read-tree: move merge functions to the library

This will allow merge-recursive to use the read-tree functionality
without exec()ing git-read-tree.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 404 insertions, 0 deletions

diff --git a/unpack-trees.c b/unpack-trees.c
index 20251822e4..a20639be70 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -3,8 +3,11 @@
 #include "cache.h"
 #include "tree.h"
 #include "tree-walk.h"
+#include "cache-tree.h"
 #include "unpack-trees.h"
 
+#define DBRT_DEBUG 1
+
 struct tree_entry_list {
 	struct tree_entry_list *next;
 	unsigned directory : 1;
@@ -22,6 +25,9 @@ static struct tree_entry_list *create_tree_entry_list(struct tree *tree)
 	struct tree_entry_list *ret = NULL;
 	struct tree_entry_list **list_p = &ret;
 
+	if (!tree->object.parsed)
+		parse_tree(tree);
+
 	desc.buf = tree->buffer;
 	desc.size = tree->size;
 
@@ -368,12 +374,14 @@ int unpack_trees(struct object_list *trees, struct unpack_trees_options *o)
 
 	memset(&df_conflict_list, 0, sizeof(df_conflict_list));
 	df_conflict_list.next = &df_conflict_list;
+	memset(&state, 0, sizeof(state));
 	state.base_dir = "";
 	state.force = 1;
 	state.quiet = 1;
 	state.refresh_cache = 1;
 
 	o->merge_size = len;
+	memset(&df_conflict_entry, 0, sizeof(df_conflict_entry));
 	o->df_conflict_entry = &df_conflict_entry;
 
 	if (len) {
@@ -393,3 +401,399 @@ int unpack_trees(struct object_list *trees, struct unpack_trees_options *o)
 	check_updates(active_cache, active_nr, o);
 	return 0;
 }
+
+/* Here come the merge functions */
+
+static void reject_merge(struct cache_entry *ce)
+{
+	die("Entry '%s' would be overwritten by merge. Cannot merge.",
+	    ce->name);
+}
+
+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
+ */
+static void verify_uptodate(struct cache_entry *ce,
+		struct unpack_trees_options *o)
+{
+	struct stat st;
+
+	if (o->index_only || o->reset)
+		return;
+
+	if (!lstat(ce->name, &st)) {
+		unsigned changed = ce_match_stat(ce, &st, 1);
+		if (!changed)
+			return;
+		errno = 0;
+	}
+	if (o->reset) {
+		ce->ce_flags |= htons(CE_UPDATE);
+		return;
+	}
+	if (errno == ENOENT)
+		return;
+	die("Entry '%s' not uptodate. Cannot merge.", ce->name);
+}
+
+static void invalidate_ce_path(struct cache_entry *ce)
+{
+	if (ce)
+		cache_tree_invalidate_path(active_cache_tree, ce->name);
+}
+
+/*
+ * We do not want to remove or overwrite a working tree file that
+ * is not tracked.
+ */
+static void verify_absent(const char *path, const char *action,
+		struct unpack_trees_options *o)
+{
+	struct stat st;
+
+	if (o->index_only || o->reset || !o->update)
+		return;
+	if (!lstat(path, &st))
+		die("Untracked working tree file '%s' "
+		    "would be %s by merge.", path, action);
+}
+
+static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
+		struct unpack_trees_options *o)
+{
+	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, o);
+			invalidate_ce_path(old);
+		}
+	}
+	else {
+		verify_absent(merge->name, "overwritten", o);
+		invalidate_ce_path(merge);
+	}
+
+	merge->ce_flags &= ~htons(CE_STAGEMASK);
+	add_cache_entry(merge, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
+	return 1;
+}
+
+static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
+		struct unpack_trees_options *o)
+{
+	if (old)
+		verify_uptodate(old, o);
+	else
+		verify_absent(ce->name, "removed", o);
+	ce->ce_mode = 0;
+	add_cache_entry(ce, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
+	invalidate_ce_path(ce);
+	return 1;
+}
+
+static int keep_entry(struct cache_entry *ce)
+{
+	add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
+	return 1;
+}
+
+#if DBRT_DEBUG
+static void show_stage_entry(FILE *o,
+			     const char *label, const struct cache_entry *ce)
+{
+	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
+
+int threeway_merge(struct cache_entry **stages,
+		struct unpack_trees_options *o)
+{
+	struct cache_entry *index;
+	struct cache_entry *head;
+	struct cache_entry *remote = stages[o->head_idx + 1];
+	int count;
+	int head_match = 0;
+	int remote_match = 0;
+	const char *path = NULL;
+
+	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 < o->head_idx; i++) {
+		if (!stages[i])
+			any_anc_missing = 1;
+		else {
+			if (!path)
+				path = stages[i]->name;
+			no_anc_exists = 0;
+		}
+	}
+
+	index = stages[0];
+	head = stages[o->head_idx];
+
+	if (head == o->df_conflict_entry) {
+		df_conflict_head = 1;
+		head = NULL;
+	}
+
+	if (remote == o->df_conflict_entry) {
+		df_conflict_remote = 1;
+		remote = NULL;
+	}
+
+	if (!path && index)
+		path = index->name;
+	if (!path && head)
+		path = head->name;
+	if (!path && remote)
+		path = remote->name;
+
+	/* First, if there's a #16 situation, note that to prevent #13
+	 * and #14.
+	 */
+	if (!same(remote, head)) {
+		for (i = 1; i < o->head_idx; i++) {
+			if (same(stages[i], head)) {
+				head_match = i;
+			}
+			if (same(stages[i], remote)) {
+				remote_match = i;
+			}
+		}
+	}
+
+	/* 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, o);
+	}
+	/*
+	 * 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, o);
+		/* #13, #3ALT */
+		if (!df_conflict_remote && remote_match && !head_match)
+			return merged_entry(head, index, o);
+	}
+
+	/* #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 (o->aggressive) {
+		int head_deleted = !head && !df_conflict_head;
+		int remote_deleted = !remote && !df_conflict_remote;
+		/*
+		 * Deleted in both.
+		 * Deleted in one and unchanged in the other.
+		 */
+		if ((head_deleted && remote_deleted) ||
+		    (head_deleted && remote && remote_match) ||
+		    (remote_deleted && head && head_match)) {
+			if (index)
+				return deleted_entry(index, index, o);
+			else if (path)
+				verify_absent(path, "removed", o);
+			return 0;
+		}
+		/*
+		 * Added in both, identically.
+		 */
+		if (no_anc_exists && head && remote && same(head, remote))
+			return merged_entry(head, index, o);
+
+	}
+
+	/* 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, o);
+	}
+	else if (path)
+		verify_absent(path, "overwritten", o);
+
+	o->nontrivial_merge = 1;
+
+	/* #2, #3, #4, #6, #7, #9, #11. */
+	count = 0;
+	if (!head_match || !remote_match) {
+		for (i = 1; i < o->head_idx; i++) {
+			if (stages[i]) {
+				keep_entry(stages[i]);
+				count++;
+				break;
+			}
+		}
+	}
+#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 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>.
+ *
+ */
+int twoway_merge(struct cache_entry **src,
+		struct unpack_trees_options *o)
+{
+	struct cache_entry *current = src[0];
+	struct cache_entry *oldtree = src[1], *newtree = src[2];
+
+	if (o->merge_size != 2)
+		return error("Cannot do a twoway merge of %d trees",
+			     o->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, o);
+		}
+		else if (oldtree && newtree &&
+			 same(current, oldtree) && !same(current, newtree)) {
+			/* 20 or 21 */
+			return merged_entry(newtree, current, o);
+		}
+		else {
+			/* all other failures */
+			if (oldtree)
+				reject_merge(oldtree);
+			if (current)
+				reject_merge(current);
+			if (newtree)
+				reject_merge(newtree);
+			return -1;
+		}
+	}
+	else if (newtree)
+		return merged_entry(newtree, current, o);
+	else
+		return deleted_entry(oldtree, current, o);
+}
+
+/*
+ * Bind merge.
+ *
+ * Keep the index entries at stage0, collapse stage1 but make sure
+ * stage0 does not have anything there.
+ */
+int bind_merge(struct cache_entry **src,
+		struct unpack_trees_options *o)
+{
+	struct cache_entry *old = src[0];
+	struct cache_entry *a = src[1];
+
+	if (o->merge_size != 1)
+		return error("Cannot do a bind merge of %d trees\n",
+			     o->merge_size);
+	if (a && old)
+		die("Entry '%s' overlaps.  Cannot bind.", a->name);
+	if (!a)
+		return keep_entry(old);
+	else
+		return merged_entry(a, NULL, o);
+}
+
+/*
+ * One-way merge.
+ *
+ * The rule is:
+ * - take the stat information from stage0, take the data from stage1
+ */
+int oneway_merge(struct cache_entry **src,
+		struct unpack_trees_options *o)
+{
+	struct cache_entry *old = src[0];
+	struct cache_entry *a = src[1];
+
+	if (o->merge_size != 1)
+		return error("Cannot do a oneway merge of %d trees",
+			     o->merge_size);
+
+	if (!a)
+		return deleted_entry(old, old, o);
+	if (old && same(old, a)) {
+		if (o->reset) {
+			struct stat st;
+			if (lstat(old->name, &st) ||
+			    ce_match_stat(old, &st, 1))
+				old->ce_flags |= htons(CE_UPDATE);
+		}
+		return keep_entry(old);
+	}
+	return merged_entry(a, old, o);
+}