Formatter undocumented deviation: Formatting of long lambda as keyword argument

[henribru]

Black formatting:

def a():
    return b(
        c,
        d,
        e,
        f=lambda self, *args, **kwargs: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
            *args, **kwargs
        ),
    )

Ruff formatting:

def a():
    return b(
        c,
        d,
        e,
        f=lambda self,
        *args,
        **kwargs: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(*args, **kwargs),
    )

In addition to being incompatible, this formatting seems very strange and not very readable, as the *args and **kwargs suddenly look like they are arguments to b.

[charliermarsh]

Thanks!

[henribru]

This seems possibly related

https://black.vercel.app/?version=stable&state=_Td6WFoAAATm1rRGAgAhARYAAAB0L-Wj4ADqAHRdAD2IimZxl1N_WlXnON2nzNX9HFvHx6cBUQ15-GcjjCXTWY4lAb3LPNtN0kban15sEExCiEMHC1fqLMN_I2mNYrKs6DX7rL7K_IqhZ4f1qfF_pwoKJfLbTWpcKTtsPNouVDJpGY10D5nlGuf_NfXkJrKjOtjHACUnbTAaUKR-AAGQAesBAAAgR-_jscRn-wIAAAAABFla

https://play.ruff.rs/c9b4e3fa-4401-4248-a98d-d9ae6b984697?secondary=Format

[charliermarsh]

Yeah, looks like we have some refinements to make in the lambda formatting. On it! (Thanks for sharing playground links, it helps a lot.)

[DarthMuzammil]

@charliermarsh Can i take this issue up?

[MichaReiser]

@DarthMuzammil sure. Let me know if you need any help

[charliermarsh]

@DarthMuzammil -- have you had a chance to look into this? If not, do you still plan to? (No pressure, I just want to make sure we find an owner soon if it's not being addressed.)

[MichaReiser]

It seems black never inserts soft line breaks between parameters. This would be an easy fix... except for comments

Although Black's formatting also has its shortcomings when you have default values:

def a():
    return b(
        c,
        d,
        e,
        f=lambda self, araa, kkkwargs=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
            *args, **kwargs
        ), e=1, f=2, g=2: d,
    )

It could be nice to simply parenthesize the lambda expression and indent it by 1 level (and otherwise keep our formatting). However, that would also mean that the formatter must remove the parentheses again when the lambda fits on a single line—something we haven't really done before in sub-expression positions. And there's also no real good place to add it, because this should be done when formatting lambas in any position.

[DarthMuzammil]

@charliermarsh Hey, sorry for the delay i just saw this message, yes i will start working on this today

[DarthMuzammil]

It seems black never inserts soft line breaks between parameters. This would be an easy fix... except for comments

Although Black's formatting also has its shortcomings when you have default values:

def a():
    return b(
        c,
        d,
        e,
        f=lambda self, araa, kkkwargs=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa(
            *args, **kwargs
        ), e=1, f=2, g=2: d,
    )

It could be nice to simply parenthesize the lambda expression and indent it by 1 level (and otherwise keep our formatting). However, that would also mean that the formatter must remove the parentheses again when the lambda fits on a single line—something we haven't really done before in sub-expression positions. And there's also no real good place to add it, because this should be done when formatting lambas in any position.

@MichaReiser How should i go about solving this issue?