Formatter: Attribute and call chains "fluent interface"

[konstin]

Black supports attribute access and call chaining to provide good formatting for fluent interface style programming with extensive method chaining which is common e.g. with django (https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html#call-chains):

def example(session):
    result = (
        session.query(models.Customer.id)
        .filter(
            models.Customer.account_id == account_id,
            models.Customer.email == email_address,
        )
        .order_by(models.Customer.id.asc())
        .all()
    )

#5340 implements a part of this badly to fix a bug and #5341 adds basic function call formatting.

We need to implement a formatting where the outermost call adds the optional parentheses and formats all inner accesses and calls to not have them add parentheses. A complication is that unlike for if-statements the tree is left recursive, meaning that for a.b().c.d.e the outermost call see an access of e on a.b().c.d, while we must format first a, then .b(), .d and finally .e. We can implement by either collecting into a stack (needs allocation) or using recursing (we most not overrun the recursion and stack limits).

[olejorgenb]

Probably wrong place to comment on this, but I don't think black's approach here is sufficient. It only work when the chain is very long, and for fluent definitions you usually want one call per line regardless of the number of calls...

Personally I think a OK compromise would be to use explicit parenthesis around a call-chain as a marker that it should be formatted with one line per call?

[MichaReiser]

Hi @olejorgenb There's an ongoing discussion about this in #8598