1 file changed, 72 insertions, 7 deletions
diff --git a/source/shared.c b/source/shared.c
index c189b11..fcdcd24 100644
--- a/source/shared.c
+++ b/source/shared.c
@@ -87,15 +87,19 @@ struct cgit_repo *cgit_get_repoinfo(const char *url)
 	return NULL;
 }
 
-void cgit_diff_tree_cb(struct diff_queue_struct *q, struct diff_options *options UNUSED, void *data)
+void cgit_diff_tree_cb(struct diff_queue_struct *q, struct diff_options *options, void *data)
 {
 	filepair_fn fn = *(filepair_fn *)data;
+	const char *wanted = options->single_follow;
 	int i;
 
 	for (i = 0; i < q->nr; i++) {
 		// An unmerged path has no single pair of blobs to show.
 		if (q->queue[i]->status == 'U')
 			continue;
+		// A diff aimed at one path ran over the whole commit.
+		if (wanted && strcmp(q->queue[i]->two->path, wanted))
+			continue;
 		fn(q->queue[i]);
 	}
 }
@@ -215,11 +219,48 @@ int cgit_diff_files(const struct object_id *old_oid, const struct object_id *new
 	return 0;
 }
 
+static void set_literal_item(struct pathspec_item *item, const char *path)
+{
+	int len = path ? strlen(path) : 0;
+
+	// nowildcard_len matching len makes git treat the path as literal
+	// rather than as a glob.
+	*item = (struct pathspec_item){ .match = path, .len = len, .nowildcard_len = len };
+}
+
 void cgit_diff_limit_path(struct diff_options *opt, const char *prefix)
 {
 	cgit_literal_pathspec(&opt->pathspec, xmalloc(sizeof(struct pathspec_item)), xstrdup(prefix));
 }
 
+void cgit_diff_limit_rename(struct diff_options *opt, const char *path, const char *source)
+{
+	struct pathspec_item *items = xcalloc(2, sizeof(*items));
+
+	set_literal_item(&items[0], xstrdup(path));
+	set_literal_item(&items[1], xstrdup(source));
+	opt->pathspec.nr = 2;
+	opt->pathspec.items = items;
+	opt->detect_rename = DIFF_DETECT_RENAME;
+}
+
+/*
+ * Whether path names something other than a directory in the new tree that
+ * the old tree lacks, which is where a rename lands.
+ */
+static int path_is_new(const struct object_id *old_oid, const struct object_id *new_oid,
+	const char *path)
+{
+	struct object_id oid;
+	unsigned short mode;
+
+	if (!*path || !old_oid || is_null_oid(old_oid))
+		return 0;
+	if (get_tree_entry(the_repository, new_oid, path, &oid, &mode) || S_ISDIR(mode))
+		return 0;
+	return get_tree_entry(the_repository, old_oid, path, &oid, &mode) != 0;
+}
+
 void cgit_diff_tree(const struct object_id *old_oid, const struct object_id *new_oid,
 	filepair_fn fn, const char *prefix, int ignorews)
 {
@@ -234,7 +275,12 @@ void cgit_diff_tree(const struct object_id *old_oid, const struct object_id *new
 		DIFF_XDL_SET(&opt, IGNORE_WHITESPACE);
 	opt.format_callback = cgit_diff_tree_cb;
 	opt.format_callback_data = &fn;
-	if (prefix)
+	// The source of a rename lies outside a limit naming its destination,
+	// so a new path is diffed across the whole commit instead, with
+	// rename detection aimed at that path alone.
+	if (prefix && path_is_new(old_oid, new_oid, prefix))
+		opt.single_follow = prefix;
+	else if (prefix)
 		cgit_diff_limit_path(&opt, prefix);
 	diff_setup_done(&opt);
 
@@ -246,6 +292,29 @@ void cgit_diff_tree(const struct object_id *old_oid, const struct object_id *new
 	diff_flush(&opt);
 }
 
+// The old name cgit_rename_source's diff finds, which a filepair_fn has no
+// other way to hand back.
+static char *rename_source;
+
+static void note_rename_source(struct diff_filepair *pair)
+{
+	if (pair->status == DIFF_STATUS_RENAMED && !rename_source)
+		rename_source = xstrdup(pair->one->path);
+}
+
+char *cgit_rename_source(const struct object_id *old_oid, const struct object_id *new_oid,
+	const char *path)
+{
+	char *source;
+
+	if (!path_is_new(old_oid, new_oid, path))
+		return NULL;
+	cgit_diff_tree(old_oid, new_oid, note_rename_source, path, 0);
+	source = rename_source;
+	rename_source = NULL;
+	return source;
+}
+
 void cgit_diff_commit(struct commit *commit, filepair_fn fn, const char *prefix)
 {
 	const struct object_id *old_oid = NULL;
@@ -262,11 +331,7 @@ int cgit_blob_too_large(size_t size)
 
 void cgit_literal_pathspec(struct pathspec *ps, struct pathspec_item *item, const char *path)
 {
-	int len = path ? strlen(path) : 0;
-
-	// nowildcard_len matching len makes git treat the path as literal
-	// rather than as a glob.
-	*item = (struct pathspec_item){ .match = path, .len = len, .nowildcard_len = len };
+	set_literal_item(item, path);
 	ps->nr = path ? 1 : 0;
 	ps->items = item;
 }