bisect.con commit Merge branch 'jk/mark-edges-uninteresting' (a6bec00)
   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
  15static struct sha1_array good_revs;
  16static struct sha1_array skipped_revs;
  17
  18static unsigned char *current_bad_sha1;
  19
  20static const char *argv_checkout[] = {"checkout", "-q", NULL, "--", NULL};
  21static const char *argv_show_branch[] = {"show-branch", NULL, NULL};
  22static const char *argv_update_ref[] = {"update-ref", "--no-deref", "BISECT_HEAD", NULL, NULL};
  23
  24/* bits #0-15 in revision.h */
  25
  26#define COUNTED         (1u<<16)
  27
  28/*
  29 * This is a truly stupid algorithm, but it's only
  30 * used for bisection, and we just don't care enough.
  31 *
  32 * We care just barely enough to avoid recursing for
  33 * non-merge entries.
  34 */
  35static int count_distance(struct commit_list *entry)
  36{
  37        int nr = 0;
  38
  39        while (entry) {
  40                struct commit *commit = entry->item;
  41                struct commit_list *p;
  42
  43                if (commit->object.flags & (UNINTERESTING | COUNTED))
  44                        break;
  45                if (!(commit->object.flags & TREESAME))
  46                        nr++;
  47                commit->object.flags |= COUNTED;
  48                p = commit->parents;
  49                entry = p;
  50                if (p) {
  51                        p = p->next;
  52                        while (p) {
  53                                nr += count_distance(p);
  54                                p = p->next;
  55                        }
  56                }
  57        }
  58
  59        return nr;
  60}
  61
  62static void clear_distance(struct commit_list *list)
  63{
  64        while (list) {
  65                struct commit *commit = list->item;
  66                commit->object.flags &= ~COUNTED;
  67                list = list->next;
  68        }
  69}
  70
  71#define DEBUG_BISECT 0
  72
  73static inline int weight(struct commit_list *elem)
  74{
  75        return *((int*)(elem->item->util));
  76}
  77
  78static inline void weight_set(struct commit_list *elem, int weight)
  79{
  80        *((int*)(elem->item->util)) = weight;
  81}
  82
  83static int count_interesting_parents(struct commit *commit)
  84{
  85        struct commit_list *p;
  86        int count;
  87
  88        for (count = 0, p = commit->parents; p; p = p->next) {
  89                if (p->item->object.flags & UNINTERESTING)
  90                        continue;
  91                count++;
  92        }
  93        return count;
  94}
  95
  96static inline int halfway(struct commit_list *p, int nr)
  97{
  98        /*
  99         * Don't short-cut something we are not going to return!
 100         */
 101        if (p->item->object.flags & TREESAME)
 102                return 0;
 103        if (DEBUG_BISECT)
 104                return 0;
 105        /*
 106         * 2 and 3 are halfway of 5.
 107         * 3 is halfway of 6 but 2 and 4 are not.
 108         */
 109        switch (2 * weight(p) - nr) {
 110        case -1: case 0: case 1:
 111                return 1;
 112        default:
 113                return 0;
 114        }
 115}
 116
 117#if !DEBUG_BISECT
 118#define show_list(a,b,c,d) do { ; } while (0)
 119#else
 120static void show_list(const char *debug, int counted, int nr,
 121                      struct commit_list *list)
 122{
 123        struct commit_list *p;
 124
 125        fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
 126
 127        for (p = list; p; p = p->next) {
 128                struct commit_list *pp;
 129                struct commit *commit = p->item;
 130                unsigned flags = commit->object.flags;
 131                enum object_type type;
 132                unsigned long size;
 133                char *buf = read_sha1_file(commit->object.sha1, &type, &size);
 134                const char *subject_start;
 135                int subject_len;
 136
 137                fprintf(stderr, "%c%c%c ",
 138                        (flags & TREESAME) ? ' ' : 'T',
 139                        (flags & UNINTERESTING) ? 'U' : ' ',
 140                        (flags & COUNTED) ? 'C' : ' ');
 141                if (commit->util)
 142                        fprintf(stderr, "%3d", weight(p));
 143                else
 144                        fprintf(stderr, "---");
 145                fprintf(stderr, " %.*s", 8, sha1_to_hex(commit->object.sha1));
 146                for (pp = commit->parents; pp; pp = pp->next)
 147                        fprintf(stderr, " %.*s", 8,
 148                                sha1_to_hex(pp->item->object.sha1));
 149
 150                subject_len = find_commit_subject(buf, &subject_start);
 151                if (subject_len)
 152                        fprintf(stderr, " %.*s", subject_len, subject_start);
 153                fprintf(stderr, "\n");
 154        }
 155}
 156#endif /* DEBUG_BISECT */
 157
 158static struct commit_list *best_bisection(struct commit_list *list, int nr)
 159{
 160        struct commit_list *p, *best;
 161        int best_distance = -1;
 162
 163        best = list;
 164        for (p = list; p; p = p->next) {
 165                int distance;
 166                unsigned flags = p->item->object.flags;
 167
 168                if (flags & TREESAME)
 169                        continue;
 170                distance = weight(p);
 171                if (nr - distance < distance)
 172                        distance = nr - distance;
 173                if (distance > best_distance) {
 174                        best = p;
 175                        best_distance = distance;
 176                }
 177        }
 178
 179        return best;
 180}
 181
 182struct commit_dist {
 183        struct commit *commit;
 184        int distance;
 185};
 186
 187static int compare_commit_dist(const void *a_, const void *b_)
 188{
 189        struct commit_dist *a, *b;
 190
 191        a = (struct commit_dist *)a_;
 192        b = (struct commit_dist *)b_;
 193        if (a->distance != b->distance)
 194                return b->distance - a->distance; /* desc sort */
 195        return hashcmp(a->commit->object.sha1, b->commit->object.sha1);
 196}
 197
 198static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
 199{
 200        struct commit_list *p;
 201        struct commit_dist *array = xcalloc(nr, sizeof(*array));
 202        int cnt, i;
 203
 204        for (p = list, cnt = 0; p; p = p->next) {
 205                int distance;
 206                unsigned flags = p->item->object.flags;
 207
 208                if (flags & TREESAME)
 209                        continue;
 210                distance = weight(p);
 211                if (nr - distance < distance)
 212                        distance = nr - distance;
 213                array[cnt].commit = p->item;
 214                array[cnt].distance = distance;
 215                cnt++;
 216        }
 217        qsort(array, cnt, sizeof(*array), compare_commit_dist);
 218        for (p = list, i = 0; i < cnt; i++) {
 219                struct name_decoration *r = xmalloc(sizeof(*r) + 100);
 220                struct object *obj = &(array[i].commit->object);
 221
 222                sprintf(r->name, "dist=%d", array[i].distance);
 223                r->next = add_decoration(&name_decoration, obj, r);
 224                p->item = array[i].commit;
 225                p = p->next;
 226        }
 227        if (p)
 228                p->next = NULL;
 229        free(array);
 230        return list;
 231}
 232
 233/*
 234 * zero or positive weight is the number of interesting commits it can
 235 * reach, including itself.  Especially, weight = 0 means it does not
 236 * reach any tree-changing commits (e.g. just above uninteresting one
 237 * but traversal is with pathspec).
 238 *
 239 * weight = -1 means it has one parent and its distance is yet to
 240 * be computed.
 241 *
 242 * weight = -2 means it has more than one parent and its distance is
 243 * unknown.  After running count_distance() first, they will get zero
 244 * or positive distance.
 245 */
 246static struct commit_list *do_find_bisection(struct commit_list *list,
 247                                             int nr, int *weights,
 248                                             int find_all)
 249{
 250        int n, counted;
 251        struct commit_list *p;
 252
 253        counted = 0;
 254
 255        for (n = 0, p = list; p; p = p->next) {
 256                struct commit *commit = p->item;
 257                unsigned flags = commit->object.flags;
 258
 259                p->item->util = &weights[n++];
 260                switch (count_interesting_parents(commit)) {
 261                case 0:
 262                        if (!(flags & TREESAME)) {
 263                                weight_set(p, 1);
 264                                counted++;
 265                                show_list("bisection 2 count one",
 266                                          counted, nr, list);
 267                        }
 268                        /*
 269                         * otherwise, it is known not to reach any
 270                         * tree-changing commit and gets weight 0.
 271                         */
 272                        break;
 273                case 1:
 274                        weight_set(p, -1);
 275                        break;
 276                default:
 277                        weight_set(p, -2);
 278                        break;
 279                }
 280        }
 281
 282        show_list("bisection 2 initialize", counted, nr, list);
 283
 284        /*
 285         * If you have only one parent in the resulting set
 286         * then you can reach one commit more than that parent
 287         * can reach.  So we do not have to run the expensive
 288         * count_distance() for single strand of pearls.
 289         *
 290         * However, if you have more than one parents, you cannot
 291         * just add their distance and one for yourself, since
 292         * they usually reach the same ancestor and you would
 293         * end up counting them twice that way.
 294         *
 295         * So we will first count distance of merges the usual
 296         * way, and then fill the blanks using cheaper algorithm.
 297         */
 298        for (p = list; p; p = p->next) {
 299                if (p->item->object.flags & UNINTERESTING)
 300                        continue;
 301                if (weight(p) != -2)
 302                        continue;
 303                weight_set(p, count_distance(p));
 304                clear_distance(list);
 305
 306                /* Does it happen to be at exactly half-way? */
 307                if (!find_all && halfway(p, nr))
 308                        return p;
 309                counted++;
 310        }
 311
 312        show_list("bisection 2 count_distance", counted, nr, list);
 313
 314        while (counted < nr) {
 315                for (p = list; p; p = p->next) {
 316                        struct commit_list *q;
 317                        unsigned flags = p->item->object.flags;
 318
 319                        if (0 <= weight(p))
 320                                continue;
 321                        for (q = p->item->parents; q; q = q->next) {
 322                                if (q->item->object.flags & UNINTERESTING)
 323                                        continue;
 324                                if (0 <= weight(q))
 325                                        break;
 326                        }
 327                        if (!q)
 328                                continue;
 329
 330                        /*
 331                         * weight for p is unknown but q is known.
 332                         * add one for p itself if p is to be counted,
 333                         * otherwise inherit it from q directly.
 334                         */
 335                        if (!(flags & TREESAME)) {
 336                                weight_set(p, weight(q)+1);
 337                                counted++;
 338                                show_list("bisection 2 count one",
 339                                          counted, nr, list);
 340                        }
 341                        else
 342                                weight_set(p, weight(q));
 343
 344                        /* Does it happen to be at exactly half-way? */
 345                        if (!find_all && halfway(p, nr))
 346                                return p;
 347                }
 348        }
 349
 350        show_list("bisection 2 counted all", counted, nr, list);
 351
 352        if (!find_all)
 353                return best_bisection(list, nr);
 354        else
 355                return best_bisection_sorted(list, nr);
 356}
 357
 358struct commit_list *find_bisection(struct commit_list *list,
 359                                          int *reaches, int *all,
 360                                          int find_all)
 361{
 362        int nr, on_list;
 363        struct commit_list *p, *best, *next, *last;
 364        int *weights;
 365
 366        show_list("bisection 2 entry", 0, 0, list);
 367
 368        /*
 369         * Count the number of total and tree-changing items on the
 370         * list, while reversing the list.
 371         */
 372        for (nr = on_list = 0, last = NULL, p = list;
 373             p;
 374             p = next) {
 375                unsigned flags = p->item->object.flags;
 376
 377                next = p->next;
 378                if (flags & UNINTERESTING)
 379                        continue;
 380                p->next = last;
 381                last = p;
 382                if (!(flags & TREESAME))
 383                        nr++;
 384                on_list++;
 385        }
 386        list = last;
 387        show_list("bisection 2 sorted", 0, nr, list);
 388
 389        *all = nr;
 390        weights = xcalloc(on_list, sizeof(*weights));
 391
 392        /* Do the real work of finding bisection commit. */
 393        best = do_find_bisection(list, nr, weights, find_all);
 394        if (best) {
 395                if (!find_all)
 396                        best->next = NULL;
 397                *reaches = weight(best);
 398        }
 399        free(weights);
 400        return best;
 401}
 402
 403static int register_ref(const char *refname, const unsigned char *sha1,
 404                        int flags, void *cb_data)
 405{
 406        if (!strcmp(refname, "bad")) {
 407                current_bad_sha1 = xmalloc(20);
 408                hashcpy(current_bad_sha1, sha1);
 409        } else if (starts_with(refname, "good-")) {
 410                sha1_array_append(&good_revs, sha1);
 411        } else if (starts_with(refname, "skip-")) {
 412                sha1_array_append(&skipped_revs, sha1);
 413        }
 414
 415        return 0;
 416}
 417
 418static int read_bisect_refs(void)
 419{
 420        return for_each_ref_in("refs/bisect/", register_ref, NULL);
 421}
 422
 423static void read_bisect_paths(struct argv_array *array)
 424{
 425        struct strbuf str = STRBUF_INIT;
 426        const char *filename = git_path("BISECT_NAMES");
 427        FILE *fp = fopen(filename, "r");
 428
 429        if (!fp)
 430                die_errno("Could not open file '%s'", filename);
 431
 432        while (strbuf_getline(&str, fp, '\n') != EOF) {
 433                strbuf_trim(&str);
 434                if (sq_dequote_to_argv_array(str.buf, array))
 435                        die("Badly quoted content in file '%s': %s",
 436                            filename, str.buf);
 437        }
 438
 439        strbuf_release(&str);
 440        fclose(fp);
 441}
 442
 443static char *join_sha1_array_hex(struct sha1_array *array, char delim)
 444{
 445        struct strbuf joined_hexs = STRBUF_INIT;
 446        int i;
 447
 448        for (i = 0; i < array->nr; i++) {
 449                strbuf_addstr(&joined_hexs, sha1_to_hex(array->sha1[i]));
 450                if (i + 1 < array->nr)
 451                        strbuf_addch(&joined_hexs, delim);
 452        }
 453
 454        return strbuf_detach(&joined_hexs, NULL);
 455}
 456
 457/*
 458 * In this function, passing a not NULL skipped_first is very special.
 459 * It means that we want to know if the first commit in the list is
 460 * skipped because we will want to test a commit away from it if it is
 461 * indeed skipped.
 462 * So if the first commit is skipped, we cannot take the shortcut to
 463 * just "return list" when we find the first non skipped commit, we
 464 * have to return a fully filtered list.
 465 *
 466 * We use (*skipped_first == -1) to mean "it has been found that the
 467 * first commit is not skipped". In this case *skipped_first is set back
 468 * to 0 just before the function returns.
 469 */
 470struct commit_list *filter_skipped(struct commit_list *list,
 471                                   struct commit_list **tried,
 472                                   int show_all,
 473                                   int *count,
 474                                   int *skipped_first)
 475{
 476        struct commit_list *filtered = NULL, **f = &filtered;
 477
 478        *tried = NULL;
 479
 480        if (skipped_first)
 481                *skipped_first = 0;
 482        if (count)
 483                *count = 0;
 484
 485        if (!skipped_revs.nr)
 486                return list;
 487
 488        while (list) {
 489                struct commit_list *next = list->next;
 490                list->next = NULL;
 491                if (0 <= sha1_array_lookup(&skipped_revs,
 492                                           list->item->object.sha1)) {
 493                        if (skipped_first && !*skipped_first)
 494                                *skipped_first = 1;
 495                        /* Move current to tried list */
 496                        *tried = list;
 497                        tried = &list->next;
 498                } else {
 499                        if (!show_all) {
 500                                if (!skipped_first || !*skipped_first)
 501                                        return list;
 502                        } else if (skipped_first && !*skipped_first) {
 503                                /* This means we know it's not skipped */
 504                                *skipped_first = -1;
 505                        }
 506                        /* Move current to filtered list */
 507                        *f = list;
 508                        f = &list->next;
 509                        if (count)
 510                                (*count)++;
 511                }
 512                list = next;
 513        }
 514
 515        if (skipped_first && *skipped_first == -1)
 516                *skipped_first = 0;
 517
 518        return filtered;
 519}
 520
 521#define PRN_MODULO 32768
 522
 523/*
 524 * This is a pseudo random number generator based on "man 3 rand".
 525 * It is not used properly because the seed is the argument and it
 526 * is increased by one between each call, but that should not matter
 527 * for this application.
 528 */
 529static unsigned get_prn(unsigned count) {
 530        count = count * 1103515245 + 12345;
 531        return (count/65536) % PRN_MODULO;
 532}
 533
 534/*
 535 * Custom integer square root from
 536 * http://en.wikipedia.org/wiki/Integer_square_root
 537 */
 538static int sqrti(int val)
 539{
 540        float d, x = val;
 541
 542        if (val == 0)
 543                return 0;
 544
 545        do {
 546                float y = (x + (float)val / x) / 2;
 547                d = (y > x) ? y - x : x - y;
 548                x = y;
 549        } while (d >= 0.5);
 550
 551        return (int)x;
 552}
 553
 554static struct commit_list *skip_away(struct commit_list *list, int count)
 555{
 556        struct commit_list *cur, *previous;
 557        int prn, index, i;
 558
 559        prn = get_prn(count);
 560        index = (count * prn / PRN_MODULO) * sqrti(prn) / sqrti(PRN_MODULO);
 561
 562        cur = list;
 563        previous = NULL;
 564
 565        for (i = 0; cur; cur = cur->next, i++) {
 566                if (i == index) {
 567                        if (hashcmp(cur->item->object.sha1, current_bad_sha1))
 568                                return cur;
 569                        if (previous)
 570                                return previous;
 571                        return list;
 572                }
 573                previous = cur;
 574        }
 575
 576        return list;
 577}
 578
 579static struct commit_list *managed_skipped(struct commit_list *list,
 580                                           struct commit_list **tried)
 581{
 582        int count, skipped_first;
 583
 584        *tried = NULL;
 585
 586        if (!skipped_revs.nr)
 587                return list;
 588
 589        list = filter_skipped(list, tried, 0, &count, &skipped_first);
 590
 591        if (!skipped_first)
 592                return list;
 593
 594        return skip_away(list, count);
 595}
 596
 597static void bisect_rev_setup(struct rev_info *revs, const char *prefix,
 598                             const char *bad_format, const char *good_format,
 599                             int read_paths)
 600{
 601        struct argv_array rev_argv = ARGV_ARRAY_INIT;
 602        int i;
 603
 604        init_revisions(revs, prefix);
 605        revs->abbrev = 0;
 606        revs->commit_format = CMIT_FMT_UNSPECIFIED;
 607
 608        /* rev_argv.argv[0] will be ignored by setup_revisions */
 609        argv_array_push(&rev_argv, "bisect_rev_setup");
 610        argv_array_pushf(&rev_argv, bad_format, sha1_to_hex(current_bad_sha1));
 611        for (i = 0; i < good_revs.nr; i++)
 612                argv_array_pushf(&rev_argv, good_format,
 613                                 sha1_to_hex(good_revs.sha1[i]));
 614        argv_array_push(&rev_argv, "--");
 615        if (read_paths)
 616                read_bisect_paths(&rev_argv);
 617
 618        setup_revisions(rev_argv.argc, rev_argv.argv, revs, NULL);
 619        /* XXX leak rev_argv, as "revs" may still be pointing to it */
 620}
 621
 622static void bisect_common(struct rev_info *revs)
 623{
 624        if (prepare_revision_walk(revs))
 625                die("revision walk setup failed");
 626        if (revs->tree_objects)
 627                mark_edges_uninteresting(revs, NULL);
 628}
 629
 630static void exit_if_skipped_commits(struct commit_list *tried,
 631                                    const unsigned char *bad)
 632{
 633        if (!tried)
 634                return;
 635
 636        printf("There are only 'skip'ped commits left to test.\n"
 637               "The first bad commit could be any of:\n");
 638        print_commit_list(tried, "%s\n", "%s\n");
 639        if (bad)
 640                printf("%s\n", sha1_to_hex(bad));
 641        printf("We cannot bisect more!\n");
 642        exit(2);
 643}
 644
 645static int is_expected_rev(const unsigned char *sha1)
 646{
 647        const char *filename = git_path("BISECT_EXPECTED_REV");
 648        struct stat st;
 649        struct strbuf str = STRBUF_INIT;
 650        FILE *fp;
 651        int res = 0;
 652
 653        if (stat(filename, &st) || !S_ISREG(st.st_mode))
 654                return 0;
 655
 656        fp = fopen(filename, "r");
 657        if (!fp)
 658                return 0;
 659
 660        if (strbuf_getline(&str, fp, '\n') != EOF)
 661                res = !strcmp(str.buf, sha1_to_hex(sha1));
 662
 663        strbuf_release(&str);
 664        fclose(fp);
 665
 666        return res;
 667}
 668
 669static void mark_expected_rev(char *bisect_rev_hex)
 670{
 671        int len = strlen(bisect_rev_hex);
 672        const char *filename = git_path("BISECT_EXPECTED_REV");
 673        int fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
 674
 675        if (fd < 0)
 676                die_errno("could not create file '%s'", filename);
 677
 678        bisect_rev_hex[len] = '\n';
 679        write_or_die(fd, bisect_rev_hex, len + 1);
 680        bisect_rev_hex[len] = '\0';
 681
 682        if (close(fd) < 0)
 683                die("closing file %s: %s", filename, strerror(errno));
 684}
 685
 686static int bisect_checkout(char *bisect_rev_hex, int no_checkout)
 687{
 688        int res;
 689
 690        mark_expected_rev(bisect_rev_hex);
 691
 692        argv_checkout[2] = bisect_rev_hex;
 693        if (no_checkout) {
 694                argv_update_ref[3] = bisect_rev_hex;
 695                if (run_command_v_opt(argv_update_ref, RUN_GIT_CMD))
 696                        die("update-ref --no-deref HEAD failed on %s",
 697                            bisect_rev_hex);
 698        } else {
 699                res = run_command_v_opt(argv_checkout, RUN_GIT_CMD);
 700                if (res)
 701                        exit(res);
 702        }
 703
 704        argv_show_branch[1] = bisect_rev_hex;
 705        return run_command_v_opt(argv_show_branch, RUN_GIT_CMD);
 706}
 707
 708static struct commit *get_commit_reference(const unsigned char *sha1)
 709{
 710        struct commit *r = lookup_commit_reference(sha1);
 711        if (!r)
 712                die("Not a valid commit name %s", sha1_to_hex(sha1));
 713        return r;
 714}
 715
 716static struct commit **get_bad_and_good_commits(int *rev_nr)
 717{
 718        int len = 1 + good_revs.nr;
 719        struct commit **rev = xmalloc(len * sizeof(*rev));
 720        int i, n = 0;
 721
 722        rev[n++] = get_commit_reference(current_bad_sha1);
 723        for (i = 0; i < good_revs.nr; i++)
 724                rev[n++] = get_commit_reference(good_revs.sha1[i]);
 725        *rev_nr = n;
 726
 727        return rev;
 728}
 729
 730static void handle_bad_merge_base(void)
 731{
 732        if (is_expected_rev(current_bad_sha1)) {
 733                char *bad_hex = sha1_to_hex(current_bad_sha1);
 734                char *good_hex = join_sha1_array_hex(&good_revs, ' ');
 735
 736                fprintf(stderr, "The merge base %s is bad.\n"
 737                        "This means the bug has been fixed "
 738                        "between %s and [%s].\n",
 739                        bad_hex, bad_hex, good_hex);
 740
 741                exit(3);
 742        }
 743
 744        fprintf(stderr, "Some good revs are not ancestor of the bad rev.\n"
 745                "git bisect cannot work properly in this case.\n"
 746                "Maybe you mistake good and bad revs?\n");
 747        exit(1);
 748}
 749
 750static void handle_skipped_merge_base(const unsigned char *mb)
 751{
 752        char *mb_hex = sha1_to_hex(mb);
 753        char *bad_hex = sha1_to_hex(current_bad_sha1);
 754        char *good_hex = join_sha1_array_hex(&good_revs, ' ');
 755
 756        warning("the merge base between %s and [%s] "
 757                "must be skipped.\n"
 758                "So we cannot be sure the first bad commit is "
 759                "between %s and %s.\n"
 760                "We continue anyway.",
 761                bad_hex, good_hex, mb_hex, bad_hex);
 762        free(good_hex);
 763}
 764
 765/*
 766 * "check_merge_bases" checks that merge bases are not "bad".
 767 *
 768 * - If one is "bad", it means the user assumed something wrong
 769 * and we must exit with a non 0 error code.
 770 * - If one is "good", that's good, we have nothing to do.
 771 * - If one is "skipped", we can't know but we should warn.
 772 * - If we don't know, we should check it out and ask the user to test.
 773 */
 774static void check_merge_bases(int no_checkout)
 775{
 776        struct commit_list *result;
 777        int rev_nr;
 778        struct commit **rev = get_bad_and_good_commits(&rev_nr);
 779
 780        result = get_merge_bases_many(rev[0], rev_nr - 1, rev + 1, 0);
 781
 782        for (; result; result = result->next) {
 783                const unsigned char *mb = result->item->object.sha1;
 784                if (!hashcmp(mb, current_bad_sha1)) {
 785                        handle_bad_merge_base();
 786                } else if (0 <= sha1_array_lookup(&good_revs, mb)) {
 787                        continue;
 788                } else if (0 <= sha1_array_lookup(&skipped_revs, mb)) {
 789                        handle_skipped_merge_base(mb);
 790                } else {
 791                        printf("Bisecting: a merge base must be tested\n");
 792                        exit(bisect_checkout(sha1_to_hex(mb), no_checkout));
 793                }
 794        }
 795
 796        free(rev);
 797        free_commit_list(result);
 798}
 799
 800static int check_ancestors(const char *prefix)
 801{
 802        struct rev_info revs;
 803        struct object_array pending_copy;
 804        int res;
 805
 806        bisect_rev_setup(&revs, prefix, "^%s", "%s", 0);
 807
 808        /* Save pending objects, so they can be cleaned up later. */
 809        pending_copy = revs.pending;
 810        revs.leak_pending = 1;
 811
 812        /*
 813         * bisect_common calls prepare_revision_walk right away, which
 814         * (together with .leak_pending = 1) makes us the sole owner of
 815         * the list of pending objects.
 816         */
 817        bisect_common(&revs);
 818        res = (revs.commits != NULL);
 819
 820        /* Clean up objects used, as they will be reused. */
 821        clear_commit_marks_for_object_array(&pending_copy, ALL_REV_FLAGS);
 822        free(pending_copy.objects);
 823
 824        return res;
 825}
 826
 827/*
 828 * "check_good_are_ancestors_of_bad" checks that all "good" revs are
 829 * ancestor of the "bad" rev.
 830 *
 831 * If that's not the case, we need to check the merge bases.
 832 * If a merge base must be tested by the user, its source code will be
 833 * checked out to be tested by the user and we will exit.
 834 */
 835static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
 836{
 837        char *filename = git_pathdup("BISECT_ANCESTORS_OK");
 838        struct stat st;
 839        int fd;
 840
 841        if (!current_bad_sha1)
 842                die("a bad revision is needed");
 843
 844        /* Check if file BISECT_ANCESTORS_OK exists. */
 845        if (!stat(filename, &st) && S_ISREG(st.st_mode))
 846                goto done;
 847
 848        /* Bisecting with no good rev is ok. */
 849        if (good_revs.nr == 0)
 850                goto done;
 851
 852        /* Check if all good revs are ancestor of the bad rev. */
 853        if (check_ancestors(prefix))
 854                check_merge_bases(no_checkout);
 855
 856        /* Create file BISECT_ANCESTORS_OK. */
 857        fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
 858        if (fd < 0)
 859                warning("could not create file '%s': %s",
 860                        filename, strerror(errno));
 861        else
 862                close(fd);
 863 done:
 864        free(filename);
 865}
 866
 867/*
 868 * This does "git diff-tree --pretty COMMIT" without one fork+exec.
 869 */
 870static void show_diff_tree(const char *prefix, struct commit *commit)
 871{
 872        struct rev_info opt;
 873
 874        /* diff-tree init */
 875        init_revisions(&opt, prefix);
 876        git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
 877        opt.abbrev = 0;
 878        opt.diff = 1;
 879
 880        /* This is what "--pretty" does */
 881        opt.verbose_header = 1;
 882        opt.use_terminator = 0;
 883        opt.commit_format = CMIT_FMT_DEFAULT;
 884
 885        /* diff-tree init */
 886        if (!opt.diffopt.output_format)
 887                opt.diffopt.output_format = DIFF_FORMAT_RAW;
 888
 889        log_tree_commit(&opt, commit);
 890}
 891
 892/*
 893 * We use the convention that exiting with an exit code 10 means that
 894 * the bisection process finished successfully.
 895 * In this case the calling shell script should exit 0.
 896 *
 897 * If no_checkout is non-zero, the bisection process does not
 898 * checkout the trial commit but instead simply updates BISECT_HEAD.
 899 */
 900int bisect_next_all(const char *prefix, int no_checkout)
 901{
 902        struct rev_info revs;
 903        struct commit_list *tried;
 904        int reaches = 0, all = 0, nr, steps;
 905        const unsigned char *bisect_rev;
 906        char bisect_rev_hex[41];
 907
 908        if (read_bisect_refs())
 909                die("reading bisect refs failed");
 910
 911        check_good_are_ancestors_of_bad(prefix, no_checkout);
 912
 913        bisect_rev_setup(&revs, prefix, "%s", "^%s", 1);
 914        revs.limited = 1;
 915
 916        bisect_common(&revs);
 917
 918        revs.commits = find_bisection(revs.commits, &reaches, &all,
 919                                       !!skipped_revs.nr);
 920        revs.commits = managed_skipped(revs.commits, &tried);
 921
 922        if (!revs.commits) {
 923                /*
 924                 * We should exit here only if the "bad"
 925                 * commit is also a "skip" commit.
 926                 */
 927                exit_if_skipped_commits(tried, NULL);
 928
 929                printf("%s was both good and bad\n",
 930                       sha1_to_hex(current_bad_sha1));
 931                exit(1);
 932        }
 933
 934        if (!all) {
 935                fprintf(stderr, "No testable commit found.\n"
 936                        "Maybe you started with bad path parameters?\n");
 937                exit(4);
 938        }
 939
 940        bisect_rev = revs.commits->item->object.sha1;
 941        memcpy(bisect_rev_hex, sha1_to_hex(bisect_rev), 41);
 942
 943        if (!hashcmp(bisect_rev, current_bad_sha1)) {
 944                exit_if_skipped_commits(tried, current_bad_sha1);
 945                printf("%s is the first bad commit\n", bisect_rev_hex);
 946                show_diff_tree(prefix, revs.commits->item);
 947                /* This means the bisection process succeeded. */
 948                exit(10);
 949        }
 950
 951        nr = all - reaches - 1;
 952        steps = estimate_bisect_steps(all);
 953        printf("Bisecting: %d revision%s left to test after this "
 954               "(roughly %d step%s)\n", nr, (nr == 1 ? "" : "s"),
 955               steps, (steps == 1 ? "" : "s"));
 956
 957        return bisect_checkout(bisect_rev_hex, no_checkout);
 958}
 959
 960static inline int log2i(int n)
 961{
 962        int log2 = 0;
 963
 964        for (; n > 1; n >>= 1)
 965                log2++;
 966
 967        return log2;
 968}
 969
 970static inline int exp2i(int n)
 971{
 972        return 1 << n;
 973}
 974
 975/*
 976 * Estimate the number of bisect steps left (after the current step)
 977 *
 978 * For any x between 0 included and 2^n excluded, the probability for
 979 * n - 1 steps left looks like:
 980 *
 981 * P(2^n + x) == (2^n - x) / (2^n + x)
 982 *
 983 * and P(2^n + x) < 0.5 means 2^n < 3x
 984 */
 985int estimate_bisect_steps(int all)
 986{
 987        int n, x, e;
 988
 989        if (all < 3)
 990                return 0;
 991
 992        n = log2i(all);
 993        e = exp2i(n);
 994        x = all - e;
 995
 996        return (e < 3 * x) ? n : n - 1;
 997}