elixir-ls now recognizes umbrella projects

Previously, elixir-ls would treat each sub-project within an umbrella as
standalone, which isn't desirable from a language server perspective.

Added ale#handlers#elixir#FindMixUmbrellaRoot, which locates the current
project's root and then continues searching upwards for a potential
umbrella project root. This literally looks just two levels up to keep
things simple while keeping in line with Elixir project conventions.

Use this new function to determine elixir-ls's LSP project root.

ale_linters/elixir/elixir_ls.vim

@@ -16,6 +16,6 @@ call ale#linter#Define('elixir', {
 \   'lsp': 'stdio',
 \   'executable_callback': 'ale_linters#elixir#elixir_ls#GetExecutable',
 \   'command_callback': 'ale_linters#elixir#elixir_ls#GetExecutable',
-\   'project_root_callback': 'ale#handlers#elixir#FindMixProjectRoot',
+\   'project_root_callback': 'ale#handlers#elixir#FindMixUmbrellaRoot',
 \   'lsp_config_callback': ale#VarFunc('elixir_elixir_ls_config'),
 \})

autoload/ale/handlers/elixir.vim

@@ -1,7 +1,8 @@
 " Author: Matteo Centenaro (bugant) - https://github.com/bugant
-"
-" Description: find the root directory for an elixir project that uses mix
+" Author: Jon Parise <jon@indelible.org>
+" Description: Functions for working with Elixir projects
 
+" Find the root directory for an elixir project that uses mix.
 function! ale#handlers#elixir#FindMixProjectRoot(buffer) abort
     let l:mix_file = ale#path#FindNearestFile(a:buffer, 'mix.exs')
 
@@ -11,3 +12,17 @@ function! ale#handlers#elixir#FindMixProjectRoot(buffer) abort
 
     return '.'
 endfunction
+
+" Similar to ale#handlers#elixir#FindMixProjectRoot but also continue the
+" search upward for a potential umbrella project root. If an umbrella root
+" does not exist, the initial project root will be returned.
+function! ale#handlers#elixir#FindMixUmbrellaRoot(buffer) abort
+    let l:app_root = ale#handlers#elixir#FindMixProjectRoot(a:buffer)
+    let l:umbrella_root = fnamemodify(l:app_root, ':h:h')
+
+    if filereadable(l:umbrella_root . '/mix.exs')
+        return l:umbrella_root
+    endif
+
+    return l:app_root
+endfunction

test/command_callback/test_elixir_ls_command_callbacks.vader

@@ -22,12 +22,12 @@ Execute(should configure elixir-ls release location):
   AssertLinter 'boo/language_server.sh', 'boo/language_server.sh'
 
 Execute(should set correct LSP values):
-  call ale#test#SetFilename('mix_paths/wrapped_project/lib/app.ex')
+  call ale#test#SetFilename('elixir_paths/umbrella_project/apps/app1/lib/app.ex')
 
   AssertLSPLanguage 'elixir'
   AssertLSPOptions {}
   AssertLSPConfig {}
-  AssertLSPProject ale#path#Simplify(g:dir . '/mix_paths/wrapped_project')
+  AssertLSPProject ale#path#Simplify(g:dir . '/elixir_paths/umbrella_project')
 
 Execute(should accept configuration settings):
   AssertLSPConfig {}

test/command_callback/test_elixir_mix_command_callbacks.vader

@@ -18,9 +18,16 @@ Execute(The default mix command should be correct):
   \ . g:env_prefix
   \ . 'mix compile %s'
 
-Execute(The FindMixProjectRoot should detect the project root directory via mix.exs):                                                  
+Execute(FindMixProjectRoot should detect the project root directory via mix.exs):
   silent execute 'file ' . fnameescape(g:dir . '/elixir_paths/mix_project/lib/app.ex')
 
   AssertEqual
   \ ale#path#Simplify(g:dir . '/elixir_paths/mix_project'),
   \ ale#handlers#elixir#FindMixProjectRoot(bufnr(''))
+
+Execute(FindMixUmbrellaRoot should detect the umbrella root directory via mix.exs):
+  silent execute 'file ' . fnameescape(g:dir . '/elixir_paths/umbrella_project/apps/app1/lib/app.ex')
+
+  AssertEqual
+  \ ale#path#Simplify(g:dir . '/elixir_paths/umbrella_project'),
+  \ ale#handlers#elixir#FindMixUmbrellaRoot(bufnr(''))