handled temp file and env variable correctly; added tests

ale_linters/elixir/mix.vim

@@ -1,5 +1,6 @@
 " Author: evnu - https://github.com/evnu
 " Author: colbydehart - https://github.com/colbydehart
+" Description: Mix compile checking for Elixir files
 
 function! ale_linters#elixir#mix#Handle(buffer, lines) abort
     " Matches patterns like the following:
@@ -29,14 +30,23 @@ function! ale_linters#elixir#mix#Handle(buffer, lines) abort
     return l:output
 endfunction
 
-function! ale_linters#elixir#mix#Command(buffer) abort
-    let l:project_dir = fnamemodify(ale#path#FindNearestFile(a:buffer, 'mix.exs'), ':h')
-    return  'cd ' . l:project_dir . ' && MIX_BUILD_PATH=/tmp/mix mix compile %s'
+function! ale_linters#elixir#mix#GetCommand(buffer) abort
+    let l:project_root = fnamemodify(ale#path#FindNearestFile(a:buffer, 'mix.exs'), ':h')
+
+    let l:temp_dir = ale#engine#CreateDirectory(a:buffer)
+
+    let l:mix_build_path = has('win32')
+    \   ? 'set MIX_BUILD_PATH=' . ale#Escape(l:temp_dir) . ' && '
+    \   : 'MIX_BUILD_PATH=' . ale#Escape(l:temp_dir) . ' '
+
+    return  ale#path#CdString(l:project_root)
+          \ . l:mix_build_path
+          \ . ' mix compile %s'
 endfunction
 
 call ale#linter#Define('elixir', {
 \   'name': 'mix',
 \   'executable': 'mix',
-\   'command_callback': 'ale_linters#elixir#mix#Command',
+\   'command_callback': 'ale_linters#elixir#mix#GetCommand',
 \   'callback': 'ale_linters#elixir#mix#Handle',
 \})

test/handler/test_mix_handler.vader

@@ -0,0 +1,21 @@
+Before:
+  runtime ale_linters/elixir/mix.vim
+
+After:
+  call ale#linter#Reset()
+
+Execute(The mix handler should parse lines correctly):
+
+  AssertEqual
+  \ [
+  \   {
+  \     'bufnr': 347,
+  \     'lnum': 87,
+  \     'col': 0,
+  \     'text': 'undefined function update_in/4',
+  \     'type': 'E',
+  \   },
+  \ ],
+  \ ale_linters#elixir#mix#Handle(347, [
+  \   '** (CompileError) apps/sim/lib/sim/server.ex:87: undefined function update_in/4'
+  \ ])