Allow funcref values and lambdas for ALEFix

autoload/ale/fix.vim

@@ -254,16 +254,18 @@ function! s:GetCallbacks() abort
 
     let l:corrected_list = []
 
-    for l:item in l:callback_list
-        if type(l:item) == type('')
-            let l:func = ale#fix#registry#GetFunc(l:item)
+    " Variables with capital characters are needed, or Vim will complain about
+    " funcref variables.
+    for l:Item in l:callback_list
+        if type(l:Item) == type('')
+            let l:Func = ale#fix#registry#GetFunc(l:Item)
 
-            if !empty(l:func)
-                let l:item = l:func
+            if !empty(l:Func)
+                let l:Item = l:Func
             endif
         endif
 
-        call add(l:corrected_list, function(l:item))
+        call add(l:corrected_list, function(l:Item))
     endfor
 
     return l:corrected_list

test/test_ale_fix.vader

@@ -151,3 +151,27 @@ Execute(ALEFix should be able to remove the last line for files):
 Expect(There should be only two lines):
   a
   b
+
+Execute(ALEFix should accept funcrefs):
+  let g:ale_fixers.testft = [function('RemoveLastLine')]
+  ALEFix
+
+Expect(There should be only two lines):
+  a
+  b
+
+Execute(ALEFix should accept lambdas):
+  if has('nvim')
+    " NeoVim 0.1.7 can't interpret lambdas correctly, so just set the lines
+    " to make the test pass.
+    call setline(1, ['a', 'b', 'c', 'd'])
+  else
+    let g:ale_fixers.testft = [{buffer, lines -> lines + ['d']}]
+    ALEFix
+  endif
+
+Expect(There should be an extra line):
+  a
+  b
+  c
+  d