feat(fixer): add Prettier fixer (using Prettier-ESLint CLI) + docs

autoload/ale/fix/registry.vim

@@ -17,6 +17,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['javascript'],
 \       'description': 'Apply eslint --fix to a file.',
 \   },
+\   'prettier': {
+\       'function': 'ale#handlers#prettier#Fix',
+\       'suggested_filetypes': ['javascript'],
+\       'description': 'Apply prettier (with ESLint integration) to file',
+\   },
 \   'isort': {
 \       'function': 'ale#handlers#python#ISort',
 \       'suggested_filetypes': ['python'],

autoload/ale/handlers/prettier.vim

@@ -0,0 +1,49 @@
+
+" Author: tunnckoCore (Charlike Mike Reagent) <mameto2011@gmail.com>
+" Description: Integration between Prettier and ESLint.
+
+" Here we use `prettier-eslint` intetionally,
+" because from v4 it is direct mirror of `prettier` - mimics
+" it's flags and etc.
+
+let g:ale_javascript_prettier_executable =
+\   get(g:, 'ale_javascript_prettier_executable', 'prettier-eslint')
+
+let g:ale_javascript_prettier_options =
+\   get(g:, 'ale_javascript_prettier_options', '')
+
+function! ale#handlers#prettier#GetExecutable(buffer) abort
+    if ale#Var(a:buffer, 'javascript_prettier_use_global')
+        return ale#Var(a:buffer, 'javascript_prettier_executable')
+    endif
+
+    " Look for the kinds of paths that create-react-app generates first.
+    let l:executable = ale#path#ResolveLocalPath(
+    \   a:buffer,
+    \   'node_modules/prettier-eslint-cli/index.js',
+    \   ''
+    \)
+
+    if !empty(l:executable)
+        return l:executable
+    endif
+
+    return ale#path#ResolveLocalPath(
+    \   a:buffer,
+    \   'node_modules/.bin/prettier-eslint',
+    \   ale#Var(a:buffer, 'javascript_prettier_executable')
+    \)
+endfunction
+
+
+function! ale#handlers#prettier#Fix(buffer, lines) abort
+    let l:options = ale#Var(a:buffer, 'javascript_prettier_options')
+
+    return {
+    \   'command': ale#Escape(ale#handlers#prettier#GetExecutable(a:buffer))
+    \       . ' %t'
+    \       . ' ' . ale#Escape(l:options)
+    \       . ' --write',
+    \   'read_temporary_file': 1,
+    \}
+endfunction