total aside related to `FieldSet`… could

Target

use the same field-access mechanism?

so,

target.resolve

? That doesn't work with the Target API wanting you to say which field you're looking for,

SingleSourceField

vs

SourceField

vs

PythonSourceField

You should declare it explicitly at your call site, not rely on whatever

tgt.source

is set to imo

you can only have one value per alias though.

yeah, but it's a field-driven API, not target-driven API. It's an antipattern to be checking

isinstance(tgt, PythonSourceTarget)

. Violates extensibility of creating custom targets - we don't want you to have to subclass

PythonSourceTarget

when adding a new target

yea. makes sense for renamed field lookups. ok, thanks

Not only that, but it's important you can write

black/rules.py

without knowing that

PythonSourceTarget

exists. We want to decouple target definitions from rule implementations because we can't predict what targets plugin authors will add

sure. that still comes down to renamed field lookups i think… assuming that you always did

has_field(Sources)

before doing the field lookup. but yea, makes sense.

ah yeah, assuming you use

has_field()

. But then you have

.get()

to consider

get

wouldn’t change i don’t think.