- 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
This pull request's main intention is to wraps long strings (as requested by #182); however, it also provides better string handling in general and, in doing so, closes the following issues:
Closes#26Closes#182Closes#933Closes#1183Closes#1243
`type: ignore` shouldn't block collapsing a line, since it will still
apply fine to the merged line. This prevents an issue where a reformat
causes it to shift lines and then be merged on a subsequent pass.
There is a downside to this, which is that it can cause a `type:
ignore` to apply to more code than was originally intended. There
might be a way to apply this in a more limited situation, but I'm not
sure what it is.
Fixes#1061.
