vim-patch:8.2.0474: cannot use :write when using a plugin with BufWriteCmd

Problem:    Cannot use :write when using a plugin with BufWriteCmd.
Solution:   Reset BF_NOTEDITED after BufWriteCmd. (closes vim/vim#5807)
0fff44152d

src/nvim/fileio.c

@@ -407,11 +407,27 @@ readfile(
 
     if (newfile) {
       if (apply_autocmds_exarg(EVENT_BUFREADCMD, NULL, sfname,
-              FALSE, curbuf, eap))
-        return aborting() ? FAIL : OK;
+                               false, curbuf, eap)) {
+        int status = OK;
+
+        if (aborting()) {
+          status = FAIL;
+        }
+
+        // The BufReadCmd code usually uses ":read" to get the text and
+        // perhaps ":file" to change the buffer name. But we should
+        // consider this to work like ":edit", thus reset the
+        // BF_NOTEDITED flag.  Then ":write" will work to overwrite the
+        // same file.
+        if (status == OK) {
+          curbuf->b_flags &= ~BF_NOTEDITED;
+        }
+        return status;
+      }
     } else if (apply_autocmds_exarg(EVENT_FILEREADCMD, sfname, sfname,
-                   FALSE, NULL, eap))
+                                    false, NULL, eap)) {
       return aborting() ? FAIL : OK;
+    }
 
     curbuf->b_op_start = pos;
   }

src/nvim/testdir/test_autocmd.vim

@@ -1072,6 +1072,40 @@ func Test_Cmd_Autocmds()
   enew!
 endfunc
 
+func s:ReadFile()
+  setl noswapfile nomodified
+  let filename = resolve(expand("<afile>:p"))
+  execute 'read' fnameescape(filename)
+  1d_
+  exe 'file' fnameescape(filename)
+  setl buftype=acwrite
+endfunc
+
+func s:WriteFile()
+  let filename = resolve(expand("<afile>:p"))
+  setl buftype=
+  noautocmd execute 'write' fnameescape(filename)
+  setl buftype=acwrite
+  setl nomodified
+endfunc
+
+func Test_BufReadCmd()
+  autocmd BufReadCmd *.test call s:ReadFile()
+  autocmd BufWriteCmd *.test call s:WriteFile()
+
+  call writefile(['one', 'two', 'three'], 'Xcmd.test')
+  edit Xcmd.test
+  call assert_match('Xcmd.test" line 1 of 3', execute('file'))
+  normal! Gofour
+  write
+  call assert_equal(['one', 'two', 'three', 'four'], readfile('Xcmd.test'))
+
+  bwipe!
+  call delete('Xcmd.test')
+  au! BufReadCmd
+  au! BufWriteCmd
+endfunc
+
 func SetChangeMarks(start, end)
   exe a:start. 'mark ['
   exe a:end. 'mark ]'