vim-patch:8.1.0988: deleting location list buffer breaks location list window

Problem:    Deleting a location list buffer breaks location list window
            functionality.
Solution:   (Yegappan Lakshmanan, closes vim/vim#4056)
https://github.com/vim/vim/commit/d82a81cad93708a6c180e59119db4818cc38c1a9

Cherry-pick Xqbuf_test() changes from patch 8.1.0892.
Patch 8.1.0892 triggers a memory leak.

1 files changed, 19 insertions, 7 deletions

diff --git a/src/nvim/quickfix.c b/src/nvim/quickfix.c
index 1582ce3bd6..06fed9c2cf 100644
--- a/src/nvim/quickfix.c
+++ b/src/nvim/quickfix.c
@@ -3581,6 +3581,18 @@ static int qf_goto_cwindow(const qf_info_T *qi, bool resize, int sz,
   return OK;
 }
 
+// Set options for the buffer in the quickfix or location list window.
+static void qf_set_cwindow_options(void)
+{
+  // switch off 'swapfile'
+  set_option_value("swf", 0L, NULL, OPT_LOCAL);
+  set_option_value("bt", 0L, "quickfix", OPT_LOCAL);
+  set_option_value("bh", 0L, "hide", OPT_LOCAL);
+  RESET_BINDING(curwin);
+  curwin->w_p_diff = false;
+  set_option_value("fdm", 0L, "manual", OPT_LOCAL);
+}
+
 // Open a new quickfix or location list window, load the quickfix buffer and
 // set the appropriate options for the window.
 // Returns FAIL if the window could not be opened.
@@ -3629,17 +3641,17 @@ static int qf_open_new_cwindow(qf_info_T *qi, int height)
     // Create a new quickfix buffer
     (void)do_ecmd(0, NULL, NULL, NULL, ECMD_ONE, ECMD_HIDE, oldwin);
 
-    // switch off 'swapfile'
-    set_option_value("swf", 0L, NULL, OPT_LOCAL);
-    set_option_value("bt", 0L, "quickfix", OPT_LOCAL);
-    set_option_value("bh", 0L, "hide", OPT_LOCAL);
-    RESET_BINDING(curwin);
-    curwin->w_p_diff = false;
-    set_option_value("fdm", 0L, "manual", OPT_LOCAL);
     // save the number of the new buffer
     qi->qf_bufnr = curbuf->b_fnum;
   }
 
+  // Set the options for the quickfix buffer/window (if not already done)
+  // Do this even if the quickfix buffer was already present, as an autocmd
+  // might have previously deleted (:bdelete) the quickfix buffer.
+  if (curbuf->b_p_bt[0] != 'q') {
+    qf_set_cwindow_options();
+  }
+
   // Only set the height when still in the same tab page and there is no
   // window to the side.
   if (curtab == prevtab && curwin->w_width == Columns) {