resolve-undo: record resolved conflicts in a new index extension section

When resolving a conflict using "git add" to create a stage #0 entry, or
"git rm" to remove entries at higher stages, remove_index_entry_at()
function is eventually called to remove unmerged (i.e. higher stage)
entries from the index.  Introduce a "resolve_undo_info" structure and
keep track of the removed cache entries, and save it in a new index
extension section in the index_state.

Operations like "read-tree -m", "merge", "checkout [-m] <branch>" and
"reset" are signs that recorded information in the index is no longer
necessary.  The data is removed from the index extension when operations
start; they may leave conflicted entries in the index, and later user
actions like "git add" will record their conflicted states afresh.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/cache.h b/cache.h
index bf468e5..310d9e6 100644
--- a/cache.h
+++ b/cache.h
@@ -282,6 +282,7 @@ static inline int ce_to_dtype(const struct cache_entry *ce)
 struct index_state {
 	struct cache_entry **cache;
 	unsigned int cache_nr, cache_alloc, cache_changed;
+	struct string_list *resolve_undo;
 	struct cache_tree *cache_tree;
 	struct cache_time timestamp;
 	void *alloc;
@@ -336,6 +337,7 @@ static inline void remove_name_hash(struct cache_entry *ce)
 #define ce_modified(ce, st, options) ie_modified(&the_index, (ce), (st), (options))
 #define cache_name_exists(name, namelen, igncase) index_name_exists(&the_index, (name), (namelen), (igncase))
 #define cache_name_is_other(name, namelen) index_name_is_other(&the_index, (name), (namelen))
+#define resolve_undo_clear() resolve_undo_clear_index(&the_index)
 #endif
 
 enum object_type {