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, 14 insertions, 0 deletions

diff --git a/resolve-undo.h b/resolve-undo.h
new file mode 100644
index 0000000..74194d0
--- /dev/null
+++ b/resolve-undo.h
@@ -0,0 +1,14 @@
+#ifndef RESOLVE_UNDO_H
+#define RESOLVE_UNDO_H
+
+struct resolve_undo_info {
+	unsigned int mode[3];
+	unsigned char sha1[3][20];
+};
+
+extern void record_resolve_undo(struct index_state *, struct cache_entry *);
+extern void resolve_undo_write(struct strbuf *, struct string_list *);
+extern struct string_list *resolve_undo_read(void *, unsigned long);
+extern void resolve_undo_clear_index(struct index_state *);
+
+#endif