Code

Fix some "variable might be used uninitialized" warnings
[git.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"
15 static struct sha1_array good_revs;
16 static struct sha1_array skipped_revs;
18 static const unsigned char *current_bad_sha1;
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};
24 /* bits #0-15 in revision.h */
26 #define COUNTED         (1u<<16)
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  */
35 static int count_distance(struct commit_list *entry)
36 {
37         int nr = 0;
39         while (entry) {
40                 struct commit *commit = entry->item;
41                 struct commit_list *p;
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         }
59         return nr;
60 }
62 static 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 }
71 #define DEBUG_BISECT 0
73 static inline int weight(struct commit_list *elem)
74 {
75         return *((int*)(elem->item->util));
76 }
78 static inline void weight_set(struct commit_list *elem, int weight)
79 {
80         *((int*)(elem->item->util)) = weight;
81 }
83 static int count_interesting_parents(struct commit *commit)
84 {
85         struct commit_list *p;
86         int count;
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 }
96 static 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         }
117 #if !DEBUG_BISECT
118 #define show_list(a,b,c,d) do { ; } while (0)
119 #else
120 static void show_list(const char *debug, int counted, int nr,
121                       struct commit_list *list)
123         struct commit_list *p;
125         fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
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;
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));
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         }
156 #endif /* DEBUG_BISECT */
158 static struct commit_list *best_bisection(struct commit_list *list, int nr)
160         struct commit_list *p, *best;
161         int best_distance = -1;
163         best = list;
164         for (p = list; p; p = p->next) {
165                 int distance;
166                 unsigned flags = p->item->object.flags;
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         }
179         return best;
182 struct commit_dist {
183         struct commit *commit;
184         int distance;
185 };
187 static int compare_commit_dist(const void *a_, const void *b_)
189         struct commit_dist *a, *b;
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);
198 static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
200         struct commit_list *p;
201         struct commit_dist *array = xcalloc(nr, sizeof(*array));
202         int cnt, i;
204         for (p = list, cnt = 0; p; p = p->next) {
205                 int distance;
206                 unsigned flags = p->item->object.flags;
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);
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;
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)
250         int n, counted;
251         struct commit_list *p;
253         counted = 0;
255         for (n = 0, p = list; p; p = p->next) {
256                 struct commit *commit = p->item;
257                 unsigned flags = commit->object.flags;
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         }
282         show_list("bisection 2 initialize", counted, nr, list);
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);
306                 /* Does it happen to be at exactly half-way? */
307                 if (!find_all && halfway(p, nr))
308                         return p;
309                 counted++;
310         }
312         show_list("bisection 2 count_distance", counted, nr, list);
314         while (counted < nr) {
315                 for (p = list; p; p = p->next) {
316                         struct commit_list *q;
317                         unsigned flags = p->item->object.flags;
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;
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));
344                         /* Does it happen to be at exactly half-way? */
345                         if (!find_all && halfway(p, nr))
346                                 return p;
347                 }
348         }
350         show_list("bisection 2 counted all", counted, nr, list);
352         if (!find_all)
353                 return best_bisection(list, nr);
354         else
355                 return best_bisection_sorted(list, nr);
358 struct commit_list *find_bisection(struct commit_list *list,
359                                           int *reaches, int *all,
360                                           int find_all)
362         int nr, on_list;
363         struct commit_list *p, *best, *next, *last;
364         int *weights;
366         show_list("bisection 2 entry", 0, 0, list);
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;
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);
389         *all = nr;
390         weights = xcalloc(on_list, sizeof(*weights));
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;
403 static int register_ref(const char *refname, const unsigned char *sha1,
404                         int flags, void *cb_data)
406         if (!strcmp(refname, "bad")) {
407                 current_bad_sha1 = sha1;
408         } else if (!prefixcmp(refname, "good-")) {
409                 sha1_array_append(&good_revs, sha1);
410         } else if (!prefixcmp(refname, "skip-")) {
411                 sha1_array_append(&skipped_revs, sha1);
412         }
414         return 0;
417 static int read_bisect_refs(void)
419         return for_each_ref_in("refs/bisect/", register_ref, NULL);
422 static void read_bisect_paths(struct argv_array *array)
424         struct strbuf str = STRBUF_INIT;
425         const char *filename = git_path("BISECT_NAMES");
426         FILE *fp = fopen(filename, "r");
428         if (!fp)
429                 die_errno("Could not open file '%s'", filename);
431         while (strbuf_getline(&str, fp, '\n') != EOF) {
432                 strbuf_trim(&str);
433                 if (sq_dequote_to_argv_array(str.buf, array))
434                         die("Badly quoted content in file '%s': %s",
435                             filename, str.buf);
436         }
438         strbuf_release(&str);
439         fclose(fp);
442 static char *join_sha1_array_hex(struct sha1_array *array, char delim)
444         struct strbuf joined_hexs = STRBUF_INIT;
445         int i;
447         for (i = 0; i < array->nr; i++) {
448                 strbuf_addstr(&joined_hexs, sha1_to_hex(array->sha1[i]));
449                 if (i + 1 < array->nr)
450                         strbuf_addch(&joined_hexs, delim);
451         }
453         return strbuf_detach(&joined_hexs, NULL);
456 /*
457  * In this function, passing a not NULL skipped_first is very special.
458  * It means that we want to know if the first commit in the list is
459  * skipped because we will want to test a commit away from it if it is
460  * indeed skipped.
461  * So if the first commit is skipped, we cannot take the shortcut to
462  * just "return list" when we find the first non skipped commit, we
463  * have to return a fully filtered list.
464  *
465  * We use (*skipped_first == -1) to mean "it has been found that the
466  * first commit is not skipped". In this case *skipped_first is set back
467  * to 0 just before the function returns.
468  */
469 struct commit_list *filter_skipped(struct commit_list *list,
470                                    struct commit_list **tried,
471                                    int show_all,
472                                    int *count,
473                                    int *skipped_first)
475         struct commit_list *filtered = NULL, **f = &filtered;
477         *tried = NULL;
479         if (skipped_first)
480                 *skipped_first = 0;
481         if (count)
482                 *count = 0;
484         if (!skipped_revs.nr)
485                 return list;
487         while (list) {
488                 struct commit_list *next = list->next;
489                 list->next = NULL;
490                 if (0 <= sha1_array_lookup(&skipped_revs,
491                                            list->item->object.sha1)) {
492                         if (skipped_first && !*skipped_first)
493                                 *skipped_first = 1;
494                         /* Move current to tried list */
495                         *tried = list;
496                         tried = &list->next;
497                 } else {
498                         if (!show_all) {
499                                 if (!skipped_first || !*skipped_first)
500                                         return list;
501                         } else if (skipped_first && !*skipped_first) {
502                                 /* This means we know it's not skipped */
503                                 *skipped_first = -1;
504                         }
505                         /* Move current to filtered list */
506                         *f = list;
507                         f = &list->next;
508                         if (count)
509                                 (*count)++;
510                 }
511                 list = next;
512         }
514         if (skipped_first && *skipped_first == -1)
515                 *skipped_first = 0;
517         return filtered;
520 #define PRN_MODULO 32768
522 /*
523  * This is a pseudo random number generator based on "man 3 rand".
524  * It is not used properly because the seed is the argument and it
525  * is increased by one between each call, but that should not matter
526  * for this application.
527  */
528 static int get_prn(int count) {
529         count = count * 1103515245 + 12345;
530         return ((unsigned)(count/65536) % PRN_MODULO);
533 /*
534  * Custom integer square root from
535  * http://en.wikipedia.org/wiki/Integer_square_root
536  */
537 static int sqrti(int val)
539         float d, x = val;
541         if (val == 0)
542                 return 0;
544         do {
545                 float y = (x + (float)val / x) / 2;
546                 d = (y > x) ? y - x : x - y;
547                 x = y;
548         } while (d >= 0.5);
550         return (int)x;
553 static struct commit_list *skip_away(struct commit_list *list, int count)
555         struct commit_list *cur, *previous;
556         int prn, index, i;
558         prn = get_prn(count);
559         index = (count * prn / PRN_MODULO) * sqrti(prn) / sqrti(PRN_MODULO);
561         cur = list;
562         previous = NULL;
564         for (i = 0; cur; cur = cur->next, i++) {
565                 if (i == index) {
566                         if (hashcmp(cur->item->object.sha1, current_bad_sha1))
567                                 return cur;
568                         if (previous)
569                                 return previous;
570                         return list;
571                 }
572                 previous = cur;
573         }
575         return list;
578 static struct commit_list *managed_skipped(struct commit_list *list,
579                                            struct commit_list **tried)
581         int count, skipped_first;
583         *tried = NULL;
585         if (!skipped_revs.nr)
586                 return list;
588         list = filter_skipped(list, tried, 0, &count, &skipped_first);
590         if (!skipped_first)
591                 return list;
593         return skip_away(list, count);
596 static void bisect_rev_setup(struct rev_info *revs, const char *prefix,
597                              const char *bad_format, const char *good_format,
598                              int read_paths)
600         struct argv_array rev_argv = ARGV_ARRAY_INIT;
601         int i;
603         init_revisions(revs, prefix);
604         revs->abbrev = 0;
605         revs->commit_format = CMIT_FMT_UNSPECIFIED;
607         /* rev_argv.argv[0] will be ignored by setup_revisions */
608         argv_array_push(&rev_argv, "bisect_rev_setup");
609         argv_array_pushf(&rev_argv, bad_format, sha1_to_hex(current_bad_sha1));
610         for (i = 0; i < good_revs.nr; i++)
611                 argv_array_pushf(&rev_argv, good_format,
612                                  sha1_to_hex(good_revs.sha1[i]));
613         argv_array_push(&rev_argv, "--");
614         if (read_paths)
615                 read_bisect_paths(&rev_argv);
617         setup_revisions(rev_argv.argc, rev_argv.argv, revs, NULL);
618         /* XXX leak rev_argv, as "revs" may still be pointing to it */
621 static void bisect_common(struct rev_info *revs)
623         if (prepare_revision_walk(revs))
624                 die("revision walk setup failed");
625         if (revs->tree_objects)
626                 mark_edges_uninteresting(revs->commits, revs, NULL);
629 static void exit_if_skipped_commits(struct commit_list *tried,
630                                     const unsigned char *bad)
632         if (!tried)
633                 return;
635         printf("There are only 'skip'ped commits left to test.\n"
636                "The first bad commit could be any of:\n");
637         print_commit_list(tried, "%s\n", "%s\n");
638         if (bad)
639                 printf("%s\n", sha1_to_hex(bad));
640         printf("We cannot bisect more!\n");
641         exit(2);
644 static int is_expected_rev(const unsigned char *sha1)
646         const char *filename = git_path("BISECT_EXPECTED_REV");
647         struct stat st;
648         struct strbuf str = STRBUF_INIT;
649         FILE *fp;
650         int res = 0;
652         if (stat(filename, &st) || !S_ISREG(st.st_mode))
653                 return 0;
655         fp = fopen(filename, "r");
656         if (!fp)
657                 return 0;
659         if (strbuf_getline(&str, fp, '\n') != EOF)
660                 res = !strcmp(str.buf, sha1_to_hex(sha1));
662         strbuf_release(&str);
663         fclose(fp);
665         return res;
668 static void mark_expected_rev(char *bisect_rev_hex)
670         int len = strlen(bisect_rev_hex);
671         const char *filename = git_path("BISECT_EXPECTED_REV");
672         int fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
674         if (fd < 0)
675                 die_errno("could not create file '%s'", filename);
677         bisect_rev_hex[len] = '\n';
678         write_or_die(fd, bisect_rev_hex, len + 1);
679         bisect_rev_hex[len] = '\0';
681         if (close(fd) < 0)
682                 die("closing file %s: %s", filename, strerror(errno));
685 static int bisect_checkout(char *bisect_rev_hex, int no_checkout)
687         int res;
689         mark_expected_rev(bisect_rev_hex);
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                 res = run_command_v_opt(argv_checkout, RUN_GIT_CMD);
699                 if (res)
700                         exit(res);
701         }
703         argv_show_branch[1] = bisect_rev_hex;
704         return run_command_v_opt(argv_show_branch, RUN_GIT_CMD);
707 static struct commit *get_commit_reference(const unsigned char *sha1)
709         struct commit *r = lookup_commit_reference(sha1);
710         if (!r)
711                 die("Not a valid commit name %s", sha1_to_hex(sha1));
712         return r;
715 static struct commit **get_bad_and_good_commits(int *rev_nr)
717         int len = 1 + good_revs.nr;
718         struct commit **rev = xmalloc(len * sizeof(*rev));
719         int i, n = 0;
721         rev[n++] = get_commit_reference(current_bad_sha1);
722         for (i = 0; i < good_revs.nr; i++)
723                 rev[n++] = get_commit_reference(good_revs.sha1[i]);
724         *rev_nr = n;
726         return rev;
729 static void handle_bad_merge_base(void)
731         if (is_expected_rev(current_bad_sha1)) {
732                 char *bad_hex = sha1_to_hex(current_bad_sha1);
733                 char *good_hex = join_sha1_array_hex(&good_revs, ' ');
735                 fprintf(stderr, "The merge base %s is bad.\n"
736                         "This means the bug has been fixed "
737                         "between %s and [%s].\n",
738                         bad_hex, bad_hex, good_hex);
740                 exit(3);
741         }
743         fprintf(stderr, "Some good revs are not ancestor of the bad rev.\n"
744                 "git bisect cannot work properly in this case.\n"
745                 "Maybe you mistake good and bad revs?\n");
746         exit(1);
749 static void handle_skipped_merge_base(const unsigned char *mb)
751         char *mb_hex = sha1_to_hex(mb);
752         char *bad_hex = sha1_to_hex(current_bad_sha1);
753         char *good_hex = join_sha1_array_hex(&good_revs, ' ');
755         warning("the merge base between %s and [%s] "
756                 "must be skipped.\n"
757                 "So we cannot be sure the first bad commit is "
758                 "between %s and %s.\n"
759                 "We continue anyway.",
760                 bad_hex, good_hex, mb_hex, bad_hex);
761         free(good_hex);
764 /*
765  * "check_merge_bases" checks that merge bases are not "bad".
766  *
767  * - If one is "bad", it means the user assumed something wrong
768  * and we must exit with a non 0 error code.
769  * - If one is "good", that's good, we have nothing to do.
770  * - If one is "skipped", we can't know but we should warn.
771  * - If we don't know, we should check it out and ask the user to test.
772  */
773 static void check_merge_bases(int no_checkout)
775         struct commit_list *result;
776         int rev_nr;
777         struct commit **rev = get_bad_and_good_commits(&rev_nr);
779         result = get_merge_bases_many(rev[0], rev_nr - 1, rev + 1, 0);
781         for (; result; result = result->next) {
782                 const unsigned char *mb = result->item->object.sha1;
783                 if (!hashcmp(mb, current_bad_sha1)) {
784                         handle_bad_merge_base();
785                 } else if (0 <= sha1_array_lookup(&good_revs, mb)) {
786                         continue;
787                 } else if (0 <= sha1_array_lookup(&skipped_revs, mb)) {
788                         handle_skipped_merge_base(mb);
789                 } else {
790                         printf("Bisecting: a merge base must be tested\n");
791                         exit(bisect_checkout(sha1_to_hex(mb), no_checkout));
792                 }
793         }
795         free(rev);
796         free_commit_list(result);
799 static int check_ancestors(const char *prefix)
801         struct rev_info revs;
802         struct object_array pending_copy;
803         int i, res;
805         bisect_rev_setup(&revs, prefix, "^%s", "%s", 0);
807         /* Save pending objects, so they can be cleaned up later. */
808         memset(&pending_copy, 0, sizeof(pending_copy));
809         for (i = 0; i < revs.pending.nr; i++)
810                 add_object_array(revs.pending.objects[i].item,
811                                  revs.pending.objects[i].name,
812                                  &pending_copy);
814         bisect_common(&revs);
815         res = (revs.commits != NULL);
817         /* Clean up objects used, as they will be reused. */
818         for (i = 0; i < pending_copy.nr; i++) {
819                 struct object *o = pending_copy.objects[i].item;
820                 clear_commit_marks((struct commit *)o, ALL_REV_FLAGS);
821         }
823         return res;
826 /*
827  * "check_good_are_ancestors_of_bad" checks that all "good" revs are
828  * ancestor of the "bad" rev.
829  *
830  * If that's not the case, we need to check the merge bases.
831  * If a merge base must be tested by the user, its source code will be
832  * checked out to be tested by the user and we will exit.
833  */
834 static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
836         const char *filename = git_path("BISECT_ANCESTORS_OK");
837         struct stat st;
838         int fd;
840         if (!current_bad_sha1)
841                 die("a bad revision is needed");
843         /* Check if file BISECT_ANCESTORS_OK exists. */
844         if (!stat(filename, &st) && S_ISREG(st.st_mode))
845                 return;
847         /* Bisecting with no good rev is ok. */
848         if (good_revs.nr == 0)
849                 return;
851         /* Check if all good revs are ancestor of the bad rev. */
852         if (check_ancestors(prefix))
853                 check_merge_bases(no_checkout);
855         /* Create file BISECT_ANCESTORS_OK. */
856         fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
857         if (fd < 0)
858                 warning("could not create file '%s': %s",
859                         filename, strerror(errno));
860         else
861                 close(fd);
864 /*
865  * This does "git diff-tree --pretty COMMIT" without one fork+exec.
866  */
867 static void show_diff_tree(const char *prefix, struct commit *commit)
869         struct rev_info opt;
871         /* diff-tree init */
872         init_revisions(&opt, prefix);
873         git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
874         opt.abbrev = 0;
875         opt.diff = 1;
877         /* This is what "--pretty" does */
878         opt.verbose_header = 1;
879         opt.use_terminator = 0;
880         opt.commit_format = CMIT_FMT_DEFAULT;
882         /* diff-tree init */
883         if (!opt.diffopt.output_format)
884                 opt.diffopt.output_format = DIFF_FORMAT_RAW;
886         log_tree_commit(&opt, commit);
889 /*
890  * We use the convention that exiting with an exit code 10 means that
891  * the bisection process finished successfully.
892  * In this case the calling shell script should exit 0.
893  *
894  * If no_checkout is non-zero, the bisection process does not
895  * checkout the trial commit but instead simply updates BISECT_HEAD.
896  */
897 int bisect_next_all(const char *prefix, int no_checkout)
899         struct rev_info revs;
900         struct commit_list *tried;
901         int reaches = 0, all = 0, nr, steps;
902         const unsigned char *bisect_rev;
903         char bisect_rev_hex[41];
905         if (read_bisect_refs())
906                 die("reading bisect refs failed");
908         check_good_are_ancestors_of_bad(prefix, no_checkout);
910         bisect_rev_setup(&revs, prefix, "%s", "^%s", 1);
911         revs.limited = 1;
913         bisect_common(&revs);
915         revs.commits = find_bisection(revs.commits, &reaches, &all,
916                                        !!skipped_revs.nr);
917         revs.commits = managed_skipped(revs.commits, &tried);
919         if (!revs.commits) {
920                 /*
921                  * We should exit here only if the "bad"
922                  * commit is also a "skip" commit.
923                  */
924                 exit_if_skipped_commits(tried, NULL);
926                 printf("%s was both good and bad\n",
927                        sha1_to_hex(current_bad_sha1));
928                 exit(1);
929         }
931         if (!all) {
932                 fprintf(stderr, "No testable commit found.\n"
933                         "Maybe you started with bad path parameters?\n");
934                 exit(4);
935         }
937         bisect_rev = revs.commits->item->object.sha1;
938         memcpy(bisect_rev_hex, sha1_to_hex(bisect_rev), 41);
940         if (!hashcmp(bisect_rev, current_bad_sha1)) {
941                 exit_if_skipped_commits(tried, current_bad_sha1);
942                 printf("%s is the first bad commit\n", bisect_rev_hex);
943                 show_diff_tree(prefix, revs.commits->item);
944                 /* This means the bisection process succeeded. */
945                 exit(10);
946         }
948         nr = all - reaches - 1;
949         steps = estimate_bisect_steps(all);
950         printf("Bisecting: %d revision%s left to test after this "
951                "(roughly %d step%s)\n", nr, (nr == 1 ? "" : "s"),
952                steps, (steps == 1 ? "" : "s"));
954         return bisect_checkout(bisect_rev_hex, no_checkout);