Allow to configure haskell-language-server LSP config (#4038)

ale_linters/haskell/hls.vim

@@ -4,6 +4,7 @@
 "              <devildead13@gmail.com>).  It search more project root files.
 "
 call ale#Set('haskell_hls_executable', 'haskell-language-server-wrapper')
+call ale#Set('haskell_hls_config', {})
 
 function! ale_linters#haskell#hls#FindRootFile(buffer) abort
     let l:serach_root_files = [
@@ -60,4 +61,5 @@ call ale#linter#Define('haskell', {
 \   'command': function('ale_linters#haskell#hls#GetCommand'),
 \   'executable': {b -> ale#Var(b, 'haskell_hls_executable')},
 \   'project_root': function('ale_linters#haskell#hls#GetProjectRoot'),
+\   'lsp_config': {b -> ale#Var(b, 'haskell_hls_config')},
 \})

doc/ale-haskell.txt

@@ -142,6 +142,20 @@ g:ale_haskell_hls_executable                     *g:ale_haskell_hls_executable*
   language server.
 
 
+g:ale_haskell_hls_config                             *g:ale_haskell_hls_config*
+                                                     *b:ale_haskell_hls_config*
+  Type: |Dictionary|
+  Default: `{}`
+
+  Dictionary with configuration settings for HLS. For example, to see more
+  completions:
+>
+  let g:ale_haskell_hls_config = {'haskell': {'maxCompletions': 250}}
+<
+  Refer to HLS documentation for possible settings:
+  https://haskell-language-server.readthedocs.io/en/latest/configuration.html#language-specific-server-options
+
+
 ===============================================================================
 stack-build                                           *ale-haskell-stack-build*
 

test/linter/test_haskell_hls.vader

@@ -25,3 +25,8 @@ Execute(The executable should be configurable):
   let g:ale_haskell_hls_executable = 'foobar'
 
   AssertLinter 'foobar', ale#Escape('foobar') . ' --lsp'
+
+Execute(Should accept configuration settings):
+  AssertLSPConfig {}
+  let b:ale_haskell_hls_config = {'haskell': {'maxCompletions': 250}}
+  AssertLSPConfig {'haskell': {'maxCompletions': 250}}