From: Łukasz Langa <lukasz@langa.pl>
Date: Mon, 28 Oct 2019 23:50:42 +0000 (+0100)
Subject: Re-implement magic trailing comma handling:
X-Git-Url: https://git.madduck.net/etc/vim.git/commitdiff_plain/788268bc39a87d37a24d203fa5ee7b3953af3446?ds=inline;hp=788268bc39a87d37a24d203fa5ee7b3953af3446

Re-implement magic trailing comma handling:

- when a trailing comma is specified in any bracket pair, that signals to Black
  that this bracket pair needs to be always exploded, e.g. presented as "one
  item per line";

- this causes some changes to previously formatted code that erroneously left
  trailing commas embedded into single-line expressions;

- internally, Black needs to be able to identify trailing commas that it put
  itself compared to pre-existing trailing commas. We do this by using/abusing
  lib2to3's `was_checked` attribute.  It's True for internally generated
  trailing commas and False for pre-existing ones (in fact, for all
  pre-existing leaves and nodes).

Fixes #1288
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