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Helm Gtags layer

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1 Description

helm-gtags and ggtags are clients for GNU Global. GNU Global is a source code tagging system that allows querying symbol locations in source code, such as definitions or references. Adding the gtags layer enables both of these modes.

2 Features

  • Select any tag in a project retrieved by gtags
  • Resume previous helm-gtags session
  • Jump to a location based on context
  • Find definitions
  • Find references
  • Present tags in current function only
  • Create a tag database
  • Jump to definitions in file
  • Show stack of visited locations
  • Manually update tag database
  • Jump to next location in context stack
  • Jump to previous location in context stack
  • Jump to a file in tag database
  • Enables eldoc in modes that otherwise might not support it.
  • Enables company complete in modes that otherwise might not support it.

3 Install

3.1 GNU Global (gtags)

To use gtags, you first have to install GNU Global.

You can install global from the software repository of your OS; however, many OS distributions are out of date, and you will probably be missing support for pygments and exuberant ctags, and thus support for many languages. We recommend installing from source. If not for example to install on Ubuntu: 

sudo apt-get install global

3.1.1 Install on OSX using Homebrew

brew install global --with-pygments --with-ctags

3.1.2 Install on *nix from source

  1. Install recommended dependencies

    To take full advantage of global you should install 2 extra packages in addition to global: pygments and ctags (exuberant). You can do this using your normal OS package manager, e.g., on Ubuntu 

    sudo apt-get install exuberant-ctags python-pygments

    or e.g., Archlinux: 

    sudo pacman -S ctags python-pygments
  2. Install with recommended features

    Download the latest tar.gz archive, then run these commands: 

    tar xvf global-6.5.3.tar.gz
cd global-6.5.3
./configure --with-exuberant-ctags=/usr/bin/ctags
make
sudo make install
  3. Configure your environment to use pygments and ctags

    To be able to use pygments and ctags, you need to copy the sample gtags.conf either to /etc/gtags.conf or $HOME/.globalrc. For example: 

    cp gtags.conf ~/.globalrc

    Additionally you should define GTAGSLABEL in your shell startup file e.g. with sh/ksh: 

    echo export GTAGSLABEL=pygments >> .profile

3.2 Emacs Configuration

To use this configuration layer, add it to your ~/.spacemacs. You will need to add gtags to the existing dotspacemacs-configuration-layers. 

(setq dotspacemacs-configuration-layers
      '( ;; ...
        gtags
         ;; ...
        ))

3.2.1 Disabling by default

If ggtags-mode is too intrusive you can disable it by default, by setting the layer variable gtags-enable-by-default to nil. 

(setq-default dotspacemacs-configuration-layers
  '((gtags :variables gtags-enable-by-default t)))

This variable can also be set as a file-local or directory-local variable for additional control per project.

4 Usage

Before using the gtags, remember to create a GTAGS database by the following methods:

  • From within Emacs, runs the command helm-gtags-create-tags, which is bound to SPC m g c. If the language is not directly supported by GNU Global, you can choose ctags or pygments as a backend to generate tag database.
  • From inside terminal, runs gtags at your project root in terminal:
cd /path/to/project/root
gtags

If the language is not directly supported by gtags, and you have not set the GTAGSLABEL environment variable, use this command instead: 

gtags --gtagslabel=pygments

4.0.1 Language Support

  1. Built-in languages

    If you do not have ctags or pygments enabled gtags will only produce tags for the following languages:

    • asm
    • c/c++
    • java
    • php
    • yacc
  2. Exuberant ctags languages

    If you have enabled exuberant ctags and use that as the backend (i.e., GTAGSLABEL=ctags or –gtagslabel=ctags) the following additional languages will have tags created for them:

    • c#
    • erlang
    • javascript
    • common-lisp
    • emacs-lisp
    • lua
    • ocaml
    • python
    • ruby
    • scheme
    • vimscript
    • windows-scripts (.bat .cmd files)
  3. Universal ctags languages

    If instead you installed you the newer/beta universal ctags and use that as the backend (i.e., GTAGSLABEL=ctags or –gtagslabel=ctags) the following additional languages will have tags created for them:

    • clojure
    • d
    • go
    • rust
  4. Pygments languages (plus symbol and reference tags)

    In order to look up symbol references for any language not in the built in parser you must use the pygments backend. When this backend is used global actually uses both ctags and pygments to find the definitions and uses of functions and variables as well as "other symbols".

    If you enabled pygments (the best choice) and use that as the backend (i.e., GTAGSLABEL=pygments or –gtagslabel=pygments) the following additional languages will have tags created for them:

    • elixir
    • fsharp
    • haskell
    • octave
    • racket
    • scala
    • shell-scripts
    • tex

4.1 Eldoc integration

This layer also integrates ggtags for its Eldoc feature. That means, when writing code, you can look at the minibuffer (at the bottom) and see variable and function definition of the symbol the cursor is on. However, this feature is only activated for programming modes that are not one of these languages:

  • C
  • C++
  • Common Lisp
  • Emacs Lisp
  • Python
  • Ruby

Since these modes have better Eldoc integration already.

In addition, if output from compile (bound to SPC c C), shell-command (bound to SPC ! and M-!) or async-shell-command (bound to M-&) commands contains symbol in your project, you move cursor on such symbol and use any of the gtags commands.

5 Key bindings

Key Binding Description
SPC m g c create a tag database
SPC m g f jump to a file in tag database
SPC m g g jump to a location based on context
SPC m g G jump to a location based on context (open another window)
SPC m g d find definitions
SPC m g i present tags in current function only
SPC m g l jump to definitions in file
SPC m g n jump to next location in context stack
SPC m g p jump to previous location in context stack
SPC m g r find references
SPC m g R resume previous helm-gtags session
SPC m g s select any tag in a project retrieved by gtags
SPC m g S show stack of visited locations
SPC m g u manually update tag database

Author: Sylvain Benner

Created: 2016-10-03 Mon 00:55

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