vim-patch:9.0.0275: BufEnter not triggered when using ":edit" in "nofile" buffer

Problem:    BufEnter not triggered when using ":edit" in "nofile" buffer.
Solution:   Let readfile() return NOTDONE. (closes vim/vim#10986)
a9b5b85068

src/nvim/fileio.c

@@ -337,7 +337,7 @@ int readfile(char *fname, char *sfname, linenr_T from, linenr_T lines_to_skip,
     curbuf->b_op_start = orig_start;
 
     if (flags & READ_NOFILE) {
-      return FAIL;
+      return NOTDONE;  // so that BufEnter can be triggered
     }
   }
 

src/nvim/testdir/test_autocmd.vim

@@ -599,9 +599,19 @@ func Test_BufEnter()
   " On MS-Windows we can't edit the directory, make sure we wipe the right
   " buffer.
   bwipe! Xdir
-
   call delete('Xdir', 'd')
   au! BufEnter
+
+  " Editing a "nofile" buffer doesn't read the file but does trigger BufEnter
+  " for historic reasons.
+  new somefile
+  set buftype=nofile
+  au BufEnter somefile call setline(1, 'some text')
+  edit
+  call assert_equal('some text', getline(1))
+
+  bwipe!
+  au! BufEnter
 endfunc
 
 " Closing a window might cause an endless loop