add preview flag in vim plugin

autoload/black.vim

@@ -30,6 +30,7 @@ FLAGS = [
   Flag(name="skip_string_normalization", cast=strtobool),
   Flag(name="quiet", cast=strtobool),
   Flag(name="skip_magic_trailing_comma", cast=strtobool),
+  Flag(name="preview", cast=strtobool),
 ]
 
 
@@ -145,6 +146,7 @@ def Black(**kwargs):
     string_normalization=not configs["skip_string_normalization"],
     is_pyi=vim.current.buffer.name.endswith('.pyi'),
     magic_trailing_comma=not configs["skip_magic_trailing_comma"],
+    preview=not configs["preview"],
     **black_kwargs,
   )
   quiet = configs["quiet"]

docs/integrations/editors.md

@@ -113,6 +113,7 @@ Configuration:
 - `g:black_skip_string_normalization` (defaults to `0`)
 - `g:black_virtualenv` (defaults to `~/.vim/black` or `~/.local/share/nvim/black`)
 - `g:black_quiet` (defaults to `0`)
+- `g:black_preview` (defaults to `0`)
 
 To install with [vim-plug](https://github.com/junegunn/vim-plug):
 

plugin/black.vim

@@ -63,6 +63,9 @@ endif
 if !exists("g:black_target_version")
   let g:black_target_version = ""
 endif
+if !exists("g:black_preview")
+  let g:black_preview = 0
+endif
 
 function BlackComplete(ArgLead, CmdLine, CursorPos)
   return [