Add better support for Haskell stack compiler tools (#1851)

* Add better support for Haskell stack compiler tools

This commit adds support for `stack` as the executable of a tool. This
follows a pattern that has been implemented for `bundler`'s tool chain.

* Move hlint command to linter file
* Add vader test for stack exec handling
* Update ghc-mod to support stack execution

`ghc-mod` was previously broken into 2 linters.

1. ghc_mod
2. stack_ghc_mod

This additional linter is not necessary with proper support for
executable variables and `stack exec` handling.

* Support stack exec in hfmt
* Support stack in hdevtools

ale_linters/haskell/hlint.vim

@@ -1,9 +1,6 @@
 " Author: jparoz <jesse.paroz@gmail.com>
 " Description: hlint for Haskell files
 
-call ale#Set('haskell_hlint_executable', 'hlint')
-call ale#Set('haskell_hlint_options', get(g:, 'hlint_options', ''))
-
 function! ale_linters#haskell#hlint#Handle(buffer, lines) abort
     let l:output = []
 
@@ -32,14 +29,15 @@ endfunction
 function! ale_linters#haskell#hlint#GetCommand(buffer) abort
     let l:hlintopts = '--color=never --json'
 
-    return '%e'
+    return ale#handlers#hlint#GetExecutable(a:buffer)
     \      . ' ' . ale#Var(a:buffer, 'haskell_hlint_options')
-    \      . ' ' . l:hlintopts . ' -'
+    \      . ' ' . l:hlintopts
+    \      . ' -'
 endfunction
 
 call ale#linter#Define('haskell', {
 \   'name': 'hlint',
 \   'executable_callback': ale#VarFunc('haskell_hlint_executable'),
-\   'command_callback': 'ale_linters#haskell#hlint#GetCommand',
+\   'command_callback': 'ale_linters#haskell#hlint#GetCommand' ,
 \   'callback': 'ale_linters#haskell#hlint#Handle',
 \})