Formatter: deviation from Black when line splitting subscript assignment

[rhynix]

Ruff splits lines differently when the line length exceeds the configured line length, and the line contains assignment using subscript notation. For instance, when assigning to a dict.

I had a look at the known deviations, and at other open issues, but could not find this deviation.

Input:

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa["bbbbbbbbbbbbbbbbbbbb"] = "ccccccccccc"

Black output:

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa["bbbbbbbbbbbbbbbbbbbb"] = (
    "ccccccccccc"
)

Ruff (ruff format --isolated file.py) output:

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[
    "bbbbbbbbbbbbbbbbbbbb"
] = "ccccccccccc"

Ruff version:

% ruff version
ruff 0.2.0

[rhynix]

Black used to use the style ruff currently uses, but was changed late 2022.

This was the issue: psf/black#1498
This was the PR: psf/black#3368

[MichaReiser]

Thanks for reporting this issue.

Is it possible that you use/used black 24? Or what black version are you using?

[rhynix]

Is it possible that you use/used black 24? Or what black version are you using?

That is correct.

% black --version
black, 24.1.1 (compiled: no)
Python (CPython) 3.8.18

[rhynix]

I can confirm this change was introduced in Black 24.1:

https://github.com/psf/black/blob/main/CHANGES.md#2410

If an assignment statement is too long, we now prefer splitting on the right-hand side (#3368)

Setting the format.preview setting to true changes this behaviour to match Black.

[dhruvmanila]

So, Black 24.1 moved a lot of preview style rules into it's stable style (psf/black#4042). We've implemented the same in our own preview style formatting which can be enabled through --preview flag. Refer to the preview docs for more details.

If you run the mentioned code snippet under the preview style then you'd get the same output:

ruff format --preview --diff

--- /Users/dhruv/playground/ruff/formatter/isolated.py
+++ /Users/dhruv/playground/ruff/formatter/isolated.py
@@ -1 +1,3 @@
-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa["bbbbbbbbbbbbbbbbbbbb"] = "ccccccccccc"
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa["bbbbbbbbbbbbbbbbbbbb"] = (
+    "ccccccccccc"
+)

You can track the progress of the pull request which will promote the same preview style rules into stable style for Ruff here: #9639

I hope this helps :)

[rhynix]

So, Black 24.1 moved a lot of preview style rules into it's stable style (psf/black#4042). We've implemented the same in our own preview style formatting which can be enabled through --preview flag. Refer to the preview docs for more details.

If you run the mentioned code snippet under the preview style then you'd get the same output:

ruff format --preview --diff

--- /Users/dhruv/playground/ruff/formatter/isolated.py
+++ /Users/dhruv/playground/ruff/formatter/isolated.py
@@ -1 +1,3 @@
-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa["bbbbbbbbbbbbbbbbbbbb"] = "ccccccccccc"
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa["bbbbbbbbbbbbbbbbbbbb"] = (
+    "ccccccccccc"
+)

You can track the progress of the pull request which will promote the same preview style rules into stable style for Ruff here: #9639

I hope this helps :)

It sure does. Thank you for your help.

I'll close this issue, since I believe it does not provide any extra value at this point.