add autoflake fixer (#3779)

* first attempt

* added autoflake executable

* added Windows executable for appveyor

* delete unused files

* corrected wrong sorting

autoload/ale/fix/registry.vim

@@ -17,6 +17,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['python'],
 \       'description': 'Fix import issues with autoimport.',
 \   },
+\   'autoflake': {
+\       'function': 'ale#fixers#autoflake#Fix',
+\       'suggested_filetypes': ['python'],
+\       'description': 'Fix flake issues with autoflake.',
+\   },
 \   'autopep8': {
 \       'function': 'ale#fixers#autopep8#Fix',
 \       'suggested_filetypes': ['python'],

autoload/ale/fixers/autoflake.vim

@@ -0,0 +1,28 @@
+" Author: circld <circld1@gmail.com>
+" Description: Fixing files with autoflake.
+
+call ale#Set('python_autoflake_executable', 'autoflake')
+call ale#Set('python_autoflake_use_global', get(g:, 'ale_use_global_executables', 0))
+call ale#Set('python_autoflake_options', '')
+
+function! ale#fixers#autoflake#Fix(buffer) abort
+    let l:executable = ale#python#FindExecutable(
+    \   a:buffer,
+    \   'python_autoflake',
+    \   ['autoflake'],
+    \)
+
+    if !executable(l:executable)
+        return 0
+    endif
+
+    let l:options = ale#Var(a:buffer, 'python_autoflake_options')
+
+    return {
+    \   'command': ale#Escape(l:executable)
+    \       . (!empty(l:options) ? ' ' . l:options : '')
+    \       . ' --in-place '
+    \       . ' %t',
+    \   'read_temporary_file': 1,
+    \}
+endfunction