How to programmatically create/update a TAGS file with emacs?

Is there any plugin for emacs to automatically update the TAGS file in my C project (for example on buffer save or access) or create a new one if there is no TAGS file present?

I am running on Windows (without Cygwin), so all the fancy shell scripting does not help. I was hoping for a native emacs solution not using any external scripting.

I already tried build-tags.el and etags-table.el but none of these really worked (the way I wanted).

Any other ideas?

From stackoverflow

• Why not add an execution of ctags to your build script? You really only need a new tags file when you compile (at the most). I tend to just write a scheduled task to build the tags file every night. Seems to work pretty well.

  cschol : I want the TAGS file updated as soon as new symbols are introduced in the source. I extensively use TAGS browsing capabilities when developing to jump from file to file. Once a night is not often enough. Personal build script mods are not possible in our multi developer environment.

  Steve Rowe : How do you build your code? Wrap that command with a script that does the build, then runs the ctags command.

  jrockway : I disagree -- you want tags immediately after editing the buffer.

  cschol : @Steve Rowe: Yeah, I could probably script something together. But I dont like it. @jrockway: I agree. I NEED it immediately and not necessarily want to build every time.

• I use combination of semantic + gnu global for my day-to-day work. GNU Global's databases are updated once per day, while semantic use them for basic navigation, and re-parse changed files on the fly.

  You can find more about these packages in my article about Cedet

• Here is how I generate a TAGS file for a C project:

  1. M-x cd ( to the root of your project )
  2. M-x compile
  3. find . -name "*.[chCH]" -print | etags -

  That will create a TAGS file in the current directory for all sub directories and files.

  Here is a emacs function that does the exact same thing:

  (defun compile-tags ()
    "compile etags for the current project"
    (interactive)
    (cd "YOUR_DIRECTORY")
    (compile "find . -name \"*.[chCH]\" -print | etags -"))
  

  NOTE: if you are on windows you'll need to install cygwin and make sure c:\cygwin\bin is in your path so that you get find in your path. Also make sure the emacs bin directory is in your path so that you can get etags as well.

  justinhj : You can also use the native windows version of gnu utils including find and so on. I find them faster than cygwin. http://gnuwin32.sourceforge.net/

• This might get you close (untested):

  (defvar my-auto-update-tags-alist
    (list '("/some/path/to/TAGS" "command_to_build_tags")
          '("/another/path/to/TAGS" "another_build_command")))
  
  (defun my-auto-update-tags ()
    "Automatically update TAGS files"
    (tags-table-check-computed-list)
    (let ((filename (buffer-file-name))
          build-cmd)
      (mapc (lambda (tag-file)
              (set-buffer tag-file)
              (when (member filename (tags-table-files))
                (setq build-cmd (cdr (assoc tag-file my-auto-update-tags-alist)))
                (when build-cmd
                  (call-process build-cmd nil 0))))
            tags-table-computed-list)))
  
  (add-hook 'after-save-hook 'my-auto-update-tags)
  

  It will only work (did I mention it's untested?) on files that are in TAGS files already. If you add a new file you'd have to regenerate the TAGS file the first time yourself. The call-process part should work asynchronously, so it might be a few moments until the TAGS file is actually rebuilt (if this even works ;)

  Török Gábor : Would you make an effort to test it?

• etags-update may help in your case. I didn't test it but as of the readme:

  etags-update.el is a Emacs global minor mode that updates your TAGS when saving a file.
  

  I found it from the emacswiki on this page: http://www.emacswiki.org/emacs/BuildTags