Formatter: prefer_splitting_right_hand_side_of_assignments preview style #6975
Description
Implement Black's improved linebreaks preview style. The style is gated behind the prefer_splitting_right_hand_side_of_assignments preview flag.
It seems that the right side now always gets parenthesized regardless if it makes the right fit or not (no longer has the optimisation to omit parentheses if the content still doesn't fit after adding the parentheses).
https://play.ruff.rs/36e390bc-b3d2-41b2-80d9-87608337727a
We may be able to get away by simply not returning BestFit if the expression is an assignment value.
I expect this change to improve the performance because there are fewer cases where we'll need to fall back to use Best Fitting.
Black (and our) stable style:
def f():
"""Black's `Preview.prefer_splitting_right_hand_side_of_assignments`"""
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
] = cccccccc.ccccccccccccc.cccccccc
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
] = cccccccc.ccccccccccccc().cccccccc
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[
bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
] = cccccccc.ccccccccccccc(d).cccccccc
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = (
cccccccc.ccccccccccccc(d).cccccccc + e
)
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = (
cccccccc.ccccccccccccc.cccccccc + e
)
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = (
cccccccc.ccccccccccccc.cccccccc
+ eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
)
self._cache: dict[
DependencyCacheKey, list[list[DependencyPackage]]
] = collections.defaultdict(list)
self._cached_dependencies_by_level: dict[
int, list[DependencyCacheKey]
] = collections.defaultdict(list)Preview style, which consistently breaks the right side first:
def f():
"""Black's `Preview.prefer_splitting_right_hand_side_of_assignments`"""
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = (
cccccccc.ccccccccccccc.cccccccc
)
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = (
cccccccc.ccccccccccccc().cccccccc
)
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = (
cccccccc.ccccccccccccc(d).cccccccc
)
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = (
cccccccc.ccccccccccccc(d).cccccccc + e
)
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = (
cccccccc.ccccccccccccc.cccccccc + e
)
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb] = (
cccccccc.ccccccccccccc.cccccccc
+ eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
)
self._cache: dict[DependencyCacheKey, list[list[DependencyPackage]]] = (
collections.defaultdict(list)
)
self._cached_dependencies_by_level: dict[int, list[DependencyCacheKey]] = (
collections.defaultdict(list)
)