Add "skip_unmerged" option to unpack_trees.

This option allows the caller to reset everything that isn't unmerged,
leaving the unmerged things to be resolved. If, after a merge of
"working" and "HEAD", this is used with "HEAD" (reset, !update), the
result will be that all of the changes from "local" are in the working
tree but not added to the index (either with the index clean but
unchanged, or with the index unmerged, depending on whether there are
conflicts).

This will be used in checkout -m.

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>

unpack-trees.c

@@ -85,6 +85,7 @@ static int unpack_trees_rec(struct tree_entry_list **posns, int len,
 		int any_dirs = 0;
 		char *cache_name;
 		int ce_stage;
+		int skip_entry = 0;
 
 		/* Find the first name in the input. */
 
@@ -153,6 +154,8 @@ static int unpack_trees_rec(struct tree_entry_list **posns, int len,
 			any_files = 1;
 			src[0] = active_cache[o->pos];
 			remove = o->pos;
+			if (o->skip_unmerged && ce_stage(src[0]))
+				skip_entry = 1;
 		}
 
 		for (i = 0; i < len; i++) {
@@ -181,6 +184,12 @@ static int unpack_trees_rec(struct tree_entry_list **posns, int len,
 				continue;
 			}
 
+			if (skip_entry) {
+				subposns[i] = df_conflict_list;
+				posns[i] = posns[i]->next;
+				continue;
+			}
+
 			if (!o->merge)
 				ce_stage = 0;
 			else if (i + 1 < o->head_idx)
@@ -205,7 +214,13 @@ static int unpack_trees_rec(struct tree_entry_list **posns, int len,
 			posns[i] = posns[i]->next;
 		}
 		if (any_files) {
-			if (o->merge) {
+			if (skip_entry) {
+				o->pos++;
+				while (o->pos < active_nr &&
+				       !strcmp(active_cache[o->pos]->name,
+					       src[0]->name))
+					o->pos++;
+			} else if (o->merge) {
 				int ret;
 
 #if DBRT_DEBUG > 1
@@ -730,9 +745,8 @@ int threeway_merge(struct cache_entry **stages,
 	 * If we have an entry in the index cache, then we want to
 	 * make sure that it matches head.
 	 */
-	if (index && !same(index, head)) {
+	if (index && !same(index, head))
 		return o->gently ? -1 : reject_merge(index);
-	}
 
 	if (head) {
 		/* #5ALT, #15 */

unpack-trees.h

@@ -16,6 +16,7 @@ struct unpack_trees_options {
 	int trivial_merges_only;
 	int verbose_update;
 	int aggressive;
+	int skip_unmerged;
 	int gently;
 	const char *prefix;
 	int pos;