Support loading eslint from node_modules, re issue #118.

ale_linters/javascript/eslint.vim

@@ -4,6 +4,26 @@
 let g:ale_javascript_eslint_executable =
 \   get(g:, 'ale_javascript_eslint_executable', 'eslint')
 
+let g:ale_javascript_eslint_use_global =
+\   get(g:, 'ale_javascript_eslint_use_global', 0)
+
+function! ale_linters#javascript#eslint#GetExecutable(buffer) abort
+    if g:ale_javascript_eslint_use_global
+        return g:ale_javascript_eslint_executable
+    endif
+
+    return ale#util#ResolveLocalPath(
+    \   a:buffer,
+    \   'node_modules/.bin/eslint',
+    \   g:ale_javascript_eslint_executable
+    \)
+endfunction
+
+function! ale_linters#javascript#eslint#GetCommand(buffer) abort
+    return ale_linters#javascript#eslint#GetExecutable(a:buffer)
+    \   . ' -f unix --stdin --stdin-filename %s'
+endfunction
+
 function! ale_linters#javascript#eslint#Handle(buffer, lines)
     " Matches patterns line the following:
     "
@@ -39,7 +59,7 @@ endfunction
 
 call ale#linter#Define('javascript', {
 \   'name': 'eslint',
-\   'executable': g:ale_javascript_eslint_executable,
-\   'command': g:ale_javascript_eslint_executable . ' -f unix --stdin --stdin-filename %s',
+\   'executable_callback': 'ale_linters#javascript#eslint#GetExecutable',
+\   'command_callback': 'ale_linters#javascript#eslint#GetCommand',
 \   'callback': 'ale_linters#javascript#eslint#Handle',
 \})

autoload/ale/util.vim

@@ -44,6 +44,21 @@ function! ale#util#FindNearestFile(buffer, filename) abort
     return ''
 endfunction
 
+" Given a buffer, a string to search for, an a global fallback for when
+" the search fails, look for a file in parent paths, and if that fails,
+" use the global fallback path instead.
+function! ale#util#ResolveLocalPath(buffer, search_string, global_fallback) abort
+    " Search for a locally installed file first.
+    let l:path = ale#util#FindNearestFile(a:buffer, a:search_string)
+
+    " If the serach fails, try the global executable instead.
+    if empty(l:path)
+        let l:path = a:global_fallback
+    endif
+
+    return l:path
+endfunction
+
 function! ale#util#GetFunction(string_or_ref) abort
     if type(a:string_or_ref) == type('')
         return function(a:string_or_ref)

doc/ale.txt

@@ -370,8 +370,25 @@ g:ale_javascript_eslint_executable         *g:ale_javascript_eslint_executable*
   Type: |String|
   Default: `'eslint'`
 
-  This variable can be changed to change the path to eslint. If you have
-  eslint_d installed, you can set this option to use eslint_d instead.
+  ALE will first discover the eslint path in an ancestor node_modules
+  directory. If no such path exists, this variable will be used instead.
+
+  This variable can be set to change the path to eslint. If you have eslint_d
+  installed, you can set this option to use eslint_d instead.
+
+  If you wish to use only a globally installed version of eslint, set
+  |g:ale_javascript_eslint_use_global| to `1`.
+
+
+g:ale_javascript_eslint_use_global         *g:ale_javascript_eslint_use_global*
+
+  Type: |String|
+  Default: `0`
+
+  This variable controls whether or not ALE will search for a local path for
+  eslint first. If this variable is set to `1`, then ALE will always use the
+  global version of eslint, in preference to locally installed versions of
+  eslint in node_modules.
 
 
 -------------------------------------------------------------------------------

test/test_resolve_local_path.vader

@@ -0,0 +1,15 @@
+Execute(Open a file some directory down):
+  silent! cd /testplugin/test
+  :e! top/middle/bottom/dummy.txt
+
+Then(We should be able to to find the local version of a file):
+  AssertEqual
+  \ expand('%:p:h:h:h:h') . '/top/example.ini',
+  \  ale#util#ResolveLocalPath(bufnr('%'), 'example.ini', '/global/config.ini')
+
+Execute(Do nothing):
+
+Then(We shouldn't find anything for files which don't match):
+  AssertEqual
+  \ '/global/config.ini',
+  \  ale#util#ResolveLocalPath(bufnr('%'), 'missing.ini', '/global/config.ini')