1 files changed, 13 insertions, 8 deletions

diff --git a/src/nvim/api/buffer.c b/src/nvim/api/buffer.c
index c9ada8dfc0..12c97cfffb 100644
--- a/src/nvim/api/buffer.c
+++ b/src/nvim/api/buffer.c
@@ -70,7 +70,6 @@ String buffer_get_line(Buffer buffer, Integer index, Error *err)
 /// @param line The new line.
 /// @param[out] err Details of an error that may have occurred
 void buffer_set_line(Buffer buffer, Integer index, String line, Error *err)
-  FUNC_ATTR_DEFERRED
 {
   Object l = STRING_OBJ(line);
   Array array = {.items = &l, .size = 1};
@@ -83,7 +82,6 @@ void buffer_set_line(Buffer buffer, Integer index, String line, Error *err)
 /// @param index The line index
 /// @param[out] err Details of an error that may have occurred
 void buffer_del_line(Buffer buffer, Integer index, Error *err)
-  FUNC_ATTR_DEFERRED
 {
   Array array = ARRAY_DICT_INIT;
   buffer_set_line_slice(buffer, index, index, true, true, array, err);
@@ -108,7 +106,7 @@ 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;
   }
 
@@ -171,7 +169,6 @@ void buffer_set_line_slice(Buffer buffer,
                       Boolean include_end,
                       ArrayOf(String) replacement,
                       Error *err)
-  FUNC_ATTR_DEFERRED
 {
   buf_T *buf = find_buffer_by_handle(buffer, err);
 
@@ -179,6 +176,11 @@ void buffer_set_line_slice(Buffer buffer,
     return;
   }
 
+  if (!inbounds(buf, start)) {
+    api_set_error(err, Validation, _("Index out of bounds"));
+    return;
+  }
+
   start = normalize_index(buf, start) + (include_start ? 0 : 1);
   include_end = include_end || (end >= buf->b_ml.ml_line_count);
   end = normalize_index(buf, end) + (include_end ? 1 : 0);
@@ -334,7 +336,6 @@ Object buffer_get_var(Buffer buffer, String name, Error *err)
 /// @param[out] err Details of an error that may have occurred
 /// @return The old value
 Object buffer_set_var(Buffer buffer, String name, Object value, Error *err)
-  FUNC_ATTR_DEFERRED
 {
   buf_T *buf = find_buffer_by_handle(buffer, err);
 
@@ -370,7 +371,6 @@ Object buffer_get_option(Buffer buffer, String name, Error *err)
 /// @param value The option value
 /// @param[out] err Details of an error that may have occurred
 void buffer_set_option(Buffer buffer, String name, Object value, Error *err)
-  FUNC_ATTR_DEFERRED
 {
   buf_T *buf = find_buffer_by_handle(buffer, err);
 
@@ -421,7 +421,6 @@ String buffer_get_name(Buffer buffer, Error *err)
 /// @param name The buffer name
 /// @param[out] err Details of an error that may have occurred
 void buffer_set_name(Buffer buffer, String name, Error *err)
-  FUNC_ATTR_DEFERRED
 {
   buf_T *buf = find_buffer_by_handle(buffer, err);
 
@@ -467,7 +466,6 @@ void buffer_insert(Buffer buffer,
                    Integer lnum,
                    ArrayOf(String) lines,
                    Error *err)
-  FUNC_ATTR_DEFERRED
 {
   buffer_set_line_slice(buffer, lnum, lnum, false, true, lines, err);
 }
@@ -550,3 +548,10 @@ 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;
+}