bisect.c 25.1 KB
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#include "cache.h"
#include "commit.h"
#include "diff.h"
#include "revision.h"
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#include "refs.h"
#include "list-objects.h"
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#include "quote.h"
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#include "sha1-lookup.h"
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#include "run-command.h"
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#include "log-tree.h"
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#include "bisect.h"
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#include "sha1-array.h"
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#include "argv-array.h"
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static struct sha1_array good_revs;
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static struct sha1_array skipped_revs;
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static struct object_id *current_bad_oid;
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static const char *argv_checkout[] = {"checkout", "-q", NULL, "--", NULL};
static const char *argv_show_branch[] = {"show-branch", NULL, NULL};
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static const char *argv_update_ref[] = {"update-ref", "--no-deref", "BISECT_HEAD", NULL, NULL};
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static const char *term_bad;
static const char *term_good;

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/* Remember to update object flag allocation in object.h */
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#define COUNTED		(1u<<16)

/*
 * This is a truly stupid algorithm, but it's only
 * used for bisection, and we just don't care enough.
 *
 * We care just barely enough to avoid recursing for
 * non-merge entries.
 */
static int count_distance(struct commit_list *entry)
{
	int nr = 0;

	while (entry) {
		struct commit *commit = entry->item;
		struct commit_list *p;

		if (commit->object.flags & (UNINTERESTING | COUNTED))
			break;
		if (!(commit->object.flags & TREESAME))
			nr++;
		commit->object.flags |= COUNTED;
		p = commit->parents;
		entry = p;
		if (p) {
			p = p->next;
			while (p) {
				nr += count_distance(p);
				p = p->next;
			}
		}
	}

	return nr;
}

static void clear_distance(struct commit_list *list)
{
	while (list) {
		struct commit *commit = list->item;
		commit->object.flags &= ~COUNTED;
		list = list->next;
	}
}

#define DEBUG_BISECT 0

static inline int weight(struct commit_list *elem)
{
	return *((int*)(elem->item->util));
}

static inline void weight_set(struct commit_list *elem, int weight)
{
	*((int*)(elem->item->util)) = weight;
}

static int count_interesting_parents(struct commit *commit)
{
	struct commit_list *p;
	int count;

	for (count = 0, p = commit->parents; p; p = p->next) {
		if (p->item->object.flags & UNINTERESTING)
			continue;
		count++;
	}
	return count;
}

static inline int halfway(struct commit_list *p, int nr)
{
	/*
	 * Don't short-cut something we are not going to return!
	 */
	if (p->item->object.flags & TREESAME)
		return 0;
	if (DEBUG_BISECT)
		return 0;
	/*
	 * 2 and 3 are halfway of 5.
	 * 3 is halfway of 6 but 2 and 4 are not.
	 */
	switch (2 * weight(p) - nr) {
	case -1: case 0: case 1:
		return 1;
	default:
		return 0;
	}
}

#if !DEBUG_BISECT
#define show_list(a,b,c,d) do { ; } while (0)
#else
static void show_list(const char *debug, int counted, int nr,
		      struct commit_list *list)
{
	struct commit_list *p;

	fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);

	for (p = list; p; p = p->next) {
		struct commit_list *pp;
		struct commit *commit = p->item;
		unsigned flags = commit->object.flags;
		enum object_type type;
		unsigned long size;
		char *buf = read_sha1_file(commit->object.sha1, &type, &size);
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		const char *subject_start;
		int subject_len;
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		fprintf(stderr, "%c%c%c ",
			(flags & TREESAME) ? ' ' : 'T',
			(flags & UNINTERESTING) ? 'U' : ' ',
			(flags & COUNTED) ? 'C' : ' ');
		if (commit->util)
			fprintf(stderr, "%3d", weight(p));
		else
			fprintf(stderr, "---");
		fprintf(stderr, " %.*s", 8, sha1_to_hex(commit->object.sha1));
		for (pp = commit->parents; pp; pp = pp->next)
			fprintf(stderr, " %.*s", 8,
				sha1_to_hex(pp->item->object.sha1));

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		subject_len = find_commit_subject(buf, &subject_start);
		if (subject_len)
			fprintf(stderr, " %.*s", subject_len, subject_start);
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		fprintf(stderr, "\n");
	}
}
#endif /* DEBUG_BISECT */

static struct commit_list *best_bisection(struct commit_list *list, int nr)
{
	struct commit_list *p, *best;
	int best_distance = -1;

	best = list;
	for (p = list; p; p = p->next) {
		int distance;
		unsigned flags = p->item->object.flags;

		if (flags & TREESAME)
			continue;
		distance = weight(p);
		if (nr - distance < distance)
			distance = nr - distance;
		if (distance > best_distance) {
			best = p;
			best_distance = distance;
		}
	}

	return best;
}

struct commit_dist {
	struct commit *commit;
	int distance;
};

static int compare_commit_dist(const void *a_, const void *b_)
{
	struct commit_dist *a, *b;

	a = (struct commit_dist *)a_;
	b = (struct commit_dist *)b_;
	if (a->distance != b->distance)
		return b->distance - a->distance; /* desc sort */
	return hashcmp(a->commit->object.sha1, b->commit->object.sha1);
}

static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
{
	struct commit_list *p;
	struct commit_dist *array = xcalloc(nr, sizeof(*array));
	int cnt, i;

	for (p = list, cnt = 0; p; p = p->next) {
		int distance;
		unsigned flags = p->item->object.flags;

		if (flags & TREESAME)
			continue;
		distance = weight(p);
		if (nr - distance < distance)
			distance = nr - distance;
		array[cnt].commit = p->item;
		array[cnt].distance = distance;
		cnt++;
	}
	qsort(array, cnt, sizeof(*array), compare_commit_dist);
	for (p = list, i = 0; i < cnt; i++) {
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		char buf[100]; /* enough for dist=%d */
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		struct object *obj = &(array[i].commit->object);

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		snprintf(buf, sizeof(buf), "dist=%d", array[i].distance);
		add_name_decoration(DECORATION_NONE, buf, obj);

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		p->item = array[i].commit;
		p = p->next;
	}
	if (p)
		p->next = NULL;
	free(array);
	return list;
}

/*
 * zero or positive weight is the number of interesting commits it can
 * reach, including itself.  Especially, weight = 0 means it does not
 * reach any tree-changing commits (e.g. just above uninteresting one
 * but traversal is with pathspec).
 *
 * weight = -1 means it has one parent and its distance is yet to
 * be computed.
 *
 * weight = -2 means it has more than one parent and its distance is
 * unknown.  After running count_distance() first, they will get zero
 * or positive distance.
 */
static struct commit_list *do_find_bisection(struct commit_list *list,
					     int nr, int *weights,
					     int find_all)
{
	int n, counted;
	struct commit_list *p;

	counted = 0;

	for (n = 0, p = list; p; p = p->next) {
		struct commit *commit = p->item;
		unsigned flags = commit->object.flags;

		p->item->util = &weights[n++];
		switch (count_interesting_parents(commit)) {
		case 0:
			if (!(flags & TREESAME)) {
				weight_set(p, 1);
				counted++;
				show_list("bisection 2 count one",
					  counted, nr, list);
			}
			/*
			 * otherwise, it is known not to reach any
			 * tree-changing commit and gets weight 0.
			 */
			break;
		case 1:
			weight_set(p, -1);
			break;
		default:
			weight_set(p, -2);
			break;
		}
	}

	show_list("bisection 2 initialize", counted, nr, list);

	/*
	 * If you have only one parent in the resulting set
	 * then you can reach one commit more than that parent
	 * can reach.  So we do not have to run the expensive
	 * count_distance() for single strand of pearls.
	 *
	 * However, if you have more than one parents, you cannot
	 * just add their distance and one for yourself, since
	 * they usually reach the same ancestor and you would
	 * end up counting them twice that way.
	 *
	 * So we will first count distance of merges the usual
	 * way, and then fill the blanks using cheaper algorithm.
	 */
	for (p = list; p; p = p->next) {
		if (p->item->object.flags & UNINTERESTING)
			continue;
		if (weight(p) != -2)
			continue;
		weight_set(p, count_distance(p));
		clear_distance(list);

		/* Does it happen to be at exactly half-way? */
		if (!find_all && halfway(p, nr))
			return p;
		counted++;
	}

	show_list("bisection 2 count_distance", counted, nr, list);

	while (counted < nr) {
		for (p = list; p; p = p->next) {
			struct commit_list *q;
			unsigned flags = p->item->object.flags;

			if (0 <= weight(p))
				continue;
			for (q = p->item->parents; q; q = q->next) {
				if (q->item->object.flags & UNINTERESTING)
					continue;
				if (0 <= weight(q))
					break;
			}
			if (!q)
				continue;

			/*
			 * weight for p is unknown but q is known.
			 * add one for p itself if p is to be counted,
			 * otherwise inherit it from q directly.
			 */
			if (!(flags & TREESAME)) {
				weight_set(p, weight(q)+1);
				counted++;
				show_list("bisection 2 count one",
					  counted, nr, list);
			}
			else
				weight_set(p, weight(q));

			/* Does it happen to be at exactly half-way? */
			if (!find_all && halfway(p, nr))
				return p;
		}
	}

	show_list("bisection 2 counted all", counted, nr, list);

	if (!find_all)
		return best_bisection(list, nr);
	else
		return best_bisection_sorted(list, nr);
}

struct commit_list *find_bisection(struct commit_list *list,
					  int *reaches, int *all,
					  int find_all)
{
	int nr, on_list;
	struct commit_list *p, *best, *next, *last;
	int *weights;

	show_list("bisection 2 entry", 0, 0, list);

	/*
	 * Count the number of total and tree-changing items on the
	 * list, while reversing the list.
	 */
	for (nr = on_list = 0, last = NULL, p = list;
	     p;
	     p = next) {
		unsigned flags = p->item->object.flags;

		next = p->next;
		if (flags & UNINTERESTING)
			continue;
		p->next = last;
		last = p;
		if (!(flags & TREESAME))
			nr++;
		on_list++;
	}
	list = last;
	show_list("bisection 2 sorted", 0, nr, list);

	*all = nr;
	weights = xcalloc(on_list, sizeof(*weights));

	/* Do the real work of finding bisection commit. */
	best = do_find_bisection(list, nr, weights, find_all);
	if (best) {
		if (!find_all)
			best->next = NULL;
		*reaches = weight(best);
	}
	free(weights);
	return best;
}

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static int register_ref(const char *refname, const struct object_id *oid,
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			int flags, void *cb_data)
{
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	struct strbuf good_prefix = STRBUF_INIT;
	strbuf_addstr(&good_prefix, term_good);
	strbuf_addstr(&good_prefix, "-");

	if (!strcmp(refname, term_bad)) {
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		current_bad_oid = xmalloc(sizeof(*current_bad_oid));
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		oidcpy(current_bad_oid, oid);
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	} else if (starts_with(refname, good_prefix.buf)) {
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		sha1_array_append(&good_revs, oid->hash);
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	} else if (starts_with(refname, "skip-")) {
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		sha1_array_append(&skipped_revs, oid->hash);
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	}

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	strbuf_release(&good_prefix);

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	return 0;
}

static int read_bisect_refs(void)
{
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	return for_each_ref_in("refs/bisect/", register_ref, NULL);
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}

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static GIT_PATH_FUNC(git_path_bisect_names, "BISECT_NAMES")
static GIT_PATH_FUNC(git_path_bisect_expected_rev, "BISECT_EXPECTED_REV")

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static void read_bisect_paths(struct argv_array *array)
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{
	struct strbuf str = STRBUF_INIT;
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	const char *filename = git_path_bisect_names();
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	FILE *fp = fopen(filename, "r");

	if (!fp)
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		die_errno("Could not open file '%s'", filename);
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	while (strbuf_getline(&str, fp, '\n') != EOF) {
		strbuf_trim(&str);
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		if (sq_dequote_to_argv_array(str.buf, array))
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			die("Badly quoted content in file '%s': %s",
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			    filename, str.buf);
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	}

	strbuf_release(&str);
	fclose(fp);
}

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static char *join_sha1_array_hex(struct sha1_array *array, char delim)
{
	struct strbuf joined_hexs = STRBUF_INIT;
	int i;

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	for (i = 0; i < array->nr; i++) {
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		strbuf_addstr(&joined_hexs, sha1_to_hex(array->sha1[i]));
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		if (i + 1 < array->nr)
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			strbuf_addch(&joined_hexs, delim);
	}

	return strbuf_detach(&joined_hexs, NULL);
}

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/*
 * In this function, passing a not NULL skipped_first is very special.
 * It means that we want to know if the first commit in the list is
 * skipped because we will want to test a commit away from it if it is
 * indeed skipped.
 * So if the first commit is skipped, we cannot take the shortcut to
 * just "return list" when we find the first non skipped commit, we
 * have to return a fully filtered list.
 *
 * We use (*skipped_first == -1) to mean "it has been found that the
 * first commit is not skipped". In this case *skipped_first is set back
 * to 0 just before the function returns.
 */
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struct commit_list *filter_skipped(struct commit_list *list,
				   struct commit_list **tried,
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				   int show_all,
				   int *count,
				   int *skipped_first)
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{
	struct commit_list *filtered = NULL, **f = &filtered;

	*tried = NULL;

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	if (skipped_first)
		*skipped_first = 0;
	if (count)
		*count = 0;

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	if (!skipped_revs.nr)
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		return list;

	while (list) {
		struct commit_list *next = list->next;
		list->next = NULL;
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		if (0 <= sha1_array_lookup(&skipped_revs,
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					   list->item->object.sha1)) {
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			if (skipped_first && !*skipped_first)
				*skipped_first = 1;
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			/* Move current to tried list */
			*tried = list;
			tried = &list->next;
		} else {
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			if (!show_all) {
				if (!skipped_first || !*skipped_first)
					return list;
			} else if (skipped_first && !*skipped_first) {
				/* This means we know it's not skipped */
				*skipped_first = -1;
			}
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			/* Move current to filtered list */
			*f = list;
			f = &list->next;
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			if (count)
				(*count)++;
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		}
		list = next;
	}

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	if (skipped_first && *skipped_first == -1)
		*skipped_first = 0;

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	return filtered;
}
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#define PRN_MODULO 32768

/*
 * This is a pseudo random number generator based on "man 3 rand".
 * It is not used properly because the seed is the argument and it
 * is increased by one between each call, but that should not matter
 * for this application.
 */
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static unsigned get_prn(unsigned count) {
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	count = count * 1103515245 + 12345;
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	return (count/65536) % PRN_MODULO;
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}

/*
 * Custom integer square root from
 * http://en.wikipedia.org/wiki/Integer_square_root
 */
static int sqrti(int val)
{
	float d, x = val;

	if (val == 0)
		return 0;

	do {
		float y = (x + (float)val / x) / 2;
		d = (y > x) ? y - x : x - y;
		x = y;
	} while (d >= 0.5);

	return (int)x;
}

static struct commit_list *skip_away(struct commit_list *list, int count)
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{
	struct commit_list *cur, *previous;
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	int prn, index, i;

	prn = get_prn(count);
	index = (count * prn / PRN_MODULO) * sqrti(prn) / sqrti(PRN_MODULO);
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	cur = list;
	previous = NULL;

	for (i = 0; cur; cur = cur->next, i++) {
		if (i == index) {
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			if (hashcmp(cur->item->object.sha1, current_bad_oid->hash))
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				return cur;
			if (previous)
				return previous;
			return list;
		}
		previous = cur;
	}

	return list;
}

static struct commit_list *managed_skipped(struct commit_list *list,
					   struct commit_list **tried)
{
	int count, skipped_first;

	*tried = NULL;

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	if (!skipped_revs.nr)
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		return list;

	list = filter_skipped(list, tried, 0, &count, &skipped_first);

	if (!skipped_first)
		return list;

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	return skip_away(list, count);
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}

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static void bisect_rev_setup(struct rev_info *revs, const char *prefix,
			     const char *bad_format, const char *good_format,
			     int read_paths)
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{
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	struct argv_array rev_argv = ARGV_ARRAY_INIT;
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	int i;

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	init_revisions(revs, prefix);
	revs->abbrev = 0;
	revs->commit_format = CMIT_FMT_UNSPECIFIED;
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	/* rev_argv.argv[0] will be ignored by setup_revisions */
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	argv_array_push(&rev_argv, "bisect_rev_setup");
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	argv_array_pushf(&rev_argv, bad_format, oid_to_hex(current_bad_oid));
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	for (i = 0; i < good_revs.nr; i++)
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		argv_array_pushf(&rev_argv, good_format,
				 sha1_to_hex(good_revs.sha1[i]));
	argv_array_push(&rev_argv, "--");
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	if (read_paths)
		read_bisect_paths(&rev_argv);
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	setup_revisions(rev_argv.argc, rev_argv.argv, revs, NULL);
	/* XXX leak rev_argv, as "revs" may still be pointing to it */
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}

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static void bisect_common(struct rev_info *revs)
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{
	if (prepare_revision_walk(revs))
		die("revision walk setup failed");
	if (revs->tree_objects)
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		mark_edges_uninteresting(revs, NULL);
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}

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static void exit_if_skipped_commits(struct commit_list *tried,
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				    const struct object_id *bad)
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{
	if (!tried)
		return;

	printf("There are only 'skip'ped commits left to test.\n"
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	       "The first %s commit could be any of:\n", term_bad);
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	print_commit_list(tried, "%s\n", "%s\n");
	if (bad)
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		printf("%s\n", oid_to_hex(bad));
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	printf("We cannot bisect more!\n");
	exit(2);
}

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static int is_expected_rev(const struct object_id *oid)
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{
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	const char *filename = git_path_bisect_expected_rev();
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	struct stat st;
	struct strbuf str = STRBUF_INIT;
	FILE *fp;
	int res = 0;

	if (stat(filename, &st) || !S_ISREG(st.st_mode))
		return 0;

	fp = fopen(filename, "r");
	if (!fp)
		return 0;

	if (strbuf_getline(&str, fp, '\n') != EOF)
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		res = !strcmp(str.buf, oid_to_hex(oid));
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	strbuf_release(&str);
	fclose(fp);

	return res;
}

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static void mark_expected_rev(char *bisect_rev_hex)
{
	int len = strlen(bisect_rev_hex);
	const char *filename = git_path("BISECT_EXPECTED_REV");
	int fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);

	if (fd < 0)
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		die_errno("could not create file '%s'", filename);
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	bisect_rev_hex[len] = '\n';
	write_or_die(fd, bisect_rev_hex, len + 1);
	bisect_rev_hex[len] = '\0';

	if (close(fd) < 0)
		die("closing file %s: %s", filename, strerror(errno));
}

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static int bisect_checkout(char *bisect_rev_hex, int no_checkout)
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{

	mark_expected_rev(bisect_rev_hex);

	argv_checkout[2] = bisect_rev_hex;
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	if (no_checkout) {
		argv_update_ref[3] = bisect_rev_hex;
		if (run_command_v_opt(argv_update_ref, RUN_GIT_CMD))
			die("update-ref --no-deref HEAD failed on %s",
			    bisect_rev_hex);
	} else {
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		int res;
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		res = run_command_v_opt(argv_checkout, RUN_GIT_CMD);
		if (res)
			exit(res);
	}
715 716 717 718 719

	argv_show_branch[1] = bisect_rev_hex;
	return run_command_v_opt(argv_show_branch, RUN_GIT_CMD);
}

720 721 722 723 724 725 726 727 728 729
static struct commit *get_commit_reference(const unsigned char *sha1)
{
	struct commit *r = lookup_commit_reference(sha1);
	if (!r)
		die("Not a valid commit name %s", sha1_to_hex(sha1));
	return r;
}

static struct commit **get_bad_and_good_commits(int *rev_nr)
{
730
	int len = 1 + good_revs.nr;
731 732 733
	struct commit **rev = xmalloc(len * sizeof(*rev));
	int i, n = 0;

734
	rev[n++] = get_commit_reference(current_bad_oid->hash);
735
	for (i = 0; i < good_revs.nr; i++)
736 737 738 739 740 741 742 743
		rev[n++] = get_commit_reference(good_revs.sha1[i]);
	*rev_nr = n;

	return rev;
}

static void handle_bad_merge_base(void)
{
744 745
	if (is_expected_rev(current_bad_oid)) {
		char *bad_hex = oid_to_hex(current_bad_oid);
746
		char *good_hex = join_sha1_array_hex(&good_revs, ' ');
747 748 749 750 751 752 753 754 755 756 757
		if (!strcmp(term_bad, "bad") && !strcmp(term_good, "good")) {
			fprintf(stderr, "The merge base %s is bad.\n"
				"This means the bug has been fixed "
				"between %s and [%s].\n",
				bad_hex, bad_hex, good_hex);
		} else {
			fprintf(stderr, "The merge base %s is %s.\n"
				"This means the first '%s' commit is "
				"between %s and [%s].\n",
				bad_hex, term_bad, term_good, bad_hex, good_hex);
		}
758 759 760
		exit(3);
	}

761
	fprintf(stderr, "Some %s revs are not ancestor of the %s rev.\n"
762
		"git bisect cannot work properly in this case.\n"
763 764
		"Maybe you mistook %s and %s revs?\n",
		term_good, term_bad, term_good, term_bad);
765 766 767
	exit(1);
}

768
static void handle_skipped_merge_base(const unsigned char *mb)
769 770
{
	char *mb_hex = sha1_to_hex(mb);
771
	char *bad_hex = sha1_to_hex(current_bad_oid->hash);
772 773
	char *good_hex = join_sha1_array_hex(&good_revs, ' ');

774
	warning("the merge base between %s and [%s] "
775
		"must be skipped.\n"
776
		"So we cannot be sure the first %s commit is "
777
		"between %s and %s.\n"
778
		"We continue anyway.",
779
		bad_hex, good_hex, term_bad, mb_hex, bad_hex);
780 781 782 783 784 785 786 787 788 789 790 791
	free(good_hex);
}

/*
 * "check_merge_bases" checks that merge bases are not "bad".
 *
 * - If one is "bad", it means the user assumed something wrong
 * and we must exit with a non 0 error code.
 * - If one is "good", that's good, we have nothing to do.
 * - If one is "skipped", we can't know but we should warn.
 * - If we don't know, we should check it out and ask the user to test.
 */
792
static void check_merge_bases(int no_checkout)
793 794 795 796 797
{
	struct commit_list *result;
	int rev_nr;
	struct commit **rev = get_bad_and_good_commits(&rev_nr);

798
	result = get_merge_bases_many(rev[0], rev_nr - 1, rev + 1);
799 800 801

	for (; result; result = result->next) {
		const unsigned char *mb = result->item->object.sha1;
802
		if (!hashcmp(mb, current_bad_oid->hash)) {
803
			handle_bad_merge_base();
804
		} else if (0 <= sha1_array_lookup(&good_revs, mb)) {
805
			continue;
806
		} else if (0 <= sha1_array_lookup(&skipped_revs, mb)) {
807 808 809
			handle_skipped_merge_base(mb);
		} else {
			printf("Bisecting: a merge base must be tested\n");
810
			exit(bisect_checkout(sha1_to_hex(mb), no_checkout));
811 812 813 814 815 816 817
		}
	}

	free(rev);
	free_commit_list(result);
}

818
static int check_ancestors(const char *prefix)
819
{
820 821
	struct rev_info revs;
	struct object_array pending_copy;
822
	int res;
823

824
	bisect_rev_setup(&revs, prefix, "^%s", "%s", 0);
825

826
	/* Save pending objects, so they can be cleaned up later. */
827 828
	pending_copy = revs.pending;
	revs.leak_pending = 1;
829

830 831 832 833 834
	/*
	 * bisect_common calls prepare_revision_walk right away, which
	 * (together with .leak_pending = 1) makes us the sole owner of
	 * the list of pending objects.
	 */
835 836 837 838
	bisect_common(&revs);
	res = (revs.commits != NULL);

	/* Clean up objects used, as they will be reused. */
839
	clear_commit_marks_for_object_array(&pending_copy, ALL_REV_FLAGS);
840
	free(pending_copy.objects);
841

842
	return res;
843 844 845 846 847 848 849 850 851 852
}

/*
 * "check_good_are_ancestors_of_bad" checks that all "good" revs are
 * ancestor of the "bad" rev.
 *
 * If that's not the case, we need to check the merge bases.
 * If a merge base must be tested by the user, its source code will be
 * checked out to be tested by the user and we will exit.
 */
853
static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
854
{
855
	char *filename = git_pathdup("BISECT_ANCESTORS_OK");
856 857 858
	struct stat st;
	int fd;

859
	if (!current_bad_oid)
860
		die("a %s revision is needed", term_bad);
861 862 863

	/* Check if file BISECT_ANCESTORS_OK exists. */
	if (!stat(filename, &st) && S_ISREG(st.st_mode))
864
		goto done;
865 866

	/* Bisecting with no good rev is ok. */
867
	if (good_revs.nr == 0)
868
		goto done;
869

870 871
	/* Check if all good revs are ancestor of the bad rev. */
	if (check_ancestors(prefix))
872
		check_merge_bases(no_checkout);
873 874 875 876 877 878 879 880

	/* Create file BISECT_ANCESTORS_OK. */
	fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY, 0600);
	if (fd < 0)
		warning("could not create file '%s': %s",
			filename, strerror(errno));
	else
		close(fd);
881 882
 done:
	free(filename);
883 884
}

885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909
/*
 * This does "git diff-tree --pretty COMMIT" without one fork+exec.
 */
static void show_diff_tree(const char *prefix, struct commit *commit)
{
	struct rev_info opt;

	/* diff-tree init */
	init_revisions(&opt, prefix);
	git_config(git_diff_basic_config, NULL); /* no "diff" UI options */
	opt.abbrev = 0;
	opt.diff = 1;

	/* This is what "--pretty" does */
	opt.verbose_header = 1;
	opt.use_terminator = 0;
	opt.commit_format = CMIT_FMT_DEFAULT;

	/* diff-tree init */
	if (!opt.diffopt.output_format)
		opt.diffopt.output_format = DIFF_FORMAT_RAW;

	log_tree_commit(&opt, commit);
}

910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939
/*
 * The terms used for this bisect session are stored in BISECT_TERMS.
 * We read them and store them to adapt the messages accordingly.
 * Default is bad/good.
 */
void read_bisect_terms(const char **read_bad, const char **read_good)
{
	struct strbuf str = STRBUF_INIT;
	const char *filename = git_path("BISECT_TERMS");
	FILE *fp = fopen(filename, "r");

	if (!fp) {
		if (errno == ENOENT) {
			*read_bad = "bad";
			*read_good = "good";
			return;
		} else {
			die("could not read file '%s': %s", filename,
				strerror(errno));
		}
	} else {
		strbuf_getline(&str, fp, '\n');
		*read_bad = strbuf_detach(&str, NULL);
		strbuf_getline(&str, fp, '\n');
		*read_good = strbuf_detach(&str, NULL);
	}
	strbuf_release(&str);
	fclose(fp);
}

940 941 942 943
/*
 * We use the convention that exiting with an exit code 10 means that
 * the bisection process finished successfully.
 * In this case the calling shell script should exit 0.
944 945 946
 *
 * If no_checkout is non-zero, the bisection process does not
 * checkout the trial commit but instead simply updates BISECT_HEAD.
947
 */
948
int bisect_next_all(const char *prefix, int no_checkout)
949 950 951
{
	struct rev_info revs;
	struct commit_list *tried;
952
	int reaches = 0, all = 0, nr, steps;
953
	const unsigned char *bisect_rev;
954
	char bisect_rev_hex[GIT_SHA1_HEXSZ + 1];
955

956
	read_bisect_terms(&term_bad, &term_good);
957 958 959
	if (read_bisect_refs())
		die("reading bisect refs failed");

960
	check_good_are_ancestors_of_bad(prefix, no_checkout);
961

962 963
	bisect_rev_setup(&revs, prefix, "%s", "^%s", 1);
	revs.limited = 1;
964

965
	bisect_common(&revs);
966

967
	revs.commits = find_bisection(revs.commits, &reaches, &all,
968
				       !!skipped_revs.nr);
969
	revs.commits = managed_skipped(revs.commits, &tried);
970 971 972 973 974 975 976 977

	if (!revs.commits) {
		/*
		 * We should exit here only if the "bad"
		 * commit is also a "skip" commit.
		 */
		exit_if_skipped_commits(tried, NULL);

978 979 980 981
		printf("%s was both %s and %s\n",
		       oid_to_hex(current_bad_oid),
		       term_good,
		       term_bad);
982 983 984
		exit(1);
	}

985 986 987 988 989 990
	if (!all) {
		fprintf(stderr, "No testable commit found.\n"
			"Maybe you started with bad path parameters?\n");
		exit(4);
	}

991
	bisect_rev = revs.commits->item->object.sha1;
992
	memcpy(bisect_rev_hex, sha1_to_hex(bisect_rev), GIT_SHA1_HEXSZ + 1);
993

994 995
	if (!hashcmp(bisect_rev, current_bad_oid->hash)) {
		exit_if_skipped_commits(tried, current_bad_oid);
996 997
		printf("%s is the first %s commit\n", bisect_rev_hex,
			term_bad);
998
		show_diff_tree(prefix, revs.commits->item);
999 1000 1001 1002 1003
		/* This means the bisection process succeeded. */
		exit(10);
	}

	nr = all - reaches - 1;
1004 1005 1006 1007
	steps = estimate_bisect_steps(all);
	printf("Bisecting: %d revision%s left to test after this "
	       "(roughly %d step%s)\n", nr, (nr == 1 ? "" : "s"),
	       steps, (steps == 1 ? "" : "s"));
1008

1009
	return bisect_checkout(bisect_rev_hex, no_checkout);
1010 1011
}

1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049
static inline int log2i(int n)
{
	int log2 = 0;

	for (; n > 1; n >>= 1)
		log2++;

	return log2;
}

static inline int exp2i(int n)
{
	return 1 << n;
}

/*
 * Estimate the number of bisect steps left (after the current step)
 *
 * For any x between 0 included and 2^n excluded, the probability for
 * n - 1 steps left looks like:
 *
 * P(2^n + x) == (2^n - x) / (2^n + x)
 *
 * and P(2^n + x) < 0.5 means 2^n < 3x
 */
int estimate_bisect_steps(int all)
{
	int n, x, e;

	if (all < 3)
		return 0;

	n = log2i(all);
	e = exp2i(n);
	x = all - e;

	return (e < 3 * x) ? n : n - 1;
}