vim (not vi) runs in compatible mode by default

Binary package hint: vim

Please read this report from the user's point of view, because as a developer you probably already have tuned `vim` to run in nocompatible mode.

When you install `vim` in Ubuntu, it may run in "compatible mode". "compatible mode" causes arrow keys to output A, B, C, D in insert mode, remove --INSERT-- marker from the bottom line, 'u' to undo only the last change, 'cw' not erasing the word before editing, etc. When `vim` is switched into compatible mode - it causes a lot of frustration.

"compatible mode" is needed, because `vim` replaced `vi` editor many years ago and people used to the behavior of old editor. These people still used `vi` command to invoke the editor, but this time it was new `vim` working behind the scenes. People could set "nocompatible" option in config file to use the latest and greatest features of 'vim' while still invoking it with `vi` command.

It is logical to assume that to avoid extra configuration people could execute `vim` command to run `vim` in nocompatible mode and `vi` to work in compatible. But many Ubuntu releases have passed, installed and removed, and this is not achieved yet. I hope we all agree that by executing `vim` we want the default features of `vim` and not `vi` in Ubuntu. Let's see that this doesn't work consistently.

First, remove your current `vim`:
$ sudo rm -rf /etc/vim
$ rm ~/.viminfo
$ rm ~/.vimrc
$ sudo aptitude purge vim vim-common vim-gnome vim-gui-common vim-runtime vim-tiny

Now install `vim-tiny` as it is the version of `vim` that comes preinstalled in Ubuntu through ubuntu-minimal core package (see http://packages.ubuntu.com/source/maverick/ubuntu-meta for the full list of packages installed in Ubuntu by default):
$ sudo aptitude install vim-tiny
$ vim
bash: /usr/bin/vim: No such file or directory

There is no `vim`, but if you launch `vi` you will actually see `vim` title screen. Of course, being executed as `vi` it runs in compatible mode by default. Now installing `vim`:
$ sudo aptitude install vim
$ vim

It runs in `nocompatible` mode and seems like everything works as expected. What about `vi`:
$ vi
:set compatible?
nocompatible

This is bug#1 - installed `vim` package changes default behavior of `vi` command, i.e. implicitly changes behavior of other package. When users used to the fact that `vi` command has arrow keys and syntax highlighting support, they forget that it is was actually provided by `vim` and start to experience problems on new systems. About 80% of `vim` questions here are about "vim features that don't work in vi" - https://answers.launchpad.net/ubuntu/+source/vim That's definitely a Frequently Asked Question.

Let's try to return `vi` the original behavior, so that `vi` runs in compatible mode and `vim` is not. It is safe to assume that mode problems are caused by configuration files. Let's get rid of them:
$ sudo rm -rf /etc/vim
$ vi
:set compatible?
  compatible

Good. What about `vim`?
$ vim
:set compatible?
  compatible

This is bug #2: vim (not vi) runs in compatible mode by default.

Let's try to fix this by reinstalling vim:
$ sudo aptitude remove vim
$ sudo aptitude install vim
$ vim
:set compatible?
  compatible

As you can see it is not fixed. All these bugs could be avoided if `vi` command provided in Ubuntu as a script that launches `vim` in forced "compatible mode" while the `vim` command itself without any configuration always work in "nocompatible".