Merge branch 'jk/write-packed-refs-via-stdio'
[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 unsigned char *current_bad_sha1;
19
20 static const char *argv_checkout[] = {"checkout", "-q", NULL, "--", NULL};
21 static const char *argv_show_branch[] = {"show-branch", NULL, NULL};
22 static const char *argv_update_ref[] = {"update-ref", "--no-deref", "BISECT_HEAD", NULL, NULL};
23
24 /* Remember to update object flag allocation in object.h */
25 #define COUNTED         (1u<<16)
26
27 /*
28  * This is a truly stupid algorithm, but it's only
29  * used for bisection, and we just don't care enough.
30  *
31  * We care just barely enough to avoid recursing for
32  * non-merge entries.
33  */
34 static int count_distance(struct commit_list *entry)
35 {
36         int nr = 0;
37
38         while (entry) {
39                 struct commit *commit = entry->item;
40                 struct commit_list *p;
41
42                 if (commit->object.flags & (UNINTERESTING | COUNTED))
43                         break;
44                 if (!(commit->object.flags & TREESAME))
45                         nr++;
46                 commit->object.flags |= COUNTED;
47                 p = commit->parents;
48                 entry = p;
49                 if (p) {
50                         p = p->next;
51                         while (p) {
52                                 nr += count_distance(p);
53                                 p = p->next;
54                         }
55                 }
56         }
57
58         return nr;
59 }
60
61 static void clear_distance(struct commit_list *list)
62 {
63         while (list) {
64                 struct commit *commit = list->item;
65                 commit->object.flags &= ~COUNTED;
66                 list = list->next;
67         }
68 }
69
70 #define DEBUG_BISECT 0
71
72 static inline int weight(struct commit_list *elem)
73 {
74         return *((int*)(elem->item->util));
75 }
76
77 static inline void weight_set(struct commit_list *elem, int weight)
78 {
79         *((int*)(elem->item->util)) = weight;
80 }
81
82 static int count_interesting_parents(struct commit *commit)
83 {
84         struct commit_list *p;
85         int count;
86
87         for (count = 0, p = commit->parents; p; p = p->next) {
88                 if (p->item->object.flags & UNINTERESTING)
89                         continue;
90                 count++;
91         }
92         return count;
93 }
94
95 static inline int halfway(struct commit_list *p, int nr)
96 {
97         /*
98          * Don't short-cut something we are not going to return!
99          */
100         if (p->item->object.flags & TREESAME)
101                 return 0;
102         if (DEBUG_BISECT)
103                 return 0;
104         /*
105          * 2 and 3 are halfway of 5.
106          * 3 is halfway of 6 but 2 and 4 are not.
107          */
108         switch (2 * weight(p) - nr) {
109         case -1: case 0: case 1:
110                 return 1;
111         default:
112                 return 0;
113         }
114 }
115
116 #if !DEBUG_BISECT
117 #define show_list(a,b,c,d) do { ; } while (0)
118 #else
119 static void show_list(const char *debug, int counted, int nr,
120                       struct commit_list *list)
121 {
122         struct commit_list *p;
123
124         fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
125
126         for (p = list; p; p = p->next) {
127                 struct commit_list *pp;
128                 struct commit *commit = p->item;
129                 unsigned flags = commit->object.flags;
130                 enum object_type type;
131                 unsigned long size;
132                 char *buf = read_sha1_file(commit->object.sha1, &type, &size);
133                 const char *subject_start;
134                 int subject_len;
135
136                 fprintf(stderr, "%c%c%c ",
137                         (flags & TREESAME) ? ' ' : 'T',
138                         (flags & UNINTERESTING) ? 'U' : ' ',
139                         (flags & COUNTED) ? 'C' : ' ');
140                 if (commit->util)
141                         fprintf(stderr, "%3d", weight(p));
142                 else
143                         fprintf(stderr, "---");
144                 fprintf(stderr, " %.*s", 8, sha1_to_hex(commit->object.sha1));
145                 for (pp = commit->parents; pp; pp = pp->next)
146                         fprintf(stderr, " %.*s", 8,
147                                 sha1_to_hex(pp->item->object.sha1));
148
149                 subject_len = find_commit_subject(buf, &subject_start);
150                 if (subject_len)
151                         fprintf(stderr, " %.*s", subject_len, subject_start);
152                 fprintf(stderr, "\n");
153         }
154 }
155 #endif /* DEBUG_BISECT */
156
157 static struct commit_list *best_bisection(struct commit_list *list, int nr)
158 {
159         struct commit_list *p, *best;
160         int best_distance = -1;
161
162         best = list;
163         for (p = list; p; p = p->next) {
164                 int distance;
165                 unsigned flags = p->item->object.flags;
166
167                 if (flags & TREESAME)
168                         continue;
169                 distance = weight(p);
170                 if (nr - distance < distance)
171                         distance = nr - distance;
172                 if (distance > best_distance) {
173                         best = p;
174                         best_distance = distance;
175                 }
176         }
177
178         return best;
179 }
180
181 struct commit_dist {
182         struct commit *commit;
183         int distance;
184 };
185
186 static int compare_commit_dist(const void *a_, const void *b_)
187 {
188         struct commit_dist *a, *b;
189
190         a = (struct commit_dist *)a_;
191         b = (struct commit_dist *)b_;
192         if (a->distance != b->distance)
193                 return b->distance - a->distance; /* desc sort */
194         return hashcmp(a->commit->object.sha1, b->commit->object.sha1);
195 }
196
197 static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
198 {
199         struct commit_list *p;
200         struct commit_dist *array = xcalloc(nr, sizeof(*array));
201         int cnt, i;
202
203         for (p = list, cnt = 0; p; p = p->next) {
204                 int distance;
205                 unsigned flags = p->item->object.flags;
206
207                 if (flags & TREESAME)
208                         continue;
209                 distance = weight(p);
210                 if (nr - distance < distance)
211                         distance = nr - distance;
212                 array[cnt].commit = p->item;
213                 array[cnt].distance = distance;
214                 cnt++;
215         }
216         qsort(array, cnt, sizeof(*array), compare_commit_dist);
217         for (p = list, i = 0; i < cnt; i++) {
218                 char buf[100]; /* enough for dist=%d */
219                 struct object *obj = &(array[i].commit->object);
220
221                 snprintf(buf, sizeof(buf), "dist=%d", array[i].distance);
222                 add_name_decoration(DECORATION_NONE, buf, obj);
223
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  */
246 static 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
358 struct 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
403 static 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
418 static int read_bisect_refs(void)
419 {
420         return for_each_ref_in("refs/bisect/", register_ref, NULL);
421 }
422
423 static 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
443 static 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  */
470 struct 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  */
529 static 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  */
538 static 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
554 static 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
579 static 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
597 static 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
622 static 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
630 static 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
645 static 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
669 static 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
686 static int bisect_checkout(char *bisect_rev_hex, int no_checkout)
687 {
688
689         mark_expected_rev(bisect_rev_hex);
690
691         argv_checkout[2] = bisect_rev_hex;
692         if (no_checkout) {
693                 argv_update_ref[3] = bisect_rev_hex;
694                 if (run_command_v_opt(argv_update_ref, RUN_GIT_CMD))
695                         die("update-ref --no-deref HEAD failed on %s",
696                             bisect_rev_hex);
697         } else {
698                 int res;
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
708 static 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
716 static 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
730 static 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
750 static 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  */
774 static 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
800 static 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  */
835 static 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  */
870 static 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  */
900 int 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
960 static 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
970 static 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  */
985 int 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 }