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