781 static void check_merge_bases(int no_checkout)
 782 {
 783         struct commit_list *result;
 784         int rev_nr;
 785         struct commit **rev = get_bad_and_good_commits(&rev_nr);
 786
 787         result = get_merge_bases_many(rev[0], rev_nr - 1, rev + 1);
 788
 789         for (; result; result = result->next) {
 790                 const struct object_id *mb = &result->item->object.oid;
 791                 if (!oidcmp(mb, current_bad_oid)) {
 792                         handle_bad_merge_base();
 793                 } else if (0 <= oid_array_lookup(&good_revs, mb)) {
 794                         continue;
 795                 } else if (0 <= oid_array_lookup(&skipped_revs, mb)) {
 796                         handle_skipped_merge_base(mb);
 797                 } else {
 798                         printf(_("Bisecting: a merge base must be tested\n"));
 799                         exit(bisect_checkout(mb, no_checkout));
 800                 }
 801         }
 802
 803         free(rev);
 804         free_commit_list(result);
 805 }
 806
 807 static int check_ancestors(const char *prefix)
 808 {
 809         struct rev_info revs;
 810         struct object_array pending_copy;
 811         int res;
 812
 813         bisect_rev_setup(&revs, prefix, "^%s", "%s", 0);
 814
 815         /* Save pending objects, so they can be cleaned up later. */
 816         pending_copy = revs.pending;
 817         revs.leak_pending = 1;
 818
 819         /*
 820          * bisect_common calls prepare_revision_walk right away, which
 821          * (together with .leak_pending = 1) makes us the sole owner of
 822          * the list of pending objects.
 823          */
 824         bisect_common(&revs);
 825         res = (revs.commits != NULL);
 826
 827         /* Clean up objects used, as they will be reused. */
 828         clear_commit_marks_for_object_array(&pending_copy, ALL_REV_FLAGS);
 829
 830         object_array_clear(&pending_copy);
 831
 832         return res;
 833 }
 834
 835 /*
 836  * "check_good_are_ancestors_of_bad" checks that all "good" revs are
 837  * ancestor of the "bad" rev.
 838  *
 839  * If that's not the case, we need to check the merge bases.
 840  * If a merge base must be tested by the user, its source code will be
 841  * checked out to be tested by the user and we will exit.
 842  */
 843 static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
 844 {
 845         char *filename = git_pathdup("BISECT_ANCESTORS_OK");
 846         struct stat st;
 847         int fd;
 848
 849         if (!current_bad_oid)
 850                 die(_("a %s revision is needed"), term_bad);
 851
 852         /* Check if file BISECT_ANCESTORS_OK exists. */
 853         if (!stat(filename, &st) && S_ISREG(st.st_mode))
 854                 goto done;
 855
 856         /* Bisecting with no good rev is ok. */
 857         if (good_revs.nr == 0)
 858                 goto done;
 859
 860         /* Check if all good revs are ancestor of the bad rev. */
 861         if (check_ancestors(prefix))
 862                 check_merge_bases(no_checkout);
 863
 864         /* Create file BISECT_ANCESTORS_OK. */
 865         fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
 866         if (fd < 0)
 867                 warning_errno(_("could not create file '%s'"),
 868                               filename);
 869         else
 870                 close(fd);
 871  done:
 872         free(filename);
 873 }
 874
 875 /*
 876  * This does "git diff-tree --pretty COMMIT" without one fork+exec.
 877  */
 878 static void show_diff_tree(const char *prefix, struct commit *commit)
 879 {
 880         struct rev_info opt;
 881
 882         /* diff-tree init */
 883         init_revisions(&opt, prefix);
 884         git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
 885         opt.abbrev = 0;
 886         opt.diff = 1;
 887
 888         /* This is what "--pretty" does */
 889         opt.verbose_header = 1;
 890         opt.use_terminator = 0;
 891         opt.commit_format = CMIT_FMT_DEFAULT;
 892
 893         /* diff-tree init */
 894         if (!opt.diffopt.output_format)
 895                 opt.diffopt.output_format = DIFF_FORMAT_RAW;
 896
 897         setup_revisions(0, NULL, &opt, NULL);
 898         log_tree_commit(&opt, commit);
 899 }
 900
 901 /*
 902  * The terms used for this bisect session are stored in BISECT_TERMS.
 903  * We read them and store them to adapt the messages accordingly.
 904  * Default is bad/good.
 905  */
 906 void read_bisect_terms(const char **read_bad, const char **read_good)
 907 {
 908         struct strbuf str = STRBUF_INIT;
 909         const char *filename = git_path_bisect_terms();
 910         FILE *fp = fopen(filename, "r");
 911
 912         if (!fp) {
 913                 if (errno == ENOENT) {
 914                         *read_bad = "bad";
 915                         *read_good = "good";
 916                         return;
 917                 } else {
 918                         die_errno(_("could not read file '%s'"), filename);
 919                 }
 920         } else {
 921                 strbuf_getline_lf(&str, fp);
 922                 *read_bad = strbuf_detach(&str, NULL);
 923                 strbuf_getline_lf(&str, fp);
 924                 *read_good = strbuf_detach(&str, NULL);
 925         }
 926         strbuf_release(&str);
 927         fclose(fp);
 928 }
 929
 930 /*
 931  * We use the convention that exiting with an exit code 10 means that
 932  * the bisection process finished successfully.
 933  * In this case the calling shell script should exit 0.
 934  *
 935  * If no_checkout is non-zero, the bisection process does not
 936  * checkout the trial commit but instead simply updates BISECT_HEAD.
 937  */
 938 int bisect_next_all(const char *prefix, int no_checkout)
 939 {
 940         struct rev_info revs;
 941         struct commit_list *tried;
 942         int reaches = 0, all = 0, nr, steps;
 943         struct object_id *bisect_rev;
 944         char *steps_msg;
 945
 946         read_bisect_terms(&term_bad, &term_good);
 947         if (read_bisect_refs())
 948                 die(_("reading bisect refs failed"));
 949
 950         check_good_are_ancestors_of_bad(prefix, no_checkout);
 951
 952         bisect_rev_setup(&revs, prefix, "%s", "^%s", 1);
 953         revs.limited = 1;
 954
 955         bisect_common(&revs);
 956
 957         revs.commits = find_bisection(revs.commits, &reaches, &all,
 958                                        !!skipped_revs.nr);
 959         revs.commits = managed_skipped(revs.commits, &tried);
 960
 961         if (!revs.commits) {
 962                 /*
 963                  * We should exit here only if the "bad"
 964                  * commit is also a "skip" commit.
 965                  */
 966                 exit_if_skipped_commits(tried, NULL);
 967
 968                 printf(_("%s was both %s and %s\n"),
 969                        oid_to_hex(current_bad_oid),
 970                        term_good,
 971                        term_bad);
 972                 exit(1);
 973         }
 974
 975         if (!all) {
 976                 fprintf(stderr, _("No testable commit found.\n"
 977                         "Maybe you started with bad path parameters?\n"));
 978                 exit(4);
 979         }
 980
 981         bisect_rev = &revs.commits->item->object.oid;
 982
 983         if (!oidcmp(bisect_rev, current_bad_oid)) {
 984                 exit_if_skipped_commits(tried, current_bad_oid);
 985                 printf("%s is the first %s commit\n", oid_to_hex(bisect_rev),
 986                         term_bad);
 987                 show_diff_tree(prefix, revs.commits->item);
 988                 /* This means the bisection process succeeded. */
 989                 exit(10);
 990         }
 991
 992         nr = all - reaches - 1;
 993         steps = estimate_bisect_steps(all);
 994
 995         steps_msg = xstrfmt(Q_("(roughly %d step)", "(roughly %d steps)",
 996                   steps), steps);
 997         /*
 998          * TRANSLATORS: the last %s will be replaced with "(roughly %d
 999          * steps)" translation.
1000          */
1001         printf(Q_("Bisecting: %d revision left to test after this %s\n",
1002                   "Bisecting: %d revisions left to test after this %s\n",
1003                   nr), nr, steps_msg);
1004         free(steps_msg);
1005
1006         return bisect_checkout(bisect_rev, no_checkout);
1007 }
1008
1009 static inline int log2i(int n)
1010 {
1011         int log2 = 0;
1012
1013         for (; n > 1; n >>= 1)
1014                 log2++;
1015
1016         return log2;
1017 }
1018
1019 static inline int exp2i(int n)
1020 {
1021         return 1 << n;
1022 }
1023
1024 /*
1025  * Estimate the number of bisect steps left (after the current step)
1026  *
1027  * For any x between 0 included and 2^n excluded, the probability for
1028  * n - 1 steps left looks like:
1029  *
1030  * P(2^n + x) == (2^n - x) / (2^n + x)
1031  *
1032  * and P(2^n + x) < 0.5 means 2^n < 3x
1033  */
1034 int estimate_bisect_steps(int all)
1035 {
1036         int n, x, e;
1037
1038         if (all < 3)
1039                 return 0;
1040
1041         n = log2i(all);
1042         e = exp2i(n);
1043         x = all - e;
1044
1045         return (e < 3 * x) ? n : n - 1;
1046 }