Stack support

If a `stack.yaml` file is found in the pwd, then hdevtools commands will
be invoked by `stack exec --package hdevtools hdevtools` instead
of `hdevtools`.

`hdevtools` must be built with the same version of GHC as the project
being inspected. With Stack support for vim-hdevtools, `hdevtools` will be
built with the same version of GHC referred to by the `stack.yaml`
resolver for the project, and `hdevtools` will be automatically installed
locally the first time a vim-hdevtools command is run.

Stack support must be enabled by `g:hdevtools_stack = 1`, otherwise
vim-hdevtools will revert to the usual behavior of always looking
for `hdevtools` in the `$PATH`. This will provide continuity for users who
would be surprised by the new behavior if they weren't expecting it.

In the future, perhaps Stack support could be enabled by default.

Author: jamesdbrock

README.md

@@ -19,21 +19,55 @@ editor.
 This is the Vim plugin that integrates Vim with hdevtools.
 
 
-Installation
+Requirements
 ------------
 
-1. You must install the `hdevtools` command line program, It can be found
-   here: <https://github.com/hdevtools/hdevtools/>, or from Hackage:
+The *vim-hdevtools* plugin requires a way to run `hdevtools`. Here are the
+ways to make `hdevtools` available to the plugin.
+
+### Global `hdevtools`
+
+Install the `hdevtools` command line program so that it is on your
+executable `$PATH`.
+
+Get it from Github: <https://github.com/hdevtools/hdevtools/>
+
+Or from Hackage:
+
+    $ cabal install hdevtools
+
+Or from Stackage:
+
+    $ stack install hdevtools
 
-        $ cabal install hdevtools
+Note that `hdevtools` must be built with the same version of GHC as the
+project which you will be editing.
+
+### Local `hdevtools` with `stack`
+
+If your project is built with [stack](<https://www.haskellstack.org>) and
+if you run Vim from the directory that contains `stack.yaml`, then
+the *vim-hdevtools* plugin can employ `stack` to automatically install
+`hdevtools` built with the same version of GHC indicated by the resolver
+in your `stack.yaml`. This will not conflict with any other installations
+of `hdevtools` on your system.
+
+If you want the *vim-hdevtools* plugin to use `stack`,
+you have to enable this feature in your `.vimrc` like so:
+
+    let g:hdevtools_stack = 1
+
+
+Installation
+------------
 
-2. Install this plugin. [pathogen.vim](<https://github.com/tpope/vim-pathogen/>)
+1. Install this plugin. [pathogen.vim](<https://github.com/tpope/vim-pathogen/>)
    is the recommended way:
 
         cd ~/.vim/bundle
         git clone https://github.com/bitc/vim-hdevtools.git
 
-3. Configure your keybindings in your `.vimrc` file. I recommend something
+2. Configure your keybindings in your `.vimrc` file. I recommend something
    like:
 
         au FileType haskell nnoremap <buffer> <F1> :HdevtoolsType<CR>

autoload/hdevtools.vim

@@ -477,18 +477,15 @@ function! s:on_leave()
 endfunction
 
 function! hdevtools#build_command(command, args)
-  let l:cmd = 'hdevtools'
-  let l:cmd = l:cmd . ' ' . a:command . ' '
-
+  let l:cmd = g:hdevtools_exe . ' ' . a:command . ' '
   let l:cmd = l:cmd . get(g:, 'hdevtools_options', '') . ' '
   let l:cmd = l:cmd . a:args
   return l:cmd
 endfunction
 
 " Does not include g:hdevtools_options
 function! hdevtools#build_command_bare(command, args)
-  let l:cmd = 'hdevtools'
-  let l:cmd = l:cmd . ' ' . a:command . ' '
+  let l:cmd = g:hdevtools_exe . ' ' . a:command . ' '
   let l:cmd = l:cmd . a:args
   return l:cmd
 endfunction

ftplugin/haskell/hdevtools.vim

@@ -6,7 +6,16 @@ let b:did_ftplugin_hdevtools = 1
 if !exists('s:has_hdevtools')
   let s:has_hdevtools = 0
 
-  if !executable('hdevtools')
+  " For stack support, vim must be started in the directory containing stack.yaml
+  if exists('g:hdevtools_stack') && g:hdevtools_stack && filereadable("stack.yaml")
+    if !executable('stack')
+      call hdevtools#print_error('hdevtools: stack.yaml found, but stack is not executable!')
+      finish
+    endif
+    let g:hdevtools_exe = 'stack exec --silent --no-ghc-package-path --package hdevtools hdevtools --'
+  elseif executable('hdevtools')
+    let g:hdevtools_exe = 'hdevtools'
+  else
     call hdevtools#print_error('hdevtools: hdevtools is not executable!')
     finish
   endif