First stab at the Vim plugin!

README.md

@@ -263,8 +263,61 @@ keep it.
 
 ## Editor integration
 
-* Visual Studio Code: [joslarson.black-vscode](https://marketplace.visualstudio.com/items?itemName=joslarson.black-vscode)
+### Emacs
-* Emacs: [proofit404/blacken](https://github.com/proofit404/blacken)
+
+Use [proofit404/blacken](https://github.com/proofit404/blacken).
+
+
+### Vim
+
+Commands and shortcuts:
+
+* `,=` or `:Black` to format the entire file (ranges not supported);
+* `:BlackUpgrade` to upgrade *Black* inside the virtualenv;
+* `:BlackVersion` to get the current version of *Black* inside the
+  virtualenv.
+
+Configuration:
+* `g:black_fast` (defaults to `0`)
+* `g:black_linelength` (defaults to `88`)
+* `g:black_virtualenv` (defaults to `~/.vim/black`)
+
+To install, copy the plugin from [vim/plugin/black.vim](https://github.com/ambv/black/tree/master/vim/plugin/black.vim).
+Let me know if this requires any changes to work with Vim 8's builtin
+`packadd`, or Pathogen, or Vundle, and so on.
+
+This plugin **requires Vim 7.0+ built with Python 3.6+ support**.  It
+needs Python 3.6 to be able to run *Black* inside the Vim process which
+is much faster than calling an external command.
+
+On first run, the plugin creates its own virtualenv using the right
+Python version and automatically installs *Black*. You can upgrade it later
+by calling `:BlackUpgrade` and restarting Vim.
+
+If you need to do anything special to make your virtualenv work and
+install *Black* (for example you want to run a version from master), just
+create a virtualenv manually and point `g:black_virtualenv` to it.
+The plugin will use it.
+
+**How to get Vim with Python 3.6?**
+On Ubuntu 17.10 Vim comes with Python 3.6 by default.
+On macOS with HomeBrew run: `brew install vim --with-python3`.
+When building Vim from source, use:
+`./configure --enable-python3interp=yes`. There's many guides online how
+to do this.
+
+
+### Visual Studio Code
+
+Use [joslarson.black-vscode](https://marketplace.visualstudio.com/items?itemName=joslarson.black-vscode).
+
+
+### Other editors
+
+Atom/Nuclide integration is planned by the author, others will
+require external contributions.
+
+Patches welcome! ✨ 🍰 ✨
 
 Any tool that can pipe code through *Black* using its stdio mode (just
 [use `-` as the file name](http://www.tldp.org/LDP/abs/html/special-chars.html#DASHREF2)).
@@ -272,10 +325,7 @@ The formatted code will be returned on stdout (unless `--check` was
 passed).  *Black* will still emit messages on stderr but that shouldn't
 affect your use case.
 
-Vim and Atom/Nuclide integration is planned by the author, others will
+This can be used for example with PyCharm's [File Watchers](https://www.jetbrains.com/help/pycharm/file-watchers.html).
-require external contributions.
-
-Patches welcome! ✨ 🍰 ✨
 
 
 ## Testimonials

vim/plugin/black.vim

@@ -0,0 +1,108 @@
+" black.vim
+" Author: Łukasz Langa
+" Created: Mon Mar 26 23:27:53 2018 -0700
+" Requires: Vim Ver7.0+
+" Version:  1.0
+"
+" Documentation:
+"   This plugin formats Python files.
+"
+" History:
+"  1.0:
+"    - initial version
+
+if v:version < 700 || !has('python3')
+    echo "This script requires vim7.0+ with Python 3.6 support."
+    finish
+endif
+
+if exists("g:load_black")
+   finish
+endif
+
+let g:load_black = "py1.0"
+if !exists("g:black_virtualenv")
+  let g:black_virtualenv = "~/.vim/black"
+endif
+if !exists("g:black_fast")
+  let g:black_fast = 0
+endif
+if !exists("g:black_linelength")
+  let g:black_linelength = 88
+endif
+
+python3 << endpython3
+import sys
+import vim
+
+def _initialize_black_env(upgrade=False):
+  pyver = sys.version_info[:2]
+  if pyver < (3, 6):
+    print("Sorry, Black requires Python 3.6+ to run.")
+    return False
+
+  from pathlib import Path
+  import subprocess
+  import venv
+  virtualenv_path = Path(vim.eval("g:black_virtualenv")).expanduser()
+  virtualenv_site_packages = str(
+    virtualenv_path / 'lib' / f'python{pyver[0]}.{pyver[1]}' / 'site-packages'
+  )
+  first_install = False
+  if not virtualenv_path.is_dir():
+    print('Please wait, one time setup for Black.')
+    _executable = sys.executable
+    try:
+      sys.executable = str(Path(sys.exec_prefix) / 'bin' / 'python3')
+      print(f'Creating a virtualenv in {virtualenv_path}...')
+      print('(this path can be customized in .vimrc by setting g:black_virtualenv)')
+      venv.create(virtualenv_path, with_pip=True)
+    finally:
+      sys.executable = _executable
+    first_install = True
+  if first_install:
+    print('Installing Black with pip...')
+  if upgrade:
+    print('Upgrading Black with pip...')
+  if first_install or upgrade:
+    subprocess.run([str(virtualenv_path / 'bin' / 'pip'), 'install', '-U', 'black'])
+    print('DONE! You are all set, thanks for waiting ✨ 🍰 ✨')
+  if first_install:
+    print('Pro-tip: to upgrade Black in the future, use the :BlackUpgrade command and restart Vim.\n')
+  if sys.path[0] != virtualenv_site_packages:
+    sys.path.insert(0, virtualenv_site_packages)
+  return True
+
+if _initialize_black_env():
+  import black
+  import time
+
+def Black():
+  start = time.time()
+  fast = bool(int(vim.eval("g:black_fast")))
+  line_length = int(vim.eval("g:black_linelength"))
+  buffer_str = '\n'.join(vim.current.buffer) + '\n'
+  try:
+    new_buffer_str = black.format_file_contents(buffer_str, line_length=line_length, fast=fast)
+  except black.NothingChanged:
+    print(f'Already well formatted, good job. (took {time.time() - start:.4f}s)')
+  except Exception as exc:
+    print(exc)
+  else:
+    vim.current.buffer[:] = new_buffer_str.split('\n')[:-1]
+    print(f'Reformatted in {time.time() - start:.4f}s.')
+
+def BlackUpgrade():
+  _initialize_black_env(upgrade=True)
+
+def BlackVersion():
+  print(f'Black, version {black.__version__} on Python {sys.version}.')
+
+endpython3
+
+command! Black :py3 Black()
+command! BlackUpgrade :py3 BlackUpgrade()
+command! BlackVersion :py3 BlackVersion()
+
+nmap ,= :Black<CR>
+vmap ,= :Black<CR>