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
  14 static struct sha1_array good_revs;
  15 static struct sha1_array skipped_revs;
  16
  17 static const unsigned char *current_bad_sha1;
  18
  19 struct argv_array {
  20         const char **argv;
  21         int argv_nr;
  22         int argv_alloc;
  23 };
  24
  25 static const char *argv_checkout[] = {"checkout", "-q", NULL, "--", NULL};
  26 static const char *argv_show_branch[] = {"show-branch", NULL, NULL};
  27 static const char *argv_update_ref[] = {"update-ref", "--no-deref", "BISECT_HEAD", NULL, NULL};
  28
  29 /* bits #0-15 in revision.h */
  30
  31 #define COUNTED         (1u<<16)
  32
  33 /*
  34  * This is a truly stupid algorithm, but it's only
  35  * used for bisection, and we just don't care enough.
  36  *
  37  * We care just barely enough to avoid recursing for
  38  * non-merge entries.
  39  */
  40 static int count_distance(struct commit_list *entry)
  41 {
  42         int nr = 0;
  43
  44         while (entry) {
  45                 struct commit *commit = entry->item;
  46                 struct commit_list *p;
  47
  48                 if (commit->object.flags & (UNINTERESTING | COUNTED))
  49                         break;
  50                 if (!(commit->object.flags & TREESAME))
  51                         nr++;
  52                 commit->object.flags |= COUNTED;
  53                 p = commit->parents;
  54                 entry = p;
  55                 if (p) {
  56                         p = p->next;
  57                         while (p) {
  58                                 nr += count_distance(p);
  59                                 p = p->next;
  60                         }
  61                 }
  62         }
  63
  64         return nr;
  65 }
  66
  67 static void clear_distance(struct commit_list *list)
  68 {
  69         while (list) {
  70                 struct commit *commit = list->item;
  71                 commit->object.flags &= ~COUNTED;
  72                 list = list->next;
  73         }
  74 }
  75
  76 #define DEBUG_BISECT 0
  77
  78 static inline int weight(struct commit_list *elem)
  79 {
  80         return *((int*)(elem->item->util));
  81 }
  82
  83 static inline void weight_set(struct commit_list *elem, int weight)
  84 {
  85         *((int*)(elem->item->util)) = weight;
  86 }
  87
  88 static int count_interesting_parents(struct commit *commit)
  89 {
  90         struct commit_list *p;
  91         int count;
  92
  93         for (count = 0, p = commit->parents; p; p = p->next) {
  94                 if (p->item->object.flags & UNINTERESTING)
  95                         continue;
  96                 count++;
  97         }
  98         return count;
  99 }
 100
 101 static inline int halfway(struct commit_list *p, int nr)
 102 {
 103         /*
 104          * Don't short-cut something we are not going to return!
 105          */
 106         if (p->item->object.flags & TREESAME)
 107                 return 0;
 108         if (DEBUG_BISECT)
 109                 return 0;
 110         /*
 111          * 2 and 3 are halfway of 5.
 112          * 3 is halfway of 6 but 2 and 4 are not.
 113          */
 114         switch (2 * weight(p) - nr) {
 115         case -1: case 0: case 1:
 116                 return 1;
 117         default:
 118                 return 0;
 119         }
 120 }
 121
 122 #if !DEBUG_BISECT
 123 #define show_list(a,b,c,d) do { ; } while (0)
 124 #else
 125 static void show_list(const char *debug, int counted, int nr,
 126                       struct commit_list *list)
 127 {
 128         struct commit_list *p;
 129
 130         fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
 131
 132         for (p = list; p; p = p->next) {
 133                 struct commit_list *pp;
 134                 struct commit *commit = p->item;
 135                 unsigned flags = commit->object.flags;
 136                 enum object_type type;
 137                 unsigned long size;
 138                 char *buf = read_sha1_file(commit->object.sha1, &type, &size);
 139                 const char *subject_start;
 140                 int subject_len;
 141
 142                 fprintf(stderr, "%c%c%c ",
 143                         (flags & TREESAME) ? ' ' : 'T',
 144                         (flags & UNINTERESTING) ? 'U' : ' ',
 145                         (flags & COUNTED) ? 'C' : ' ');
 146                 if (commit->util)
 147                         fprintf(stderr, "%3d", weight(p));
 148                 else
 149                         fprintf(stderr, "---");
 150                 fprintf(stderr, " %.*s", 8, sha1_to_hex(commit->object.sha1));
 151                 for (pp = commit->parents; pp; pp = pp->next)
 152                         fprintf(stderr, " %.*s", 8,
 153                                 sha1_to_hex(pp->item->object.sha1));
 154
 155                 subject_len = find_commit_subject(buf, &subject_start);
 156                 if (subject_len)
 157                         fprintf(stderr, " %.*s", subject_len, subject_start);
 158                 fprintf(stderr, "\n");
 159         }
 160 }
 161 #endif /* DEBUG_BISECT */
 162
 163 static struct commit_list *best_bisection(struct commit_list *list, int nr)
 164 {
 165         struct commit_list *p, *best;
 166         int best_distance = -1;
 167
 168         best = list;
 169         for (p = list; p; p = p->next) {
 170                 int distance;
 171                 unsigned flags = p->item->object.flags;
 172
 173                 if (flags & TREESAME)
 174                         continue;
 175                 distance = weight(p);
 176                 if (nr - distance < distance)
 177                         distance = nr - distance;
 178                 if (distance > best_distance) {
 179                         best = p;
 180                         best_distance = distance;
 181                 }
 182         }
 183
 184         return best;
 185 }
 186
 187 struct commit_dist {
 188         struct commit *commit;
 189         int distance;
 190 };
 191
 192 static int compare_commit_dist(const void *a_, const void *b_)
 193 {
 194         struct commit_dist *a, *b;
 195
 196         a = (struct commit_dist *)a_;
 197         b = (struct commit_dist *)b_;
 198         if (a->distance != b->distance)
 199                 return b->distance - a->distance; /* desc sort */
 200         return hashcmp(a->commit->object.sha1, b->commit->object.sha1);
 201 }
 202
 203 static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
 204 {
 205         struct commit_list *p;
 206         struct commit_dist *array = xcalloc(nr, sizeof(*array));
 207         int cnt, i;
 208
 209         for (p = list, cnt = 0; p; p = p->next) {
 210                 int distance;
 211                 unsigned flags = p->item->object.flags;
 212
 213                 if (flags & TREESAME)
 214                         continue;
 215                 distance = weight(p);
 216                 if (nr - distance < distance)
 217                         distance = nr - distance;
 218                 array[cnt].commit = p->item;
 219                 array[cnt].distance = distance;
 220                 cnt++;
 221         }
 222         qsort(array, cnt, sizeof(*array), compare_commit_dist);
 223         for (p = list, i = 0; i < cnt; i++) {
 224                 struct name_decoration *r = xmalloc(sizeof(*r) + 100);
 225                 struct object *obj = &(array[i].commit->object);
 226
 227                 sprintf(r->name, "dist=%d", array[i].distance);
 228                 r->next = add_decoration(&name_decoration, obj, r);
 229                 p->item = array[i].commit;
 230                 p = p->next;
 231         }
 232         if (p)
 233                 p->next = NULL;
 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 void argv_array_push(struct argv_array *array, const char *string)
 409 {
 410         ALLOC_GROW(array->argv, array->argv_nr + 1, array->argv_alloc);
 411         array->argv[array->argv_nr++] = string;
 412 }
 413
 414 static void argv_array_push_sha1(struct argv_array *array,
 415                                  const unsigned char *sha1,
 416                                  const char *format)
 417 {
 418         struct strbuf buf = STRBUF_INIT;
 419         strbuf_addf(&buf, format, sha1_to_hex(sha1));
 420         argv_array_push(array, strbuf_detach(&buf, NULL));
 421 }
 422
 423 static int register_ref(const char *refname, const unsigned char *sha1,
 424                         int flags, void *cb_data)
 425 {
 426         if (!strcmp(refname, "bad")) {
 427                 current_bad_sha1 = sha1;
 428         } else if (!prefixcmp(refname, "good-")) {
 429                 sha1_array_append(&good_revs, sha1);
 430         } else if (!prefixcmp(refname, "skip-")) {
 431                 sha1_array_append(&skipped_revs, sha1);
 432         }
 433
 434         return 0;
 435 }
 436
 437 static int read_bisect_refs(void)
 438 {
 439         return for_each_ref_in("refs/bisect/", register_ref, NULL);
 440 }
 441
 442 static void read_bisect_paths(struct argv_array *array)
 443 {
 444         struct strbuf str = STRBUF_INIT;
 445         const char *filename = git_path("BISECT_NAMES");
 446         FILE *fp = fopen(filename, "r");
 447
 448         if (!fp)
 449                 die_errno("Could not open file '%s'", filename);
 450
 451         while (strbuf_getline(&str, fp, '\n') != EOF) {
 452                 char *quoted;
 453                 int res;
 454
 455                 strbuf_trim(&str);
 456                 quoted = strbuf_detach(&str, NULL);
 457                 res = sq_dequote_to_argv(quoted, &array->argv,
 458                                          &array->argv_nr, &array->argv_alloc);
 459                 if (res)
 460                         die("Badly quoted content in file '%s': %s",
 461                             filename, quoted);
 462         }
 463
 464         strbuf_release(&str);
 465         fclose(fp);
 466 }
 467
 468 static char *join_sha1_array_hex(struct sha1_array *array, char delim)
 469 {
 470         struct strbuf joined_hexs = STRBUF_INIT;
 471         int i;
 472
 473         for (i = 0; i < array->nr; i++) {
 474                 strbuf_addstr(&joined_hexs, sha1_to_hex(array->sha1[i]));
 475                 if (i + 1 < array->nr)
 476                         strbuf_addch(&joined_hexs, delim);
 477         }
 478
 479         return strbuf_detach(&joined_hexs, NULL);
 480 }
 481
 482 /*
 483  * In this function, passing a not NULL skipped_first is very special.
 484  * It means that we want to know if the first commit in the list is
 485  * skipped because we will want to test a commit away from it if it is
 486  * indeed skipped.
 487  * So if the first commit is skipped, we cannot take the shortcut to
 488  * just "return list" when we find the first non skipped commit, we
 489  * have to return a fully filtered list.
 490  *
 491  * We use (*skipped_first == -1) to mean "it has been found that the
 492  * first commit is not skipped". In this case *skipped_first is set back
 493  * to 0 just before the function returns.
 494  */
 495 struct commit_list *filter_skipped(struct commit_list *list,
 496                                    struct commit_list **tried,
 497                                    int show_all,
 498                                    int *count,
 499                                    int *skipped_first)
 500 {
 501         struct commit_list *filtered = NULL, **f = &filtered;
 502
 503         *tried = NULL;
 504
 505         if (skipped_first)
 506                 *skipped_first = 0;
 507         if (count)
 508                 *count = 0;
 509
 510         if (!skipped_revs.nr)
 511                 return list;
 512
 513         while (list) {
 514                 struct commit_list *next = list->next;
 515                 list->next = NULL;
 516                 if (0 <= sha1_array_lookup(&skipped_revs,
 517                                            list->item->object.sha1)) {
 518                         if (skipped_first && !*skipped_first)
 519                                 *skipped_first = 1;
 520                         /* Move current to tried list */
 521                         *tried = list;
 522                         tried = &list->next;
 523                 } else {
 524                         if (!show_all) {
 525                                 if (!skipped_first || !*skipped_first)
 526                                         return list;
 527                         } else if (skipped_first && !*skipped_first) {
 528                                 /* This means we know it's not skipped */
 529                                 *skipped_first = -1;
 530                         }
 531                         /* Move current to filtered list */
 532                         *f = list;
 533                         f = &list->next;
 534                         if (count)
 535                                 (*count)++;
 536                 }
 537                 list = next;
 538         }
 539
 540         if (skipped_first && *skipped_first == -1)
 541                 *skipped_first = 0;
 542
 543         return filtered;
 544 }
 545
 546 #define PRN_MODULO 32768
 547
 548 /*
 549  * This is a pseudo random number generator based on "man 3 rand".
 550  * It is not used properly because the seed is the argument and it
 551  * is increased by one between each call, but that should not matter
 552  * for this application.
 553  */
 554 static int get_prn(int count) {
 555         count = count * 1103515245 + 12345;
 556         return ((unsigned)(count/65536) % PRN_MODULO);
 557 }
 558
 559 /*
 560  * Custom integer square root from
 561  * http://en.wikipedia.org/wiki/Integer_square_root
 562  */
 563 static int sqrti(int val)
 564 {
 565         float d, x = val;
 566
 567         if (val == 0)
 568                 return 0;
 569
 570         do {
 571                 float y = (x + (float)val / x) / 2;
 572                 d = (y > x) ? y - x : x - y;
 573                 x = y;
 574         } while (d >= 0.5);
 575
 576         return (int)x;
 577 }
 578
 579 static struct commit_list *skip_away(struct commit_list *list, int count)
 580 {
 581         struct commit_list *cur, *previous;
 582         int prn, index, i;
 583
 584         prn = get_prn(count);
 585         index = (count * prn / PRN_MODULO) * sqrti(prn) / sqrti(PRN_MODULO);
 586
 587         cur = list;
 588         previous = NULL;
 589
 590         for (i = 0; cur; cur = cur->next, i++) {
 591                 if (i == index) {
 592                         if (hashcmp(cur->item->object.sha1, current_bad_sha1))
 593                                 return cur;
 594                         if (previous)
 595                                 return previous;
 596                         return list;
 597                 }
 598                 previous = cur;
 599         }
 600
 601         return list;
 602 }
 603
 604 static struct commit_list *managed_skipped(struct commit_list *list,
 605                                            struct commit_list **tried)
 606 {
 607         int count, skipped_first;
 608
 609         *tried = NULL;
 610
 611         if (!skipped_revs.nr)
 612                 return list;
 613
 614         list = filter_skipped(list, tried, 0, &count, &skipped_first);
 615
 616         if (!skipped_first)
 617                 return list;
 618
 619         return skip_away(list, count);
 620 }
 621
 622 static void bisect_rev_setup(struct rev_info *revs, const char *prefix,
 623                              const char *bad_format, const char *good_format,
 624                              int read_paths)
 625 {
 626         struct argv_array rev_argv = { NULL, 0, 0 };
 627         int i;
 628
 629         init_revisions(revs, prefix);
 630         revs->abbrev = 0;
 631         revs->commit_format = CMIT_FMT_UNSPECIFIED;
 632
 633         /* rev_argv.argv[0] will be ignored by setup_revisions */
 634         argv_array_push(&rev_argv, xstrdup("bisect_rev_setup"));
 635         argv_array_push_sha1(&rev_argv, current_bad_sha1, bad_format);
 636         for (i = 0; i < good_revs.nr; i++)
 637                 argv_array_push_sha1(&rev_argv, good_revs.sha1[i],
 638                                      good_format);
 639         argv_array_push(&rev_argv, xstrdup("--"));
 640         if (read_paths)
 641                 read_bisect_paths(&rev_argv);
 642         argv_array_push(&rev_argv, NULL);
 643
 644         setup_revisions(rev_argv.argv_nr, rev_argv.argv, revs, NULL);
 645 }
 646
 647 static void bisect_common(struct rev_info *revs)
 648 {
 649         if (prepare_revision_walk(revs))
 650                 die("revision walk setup failed");
 651         if (revs->tree_objects)
 652                 mark_edges_uninteresting(revs->commits, revs, NULL);
 653 }
 654
 655 static void exit_if_skipped_commits(struct commit_list *tried,
 656                                     const unsigned char *bad)
 657 {
 658         if (!tried)
 659                 return;
 660
 661         printf("There are only 'skip'ped commits left to test.\n"
 662                "The first bad commit could be any of:\n");
 663         print_commit_list(tried, "%s\n", "%s\n");
 664         if (bad)
 665                 printf("%s\n", sha1_to_hex(bad));
 666         printf("We cannot bisect more!\n");
 667         exit(2);
 668 }
 669
 670 static int is_expected_rev(const unsigned char *sha1)
 671 {
 672         const char *filename = git_path("BISECT_EXPECTED_REV");
 673         struct stat st;
 674         struct strbuf str = STRBUF_INIT;
 675         FILE *fp;
 676         int res = 0;
 677
 678         if (stat(filename, &st) || !S_ISREG(st.st_mode))
 679                 return 0;
 680
 681         fp = fopen(filename, "r");
 682         if (!fp)
 683                 return 0;
 684
 685         if (strbuf_getline(&str, fp, '\n') != EOF)
 686                 res = !strcmp(str.buf, sha1_to_hex(sha1));
 687
 688         strbuf_release(&str);
 689         fclose(fp);
 690
 691         return res;
 692 }
 693
 694 static void mark_expected_rev(char *bisect_rev_hex)
 695 {
 696         int len = strlen(bisect_rev_hex);
 697         const char *filename = git_path("BISECT_EXPECTED_REV");
 698         int fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
 699
 700         if (fd < 0)
 701                 die_errno("could not create file '%s'", filename);
 702
 703         bisect_rev_hex[len] = '\n';
 704         write_or_die(fd, bisect_rev_hex, len + 1);
 705         bisect_rev_hex[len] = '\0';
 706
 707         if (close(fd) < 0)
 708                 die("closing file %s: %s", filename, strerror(errno));
 709 }
 710
 711 static int bisect_checkout(char *bisect_rev_hex, int no_checkout)
 712 {
 713         int res;
 714
 715         mark_expected_rev(bisect_rev_hex);
 716
 717         argv_checkout[2] = bisect_rev_hex;
 718         if (no_checkout) {
 719                 argv_update_ref[3] = bisect_rev_hex;
 720                 if (run_command_v_opt(argv_update_ref, RUN_GIT_CMD))
 721                         die("update-ref --no-deref HEAD failed on %s",
 722                             bisect_rev_hex);
 723         } else {
 724                 res = run_command_v_opt(argv_checkout, RUN_GIT_CMD);
 725                 if (res)
 726                         exit(res);
 727         }
 728
 729         argv_show_branch[1] = bisect_rev_hex;
 730         return run_command_v_opt(argv_show_branch, RUN_GIT_CMD);
 731 }
 732
 733 static struct commit *get_commit_reference(const unsigned char *sha1)
 734 {
 735         struct commit *r = lookup_commit_reference(sha1);
 736         if (!r)
 737                 die("Not a valid commit name %s", sha1_to_hex(sha1));
 738         return r;
 739 }
 740
 741 static struct commit **get_bad_and_good_commits(int *rev_nr)
 742 {
 743         int len = 1 + good_revs.nr;
 744         struct commit **rev = xmalloc(len * sizeof(*rev));
 745         int i, n = 0;
 746
 747         rev[n++] = get_commit_reference(current_bad_sha1);
 748         for (i = 0; i < good_revs.nr; i++)
 749                 rev[n++] = get_commit_reference(good_revs.sha1[i]);
 750         *rev_nr = n;
 751
 752         return rev;
 753 }
 754
 755 static void handle_bad_merge_base(void)
 756 {
 757         if (is_expected_rev(current_bad_sha1)) {
 758                 char *bad_hex = sha1_to_hex(current_bad_sha1);
 759                 char *good_hex = join_sha1_array_hex(&good_revs, ' ');
 760
 761                 fprintf(stderr, "The merge base %s is bad.\n"
 762                         "This means the bug has been fixed "
 763                         "between %s and [%s].\n",
 764                         bad_hex, bad_hex, good_hex);
 765
 766                 exit(3);
 767         }
 768
 769         fprintf(stderr, "Some good revs are not ancestor of the bad rev.\n"
 770                 "git bisect cannot work properly in this case.\n"
 771                 "Maybe you mistake good and bad revs?\n");
 772         exit(1);
 773 }
 774
 775 static void handle_skipped_merge_base(const unsigned char *mb)
 776 {
 777         char *mb_hex = sha1_to_hex(mb);
 778         char *bad_hex = sha1_to_hex(current_bad_sha1);
 779         char *good_hex = join_sha1_array_hex(&good_revs, ' ');
 780
 781         warning("the merge base between %s and [%s] "
 782                 "must be skipped.\n"
 783                 "So we cannot be sure the first bad commit is "
 784                 "between %s and %s.\n"
 785                 "We continue anyway.",
 786                 bad_hex, good_hex, mb_hex, bad_hex);
 787         free(good_hex);
 788 }
 789
 790 /*
 791  * "check_merge_bases" checks that merge bases are not "bad".
 792  *
 793  * - If one is "bad", it means the user assumed something wrong
 794  * and we must exit with a non 0 error code.
 795  * - If one is "good", that's good, we have nothing to do.
 796  * - If one is "skipped", we can't know but we should warn.
 797  * - If we don't know, we should check it out and ask the user to test.
 798  */
 799 static void check_merge_bases(int no_checkout)
 800 {
 801         struct commit_list *result;
 802         int rev_nr;
 803         struct commit **rev = get_bad_and_good_commits(&rev_nr);
 804
 805         result = get_merge_bases_many(rev[0], rev_nr - 1, rev + 1, 0);
 806
 807         for (; result; result = result->next) {
 808                 const unsigned char *mb = result->item->object.sha1;
 809                 if (!hashcmp(mb, current_bad_sha1)) {
 810                         handle_bad_merge_base();
 811                 } else if (0 <= sha1_array_lookup(&good_revs, mb)) {
 812                         continue;
 813                 } else if (0 <= sha1_array_lookup(&skipped_revs, mb)) {
 814                         handle_skipped_merge_base(mb);
 815                 } else {
 816                         printf("Bisecting: a merge base must be tested\n");
 817                         exit(bisect_checkout(sha1_to_hex(mb), no_checkout));
 818                 }
 819         }
 820
 821         free(rev);
 822         free_commit_list(result);
 823 }
 824
 825 static int check_ancestors(const char *prefix)
 826 {
 827         struct rev_info revs;
 828         struct object_array pending_copy;
 829         int i, res;
 830
 831         bisect_rev_setup(&revs, prefix, "^%s", "%s", 0);
 832
 833         /* Save pending objects, so they can be cleaned up later. */
 834         memset(&pending_copy, 0, sizeof(pending_copy));
 835         for (i = 0; i < revs.pending.nr; i++)
 836                 add_object_array(revs.pending.objects[i].item,
 837                                  revs.pending.objects[i].name,
 838                                  &pending_copy);
 839
 840         bisect_common(&revs);
 841         res = (revs.commits != NULL);
 842
 843         /* Clean up objects used, as they will be reused. */
 844         for (i = 0; i < pending_copy.nr; i++) {
 845                 struct object *o = pending_copy.objects[i].item;
 846                 clear_commit_marks((struct commit *)o, ALL_REV_FLAGS);
 847         }
 848
 849         return res;
 850 }
 851
 852 /*
 853  * "check_good_are_ancestors_of_bad" checks that all "good" revs are
 854  * ancestor of the "bad" rev.
 855  *
 856  * If that's not the case, we need to check the merge bases.
 857  * If a merge base must be tested by the user, its source code will be
 858  * checked out to be tested by the user and we will exit.
 859  */
 860 static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
 861 {
 862         const char *filename = git_path("BISECT_ANCESTORS_OK");
 863         struct stat st;
 864         int fd;
 865
 866         if (!current_bad_sha1)
 867                 die("a bad revision is needed");
 868
 869         /* Check if file BISECT_ANCESTORS_OK exists. */
 870         if (!stat(filename, &st) && S_ISREG(st.st_mode))
 871                 return;
 872
 873         /* Bisecting with no good rev is ok. */
 874         if (good_revs.nr == 0)
 875                 return;
 876
 877         /* Check if all good revs are ancestor of the bad rev. */
 878         if (check_ancestors(prefix))
 879                 check_merge_bases(no_checkout);
 880
 881         /* Create file BISECT_ANCESTORS_OK. */
 882         fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
 883         if (fd < 0)
 884                 warning("could not create file '%s': %s",
 885                         filename, strerror(errno));
 886         else
 887                 close(fd);
 888 }
 889
 890 /*
 891  * This does "git diff-tree --pretty COMMIT" without one fork+exec.
 892  */
 893 static void show_diff_tree(const char *prefix, struct commit *commit)
 894 {
 895         struct rev_info opt;
 896
 897         /* diff-tree init */
 898         init_revisions(&opt, prefix);
 899         git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
 900         opt.abbrev = 0;
 901         opt.diff = 1;
 902
 903         /* This is what "--pretty" does */
 904         opt.verbose_header = 1;
 905         opt.use_terminator = 0;
 906         opt.commit_format = CMIT_FMT_DEFAULT;
 907
 908         /* diff-tree init */
 909         if (!opt.diffopt.output_format)
 910                 opt.diffopt.output_format = DIFF_FORMAT_RAW;
 911
 912         log_tree_commit(&opt, commit);
 913 }
 914
 915 /*
 916  * We use the convention that exiting with an exit code 10 means that
 917  * the bisection process finished successfully.
 918  * In this case the calling shell script should exit 0.
 919  *
 920  * If no_checkout is non-zero, the bisection process does not
 921  * checkout the trial commit but instead simply updates BISECT_HEAD.
 922  */
 923 int bisect_next_all(const char *prefix, int no_checkout)
 924 {
 925         struct rev_info revs;
 926         struct commit_list *tried;
 927         int reaches = 0, all = 0, nr, steps;
 928         const unsigned char *bisect_rev;
 929         char bisect_rev_hex[41];
 930
 931         if (read_bisect_refs())
 932                 die("reading bisect refs failed");
 933
 934         check_good_are_ancestors_of_bad(prefix, no_checkout);
 935
 936         bisect_rev_setup(&revs, prefix, "%s", "^%s", 1);
 937         revs.limited = 1;
 938
 939         bisect_common(&revs);
 940
 941         revs.commits = find_bisection(revs.commits, &reaches, &all,
 942                                        !!skipped_revs.nr);
 943         revs.commits = managed_skipped(revs.commits, &tried);
 944
 945         if (!revs.commits) {
 946                 /*
 947                  * We should exit here only if the "bad"
 948                  * commit is also a "skip" commit.
 949                  */
 950                 exit_if_skipped_commits(tried, NULL);
 951
 952                 printf("%s was both good and bad\n",
 953                        sha1_to_hex(current_bad_sha1));
 954                 exit(1);
 955         }
 956
 957         if (!all) {
 958                 fprintf(stderr, "No testable commit found.\n"
 959                         "Maybe you started with bad path parameters?\n");
 960                 exit(4);
 961         }
 962
 963         bisect_rev = revs.commits->item->object.sha1;
 964         memcpy(bisect_rev_hex, sha1_to_hex(bisect_rev), 41);
 965
 966         if (!hashcmp(bisect_rev, current_bad_sha1)) {
 967                 exit_if_skipped_commits(tried, current_bad_sha1);
 968                 printf("%s is the first bad commit\n", bisect_rev_hex);
 969                 show_diff_tree(prefix, revs.commits->item);
 970                 /* This means the bisection process succeeded. */
 971                 exit(10);
 972         }
 973
 974         nr = all - reaches - 1;
 975         steps = estimate_bisect_steps(all);
 976         printf("Bisecting: %d revision%s left to test after this "
 977                "(roughly %d step%s)\n", nr, (nr == 1 ? "" : "s"),
 978                steps, (steps == 1 ? "" : "s"));
 979
 980         return bisect_checkout(bisect_rev_hex, no_checkout);
 981 }
 982