How to switch between multiple vim configurations with a command or local vimrc files?

I have this in $HOME/.vimrc:

if filereadable(".vim.custom")
    so .vim.custom
endif

This allows me to put a .vim.custom file in every directory to load commands and options specific to that directory. If you're working on multiple projects that have deep directory structures you might need something more sophisticated (e.g. walk up the directory tree until a .vim.custom is found), but the same basic idea will work.

UPDATE:

I now do something like this in order to read a .vim file from the same directory as the file I'm editing, regardless of what the current directory is.

let b:thisdir=expand("%:p:h")
let b:vim=b:thisdir."/.vim"
if (filereadable(b:vim))
    execute "source ".b:vim
endif

In Summary

There are a few ways to do this, of which most have been suggested, but I thought I'd summarise them with two extra ones:

• Per-directory vimrc - has the disadvantage that Vim must be started in the right directory: if your project is in ~/project1 and you have ~/project1/.vim.custom and do cd ~ ; vim project1/file.c, the custom settings won't be found.
• Modelines - very effective, but has the disadvantage of needing to add them to all files (and remember to add them to new files)
• Directory specific autocommands - this is very effective
• Scan for a specific header in the file (see below) - this is the one I've used most in the past where working for different companies or on clearly named projects
• Per-directory vimrc that's checked when the file is opened (see below). Another fairly easy one to implement, especially if your project code is all in one place.

Scanning for a Header

In a lot of organisations, there's a standard header (with a copyright notice and project name etc) at the top of every source file. If this is the case, you can get Vim to automatically scan the first (e.g.) 10 lines of the file looking for a keyword. If it finds it, it can change your settings. I've modified this to make it simpler than the form I use (which does lots of other things), but create a ~/.vim/after/filetype.vim (if you don't have one yet) and add something like this:

au FileType * call <SID>ConfigureFiletypes(expand("<amatch>"))

" List of file types to customise
let s:GROUPNAMETypes = ['c', 'cpp', 'vhdl', 'c.doxygen']

func! <SID>CheckForGROUPNAMECode()
    " Check if any of the first ten lines contain "GROUPNAME".

    " Read the first ten lines into a variable
    let header = getline(1)
    for i in range(2, 10)
        let header = header . getline(i)
    endfor

    if header =~ '\<GROUPNAME\>'
        " Change the status line to make it clear which
        " group we're using
        setlocal statusline=%<%f\ (GROUPNAME)\ %h%m%r%=%-14.(%l,%c%V%)\ %P
        " Do other customisation here
        setlocal et
        " etc
    endif
endfunc

func! <SID>ConfigureFiletypes(filetype)
    if index(s:GROUPNAMETypes, a:filetype) != -1
        call <SID>CheckForGROUPNAMECode()
    endif
endfunc

Whenever a file of any type is opened and the file type is set (the au FileType * line), the ConfigureFiletypes function is called. This checks whether the file type is in the list of file types associated with the current group (GROUPNAME), in this case 'c', 'cpp', 'vhdl' or 'c.doxygen'. If it is, it calls CheckForGROUPNAMECode(), which reads the first 10 lines of the file and if they contain GROUPNAME, it does some customisation. As well as setting expandtabs or whatever, this also changes the status bar to show the group name clearly so you know it's worked at a glance.

Checking for Configuration When Opening

Much like JS Bangs' suggestion, having a custom configuration file can be useful. However, instead of loading it in vimrc, consider something like this, which will check when a .c file is opened for a .vim.custom in the same directory as the .c file.

au BufNewFile,BufRead *.c call CheckForCustomConfiguration()

function! CheckForCustomConfiguration()
    " Check for .vim.custom in the directory containing the newly opened file
    let custom_config_file = expand('%:p:h') . '/.vim.custom'
    if filereadable(custom_config_file)
        exe 'source' custom_config_file
    endif
endfunction

You can also put autocommands in your .vimrc which set specific options on a per-path basis.

au BufRead,BufNewFile /path/to/project1/* setl sw=4 et
au BufRead,BufNewFile /path/to/project2/* setl sw=3 noet

Assuming your fellow developers won't complain about it, you can always add vim settings to each file in the comments.

/*
 * vim:ts=4:sw=4:expandtab:...
 */

int main(int argc, char **argv)
{
    ...

I work in several groups, each of which has its own tab/indentation/spacing standards in C.

I work with all sorts of open source, all at the same time. It's not practical to be creating separate .vimrc files and reconfiguring the formatting standards. More than a decade ago, I finally got tired of dealing with the editor configuration and wrote a program called autotab to handle it.

When autotab is set up with Vim suggested, each time you load a file into Vim, autotab is invoked on it, and the Vim settings output autotab are passed to a :set command.

autotab reads several thousand lines from the file, analyzes them and determines the settings for the expandtab, tabstop and shiftwidth parameters.

It figures out whether the file uses hard tabs or just spaces for indentation, and it figures out the indentation size. If the file is indented with tabs, it figures out the right tab size, based on rendering the file sample using various tab sizes and judging it according to heuristics like line-over-line alignment of internal elements.

It works well enough that I stopped tweaking the algorithm years ago. If it gets confused, it's almost always because the file has formatting issues, such as the use of multiple conventions at the same time.

It is also "agnostic" of the file type and works well with a variety of different languages. I use it not only over C, but shell scripts, Lisp, Makefiles, HTML, and what have you.

Note that it doesn't handle other parameters of formatting that may be project-specific, like for instance, in C files, whether case labels in a switch statement are indented or not, or whether wrapped function argument lists are simply indented, or aligned to the opening parenthesis of the argument list. Vim does have settings for that sort of thing, and so the program could be plausibly extended to analyze the style and output those parameters.

You can use stow for switching configuration (any dotfiles, not only .vimrc)

Install stow:

$ apt install stow

Create multiple directories for each configurations:

~$ ls -d ~/dotfiles/vim*
vim-all vim-webdev vim-go

Put different .vimrc's in them:

$ find ~/dotfiles -name .vimrc
/home/username/vim-golang/.vimrc
/home/username/vim-webdev/.vimrc
/home/username/vim-all/.vimrc

Now you can instantinate vim-golang config with this command (should be run inside dotfiles directory):

~$ cd ~/dotfiles

dotfiles$ stow -v vim-golang
LINK: .vimrc => dotfiles/vim-golang/.vimrc

Now it's linked:

$ cd ~ && ls -l .vimrc 
.vimrc -> dotfiles/vim-golang/.vimrc

If you need to switch config, just re-stow it:

~$ cd dotfiles

dotfiles$ stow -v -D vim-golang
UNLINK: .vimrc

dotfiles$ stow -v vim-webdev
LINK: .vimrc => dotfiles/vim-webdev/.vimrc

$ cd ~ && ls -l .vimrc 
.vimrc -> dotfiles/vim-webdev/.vimrc

More reading of it here: Managing dotfiles with GNU stow

Pros: pretty simple, no vim plugin dependencies, can be used for managing all dotfiles, not only .vimrc.

Cons: configs are independent of each other, you need to manage/update each of them separately (if you dont switch/update you configs too often - it'll not be the issue).