vim-patch:9.0.1877: missing test for patch 9.0.1873

Problem:  missing test for patch 9.0.1873
Solution: add a test trying to exchange windows

Add a test, making sure that switching windows is not allowed when
textlock is active, e.g. when running `:s/<pat>/\=func()/`

18d2709aa1

Co-authored-by: Christian Brabandt <cb@256bit.org>

src/nvim/ex_cmds.c

@@ -3888,6 +3888,10 @@ static int do_sub(exarg_T *eap, const proftime_T timeout, const long cmdpreview_
           nmatch = curbuf->b_ml.ml_line_count - sub_firstlnum + 1;
           current_match.end.lnum = sub_firstlnum + (linenr_T)nmatch;
           skip_match = true;
+          // safety check
+          if (nmatch < 0) {
+            goto skip;
+          }
         }
 
         // Save the line numbers for the preview buffer

src/nvim/window.c

@@ -1884,6 +1884,10 @@ static void win_exchange(int Prenum)
     beep_flush();
     return;
   }
+  if (text_or_buf_locked()) {
+    beep_flush();
+    return;
+  }
 
   frame_T *frp;
 

test/old/testdir/test_substitute.vim

@@ -1425,4 +1425,18 @@ func Test_z_substitute_expr_leak()
   delfunc SubExpr
 endfunc
 
+func Test_substitute_expr_switch_win()
+  func R()
+    wincmd x
+    return 'XXXX'
+  endfunc
+  new Xfoobar
+  let bufnr = bufnr('%')
+  put ="abcdef"
+  silent! s/\%')/\=R()
+  call assert_fails(':%s/./\=R()/g', 'E565')
+  delfunc R
+  exe bufnr .. "bw!"
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab