How to automatically update tag file in vim?

Question

I use vim C++ tag file for navigation using Ctrl-]. The problem is whenever some file gets modified, the links are no longer valid and I have to re-run ctags and update the tag file. Our code base is huge and it takes quite a while for generating tag file.

Is there any tool which periodically updates the tag file in background? Can I configure VIM to do the same?

I use gvim under Windows.

Answer 1

An idea:

Use Vim autocommands (:help autocommand) to trigger running of a script every time a buffer is saved using the BufWritePost event.

This script starts the ctags generation and contains some additional small logic to not run while it's already running (or to run at most every 10 minutes, etc.).

Edit:

Something similar was asked here beforehand, see http://stackoverflow.com/questions/155449/vim-auto-generate-ctags

Answer 2

Further to Blixtor's answer, you'll need to think a little carefully about the design of the script. I'd recommend segregating the design such that the autocommand uses the Windows "start" command or similar to run an external script in the background: thereby preventing Vim from being unresponsive while the tag file is generated.

That script could then generate the tag file using a different file name (i.e. not "tags": ctags -R -o newtags .) and, when ctags is complete, delete tags and rename newtags to tags. This will prevent the tag file from being unavailable in Vim while the generation is done.

Answer 3

This logic works for most cases: When opening a new file in vim, change to the directory of that file and generate a tags file there if it does not already exist. When saving a changed buffer, generate a tags file in the directory of the file being saved:

---

function! GenerateTagsFile()
  if (!filereadable("tags"))
    exec ":!start /min ctags -R --c++-kinds=+p --fields=+iaS --extra=+q --sort=foldcase ."
  endif
endfunction

" Always change to directory of the buffer currently in focus.
autocmd! bufenter *.* :cd %:p:h
autocmd! bufread  *.* :cd %:p:h

" Generate tags on opening an existing file.
autocmd! bufreadpost *.cpp :call GenerateTagsFile()
autocmd! bufreadpost *.c   :call GenerateTagsFile()
autocmd! bufreadpost *.h   :call GenerateTagsFile()

" Generate tags on save. Note that this regenerates tags for all files in current folder.
autocmd! bufwritepost *.cpp :call GenerateTagsFile()
autocmd! bufwritepost *.c   :call GenerateTagsFile()
autocmd! bufwritepost *.h   :call GenerateTagsFile()