Ghc Tags Plugin published on hackage

Geting vim tags from Haskell's parsed tree

Working on a large code base, which many type level features could be easier with a proper editor support. Finding associated type class instances or open type families isn't easy at the moment. Existing solutions like hasktags do not cover all the new language features, so at times one is left is searching the tree by hand. Haskell IDE engine, will deliver a very good solution, but at this time it is still quite hard to find a good language client for vim which works out of the box.

Ghc plugin is a good fit for solving this problem, and here are the reasons why:

  • CPP pragmas are resolved;
  • it doesn't matter whether you write literate haskell, regular haskell or you are using hsc2hs or some other preprocessor;
  • contains accurate source information;
  • one can derive additional information: tag kinds, whether its static or not (i.e. exported or not) - vim decides how to order tags depending on this information;
  • regularly updated, as you build your project; possibly it could be integrated with ghcid (I haven't tried yet).
In the future it could be even extended with type level information.

Over last two weeks I worked out a quite nice solution ghc-tags-plugin using ghc plugin system: at the moment only the part which has access to parsed tree. This allows to output tags for:

  • top level terms
  • data types
  • record fields
  • type synonyms
  • type classes
  • type class members
  • type class instances
  • type families standalone and associated
  • type family instances standalone and associated
  • data type families standalone and associated
  • data type families instances standalone and associated
  • data type family instances constructors standalone and associated
And it includes support for:
  • tag kinds (as given above)
  • whether terms, type constructor, class method, etc. are exported or not
  • its tags file parser is compatible with output of ctags, so if you want you could append tags generated by ctags (i.e. for C in your project).

Configuration is simple (and possibly can be still improved). For cabal you don't need to modify checked files (only cabal.project.local). Check out the readme file for instructions.

If you encounter problems with installation, the github repo contains a Makefile to remove the plugin from the cabal store, install it, list installed versions. This turned out to be quite useful during development (co-existence of the same version of the plugin which depends on an internal library may cause problems).

I have been using this plugin on a daily basis while working on IOHK code base which contains

haskell:     214521 (96.22%)
ansic:         5285 (2.37%)
sh:            1868 (0.84%)
javascript:      1019 (0.46%)
cpp:            197 (0.09%)
perl:            63 (0.03%)
lisp:             7 (0.00%)
Navigating the codebase, re-discovering where things were moved after a refactoring, discovering code in far away from my area of expertise became much easier.

It has been tested on Windows and Linux. The only requirement is: GHC version 8.6.5 or later.

Happy Haskelling!