git/bisect.c

#include "cache.h"
#include "config.h"
#include "commit.h"
#include "diff.h"
#include "revision.h"
#include "refs.h"
#include "list-objects.h"
#include "quote.h"
#include "hash-lookup.h"
#include "run-command.h"
#include "log-tree.h"
#include "bisect.h"
#include "oid-array.h"
#include "strvec.h"
#include "commit-slab.h"
#include "commit-reach.h"
#include "object-store.h"
#include "dir.h"

static struct oid_array good_revs;
static struct oid_array skipped_revs;

static struct object_id *current_bad_oid;

static const char *argv_checkout[] = {"checkout", "-q", NULL, "--", NULL};

static const char *term_bad;
static const char *term_good;

/* Remember to update object flag allocation in object.h */
#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_commit_slab(commit_weight, int *);
static struct commit_weight commit_weight;

#define DEBUG_BISECT 0

static inline int weight(struct commit_list *elem)
{
	return **commit_weight_at(&commit_weight, elem->item);
}

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

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

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

static inline int approx_halfway(struct commit_list *p, int nr)
{
	int diff;

	/*
	 * Don't short-cut something we are not going to return!
	 */
	if (p->item->object.flags & TREESAME)
		return 0;
	if (DEBUG_BISECT)
		return 0;
	/*
	 * For small number of commits 2 and 3 are halfway of 5, and
	 * 3 is halfway of 6 but 2 and 4 are not.
	 */
	diff = 2 * weight(p) - nr;
	switch (diff) {
	case -1: case 0: case 1:
		return 1;
	default:
		/*
		 * For large number of commits we are not so strict, it's
		 * good enough if it's within ~0.1% of the halfway point,
		 * e.g. 5000 is exactly halfway of 10000, but we consider
		 * the values [4996, 5004] as halfway as well.
		 */
		if (abs(diff) < nr / 1024)
			return 1;
		return 0;
	}
}

static void show_list(const char *debug, int counted, int nr,
		      struct commit_list *list)
{
	struct commit_list *p;

	if (!DEBUG_BISECT)
		return;

	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 commit_flags = commit->object.flags;
		enum object_type type;
		unsigned long size;
		char *buf = read_object_file(&commit->object.oid, &type,
					     &size);
		const char *subject_start;
		int subject_len;

		fprintf(stderr, "%c%c%c ",
			(commit_flags & TREESAME) ? ' ' : 'T',
			(commit_flags & UNINTERESTING) ? 'U' : ' ',
			(commit_flags & COUNTED) ? 'C' : ' ');
		if (*commit_weight_at(&commit_weight, p->item))
			fprintf(stderr, "%3d", weight(p));
		else
			fprintf(stderr, "---");
		fprintf(stderr, " %.*s", 8, oid_to_hex(&commit->object.oid));
		for (pp = commit->parents; pp; pp = pp->next)
			fprintf(stderr, " %.*s", 8,
				oid_to_hex(&pp->item->object.oid));

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

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 commit_flags = p->item->object.flags;

		if (commit_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 oidcmp(&a->commit->object.oid, &b->commit->object.oid);
}

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));
	struct strbuf buf = STRBUF_INIT;
	int cnt, i;

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

		if (commit_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, compare_commit_dist);
	for (p = list, i = 0; i < cnt; i++) {
		struct object *obj = &(array[i].commit->object);

		strbuf_reset(&buf);
		strbuf_addf(&buf, "dist=%d", array[i].distance);
		add_name_decoration(DECORATION_NONE, buf.buf, obj);

		p->item = array[i].commit;
		if (i < cnt - 1)
			p = p->next;
	}
	if (p) {
		free_commit_list(p->next);
		p->next = NULL;
	}
	strbuf_release(&buf);
	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,
					     unsigned bisect_flags)
{
	int n, counted;
	struct commit_list *p;

	counted = 0;

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

		*commit_weight_at(&commit_weight, p->item) = &weights[n++];
		switch (count_interesting_parents(commit, bisect_flags)) {
		case 0:
			if (!(commit_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;
		if (bisect_flags & FIND_BISECTION_FIRST_PARENT_ONLY)
			BUG("shouldn't be calling count-distance in fp mode");
		weight_set(p, count_distance(p));
		clear_distance(list);

		/* Does it happen to be at half-way? */
		if (!(bisect_flags & FIND_BISECTION_ALL) &&
		      approx_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 commit_flags = p->item->object.flags;

			if (0 <= weight(p))
				continue;

			for (q = p->item->parents;
			     q;
			     q = bisect_flags & FIND_BISECTION_FIRST_PARENT_ONLY ? NULL : 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 (!(commit_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 half-way? */
			if (!(bisect_flags & FIND_BISECTION_ALL) &&
			      approx_halfway(p, nr))
				return p;
		}
	}

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

	if (!(bisect_flags & FIND_BISECTION_ALL))
		return best_bisection(list, nr);
	else
		return best_bisection_sorted(list, nr);
}

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

	show_list("bisection 2 entry", 0, 0, *commit_list);
	init_commit_weight(&commit_weight);

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

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

	*all = nr;
	CALLOC_ARRAY(weights, on_list);

	/* Do the real work of finding bisection commit. */
	best = do_find_bisection(list, nr, weights, bisect_flags);
	if (best) {
		if (!(bisect_flags & FIND_BISECTION_ALL)) {
			list->item = best->item;
			free_commit_list(list->next);
			best = list;
			best->next = NULL;
		}
		*reaches = weight(best);
	}
	free(weights);
	*commit_list = best;
	clear_commit_weight(&commit_weight);
}

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

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

	strbuf_release(&good_prefix);

	return 0;
}

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

static GIT_PATH_FUNC(git_path_bisect_names, "BISECT_NAMES")
static GIT_PATH_FUNC(git_path_bisect_expected_rev, "BISECT_EXPECTED_REV")
static GIT_PATH_FUNC(git_path_bisect_ancestors_ok, "BISECT_ANCESTORS_OK")
static GIT_PATH_FUNC(git_path_bisect_run, "BISECT_RUN")
static GIT_PATH_FUNC(git_path_bisect_start, "BISECT_START")
static GIT_PATH_FUNC(git_path_bisect_log, "BISECT_LOG")
static GIT_PATH_FUNC(git_path_bisect_terms, "BISECT_TERMS")
static GIT_PATH_FUNC(git_path_bisect_first_parent, "BISECT_FIRST_PARENT")
static GIT_PATH_FUNC(git_path_head_name, "head-name")

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

	while (strbuf_getline_lf(&str, fp) != EOF) {
		strbuf_trim(&str);
		if (sq_dequote_to_strvec(str.buf, array))
			die(_("Badly quoted content in file '%s': %s"),
			    filename, str.buf);
	}

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

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

	for (i = 0; i < array->nr; i++) {
		strbuf_addstr(&joined_hexs, oid_to_hex(array->oid + i));
		if (i + 1 < array->nr)
			strbuf_addch(&joined_hexs, delim);
	}

	return strbuf_detach(&joined_hexs, NULL);
}

/*
 * 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.
 */
struct commit_list *filter_skipped(struct commit_list *list,
				   struct commit_list **tried,
				   int show_all,
				   int *count,
				   int *skipped_first)
{
	struct commit_list *filtered = NULL, **f = &filtered;

	*tried = NULL;

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

	if (!skipped_revs.nr)
		return list;

	while (list) {
		struct commit_list *next = list->next;
		list->next = NULL;
		if (0 <= oid_array_lookup(&skipped_revs, &list->item->object.oid)) {
			if (skipped_first && !*skipped_first)
				*skipped_first = 1;
			/* Move current to tried list */
			*tried = list;
			tried = &list->next;
		} else {
			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;
			}
			/* Move current to filtered list */
			*f = list;
			f = &list->next;
			if (count)
				(*count)++;
		}
		list = next;
	}

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

	return filtered;
}

#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.
 */
static unsigned get_prn(unsigned count)
{
	count = count * 1103515245 + 12345;
	return (count/65536) % PRN_MODULO;
}

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

	if (!val)
		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)
{
	struct commit_list *cur, *previous;