Close #4541 - Fix Haskell project root detection

We weren't joining and returning paths correctly for detecting project
roots for Haskell projects, and now we are.

Co-authored-by: Rodrigo Mesquita <rodrigo.m.mesquita@gmail.com>

ale_linters/haskell/hls.vim

@@ -16,8 +16,9 @@ function! ale_linters#haskell#hls#FindRootFile(buffer) abort
 
     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)
+            if filereadable(l:path . '/' . l:root_file)
-                return l:path
+                " Add on / so fnamemodify(..., ':h') below keeps the path.
+                return l:path . '/'
             endif
         endfor
     endfor

test/linter/test_haskell_hls.vader

@@ -30,3 +30,13 @@ Execute(Should accept configuration settings):
   AssertLSPConfig {}
   let b:ale_haskell_hls_config = {'haskell': {'maxCompletions': 250}}
   AssertLSPConfig {'haskell': {'maxCompletions': 250}}
+
+Execute(We should detect the root with cabal.project files, preferred over *.cabal files):
+  call ale#test#SetFilename('../test-files/haskell/haskell-packages-project/package-a/src/folder/dummy.hs')
+
+  AssertLSPProject ale#test#GetFilename('../test-files/haskell/haskell-packages-project')
+
+Execute(We should a project root with *.cabal files):
+  call ale#test#SetFilename('../test-files/haskell/haskell-simple-package/package-a/src/folder/dummy.hs')
+
+  AssertLSPProject ale#test#GetFilename('../test-files/haskell/haskell-simple-package/package-a')