X-Git-Url: https://git.octo.it/?a=blobdiff_plain;f=read-tree.c;h=5580f15ba2c89f9fd1ed35de0b0183487d024bf8;hb=8e1618f9612a78ea09b2a926797c781fe06027c9;hp=8c9ffe123255bfeb199ea90f055ac8d1df49ddb8;hpb=e6ee623b7be2a59a3f3d1ff8c513d72b6f15344f;p=git.git

diff --git a/read-tree.c b/read-tree.c
index 8c9ffe12..5580f15b 100644
--- a/read-tree.c
+++ b/read-tree.c
@@ -3,97 +3,340 @@
  *
  * Copyright (C) Linus Torvalds, 2005
  */
+#define DBRT_DEBUG 1
+
 #include "cache.h"
 
-static int stage = 0;
+#include "object.h"
+#include "tree.h"
+
+static int merge = 0;
 static int update = 0;
+static int index_only = 0;
+static int nontrivial_merge = 0;
+static int trivial_merges_only = 0;
+static int aggressive = 0;
 
-static int unpack_tree(unsigned char *sha1)
-{
-	void *buffer;
-	unsigned long size;
-	int ret;
+static int head_idx = -1;
+static int merge_size = 0;
 
-	buffer = read_object_with_reference(sha1, "tree", &size, NULL);
-	if (!buffer)
-		return -1;
-	ret = read_tree(buffer, size, stage);
-	free(buffer);
+static struct object_list *trees = NULL;
+
+static struct cache_entry df_conflict_entry = { 
+};
+
+static struct tree_entry_list df_conflict_list = {
+	.name = NULL,
+	.next = &df_conflict_list
+};
+
+typedef int (*merge_fn_t)(struct cache_entry **src);
+
+static int entcmp(char *name1, int dir1, char *name2, int dir2)
+{
+	int len1 = strlen(name1);
+	int len2 = strlen(name2);
+	int len = len1 < len2 ? len1 : len2;
+	int ret = memcmp(name1, name2, len);
+	unsigned char c1, c2;
+	if (ret)
+		return ret;
+	c1 = name1[len];
+	c2 = name2[len];
+	if (!c1 && dir1)
+		c1 = '/';
+	if (!c2 && dir2)
+		c2 = '/';
+	ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
+	if (c1 && c2 && !ret)
+		ret = len1 - len2;
 	return ret;
 }
 
-static char *lockfile_name;
-
-static void remove_lock_file(void)
+static int unpack_trees_rec(struct tree_entry_list **posns, int len,
+			    const char *base, merge_fn_t fn, int *indpos)
 {
-	if (lockfile_name)
-		unlink(lockfile_name);
+	int baselen = strlen(base);
+	int src_size = len + 1;
+	do {
+		int i;
+		char *first;
+		int firstdir = 0;
+		int pathlen;
+		unsigned ce_size;
+		struct tree_entry_list **subposns;
+		struct cache_entry **src;
+		int any_files = 0;
+		int any_dirs = 0;
+		char *cache_name;
+		int ce_stage;
+
+		/* Find the first name in the input. */
+
+		first = NULL;
+		cache_name = NULL;
+
+		/* Check the cache */
+		if (merge && *indpos < active_nr) {
+			/* This is a bit tricky: */
+			/* If the index has a subdirectory (with
+			 * contents) as the first name, it'll get a
+			 * filename like "foo/bar". But that's after
+			 * "foo", so the entry in trees will get
+			 * handled first, at which point we'll go into
+			 * "foo", and deal with "bar" from the index,
+			 * because the base will be "foo/". The only
+			 * way we can actually have "foo/bar" first of
+			 * all the things is if the trees don't
+			 * contain "foo" at all, in which case we'll
+			 * handle "foo/bar" without going into the
+			 * directory, but that's fine (and will return
+			 * an error anyway, with the added unknown
+			 * file case.
+			 */
+
+			cache_name = active_cache[*indpos]->name;
+			if (strlen(cache_name) > baselen &&
+			    !memcmp(cache_name, base, baselen)) {
+				cache_name += baselen;
+				first = cache_name;
+			} else {
+				cache_name = NULL;
+			}
+		}
+
+#if DBRT_DEBUG > 1
+		if (first)
+			printf("index %s\n", first);
+#endif
+		for (i = 0; i < len; i++) {
+			if (!posns[i] || posns[i] == &df_conflict_list)
+				continue;
+#if DBRT_DEBUG > 1
+			printf("%d %s\n", i + 1, posns[i]->name);
+#endif
+			if (!first || entcmp(first, firstdir,
+					     posns[i]->name, 
+					     posns[i]->directory) > 0) {
+				first = posns[i]->name;
+				firstdir = posns[i]->directory;
+			}
+		}
+		/* No name means we're done */
+		if (!first)
+			return 0;
+
+		pathlen = strlen(first);
+		ce_size = cache_entry_size(baselen + pathlen);
+
+		src = xmalloc(sizeof(struct cache_entry *) * src_size);
+		memset(src, 0, sizeof(struct cache_entry *) * src_size);
+
+		subposns = xmalloc(sizeof(struct tree_list_entry *) * len);
+		memset(subposns, 0, sizeof(struct tree_list_entry *) * len);
+
+		if (cache_name && !strcmp(cache_name, first)) {
+			any_files = 1;
+			src[0] = active_cache[*indpos];
+			remove_cache_entry_at(*indpos);
+		}
+
+		for (i = 0; i < len; i++) {
+			struct cache_entry *ce;
+
+			if (!posns[i] ||
+			    (posns[i] != &df_conflict_list &&
+			     strcmp(first, posns[i]->name))) {
+				continue;
+			}
+
+			if (posns[i] == &df_conflict_list) {
+				src[i + merge] = &df_conflict_entry;
+				continue;
+			}
+
+			if (posns[i]->directory) {
+				any_dirs = 1;
+				parse_tree(posns[i]->item.tree);
+				subposns[i] = posns[i]->item.tree->entries;
+				posns[i] = posns[i]->next;
+				src[i + merge] = &df_conflict_entry;
+				continue;
+			}
+
+			if (!merge)
+				ce_stage = 0;
+			else if (i + 1 < head_idx)
+				ce_stage = 1;
+			else if (i + 1 > head_idx)
+				ce_stage = 3;
+			else
+				ce_stage = 2;
+
+			ce = xmalloc(ce_size);
+			memset(ce, 0, ce_size);
+			ce->ce_mode = create_ce_mode(posns[i]->mode);
+			ce->ce_flags = create_ce_flags(baselen + pathlen,
+						       ce_stage);
+			memcpy(ce->name, base, baselen);
+			memcpy(ce->name + baselen, first, pathlen + 1);
+
+			any_files = 1;
+
+			memcpy(ce->sha1, posns[i]->item.any->sha1, 20);
+			src[i + merge] = ce;
+			subposns[i] = &df_conflict_list;
+			posns[i] = posns[i]->next;
+		}
+		if (any_files) {
+			if (merge) {
+				int ret;
+
+#if DBRT_DEBUG > 1
+				printf("%s:\n", first);
+				for (i = 0; i < src_size; i++) {
+					printf(" %d ", i);
+					if (src[i])
+						printf("%s\n", sha1_to_hex(src[i]->sha1));
+					else
+						printf("\n");
+				}
+#endif
+				ret = fn(src);
+				
+#if DBRT_DEBUG > 1
+				printf("Added %d entries\n", ret);
+#endif
+				*indpos += ret;
+			} else {
+				for (i = 0; i < src_size; i++) {
+					if (src[i]) {
+						add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
+					}
+				}
+			}
+		}
+		if (any_dirs) {
+			char *newbase = xmalloc(baselen + 2 + pathlen);
+			memcpy(newbase, base, baselen);
+			memcpy(newbase + baselen, first, pathlen);
+			newbase[baselen + pathlen] = '/';
+			newbase[baselen + pathlen + 1] = '\0';
+			if (unpack_trees_rec(subposns, len, newbase, fn,
+					     indpos))
+				return -1;
+			free(newbase);
+		}
+		free(subposns);
+		free(src);
+	} while (1);
 }
 
-static int path_matches(struct cache_entry *a, struct cache_entry *b)
+static void reject_merge(struct cache_entry *ce)
 {
-	int len = ce_namelen(a);
-	return ce_namelen(b) == len &&
-		!memcmp(a->name, b->name, len);
+	die("Entry '%s' would be overwritten by merge. Cannot merge.", 
+	    ce->name);
 }
 
-static int same(struct cache_entry *a, struct cache_entry *b)
+/* Unlink the last component and attempt to remove leading
+ * directories, in case this unlink is the removal of the
+ * last entry in the directory -- empty directories are removed.
+ */
+static void unlink_entry(char *name)
 {
-	return a->ce_mode == b->ce_mode && 
-		!memcmp(a->sha1, b->sha1, 20);
+	char *cp, *prev;
+
+	if (unlink(name))
+		return;
+	prev = NULL;
+	while (1) {
+		int status;
+		cp = strrchr(name, '/');
+		if (prev)
+			*prev = '/';
+		if (!cp)
+			break;
+
+		*cp = 0;
+		status = rmdir(name);
+		if (status) {
+			*cp = '/';
+			break;
+		}
+		prev = cp;
+	}
 }
 
+static void check_updates(struct cache_entry **src, int nr)
+{
+	static struct checkout state = {
+		.base_dir = "",
+		.force = 1,
+		.quiet = 1,
+		.refresh_cache = 1,
+	};
+	unsigned short mask = htons(CE_UPDATE);
+	while (nr--) {
+		struct cache_entry *ce = *src++;
+		if (!ce->ce_mode) {
+			if (update)
+				unlink_entry(ce->name);
+			continue;
+		}
+		if (ce->ce_flags & mask) {
+			ce->ce_flags &= ~mask;
+			if (update)
+				checkout_entry(ce, &state);
+		}
+	}
+}
 
-/*
- * This removes all trivial merges that don't change the tree
- * and collapses them to state 0.
- *
- * _Any_ other merge is left to user policy.  That includes "both
- * created the same file", and "both removed the same file" - which are
- * trivial, but the user might still want to _note_ it. 
- */
-static struct cache_entry *merge_entries(struct cache_entry *a,
-					 struct cache_entry *b,
-					 struct cache_entry *c)
+static int unpack_trees(merge_fn_t fn)
 {
-	int len = ce_namelen(a);
+	int indpos = 0;
+	unsigned len = object_list_length(trees);
+	struct tree_entry_list **posns;
+	int i;
+	struct object_list *posn = trees;
+	merge_size = len;
+
+	if (len) {
+		posns = xmalloc(len * sizeof(struct tree_entry_list *));
+		for (i = 0; i < len; i++) {
+			posns[i] = ((struct tree *) posn->item)->entries;
+			posn = posn->next;
+		}
+		if (unpack_trees_rec(posns, len, "", fn, &indpos))
+			return -1;
+	}
 
-	/*
-	 * Are they all the same filename? We won't do
-	 * any name merging
-	 */
-	if (ce_namelen(b) != len ||
-	    ce_namelen(c) != len ||
-	    memcmp(a->name, b->name, len) ||
-	    memcmp(a->name, c->name, len))
-		return NULL;
+	if (trivial_merges_only && nontrivial_merge)
+		die("Merge requires file-level merging");
 
-	/*
-	 * Ok, all three entries describe the same
-	 * filename, but maybe the contents or file
-	 * mode have changed?
-	 *
-	 * The trivial cases end up being the ones where two
-	 * out of three files are the same:
-	 *  - both destinations the same, trivially take either
-	 *  - one of the destination versions hasn't changed,
-	 *    take the other.
-	 *
-	 * The "all entries exactly the same" case falls out as
-	 * a special case of any of the "two same" cases.
-	 *
-	 * Here "a" is "original", and "b" and "c" are the two
-	 * trees we are merging.
-	 */
-	if (same(b,c))
-		return c;
-	if (same(a,b))
-		return c;
-	if (same(a,c))
-		return b;
-	return NULL;
+	check_updates(active_cache, active_nr);
+	return 0;
+}
+
+static int list_tree(unsigned char *sha1)
+{
+	struct tree *tree = parse_tree_indirect(sha1);
+	if (!tree)
+		return -1;
+	object_list_append(&tree->object, &trees);
+	return 0;
 }
 
+static int same(struct cache_entry *a, struct cache_entry *b)
+{
+	if (!!a != !!b)
+		return 0;
+	if (!a && !b)
+		return 1;
+	return a->ce_mode == b->ce_mode && 
+		!memcmp(a->sha1, b->sha1, 20);
+}
+
+
 /*
  * When a CE gets turned into an unmerged entry, we
  * want it to be up-to-date
@@ -102,6 +345,9 @@ static void verify_uptodate(struct cache_entry *ce)
 {
 	struct stat st;
 
+	if (index_only)
+		return;
+
 	if (!lstat(ce->name, &st)) {
 		unsigned changed = ce_match_stat(ce, &st);
 		if (!changed)
@@ -113,271 +359,407 @@ static void verify_uptodate(struct cache_entry *ce)
 	die("Entry '%s' not uptodate. Cannot merge.", ce->name);
 }
 
-/*
- * If the old tree contained a CE that isn't even in the
- * result, that's always a problem, regardless of whether
- * it's up-to-date or not (ie it can be a file that we
- * have updated but not committed yet).
- */
-static void reject_merge(struct cache_entry *ce)
+static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
+{
+	merge->ce_flags |= htons(CE_UPDATE);
+	if (old) {
+		/*
+		 * See if we can re-use the old CE directly?
+		 * That way we get the uptodate stat info.
+		 *
+		 * This also removes the UPDATE flag on
+		 * a match.
+		 */
+		if (same(old, merge)) {
+			*merge = *old;
+		} else {
+			verify_uptodate(old);
+		}
+	}
+	merge->ce_flags &= ~htons(CE_STAGEMASK);
+	add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
+	return 1;
+}
+
+static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
 {
-	die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name);
+	if (old)
+		verify_uptodate(old);
+	ce->ce_mode = 0;
+	add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
+	return 1;
 }
 
-#define CHECK_OLD(ce) if (old && same(old, ce)) { verify_uptodate(old); old = NULL; }
+static int keep_entry(struct cache_entry *ce)
+{
+	add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
+	return 1;
+}
 
-static void trivially_merge_cache(struct cache_entry **src, int nr)
+#if DBRT_DEBUG
+static void show_stage_entry(FILE *o,
+			     const char *label, const struct cache_entry *ce)
 {
-	struct cache_entry **dst = src;
-	struct cache_entry *old = NULL;
+	if (!ce)
+		fprintf(o, "%s (missing)\n", label);
+	else
+		fprintf(o, "%s%06o %s %d\t%s\n",
+			label,
+			ntohl(ce->ce_mode),
+			sha1_to_hex(ce->sha1),
+			ce_stage(ce),
+			ce->name);
+}
+#endif
 
-	while (nr--) {
-		struct cache_entry *ce, *result;
+static int threeway_merge(struct cache_entry **stages)
+{
+	struct cache_entry *index;
+	struct cache_entry *head; 
+	struct cache_entry *remote = stages[head_idx + 1];
+	int count;
+	int head_match = 0;
+	int remote_match = 0;
+
+	int df_conflict_head = 0;
+	int df_conflict_remote = 0;
+
+	int any_anc_missing = 0;
+	int no_anc_exists = 1;
+	int i;
+
+	for (i = 1; i < head_idx; i++) {
+		if (!stages[i])
+			any_anc_missing = 1;
+		else
+			no_anc_exists = 0;
+	}
 
-		ce = *src++;
+	index = stages[0];
+	head = stages[head_idx];
 
-		/* We throw away original cache entries except for the stat information */
-		if (!ce_stage(ce)) {
-			if (old)
-				reject_merge(old);
-			old = ce;
-			active_nr--;
-			continue;
-		}
-		if (old && !path_matches(old, ce))
-			reject_merge(old);
-		if (nr > 2 && (result = merge_entries(ce, src[1], src[2])) != NULL) {
-			result->ce_flags |= htons(CE_UPDATE);
-			/*
-			 * See if we can re-use the old CE directly?
-			 * That way we get the uptodate stat info.
-			 *
-			 * This also removes the UPDATE flag on
-			 * a match.
-			 */
-			if (old && same(old, result)) {
-				*result = *old;
-				old = NULL;
+	if (head == &df_conflict_entry) {
+		df_conflict_head = 1;
+		head = NULL;
+	}
+
+	if (remote == &df_conflict_entry) {
+		df_conflict_remote = 1;
+		remote = NULL;
+	}
+
+	/* First, if there's a #16 situation, note that to prevent #13
+	 * and #14. 
+	 */
+	if (!same(remote, head)) {
+		for (i = 1; i < head_idx; i++) {
+			if (same(stages[i], head)) {
+				head_match = i;
+			}
+			if (same(stages[i], remote)) {
+				remote_match = i;
 			}
-			CHECK_OLD(ce);
-			CHECK_OLD(src[1]);
-			CHECK_OLD(src[2]);
-			ce = result;
-			ce->ce_flags &= ~htons(CE_STAGEMASK);
-			src += 2;
-			nr -= 2;
-			active_nr -= 2;
 		}
+	}
 
+	/* We start with cases where the index is allowed to match
+	 * something other than the head: #14(ALT) and #2ALT, where it
+	 * is permitted to match the result instead.
+	 */
+	/* #14, #14ALT, #2ALT */
+	if (remote && !df_conflict_head && head_match && !remote_match) {
+		if (index && !same(index, remote) && !same(index, head))
+			reject_merge(index);
+		return merged_entry(remote, index);
+	}
+	/*
+	 * If we have an entry in the index cache, then we want to
+	 * make sure that it matches head.
+	 */
+	if (index && !same(index, head)) {
+		reject_merge(index);
+	}
+
+	if (head) {
+		/* #5ALT, #15 */
+		if (same(head, remote))
+			return merged_entry(head, index);
+		/* #13, #3ALT */
+		if (!df_conflict_remote && remote_match && !head_match)
+			return merged_entry(head, index);
+	}
+
+	/* #1 */
+	if (!head && !remote && any_anc_missing)
+		return 0;
+
+	/* Under the new "aggressive" rule, we resolve mostly trivial
+	 * cases that we historically had git-merge-one-file resolve.
+	 */
+	if (aggressive) {
+		int head_deleted = !head && !df_conflict_head;
+		int remote_deleted = !remote && !df_conflict_remote;
 		/*
-		 * If we had an old entry that we now effectively
-		 * overwrite, make sure it wasn't dirty.
+		 * Deleted in both.
+		 * Deleted in one and unchanged in the other.
 		 */
-		CHECK_OLD(ce);
-		*dst++ = ce;
-	}
-	if (old)
-		reject_merge(old);
-}
+		if ((head_deleted && remote_deleted) ||
+		    (head_deleted && remote && remote_match) ||
+		    (remote_deleted && head && head_match))
+			return 0;
 
-/*
- * When we find a "stage2" entry in the two-way merge, that's
- * the one that will remain. If we have an exact old match,
- * we don't care whether the file is up-to-date or not, we just
- * re-use the thing directly.
- *
- * If we didn't have an exact match, then we want to make sure
- * that we've seen a stage1 that matched the old, and that the
- * old file was up-to-date. Because it will be gone after this
- * merge..
- */
-static void twoway_check(struct cache_entry *old, int seen_stage1, struct cache_entry *ce)
-{
-	if (path_matches(old, ce)) {
 		/*
-		 * This also removes the UPDATE flag on
-		 * a match
+		 * Added in both, identically.
 		 */
-		if (same(old, ce)) {
-			*ce = *old;
-			return;
+		if (no_anc_exists && head && remote && same(head, remote))
+			return merged_entry(head, index);
+
+	}
+
+	/* Below are "no merge" cases, which require that the index be
+	 * up-to-date to avoid the files getting overwritten with
+	 * conflict resolution files. 
+	 */
+	if (index) {
+		verify_uptodate(index);
+	}
+
+	nontrivial_merge = 1;
+
+	/* #2, #3, #4, #6, #7, #9, #11. */
+	count = 0;
+	if (!head_match || !remote_match) {
+		for (i = 1; i < head_idx; i++) {
+			if (stages[i]) {
+				keep_entry(stages[i]);
+				count++;
+				break;
+			}
 		}
-		if (!seen_stage1)
-			reject_merge(old);
 	}
-	verify_uptodate(old);
+#if DBRT_DEBUG
+	else {
+		fprintf(stderr, "read-tree: warning #16 detected\n");
+		show_stage_entry(stderr, "head   ", stages[head_match]);
+		show_stage_entry(stderr, "remote ", stages[remote_match]);
+	}
+#endif
+	if (head) { count += keep_entry(head); }
+	if (remote) { count += keep_entry(remote); }
+	return count;
 }
 
 /*
  * Two-way merge.
  *
- * The rule is: 
- *  - every current entry has to match the old tree
- *  - if the current entry matches the new tree, we leave it
- *    as-is. Otherwise we require that it be up-to-date.
+ * The rule is to "carry forward" what is in the index without losing
+ * information across a "fast forward", favoring a successful merge
+ * over a merge failure when it makes sense.  For details of the
+ * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
+ *
  */
-static void twoway_merge(struct cache_entry **src, int nr)
+static int twoway_merge(struct cache_entry **src)
 {
-	int seen_stage1 = 0;
-	struct cache_entry *old = NULL;
-	struct cache_entry **dst = src;
-
-	while (nr--) {
-		struct cache_entry *ce = *src++;
-		int stage = ce_stage(ce);
-
-		switch (stage) {
-		case 0:
-			if (old)
-				reject_merge(old);
-			old = ce;
-			seen_stage1 = 0;
-			active_nr--;
-			continue;
-
-		case 1:
-			active_nr--;
-			if (!old)
-				continue;
-			if (!path_matches(old, ce) || !same(old, ce))
-				reject_merge(old);
-			seen_stage1 = 1;
-			continue;
-
-		case 2:
-			ce->ce_flags |= htons(CE_UPDATE);
-			if (old) {
-				twoway_check(old, seen_stage1, ce);
-				old = NULL;
-			}
-			ce->ce_flags &= ~htons(CE_STAGEMASK);
-			*dst++ = ce;
-			continue;
+	struct cache_entry *current = src[0];
+	struct cache_entry *oldtree = src[1], *newtree = src[2];
+
+	if (merge_size != 2)
+		return error("Cannot do a twoway merge of %d trees\n",
+			     merge_size);
+
+	if (current) {
+		if ((!oldtree && !newtree) || /* 4 and 5 */
+		    (!oldtree && newtree &&
+		     same(current, newtree)) || /* 6 and 7 */
+		    (oldtree && newtree &&
+		     same(oldtree, newtree)) || /* 14 and 15 */
+		    (oldtree && newtree &&
+		     !same(oldtree, newtree) && /* 18 and 19*/
+		     same(current, newtree))) {
+			return keep_entry(current);
+		}
+		else if (oldtree && !newtree && same(current, oldtree)) {
+			/* 10 or 11 */
+			return deleted_entry(oldtree, current);
+		}
+		else if (oldtree && newtree &&
+			 same(current, oldtree) && !same(current, newtree)) {
+			/* 20 or 21 */
+			return merged_entry(newtree, current);
+		}
+		else {
+			/* all other failures */
+			if (oldtree)
+				reject_merge(oldtree);
+			if (current)
+				reject_merge(current);
+			if (newtree)
+				reject_merge(newtree);
+			return -1;
 		}
-		die("impossible two-way stage");
-	}
-
-	/*
-	 * Unmatched with a new entry? Make sure it was
-	 * at least uptodate in the working directory _and_
-	 * the original tree..
-	 */
-	if (old) {
-		if (!seen_stage1)
-			reject_merge(old);
-		verify_uptodate(old);
 	}
+	else if (newtree)
+		return merged_entry(newtree, current);
+	else
+		return deleted_entry(oldtree, current);
 }
 
-static void merge_stat_info(struct cache_entry **src, int nr)
+/*
+ * One-way merge.
+ *
+ * The rule is:
+ * - take the stat information from stage0, take the data from stage1
+ */
+static int oneway_merge(struct cache_entry **src)
 {
-	static struct cache_entry null_entry;
-	struct cache_entry **dst = src;
-	struct cache_entry *stat = &null_entry;
+	struct cache_entry *old = src[0];
+	struct cache_entry *a = src[1];
 
-	while (nr--) {
-		struct cache_entry *ce = *src++;
+	if (merge_size != 1)
+		return error("Cannot do a oneway merge of %d trees\n",
+			     merge_size);
 
-		/* We throw away original cache entries except for the stat information */
-		if (!ce_stage(ce)) {
-			stat = ce;
-			active_nr--;
-			continue;
-		}
-		if (path_matches(ce, stat) && same(ce, stat))
-			*ce = *stat;
-		ce->ce_flags &= ~htons(CE_STAGEMASK);
-		*dst++ = ce;
+	if (!a)
+		return 0;
+	if (old && same(old, a)) {
+		return keep_entry(old);
 	}
+	return merged_entry(a, NULL);
 }
 
-static void check_updates(struct cache_entry **src, int nr)
+static int read_cache_unmerged(void)
 {
-	static struct checkout state = {
-		.base_dir = "",
-		.force = 1,
-		.quiet = 1,
-		.refresh_cache = 1,
-	};
-	unsigned short mask = htons(CE_UPDATE);
-	while (nr--) {
-		struct cache_entry *ce = *src++;
-		if (ce->ce_flags & mask) {
-			ce->ce_flags &= ~mask;
-			if (update)
-				checkout_entry(ce, &state);
+	int i, deleted;
+	struct cache_entry **dst;
+
+	read_cache();
+	dst = active_cache;
+	deleted = 0;
+	for (i = 0; i < active_nr; i++) {
+		struct cache_entry *ce = active_cache[i];
+		if (ce_stage(ce)) {
+			deleted++;
+			continue;
 		}
+		if (deleted)
+			*dst = ce;
+		dst++;
 	}
+	active_nr -= deleted;
+	return deleted;
 }
 
-static char *read_tree_usage = "git-read-tree (<sha> | -m <sha1> [<sha2> [<sha3>]])";
+static const char read_tree_usage[] = "git-read-tree (<sha> | -m [-u | -i] <sha1> [<sha2> [<sha3>]])";
+
+static struct cache_file cache_file;
 
 int main(int argc, char **argv)
 {
-	int i, newfd, merge;
+	int i, newfd, reset, stage = 0;
 	unsigned char sha1[20];
-	static char lockfile[MAXPATHLEN+1];
-	const char *indexfile = get_index_file();
+	merge_fn_t fn = NULL;
 
-	snprintf(lockfile, sizeof(lockfile), "%s.lock", indexfile);
+	setup_git_directory();
 
-	newfd = open(lockfile, O_RDWR | O_CREAT | O_EXCL, 0600);
+	newfd = hold_index_file_for_update(&cache_file, get_index_file());
 	if (newfd < 0)
 		die("unable to create new cachefile");
-	atexit(remove_lock_file);
-	lockfile_name = lockfile;
+
+	git_config(git_default_config);
 
 	merge = 0;
+	reset = 0;
 	for (i = 1; i < argc; i++) {
 		const char *arg = argv[i];
 
-		/* "-u" means "update", meaning that a merge will update the working directory */
+		/* "-u" means "update", meaning that a merge will update
+		 * the working tree.
+		 */
 		if (!strcmp(arg, "-u")) {
 			update = 1;
 			continue;
 		}
 
+		/* "-i" means "index only", meaning that a merge will
+		 * not even look at the working tree.
+		 */
+		if (!strcmp(arg, "-i")) {
+			index_only = 1;
+			continue;
+		}
+
+		/* This differs from "-m" in that we'll silently ignore unmerged entries */
+		if (!strcmp(arg, "--reset")) {
+			if (stage || merge)
+				usage(read_tree_usage);
+			reset = 1;
+			merge = 1;
+			stage = 1;
+			read_cache_unmerged();
+			continue;
+		}
+
+		if (!strcmp(arg, "--trivial")) {
+			trivial_merges_only = 1;
+			continue;
+		}
+
+		if (!strcmp(arg, "--aggressive")) {
+			aggressive = 1;
+			continue;
+		}
+
 		/* "-m" stands for "merge", meaning we start in stage 1 */
 		if (!strcmp(arg, "-m")) {
-			int i;
-			if (stage)
-				die("-m needs to come first");
-			read_cache();
-			for (i = 0; i < active_nr; i++) {
-				if (ce_stage(active_cache[i]))
-					die("you need to resolve your current index first");
-			}
+			if (stage || merge)
+				usage(read_tree_usage);
+			if (read_cache_unmerged())
+				die("you need to resolve your current index first");
 			stage = 1;
 			merge = 1;
 			continue;
 		}
-		if (get_sha1(arg, sha1) < 0)
+
+		/* using -u and -i at the same time makes no sense */
+		if (1 < index_only + update)
 			usage(read_tree_usage);
-		if (stage > 3)
+
+		if (get_sha1(arg, sha1) < 0)
 			usage(read_tree_usage);
-		if (unpack_tree(sha1) < 0)
+		if (list_tree(sha1) < 0)
 			die("failed to unpack tree object %s", arg);
 		stage++;
 	}
+	if ((update||index_only) && !merge)
+		usage(read_tree_usage);
+
 	if (merge) {
-		switch (stage) {
-		case 4:	/* Three-way merge */
-			trivially_merge_cache(active_cache, active_nr);
-			check_updates(active_cache, active_nr);
+		if (stage < 2)
+			die("just how do you expect me to merge %d trees?", stage-1);
+		switch (stage - 1) {
+		case 1:
+			fn = oneway_merge;
 			break;
-		case 3:	/* Update from one tree to another */
-			twoway_merge(active_cache, active_nr);
-			check_updates(active_cache, active_nr);
+		case 2:
+			fn = twoway_merge;
 			break;
-		case 2:	/* Just read a tree, merge with old cache contents */
-			merge_stat_info(active_cache, active_nr);
+		case 3:
+			fn = threeway_merge;
 			break;
 		default:
-			die("just how do you expect me to merge %d trees?", stage-1);
+			fn = threeway_merge;
+			break;
 		}
+
+		if (stage - 1 >= 3)
+			head_idx = stage - 2;
+		else
+			head_idx = 1;
 	}
-	if (write_cache(newfd, active_cache, active_nr) || rename(lockfile, indexfile))
+
+	unpack_trees(fn);
+	if (write_cache(newfd, active_cache, active_nr) ||
+	    commit_index_file(&cache_file))
 		die("unable to write new index file");
-	lockfile_name = NULL;
 	return 0;
 }