[PATCH v2 23/33] merge-recursive: add a new hashmap for storing file collisions

[Elijah Newren <newren@gmail.com>]

Directory renames with the ability to merge directories opens up the
possibility of add/add/add/.../add conflicts, if each of the N
directories being merged into one target directory all had a file with
the same name.  We need a way to check for and report on such
collisions; this hashmap will be used for this purpose.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 merge-recursive.c | 23 +++++++++++++++++++++++
 merge-recursive.h |  7 +++++++
 2 files changed, 30 insertions(+)

diff --git a/merge-recursive.c b/merge-recursive.c
index 03897af883..472754c493 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -84,6 +84,29 @@ static void dir_rename_entry_init(struct dir_rename_entry *entry,
 	string_list_init(&entry->possible_new_dirs, 0);
 }
 
+static struct collision_entry *collision_find_entry(struct hashmap *hashmap,
+						    char *target_file)
+{
+	struct collision_entry key;
+
+	hashmap_entry_init(&key, strhash(target_file));
+	key.target_file = target_file;
+	return hashmap_get(hashmap, &key, NULL);
+}
+
+static int collision_cmp(void *unused_cmp_data,
+			 const struct collision_entry *e1,
+			 const struct collision_entry *e2,
+			 const void *unused_keydata)
+{
+	return strcmp(e1->target_file, e2->target_file);
+}
+
+static void collision_init(struct hashmap *map)
+{
+	hashmap_init(map, (hashmap_cmp_fn) collision_cmp, NULL, 0);
+}
+
 static void flush_output(struct merge_options *o)
 {
 	if (o->buffer_output < 2 && o->obuf.len) {
diff --git a/merge-recursive.h b/merge-recursive.h
index a024949739..e02c1e1243 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -37,6 +37,13 @@ struct dir_rename_entry {
 	struct string_list possible_new_dirs;
 };
 
+struct collision_entry {
+	struct hashmap_entry ent; /* must be the first member! */
+	char *target_file;
+	struct string_list source_files;
+	unsigned reported_already:1;
+};
+
 /* merge_trees() but with recursive ancestor consolidation */
 int merge_recursive(struct merge_options *o,
 		    struct commit *h1,
-- 
2.15.0.309.g00c152f825