Do we actually care about a plugin author being able to add

Question

Do we actually care about a plugin author being able to add additional fields to a built in core target types like `python library` For example do we want plugin authors to be able to add a boolean field `type checked` to every `python library` Or do we expect them to develop a new custom type like `typed python library`

hundreds-father-404 · Answer

V1 does not allow changing the built in targets afaict you must subclass and have a new target type The current sketch of V2 Target API allows adding additional fields to pre existing targets But I think we can simplify it by removing that functionality still early in the experiment cc < happy kitchen 89482> < witty crayon 22786>

happy-kitchen-89482 · Answer

I think being able to add fields to existing targets makes sense

happy-kitchen-89482 · Answer

E g if a custom goal needs extra information we don t want to force a new type Especially if two unrelated custom goals each need different extra information which type would you even choose then

happy-kitchen-89482 · Answer

This would be like tags but waaaay better since your custom fields would be first class things

happy-kitchen-89482 · Answer

So yes I think we do care

hundreds-father-404 · Answer

I agree It would be an awesome feature to be able to add the bool field `type checked` to `python library` `python tests` etc without any changes to core Pants Core Pants will still behave the same way because it doesn t ever try to consume the new field but your custom Plugin now has a first class way to do consume that new field

hundreds-father-404 · Answer

< dry analyst 73584> raised some valid points about the tradeoff that this results in the code being less easy to understand and debug Here I think the extensibility is worth it much better tags would be incredible and I think we can reduce the negative impact Generally I added a new goal to the design doc called Easy to debug I think we will frequently run into the tradeoff between Easy to debug vs Extensible in this project

witty-crayon-22786 · Answer

adding additional fields to targets is a really common thing that folks want to do in plugins

witty-crayon-22786 · Answer

people attempt to do it with 1 data stored in tags a bit awkward and schemaless but doesn t require subclassing 2 subclassing which breaks anything that is based on exact type matches which are fairly common

witty-crayon-22786 · Answer

that was one of the reasons behind having a union of the legal fields so that it can be extended at runtime

hundreds-father-404 · Answer

Awesome thank you both And to Tansy for the very valid concerns

hundreds-father-404 · Answer

gt that was one of the reasons behind having a union of the legal fields so that it can be extended at runtime Right This was the part that I was playing devils advocate if we could avoid Looks like no

witty-crayon-22786 · Answer

i think that generating docs for both 1 unions themselves 2 known union members will be really critical to explaining and authoring plugins and it should lead naturally to a clean way to generate the BUILD dictionary like we do on the site now

witty-crayon-22786 · Answer

< dry analyst 73584> agreed that people are more familiar with subclassing but explaining how do i know which fields are legal for a target in my BUILD file and how do i make an additional field legal is i think easier to explain with unions and fields than it is with subclassing maybe

witty-crayon-22786 · Answer

who is ` Tony` heh oops

hundreds-father-404 · Answer

gt but explaining how do i know which fields are legal for a target in my BUILD file and how do i make an additional field legal is i think easier to explain with unions and fields than it is with subclassing maybe I think so too The main point that Tansy made is how difficult it is with Target Adaptors to call `dir my adaptor ` and see what all the fields are We should ensure there s an ergonomic way to say ~`my target all valid fields` for the sake of debugging I think that s solvable

witty-crayon-22786 · Answer

true but the flipside is `dir my adaptor ` also renders a bunch of stuff that is not relevant to the target

witty-crayon-22786 · Answer

because inheritance conflates a lot of things