Close #1439 - Add an :ALEInfoToFile command

test/test_ale_info.vader

@@ -105,6 +105,8 @@ Before:
     AssertEqual a:expected_list, split(l:output, "\n")
   endfunction
 
+  call ale#test#SetDirectory('/testplugin/test')
+
 After:
   Restore
 
@@ -123,6 +125,8 @@ After:
   unlet! g:ale_testft2_testlinter2_bar
   delfunction CheckInfo
 
+  call ale#test#RestoreDirectory()
+
 Given nolintersft (Empty buffer with no linters):
 Execute (ALEInfo with no linters should return the right output):
   call CheckInfo([
@@ -251,6 +255,33 @@ Execute (ALEInfo should return appropriately named global variables):
   \ 'let g:ale_testft_testlinter1_foo = ''abc''',
   \] + g:globals_lines + g:command_header)
 
+Execute (ALEInfoToFile should write to a file correctly):
+  if filereadable(g:dir . '/ale-info-test-file')
+    call delete(g:dir . '/ale-info-test-file')
+  endif
+
+  let g:ale_testft_testlinter1_foo = 'abc'
+  let g:ale_testft_testlinter1_bar = ['abc']
+  let g:ale_testft2_testlinter2_foo = 123
+  let g:ale_testft2_testlinter2_bar = {'x': 'y'}
+
+  call ale#linter#Define('testft', g:testlinter1)
+  call ale#linter#Define('testft2', g:testlinter2)
+
+  execute 'ALEInfoToFile ' . fnameescape(g:dir . '/ale-info-test-file')
+
+  AssertEqual [
+  \ ' Current Filetype: testft.testft2',
+  \ 'Available Linters: [''testlinter1'', ''testlinter2'']',
+  \ '  Enabled Linters: [''testlinter1'', ''testlinter2'']',
+  \ ' Linter Variables:',
+  \ '',
+  \ 'let g:ale_testft2_testlinter2_bar = {''x'': ''y''}',
+  \ 'let g:ale_testft2_testlinter2_foo = 123',
+  \ 'let g:ale_testft_testlinter1_bar = [''abc'']',
+  \ 'let g:ale_testft_testlinter1_foo = ''abc''',
+  \] + g:globals_lines + g:command_header, readfile(g:dir . '/ale-info-test-file')
+
 Given testft.testft2 (Empty buffer with two filetypes):
 Execute (ALEInfo should buffer-local linter variables):
   let g:ale_testft2_testlinter2_foo = 123