commit https://github.com/vim/vim/commit/b681be175b6991cdc2b8ddd49b0e97e3fe2b201e Author: Bram Moolenaar <Bram@vim.org> Date: Thu Mar 31 23:02:16 2016 +0200 patch 7.4.1691 Problem: When switching to a new buffer and an autocommand applies syntax highlighting an ml_get error may occur. Solution: Check "syn_buf" against the buffer in the window. (Alexander von Buddenbrock, closes #676)

the first targets to make vim are: scratch config myself
srcdir = .
VIMNAME = vim
EXNAME = ex
VIEWNAME = view