git/commit.c

#include "cache.h"
#include "tag.h"
#include "commit.h"

int save_commit_buffer = 1;

struct sort_node
{
	/*
         * the number of children of the associated commit
         * that also occur in the list being sorted.
         */
	unsigned int indegree;

	/*
         * reference to original list item that we will re-use
         * on output.
         */
	struct commit_list * list_item;

};

const char *commit_type = "commit";

struct cmt_fmt_map {
	const char *n;
	size_t cmp_len;
	enum cmit_fmt v;
} cmt_fmts[] = {
	{ "raw",	1,	CMIT_FMT_RAW },
	{ "medium",	1,	CMIT_FMT_MEDIUM },
	{ "short",	1,	CMIT_FMT_SHORT },
	{ "email",	1,	CMIT_FMT_EMAIL },
	{ "full",	5,	CMIT_FMT_FULL },
	{ "fuller",	5,	CMIT_FMT_FULLER },
	{ "oneline",	1,	CMIT_FMT_ONELINE },
};

enum cmit_fmt get_commit_format(const char *arg)
{
	int i;

	if (!arg || !*arg)
		return CMIT_FMT_DEFAULT;
	if (*arg == '=')
		arg++;
	for (i = 0; i < ARRAY_SIZE(cmt_fmts); i++) {
		if (!strncmp(arg, cmt_fmts[i].n, cmt_fmts[i].cmp_len))
			return cmt_fmts[i].v;
	}

	die("invalid --pretty format: %s", arg);
}

static struct commit *check_commit(struct object *obj,
				   const unsigned char *sha1,
				   int quiet)
{
	if (obj->type != TYPE_COMMIT) {
		if (!quiet)
			error("Object %s is a %s, not a commit",
			      sha1_to_hex(sha1), typename(obj->type));
		return NULL;
	}
	return (struct commit *) obj;
}

struct commit *lookup_commit_reference_gently(const unsigned char *sha1,
					      int quiet)
{
	struct object *obj = deref_tag(parse_object(sha1), NULL, 0);

	if (!obj)
		return NULL;
	return check_commit(obj, sha1, quiet);
}

struct commit *lookup_commit_reference(const unsigned char *sha1)
{
	return lookup_commit_reference_gently(sha1, 0);
}

struct commit *lookup_commit(const unsigned char *sha1)
{
	struct object *obj = lookup_object(sha1);
	if (!obj) {
		struct commit *ret = alloc_commit_node();
		created_object(sha1, &ret->object);
		ret->object.type = TYPE_COMMIT;
		return ret;
	}
	if (!obj->type)
		obj->type = TYPE_COMMIT;
	return check_commit(obj, sha1, 0);
}

static unsigned long parse_commit_date(const char *buf)
{
	unsigned long date;

	if (memcmp(buf, "author", 6))
		return 0;
	while (*buf++ != '\n')
		/* nada */;
	if (memcmp(buf, "committer", 9))
		return 0;
	while (*buf++ != '>')
		/* nada */;
	date = strtoul(buf, NULL, 10);
	if (date == ULONG_MAX)
		date = 0;
	return date;
}

static struct commit_graft **commit_graft;
static int commit_graft_alloc, commit_graft_nr;

static int commit_graft_pos(const unsigned char *sha1)
{
	int lo, hi;
	lo = 0;
	hi = commit_graft_nr;
	while (lo < hi) {
		int mi = (lo + hi) / 2;
		struct commit_graft *graft = commit_graft[mi];
		int cmp = memcmp(sha1, graft->sha1, 20);
		if (!cmp)
			return mi;
		if (cmp < 0)
			hi = mi;
		else
			lo = mi + 1;
	}
	return -lo - 1;
}

int register_commit_graft(struct commit_graft *graft, int ignore_dups)
{
	int pos = commit_graft_pos(graft->sha1);
	
	if (0 <= pos) {
		if (ignore_dups)
			free(graft);
		else {
			free(commit_graft[pos]);
			commit_graft[pos] = graft;
		}
		return 1;
	}
	pos = -pos - 1;
	if (commit_graft_alloc <= ++commit_graft_nr) {
		commit_graft_alloc = alloc_nr(commit_graft_alloc);
		commit_graft = xrealloc(commit_graft,
					sizeof(*commit_graft) *
					commit_graft_alloc);
	}
	if (pos < commit_graft_nr)
		memmove(commit_graft + pos + 1,
			commit_graft + pos,
			(commit_graft_nr - pos - 1) *
			sizeof(*commit_graft));
	commit_graft[pos] = graft;
	return 0;
}

struct commit_graft *read_graft_line(char *buf, int len)
{
	/* The format is just "Commit Parent1 Parent2 ...\n" */
	int i;
	struct commit_graft *graft = NULL;

	if (buf[len-1] == '\n')
		buf[--len] = 0;
	if (buf[0] == '#' || buf[0] == '\0')
		return NULL;
	if ((len + 1) % 41) {
	bad_graft_data:
		error("bad graft data: %s", buf);
		free(graft);
		return NULL;
	}
	i = (len + 1) / 41 - 1;
	graft = xmalloc(sizeof(*graft) + 20 * i);
	graft->nr_parent = i;
	if (get_sha1_hex(buf, graft->sha1))
		goto bad_graft_data;
	for (i = 40; i < len; i += 41) {
		if (buf[i] != ' ')
			goto bad_graft_data;
		if (get_sha1_hex(buf + i + 1, graft->parent[i/41]))
			goto bad_graft_data;
	}
	return graft;
}

int read_graft_file(const char *graft_file)
{
	FILE *fp = fopen(graft_file, "r");
	char buf[1024];
	if (!fp)
		return -1;
	while (fgets(buf, sizeof(buf), fp)) {
		/* The format is just "Commit Parent1 Parent2 ...\n" */
		int len = strlen(buf);
		struct commit_graft *graft = read_graft_line(buf, len);
		if (!graft)
			continue;
		if (register_commit_graft(graft, 1))
			error("duplicate graft data: %s", buf);
	}
	fclose(fp);
	return 0;
}

static void prepare_commit_graft(void)
{
	static int commit_graft_prepared;
	char *graft_file;

	if (commit_graft_prepared)
		return;
	graft_file = get_graft_file();
	read_graft_file(graft_file);
	commit_graft_prepared = 1;
}

static struct commit_graft *lookup_commit_graft(const unsigned char *sha1)
{
	int pos;
	prepare_commit_graft();
	pos = commit_graft_pos(sha1);
	if (pos < 0)
		return NULL;
	return commit_graft[pos];
}

int parse_commit_buffer(struct commit *item, void *buffer, unsigned long size)
{
	char *tail = buffer;
	char *bufptr = buffer;
	unsigned char parent[20];
	struct commit_list **pptr;
	struct commit_graft *graft;
	unsigned n_refs = 0;

	if (item->object.parsed)
		return 0;
	item->object.parsed = 1;
	tail += size;
	if (tail <= bufptr + 5 || memcmp(bufptr, "tree ", 5))
		return error("bogus commit object %s", sha1_to_hex(item->object.sha1));
	if (tail <= bufptr + 45 || get_sha1_hex(bufptr + 5, parent) < 0)
		return error("bad tree pointer in commit %s",
			     sha1_to_hex(item->object.sha1));
	item->tree = lookup_tree(parent);
	if (item->tree)
		n_refs++;
	bufptr += 46; /* "tree " + "hex sha1" + "\n" */
	pptr = &item->parents;

	graft = lookup_commit_graft(item->object.sha1);
	while (bufptr + 48 < tail && !memcmp(bufptr, "parent ", 7)) {
		struct commit *new_parent;

		if (tail <= bufptr + 48 ||
		    get_sha1_hex(bufptr + 7, parent) ||
		    bufptr[47] != '\n')
			return error("bad parents in commit %s", sha1_to_hex(item->object.sha1));
		bufptr += 48;
		if (graft)
			continue;
		new_parent = lookup_commit(parent);
		if (new_parent) {
			pptr = &commit_list_insert(new_parent, pptr)->next;
			n_refs++;
		}
	}
	if (graft) {
		int i;
		struct commit *new_parent;
		for (i = 0; i < graft->nr_parent; i++) {
			new_parent = lookup_commit(graft->parent[i]);
			if (!new_parent)
				continue;
			pptr = &commit_list_insert(new_parent, pptr)->next;
			n_refs++;
		}
	}
	item->date = parse_commit_date(bufptr);

	if (track_object_refs) {
		unsigned i = 0;
		struct commit_list *p;
		struct object_refs *refs = alloc_object_refs(n_refs);
		if (item->tree)
			refs->ref[i++] = &item->tree->object;
		for (p = item->parents; p; p = p->next)
			refs->ref[i++] = &p->item->object;
		set_object_refs(&item->object, refs);
	}

	return 0;
}

int parse_commit(struct commit *item)
{
	char type[20];
	void *buffer;
	unsigned long size;
	int ret;

	if (item->object.parsed)
		return 0;
	buffer = read_sha1_file(item->object.sha1, type, &size);
	if (!buffer)
		return error("Could not read %s",
			     sha1_to_hex(item->object.sha1));
	if (strcmp(type, commit_type)) {
		free(buffer);
		return error("Object %s not a commit",
			     sha1_to_hex(item->object.sha1));
	}
	ret = parse_commit_buffer(item, buffer, size);
	if (save_commit_buffer && !ret) {
		item->buffer = buffer;
		return 0;
	}
	free(buffer);
	return ret;
}

struct commit_list *commit_list_insert(struct commit *item, struct commit_list **list_p)
{
	struct commit_list *new_list = xmalloc(sizeof(struct commit_list));
	new_list->item = item;
	new_list->next = *list_p;
	*list_p = new_list;
	return new_list;
}

void free_commit_list(struct commit_list *list)
{
	while (list) {
		struct commit_list *temp = list;
		list = temp->next;
		free(temp);
	}
}

struct commit_list * insert_by_date(struct commit *item, struct commit_list **list)
{
	struct commit_list **pp = list;
	struct commit_list *p;
	while ((p = *pp) != NULL) {
		if (p->item->date < item->date) {
			break;
		}
		pp = &p->next;
	}
	return commit_list_insert(item, pp);
}

	
void sort_by_date(struct commit_list **list)
{
	struct commit_list *ret = NULL;
	while (*list) {
		insert_by_date((*list)->item, &ret);
		*list = (*list)->next;
	}
	*list = ret;
}

struct commit *pop_most_recent_commit(struct commit_list **list,
				      unsigned int mark)
{
	struct commit *ret = (*list)->item;
	struct commit_list *parents = ret->parents;
	struct commit_list *old = *list;

	*list = (*list)->next;
	free(old);

	while (parents) {
		struct commit *commit = parents->item;
		parse_commit(commit);
		if (!(commit->object.flags & mark)) {
			commit->object.flags |= mark;
			insert_by_date(commit, list);
		}
		parents = parents->next;
	}
	return ret;
}

void clear_commit_marks(struct commit *commit, unsigned int mark)
{
	struct commit_list *parents;

	if (!commit)
		return;
	parents = commit->parents;
	commit->object.flags &= ~mark;
	while (parents) {
		clear_commit_marks(parents->item, mark);
		parents = parents->next;
	}
}

/*
 * Generic support for pretty-printing the header
 */
static int get_one_line(const char *msg, unsigned long len)
{
	int ret = 0;

	while (len--) {
		char c = *msg++;
		if (!c)
			break;
		ret++;
		if (c == '\n')
			break;
	}
	return ret;
}

static int is_rfc2047_special(char ch)
{
	return ((ch & 0x80) || (ch == '=') || (ch == '?') || (ch == '_'));
}

static int add_rfc2047(char *buf, const char *line, int len)
{
	char *bp = buf;
	int i, needquote;
	static const char q_utf8[] = "=?utf-8?q?";

	for (i = needquote = 0; !needquote && i < len; i++) {
		unsigned ch = line[i];
		if (ch & 0x80)
			needquote++;
		if ((i + 1 < len) &&
		    (ch == '=' && line[i+1] == '?'))
			needquote++;
	}
	if (!needquote)
		return sprintf(buf, "%.*s", len, line);

	memcpy(bp, q_utf8, sizeof(q_utf8)-1);
	bp += sizeof(q_utf8)-1;
	for (i = 0; i < len; i++) {
		unsigned ch = line[i] & 0xFF;
		if (is_rfc2047_special(ch)) {
			sprintf(bp, "=%02X", ch);
			bp += 3;
		}
		else if (ch == ' ')
			*bp++ = '_';
		else
			*bp++ = ch;
	}
	memcpy(bp, "?=", 2);
	bp += 2;
	return bp - buf;
}

static int add_user_info(const char *what, enum cmit_fmt fmt, char *buf, const char *line)
{
	char *date;
	int namelen;
	unsigned long time;
	int tz, ret;
	const char *filler = "    ";

	if (fmt == CMIT_FMT_ONELINE)
		return 0;
	date = strchr(line, '>');
	if (!date)
		return 0;
	namelen = ++date - line;
	time = strtoul(date, &date, 10);
	tz = strtol(date, NULL, 10);

	if (fmt == CMIT_FMT_EMAIL) {
		char *name_tail = strchr(line, '<');
		int display_name_length;
		if (!name_tail)
			return 0;
		while (line < name_tail && isspace(name_tail[-1]))
			name_tail--;
		display_name_length = name_tail - line;
		filler = "";
		strcpy(buf, "From: ");
		ret = strlen(buf);
		ret += add_rfc2047(buf + ret, line, display_name_length);
		memcpy(buf + ret, name_tail, namelen - display_name_length);
		ret += namelen - display_name_length;
		buf[ret++] = '\n';
	}
	else {
		ret = sprintf(buf, "%s: %.*s%.*s\n", what,
			      (fmt == CMIT_FMT_FULLER) ? 4 : 0,
			      filler, namelen, line);
	}
	switch (fmt) {
	case CMIT_FMT_MEDIUM:
		ret += sprintf(buf + ret, "Date:   %s\n", show_date(time, tz));
		break;
	case CMIT_FMT_EMAIL:
		ret += sprintf(buf + ret, "Date: %s\n",
			       show_rfc2822_date(time, tz));
		break;
	case CMIT_FMT_FULLER:
		ret += sprintf(buf + ret, "%sDate: %s\n", what, show_date(time, tz));
		break;
	default:
		/* notin' */
		break;
	}
	return ret;
}

static int is_empty_line(const char *line, int *len_p)
{
	int len = *len_p;
	while (len && isspace(line[len-1]))
		len--;
	*len_p = len;
	return !len;
}

static int add_merge_info(enum cmit_fmt fmt, char *buf, const struct commit *commit, int abbrev)
{
	struct commit_list *parent = commit->parents;
	int offset;

	if ((fmt == CMIT_FMT_ONELINE) || (fmt == CMIT_FMT_EMAIL) ||
	    !parent || !parent->next)
		return 0;

	offset = sprintf(buf, "Merge:");

	while (parent) {
		struct commit *p = parent->item;
		const char *hex = abbrev
			? find_unique_abbrev(p->object.sha1, abbrev)
			: sha1_to_hex(p->object.sha1);
		const char *dots = (abbrev && strlen(hex) != 40) ? "..." : "";
		parent = parent->next;

		offset += sprintf(buf + offset, " %s%s", hex, dots);
	}
	buf[offset++] = '\n';
	return offset;
}

unsigned long pretty_print_commit(enum cmit_fmt fmt, const struct commit *commit, unsigned long len, char *buf, unsigned long space, int abbrev, const char *subject, const char *after_subject)
{
	int hdr = 1, body = 0;
	unsigned long offset = 0;
	int indent = 4;
	int parents_shown = 0;
	const char *msg = commit->buffer;
	int plain_non_ascii = 0;

	if (fmt == CMIT_FMT_ONELINE || fmt == CMIT_FMT_EMAIL)
		indent = 0;

	/* After-subject is used to pass in Content-Type: multipart
	 * MIME header; in that case we do not have to do the
	 * plaintext content type even if the commit message has
	 * non 7-bit ASCII character.  Otherwise, check if we need
	 * to say this is not a 7-bit ASCII.
	 */
	if (fmt == CMIT_FMT_EMAIL && !after_subject) {
		int i, ch, in_body;

		for (in_body = i = 0; (ch = msg[i]) && i < len; i++) {
			if (!in_body) {
				/* author could be non 7-bit ASCII but
				 * the log may so; skip over the
				 * header part first.
				 */
				if (ch == '\n' &&
				    i + 1 < len && msg[i+1] == '\n')
					in_body = 1;
			}
			else if (ch & 0x80) {
				plain_non_ascii = 1;
				break;
			}
		}
	}

	for (;;) {
		const char *line = msg;
		int linelen = get_one_line(msg, len);

		if (!linelen)
			break;

		/*
		 * We want some slop for indentation and a possible
		 * final "...". Thus the "+ 20".
		 */
		if (offset + linelen + 20 > space) {
			memcpy(buf + offset, "    ...\n", 8);
			offset += 8;
			break;
		}

		msg += linelen;
		len -= linelen;
		if (hdr) {
			if (linelen == 1) {
				hdr = 0;
				if ((fmt != CMIT_FMT_ONELINE) && !subject)
					buf[offset++] = '\n';
				continue;
			}
			if (fmt == CMIT_FMT_RAW) {
				memcpy(buf + offset, line, linelen);
				offset += linelen;
				continue;
			}
			if (!memcmp(line, "parent ", 7)) {
				if (linelen != 48)
					die("bad parent line in commit");
				continue;
			}

			if (!parents_shown) {
				offset += add_merge_info(fmt, buf + offset,
							 commit, abbrev);
				parents_shown = 1;
				continue;
			}
			/*
			 * MEDIUM == DEFAULT shows only author with dates.
			 * FULL shows both authors but not dates.
			 * FULLER shows both authors and dates.
			 */
			if (!memcmp(line, "author ", 7))
				offset += add_user_info("Author", fmt,
							buf + offset,
							line + 7);
			if (!memcmp(line, "committer ", 10) &&
			    (fmt == CMIT_FMT_FULL || fmt == CMIT_FMT_FULLER))
				offset += add_user_info("Commit", fmt,
							buf + offset,
							line + 10);
			continue;
		}

		if (is_empty_line(line, &linelen)) {
			if (!body)
				continue;
			if (subject)
				continue;
			if (fmt == CMIT_FMT_SHORT)
				break;
		} else {
			body = 1;
		}

		if (subject) {
			int slen = strlen(subject);
			memcpy(buf + offset, subject, slen);
			offset += slen;
			offset += add_rfc2047(buf + offset, line, linelen);
		}
		else {
			memset(buf + offset, ' ', indent);
			memcpy(buf + offset + indent, line, linelen);
			offset += linelen + indent;
		}
		buf[offset++] = '\n';
		if (fmt == CMIT_FMT_ONELINE)
			break;
		if (subject && plain_non_ascii) {
			static const char header[] =
				"Content-Type: text/plain; charset=UTF-8\n"
				"Content-Transfer-Encoding: 8bit\n";
			memcpy(buf + offset, header, sizeof(header)-1);
			offset += sizeof(header)-1;
		}
		if (after_subject) {
			int slen = strlen(after_subject);
			if (slen > space - offset - 1)
				slen = space - offset - 1;
			memcpy(buf + offset, after_subject, slen);
			offset += slen;
			after_subject = NULL;
		}
		subject = NULL;
	}
	while (offset && isspace(buf[offset-1]))
		offset--;
	/* Make sure there is an EOLN for the non-oneline case */
	if (fmt != CMIT_FMT_ONELINE)
		buf[offset++] = '\n';
	buf[offset] = '\0';
	return offset;
}

struct commit *pop_commit(struct commit_list **stack)
{
	struct commit_list *top = *stack;
	struct commit *item = top ? top->item : NULL;

	if (top) {
		*stack = top->next;
		free(top);
	}
	return item;
}

int count_parents(struct commit * commit)
{
        int count = 0;
        struct commit_list * parents = commit->parents;
        for (count=0;parents; parents=parents->next,count++)
          ;
        return count;
}

void topo_sort_default_setter(struct commit *c, void *data)
{
	c->util = data;
}

void *topo_sort_default_getter(struct commit *c)
{
	return c->util;
}

/*
 * Performs an in-place topological sort on the list supplied.
 */
void sort_in_topological_order(struct commit_list ** list, int lifo)
{
	sort_in_topological_order_fn(list, lifo, topo_sort_default_setter,
				     topo_sort_default_getter);
}

void sort_in_topological_order_fn(struct commit_list ** list, int lifo,
				  topo_sort_set_fn_t setter,
				  topo_sort_get_fn_t getter)
{
	struct commit_list * next = *list;
	struct commit_list * work = NULL, **insert;
	struct commit_list ** pptr = list;
	struct sort_node * nodes;
	struct sort_node * next_nodes;
	int count = 0;

	/* determine the size of the list */
	while (next) {
		next = next->next;
		count++;
	}
	
	if (!count)
		return;
	/* allocate an array to help sort the list */
	nodes = xcalloc(count, sizeof(*nodes));
	/* link the list to the array */
	next_nodes = nodes;
	next=*list;
	while (next) {
		next_nodes->list_item = next;
		setter(next->item, next_nodes);
		next_nodes++;
		next = next->next;
	}
	/* update the indegree */
	next=*list;
	while (next) {
		struct commit_list * parents = next->item->parents;
		while (parents) {
			struct commit * parent=parents->item;
			struct sort_node * pn = (struct sort_node *) getter(parent);

			if (pn)
				pn->indegree++;
			parents=parents->next;
		}
		next=next->next;
	}
	/* 
         * find the tips
         *
         * tips are nodes not reachable from any other node in the list 
         * 
         * the tips serve as a starting set for the work queue.
         */
	next=*list;
	insert = &work;
	while (next) {
		struct sort_node * node = (struct sort_node *) getter(next->item);

		if (node->indegree == 0) {
			insert = &commit_list_insert(next->item, insert)->next;
		}
		next=next->next;
	}

	/* process the list in topological order */
	if (!lifo)
		sort_by_date(&work);
	while (work) {
		struct commit * work_item = pop_commit(&work);
		struct sort_node * work_node = (struct sort_node *) getter(work_item);
		struct commit_list * parents = work_item->parents;

		while (parents) {
			struct commit * parent=parents->item;
			struct sort_node * pn = (struct sort_node *) getter(parent);

			if (pn) {
				/*
				 * parents are only enqueued for emission 
                                 * when all their children have been emitted thereby
                                 * guaranteeing topological order.
                                 */
				pn->indegree--;
				if (!pn->indegree) {
					if (!lifo)
						insert_by_date(parent, &work);
					else
						commit_list_insert(parent, &work);
				}
			}
			parents=parents->next;
		}
		/*
                 * work_item is a commit all of whose children
                 * have already been emitted. we can emit it now.
                 */
		*pptr = work_node->list_item;
		pptr = &(*pptr)->next;
		*pptr = NULL;
		setter(work_item, NULL);
	}
	free(nodes);
}

/* merge-rebase stuff */

/* bits #0..7 in revision.h */
#define PARENT1		(1u<< 8)
#define PARENT2		(1u<< 9)
#define UNINTERESTING	(1u<<10)

static struct commit *interesting(struct commit_list *list)
{
	while (list) {
		struct commit *commit = list->item;
		list = list->next;
		if (commit->object.flags & UNINTERESTING)
			continue;
		return commit;
	}
	return NULL;
}

/*
 * A pathological example of how this thing works.
 *
 * Suppose we had this commit graph, where chronologically
 * the timestamp on the commit are A <= B <= C <= D <= E <= F
 * and we are trying to figure out the merge base for E and F
 * commits.
 *
 *                  F
 *                 / \
 *            E   A   D
 *             \ /   /
 *              B   /
 *               \ /
 *                C
 *
 * First we push E and F to list to be processed.  E gets bit 1
 * and F gets bit 2.  The list becomes:
 *
 *     list=F(2) E(1), result=empty
 *
 * Then we pop F, the newest commit, from the list.  Its flag is 2.
 * We scan its parents, mark them reachable from the side that F is
 * reachable from, and push them to the list:
 *
 *     list=E(1) D(2) A(2), result=empty
 *
 * Next pop E and do the same.
 *
 *     list=D(2) B(1) A(2), result=empty
 *
 * Next pop D and do the same.
 *
 *     list=C(2) B(1) A(2), result=empty
 *
 * Next pop C and do the same.
 *
 *     list=B(1) A(2), result=empty
 *
 * Now it is B's turn.  We mark its parent, C, reachable from B's side,
 * and push it to the list:
 *
 *     list=C(3) A(2), result=empty
 *
 * Now pop C and notice it has flags==3.  It is placed on the result list,
 * and the list now contains:
 *
 *     list=A(2), result=C(3)
 *
 * We pop A and do the same.
 *
 *     list=B(3), result=C(3)
 *
 * Next, we pop B and something very interesting happens.  It has flags==3
 * so it is also placed on the result list, and its parents are marked
 * uninteresting, retroactively, and placed back on the list:
 *
 *    list=C(7), result=C(7) B(3)
 *
 * Now, list does not have any interesting commit.  So we find the newest
 * commit from the result list that is not marked uninteresting.  Which is
 * commit B.
 *
 *
 * Another pathological example how this thing used to fail to mark an
 * ancestor of a merge base as UNINTERESTING before we introduced the
 * postprocessing phase (mark_reachable_commits).
 *
 *		  2
 *		  H
 *	    1    / \
 *	    G   A   \
 *	    |\ /     \
 *	    | B       \
 *	    |  \       \
 *	     \  C       F
 *	      \  \     /
 *	       \  D   /
 *		\ |  /
 *		 \| /
 *		  E
 *
 *	 list			A B C D E F G H
 *	 G1 H2			- - - - - - 1 2
 *	 H2 E1 B1		- 1 - - 1 - 1 2
 *	 F2 E1 B1 A2		2 1 - - 1 2 1 2
 *	 E3 B1 A2		2 1 - - 3 2 1 2
 *	 B1 A2			2 1 - - 3 2 1 2
 *	 C1 A2			2 1 1 - 3 2 1 2
 *	 D1 A2			2 1 1 1 3 2 1 2
 *	 A2			2 1 1 1 3 2 1 2
 *	 B3			2 3 1 1 3 2 1 2
 *	 C7			2 3 7 1 3 2 1 2
 *
 * At this point, unfortunately, everybody in the list is
 * uninteresting, so we fail to complete the following two
 * steps to fully marking uninteresting commits.
 *
 *	 D7			2 3 7 7 3 2 1 2
 *	 E7			2 3 7 7 7 2 1 2
 *
 * and we ended up showing E as an interesting merge base.
 * The postprocessing phase re-injects C and continues traversal
 * to contaminate D and E.
 */

static void mark_reachable_commits(struct commit_list *result,
				   struct commit_list *list)
{
	struct commit_list *tmp;

	/*
	 * Postprocess to fully contaminate the well.
	 */
	for (tmp = result; tmp; tmp = tmp->next) {
		struct commit *c = tmp->item;
		/* Reinject uninteresting ones to list,
		 * so we can scan their parents.
		 */
		if (c->object.flags & UNINTERESTING)
			commit_list_insert(c, &list);
	}
	while (list) {
		struct commit *c = list->item;
		struct commit_list *parents;

		tmp = list;
		list = list->next;
		free(tmp);

		/* Anything taken out of the list is uninteresting, so
		 * mark all its parents uninteresting.  We do not
		 * parse new ones (we already parsed all the relevant
		 * ones).
		 */
		parents = c->parents;
		while (parents) {
			struct commit *p = parents->item;
			parents = parents->next;
			if (!(p->object.flags & UNINTERESTING)) {
				p->object.flags |= UNINTERESTING;
				commit_list_insert(p, &list);
			}
		}
	}
}

struct commit_list *get_merge_bases(struct commit *rev1, struct commit *rev2,
                                    int cleanup)
{
	struct commit_list *list = NULL;
	struct commit_list *result = NULL;
	struct commit_list *tmp = NULL;

	if (rev1 == rev2)
		return commit_list_insert(rev1, &result);

	parse_commit(rev1);
	parse_commit(rev2);

	rev1->object.flags |= PARENT1;
	rev2->object.flags |= PARENT2;
	insert_by_date(rev1, &list);
	insert_by_date(rev2, &list);

	while (interesting(list)) {
		struct commit *commit = list->item;
		struct commit_list *parents;
		int flags = commit->object.flags
			& (PARENT1 | PARENT2 | UNINTERESTING);

		tmp = list;
		list = list->next;
		free(tmp);
		if (flags == (PARENT1 | PARENT2)) {
			insert_by_date(commit, &result);

			/* Mark parents of a found merge uninteresting */
			flags |= UNINTERESTING;
		}
		parents = commit->parents;
		while (parents) {
			struct commit *p = parents->item;
			parents = parents->next;
			if ((p->object.flags & flags) == flags)
				continue;
			parse_commit(p);
			p->object.flags |= flags;
			insert_by_date(p, &list);
		}
	}

	if (!result)
		return NULL;

	if (result->next && list)
		mark_reachable_commits(result, list);

	/* cull duplicates */
	for (tmp = result, list = NULL; tmp; ) {
		struct commit *commit = tmp->item;
		struct commit_list *next = tmp->next;
		if (commit->object.flags & UNINTERESTING) {
			if (list != NULL)
				list->next = next;
			free(tmp);
		} else {
			if (list == NULL)
				result = tmp;
			list = tmp;
			commit->object.flags |= UNINTERESTING;
		}

		tmp = next;
	}

	if (cleanup) {
		clear_commit_marks(rev1, PARENT1 | PARENT2 | UNINTERESTING);
		clear_commit_marks(rev2, PARENT1 | PARENT2 | UNINTERESTING);
	}

	return result;
}