merge-ort: implement compute_collisions()

This is nearly a wholesale copy of compute_collisions() from
merge-recursive.c, and the logic remains the same, but it has been
tweaked slightly due to:

  * using strmap.h API (instead of direct hashmaps)
  * allocation/freeing of data structures were done separately in
    merge_start() and clear_or_reinit_internal_opts() in an earlier
    patch in this series
  * there is no non_unique_new_dir data field in merge-ort; that will
    be handled a different way

It does depend on two new functions, apply_dir_rename() and
check_dir_renamed() which were introduced with simple
die-not-yet-implemented shells and will be implemented in subsequent
patches.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/merge-ort.c b/merge-ort.c
index c86ed85b097f9fd0acf62c44026fc936f4c56bdc..22028d57f3d3a99e03e8041ad57d34132accbdb2 100644 (file)
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -726,6 +726,19 @@ struct collision_info {
        unsigned reported_already:1;
 };
 
+/*
+ * Return a new string that replaces the beginning portion (which matches
+ * rename_info->key), with rename_info->util.new_dir.  In perl-speak:
+ *   new_path_name = (old_path =~ s/rename_info->key/rename_info->value/);
+ * NOTE:
+ *   Caller must ensure that old_path starts with rename_info->key + '/'.
+ */
+static char *apply_dir_rename(struct strmap_entry *rename_info,
+                             const char *old_path)
+{
+       die("Not yet implemented!");
+}
+
 static void get_renamed_dir_portion(const char *old_path, const char *new_path,
                                    char **old_dir, char **new_dir)
 {
@@ -964,11 +977,64 @@ static void handle_directory_level_conflicts(struct merge_options *opt)
        string_list_clear(&duplicated, 0);
 }
 
+static struct strmap_entry *check_dir_renamed(const char *path,
+                                             struct strmap *dir_renames)
+{
+       die("Not yet implemented!");
+}
+
 static void compute_collisions(struct strmap *collisions,
                               struct strmap *dir_renames,
                               struct diff_queue_struct *pairs)
 {
-       die("Not yet implemented.");
+       int i;
+
+       strmap_init_with_options(collisions, NULL, 0);
+       if (strmap_empty(dir_renames))
+               return;
+
+       /*
+        * Multiple files can be mapped to the same path due to directory
+        * renames done by the other side of history.  Since that other
+        * side of history could have merged multiple directories into one,
+        * if our side of history added the same file basename to each of
+        * those directories, then all N of them would get implicitly
+        * renamed by the directory rename detection into the same path,
+        * and we'd get an add/add/.../add conflict, and all those adds
+        * from *this* side of history.  This is not representable in the
+        * index, and users aren't going to easily be able to make sense of
+        * it.  So we need to provide a good warning about what's
+        * happening, and fall back to no-directory-rename detection
+        * behavior for those paths.
+        *
+        * See testcases 9e and all of section 5 from t6043 for examples.
+        */
+       for (i = 0; i < pairs->nr; ++i) {
+               struct strmap_entry *rename_info;
+               struct collision_info *collision_info;
+               char *new_path;
+               struct diff_filepair *pair = pairs->queue[i];
+
+               if (pair->status != 'A' && pair->status != 'R')
+                       continue;
+               rename_info = check_dir_renamed(pair->two->path, dir_renames);
+               if (!rename_info)
+                       continue;
+
+               new_path = apply_dir_rename(rename_info, pair->two->path);
+               assert(new_path);
+               collision_info = strmap_get(collisions, new_path);
+               if (collision_info) {
+                       free(new_path);
+               } else {
+                       collision_info = xcalloc(1,
+                                                sizeof(struct collision_info));
+                       string_list_init(&collision_info->source_files, 0);
+                       strmap_put(collisions, new_path, collision_info);
+               }
+               string_list_insert(&collision_info->source_files,
+                                  pair->two->path);
+       }
 }
 
 static char *check_for_directory_rename(struct merge_options *opt,