Add linter for haskell-language-server

The patch adds a new linter for haskell-language-server (hls). hls is
the integration point of haskell-ide-engine (hie) and ghcide.

ale_linters/haskell/hls.vim

@@ -0,0 +1,63 @@
+" Author: Yen3 <yen3rc@gmail.com>
+" Description: A language server for haskell
+"              The file is based on hie.vim (author: Luxed
+"              <devildead13@gmail.com>).  It search more project root files.
+"
+call ale#Set('haskell_hls_executable', 'haskell-language-server-wrapper')
+
+function! ale_linters#haskell#hls#FindRootFile(buffer) abort
+    let l:serach_root_files = [
+    \ 'stack.yaml',
+    \ 'cabal.project',
+    \ 'package.yaml',
+    \ 'hie.yaml'
+    \ ]
+
+    for l:path in ale#path#Upwards(expand('#' . a:buffer . ':p:h'))
+        for l:root_file in l:serach_root_files
+            if filereadable(l:path . l:root_file)
+                return l:path
+            endif
+        endfor
+    endfor
+
+    return ''
+endfunction
+
+function! ale_linters#haskell#hls#GetProjectRoot(buffer) abort
+    " Search for the project file first
+    let l:project_file = ale_linters#haskell#hls#FindRootFile(a:buffer)
+
+    " If it's empty, search for the cabal file
+    if empty(l:project_file)
+        " Search all of the paths except for the root filesystem path.
+        let l:paths = join(
+        \   ale#path#Upwards(expand('#' . a:buffer . ':p:h'))[:-2],
+        \   ','
+        \)
+        let l:project_file = globpath(l:paths, '*.cabal')
+    endif
+
+    " If we still can't find one, use the current file.
+    if empty(l:project_file)
+        let l:project_file = expand('#' . a:buffer . ':p')
+    endif
+
+    return fnamemodify(l:project_file, ':h')
+endfunction
+
+function! ale_linters#haskell#hls#GetCommand(buffer) abort
+    let l:executable = ale#Var(a:buffer, 'haskell_hls_executable')
+
+    return ale#handlers#haskell_stack#EscapeExecutable(l:executable,
+    \ 'haskell-language-server-wrapper')
+    \ . ' --lsp'
+endfunction
+
+call ale#linter#Define('haskell', {
+\   'name': 'hls',
+\   'lsp': 'stdio',
+\   'command': function('ale_linters#haskell#hls#GetCommand'),
+\   'executable': {b -> ale#Var(b, 'haskell_hls_executable')},
+\   'project_root': function('ale_linters#haskell#hls#GetProjectRoot'),
+\})

doc/ale-haskell.txt

@@ -124,6 +124,18 @@ g:ale_haskell_hlint_options                       g:ale_haskell_hlint_options
   executable.
 
 
+===============================================================================
+hls                                                           *ale-haskell-hls*
+
+g:ale_haskell_hls_executable                     *g:ale_haskell_hls_executable*
+                                                 *b:ale_haskell_his_executable*
+  Type: |String|
+  Default: `'haskell-language-server-wrapper'`
+
+  This variable can be changed to use a different executable for the haskell
+  language server.
+
+
 ===============================================================================
 stack-build                                           *ale-haskell-stack-build*
 

doc/ale-supported-languages-and-tools.txt

@@ -203,6 +203,7 @@ Notes:
   * `hie`
   * `hindent`
   * `hlint`
+  * `hls`
   * `ormolu`
   * `stack-build`!!
   * `stack-ghc`

doc/ale.txt

@@ -2741,6 +2741,7 @@ documented in additional help files.
     hfmt..................................|ale-haskell-hfmt|
     hindent...............................|ale-haskell-hindent|
     hlint.................................|ale-haskell-hlint|
+    hls...................................|ale-haskell-hls|
     stack-build...........................|ale-haskell-stack-build|
     stack-ghc.............................|ale-haskell-stack-ghc|
     stylish-haskell.......................|ale-haskell-stylish-haskell|

supported-tools.md

@@ -212,6 +212,7 @@ formatting.
   * [hie](https://github.com/haskell/haskell-ide-engine)
   * [hindent](https://hackage.haskell.org/package/hindent)
   * [hlint](https://hackage.haskell.org/package/hlint)
+  * [hls](https://github.com/haskell/haskell-language-server)
   * [ormolu](https://github.com/tweag/ormolu)
   * [stack-build](https://haskellstack.org/) :floppy_disk:
   * [stack-ghc](https://haskellstack.org/)

test/command_callback/test_haskell_hls_callbacks.vader

@@ -0,0 +1,27 @@
+Before:
+  call ale#assert#SetUpLinterTest('haskell', 'hls')
+
+  Save &filetype
+  let &filetype = 'haskell'
+
+After:
+  call ale#assert#TearDownLinterTest()
+
+Execute(The language string should be correct):
+  AssertLSPLanguage 'haskell'
+
+Execute(The default executable should be correct):
+  AssertLinter 'haskell-language-server-wrapper',
+  \ ale#Escape('haskell-language-server-wrapper') . ' --lsp'
+
+Execute(The project root should be detected correctly):
+  AssertLSPProject g:dir
+
+  call ale#test#SetFilename('hls_paths/file.hs')
+
+  AssertLSPProject ale#path#Simplify(g:dir . '/hls_paths')
+
+Execute(The executable should be configurable):
+  let g:ale_haskell_hls_executable = 'foobar'
+
+  AssertLinter 'foobar', ale#Escape('foobar') . ' --lsp'