+static void setup_path_info(struct merge_options *opt,
+			    struct string_list_item *result,
+			    const char *current_dir_name,
+			    int current_dir_name_len,
+			    char *fullpath, /* we'll take over ownership */
+			    struct name_entry *names,
+			    struct name_entry *merged_version,
+			    unsigned is_null,     /* boolean */
+			    unsigned df_conflict, /* boolean */

Booleans could be int, I think?

+			    unsigned filemask,
+			    unsigned dirmask,
+			    int resolved          /* boolean */)
+{
+	struct conflict_info *path_info;
+
+	assert(!is_null || resolved);
+	assert(!df_conflict || !resolved); /* df_conflict implies !resolved */
+	assert(resolved == (merged_version != NULL));
+
+	path_info = xcalloc(1, resolved ? sizeof(struct merged_info) :
+					  sizeof(struct conflict_info));
+	path_info->merged.directory_name = current_dir_name;
+	path_info->merged.basename_offset = current_dir_name_len;
+	path_info->merged.clean = !!resolved;
+	if (resolved) {
+		path_info->merged.result.mode = merged_version->mode;
+		oidcpy(&path_info->merged.result.oid, &merged_version->oid);
+		path_info->merged.is_null = !!is_null;
+	} else {
+		int i;
+
+		for (i = 0; i < 3; i++) {
+			path_info->pathnames[i] = fullpath;
+			path_info->stages[i].mode = names[i].mode;
+			oidcpy(&path_info->stages[i].oid, &names[i].oid);
+		}
+		path_info->filemask = filemask;
+		path_info->dirmask = dirmask;
+		path_info->df_conflict = !!df_conflict;
+	}
+	strmap_put(&opt->priv->paths, fullpath, path_info);

So these are placed in paths but not unmerged. I'm starting to wonder if
struct merge_options_internal should be called merge_options_state or
something, and each field having documentation about when they're used
(or better yet, have functions like collect_merge_info() return their
calculations in return values (which may be "out" parameters) instead of
in this struct).

Looking ahead to patch 10, this seems more like "pi.util unless we know
for sure that there's no conflict".