fix(diagnostic): check if delete failed in `qf_fill_buffer()` (#25932)

When the contents of a quickfix buffer are replaced, there is a chance
that deletion of the previous lines fails. This ensures that we don't
get stuck in an infinite loop of retrying.

Fix #25402

1 files changed, 6 insertions, 1 deletions

diff --git a/src/nvim/quickfix.c b/src/nvim/quickfix.c
index 2e3cc4f170..61157301b6 100644
--- a/src/nvim/quickfix.c
+++ b/src/nvim/quickfix.c
@@ -4135,7 +4135,12 @@ static void qf_fill_buffer(qf_list_T *qfl, buf_T *buf, qfline_T *old_last, int q
 
     // delete all existing lines
     while ((curbuf->b_ml.ml_flags & ML_EMPTY) == 0) {
-      (void)ml_delete((linenr_T)1, false);
+      // If deletion fails, this loop may run forever, so
+      // signal error and return.
+      if (ml_delete((linenr_T)1, false) == FAIL) {
+        internal_error("qf_fill_buffer()");
+        return;
+      }
     }
   }