vim81 configuration wrong after I added .vimrc

Question

I uninstalled vim74 and compiled vim81 and installed it. However I found it strange, comparing to vim74. When there's no .vimrc file under HOME dir, I open a c++ file and syntax highlight is working and I can use Backspace to delete letters. However when I add a .vimrc under HOME dir and just put set number into it, when the c++ source file is opened, no highlight, and Backspace not working. Why is that ? I used to add some configurations in .vimrc under vim74 before, and this situation never happens.

Answer 1

After complaints that Vim in its default configuration is hard to use (especially for beginners), it was decided to enable a default configuration if the user hasn't created his own ~/.vimrc (yet). This was introduced with Vim 8.0, and explains what you're seeing (namely: syntax highlighting and sensible backspace behavior). Read more about the details at :help defaults.vim.

The help also has instructions how to keep the defaults when adding your own ~/.vimrc configuration:

If you create your own .vimrc, it is recommended to add these lines somewhere near the top:

unlet! skip_defaults_vim
source $VIMRUNTIME/defaults.vim

Then Vim works like before you had a .vimrc.

Tip: Don't go all crazy with adding various snippets (especially not those you don't fully understand) and plugins to your ~/.vimrc, even though the Internet is full of them. Rather, build it up gradually, depending on needs, and back up your understanding with careful studying of the excellent :help. Also, avoid pre-packaged Vim distributions; they're even worse.