api: return empty array when slicing out of bounds.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/nvim/api/buffer.c b/src/nvim/api/buffer.c
index c9ada8dfc0..9c29d41009 100644
--- a/src/nvim/api/buffer.c
+++ b/src/nvim/api/buffer.c
@@ -108,7 +108,7 @@ ArrayOf(String) buffer_get_line_slice(Buffer buffer,
   Array rv = ARRAY_DICT_INIT;
   buf_T *buf = find_buffer_by_handle(buffer, err);
 
-  if (!buf) {
+  if (!buf || !inbounds(buf, start)) {
     return rv;
   }
 
@@ -550,3 +550,10 @@ static int64_t normalize_index(buf_T *buf, int64_t index)
   index = index > buf->b_ml.ml_line_count ? buf->b_ml.ml_line_count : index;
   return index;
 }
+
+// Returns true if the 0-indexed `index` is within the 1-indexed buffer bounds.
+static bool inbounds(buf_T *buf, int64_t index)
+{
+  linenr_T nlines = buf->b_ml.ml_line_count;
+  return index >= -nlines && index < nlines;
+}