I wanted to get peoples opinion on the following idea for V2

Question

I wanted to get peoples opinion on the following idea for V2 repl

hundreds-breakfast-49010 · Answer

what if we don t actually have one top level `repl` goal that tries to figure out which language s repl to run based on the targets

hundreds-breakfast-49010 · Answer

but instead we have many goals of the form `repl lt language name gt ` i e explicitly requiring the user to specify which repl they want

hundreds-breakfast-49010 · Answer

or maybe even `repl lt repl name gt ` in cases where there are multiple supported repl programs for a single language

hundreds-breakfast-49010 · Answer

this has the downside of introducing potentially many top level goals

hundreds-breakfast-49010 · Answer

but has the upside that users could then regularly type things like ` pants repl ipython ` and have pants filter out all the targets that are incompatible with a python repl

hundreds-breakfast-49010 · Answer

and in the long term we might want to introduce an new intermediate level of goal namespacing that allows all `goal rule`s of the form `repl ` to be collapsed into a single entry in ` pants goals` or otherwise have similar option sets which would mitigate the potentially large numbers of `repl lt something gt ` goals in the goal list problem

hundreds-father-404 · Answer

If we registered every V2 backend by default I d be concerned about how much this adds to ` pants goals` Because we don t do that and you must opt in to certain backends I m not concerned about how many new goals it introduces It would be nice to be able to do ` pants repl python ` meaning load every single Python target in the project ` pants repl ` doesn t make sense because which REPL should you use We couldn t safely assume anything Alternatively we could do something like ` pants repl language=python ` but if you had to do that every single time then that is a smell that we should have distinct goals

happy-kitchen-89482 · Answer

Yep this was the conclusion I inched towards over lunch convo with Greg Unlike say `test` or `run` where the behavior is well defined in all cases I think it s not clear what ` pants repl ` should mean in various cases e g what if you have a python target with a dep on a scala target for some reason or what if you cannot induce the repl type from the language e g you can look at java code in jshell but also in the scala repl so languagesXrepls can be many to many

happy-kitchen-89482 · Answer

Whereas ` pants repl py` or ` pants repl ipython` is crystal clear and you can just ignore the non python targets in the target set as you would in any other use of ` `

happy-kitchen-89482 · Answer

Or maybe the goals should just be ` pants python` ` pants ipython` and so on

happy-kitchen-89482 · Answer

I m not fussy about the names

hundreds-father-404 · Answer

` pants ammonite` ` pants java` ` pants ipython` ` pants python` ` pants jupyter` I think that makes sense Originally I was thinking ` pants repl python ipython` or ` pants ipython enabled repl python` but I think ` pants ipython` is better It also naturally expresses the mutex that you can only have one of `python` `ipython` and `jupyter`

hundreds-breakfast-49010 · Answer

<https github com pantsbuild pants pull 9077> is a PR for a `repl python` goal and other types of `repl ` goals would look much like this

witty-crayon-22786 · Answer

the current behavior explode if ambiguous has ~never been an issue afaict

witty-crayon-22786 · Answer

i m not sure if that s because people don t glob over large swaths of their code or what

witty-crayon-22786 · Answer

lots of goals is fine i guess but doesn t really seem necessary

witty-crayon-22786 · Answer

it should be possible to use UnionMembership to filter repl able roots and then group by target language

aloof-angle-91616 · Answer

i was thinking this could use the ` only` argument like we have with `lint` not sure if that s way off base

witty-crayon-22786 · Answer

yea that too

hundreds-breakfast-49010 · Answer

< aloof angle 91616> I don t have a problem with just creating one top level goal called `repl` and using an argument to allow the user to select which of several repls they might want

hundreds-breakfast-49010 · Answer

I don t think I d call it ` only` though

hundreds-breakfast-49010 · Answer

so maybe something like ` pants repl name=ammonite ` or ` pants repl name=python `

hundreds-breakfast-49010 · Answer

and that would do the same thing as ` pants repl ammonite ` or ` pants repl python `

aloof-angle-91616 · Answer

we may not have to do it now but conceptually it seems similar to what we re trying to do with ` only` for linting so it might be useful to eventually converge on the same option name

hundreds-breakfast-49010 · Answer

the important thing is that the user would always specify which repl they want somehow and pants would just filter every target that isn t compatible with that repl and also it would be expected that multiple repls are compatible with the exact same targets which is why we ask the user to specify

aloof-angle-91616 · Answer

gt and also it would be expected that multiple repls are compatible with the exact same targets when would this be the case

hundreds-breakfast-49010 · Answer

as benjy mentioned both scala and java repls can interpret java source files

hundreds-breakfast-49010 · Answer

and some languages have multiple repls

hundreds-breakfast-49010 · Answer

e g python vs ipython vs jupyter maybe

aloof-angle-91616 · Answer

are scala and java repls different

hundreds-breakfast-49010 · Answer

I believe so

hundreds-breakfast-49010 · Answer

scala is also a language that has at least two repls I know about `sbt repl` and `ammonite`

aloof-angle-91616 · Answer

ammonite could potentially work on both though and ammonite also has the ability to import things from coursier on the fly which is nice

hundreds-breakfast-49010 · Answer

coursier

aloof-angle-91616 · Answer

coursier is like ivy but cooler

hundreds-breakfast-49010 · Answer

in general I would expect that any JVM repl might be able to handle source files from any other JVM language

hundreds-breakfast-49010 · Answer

and that s a case for requiring that the user always specify what repl they want

aloof-angle-91616 · Answer

yes and it seems like it might be easier in that case for pants to support a single jvm repl instead of trying to support multiple jvm repls

hundreds-breakfast-49010 · Answer

once we know what repl they want pants can figure out what is and is not compatible with it and only present compatible source files to the repl

hundreds-breakfast-49010 · Answer

but it can t automatically guess what repl someone wants from the source files

witty-crayon-22786 · Answer

The difference between lots of goals and options is probably just whether you can make the options compact enough

witty-crayon-22786 · Answer

But a distinct advantage of options is that it lets you set a default for the repo

hundreds-breakfast-49010 · Answer

< witty crayon 22786> yeah that s a point in favor of one `repl` goal with options

witty-crayon-22786 · Answer

Which users could override on a case by case basis

witty-crayon-22786 · Answer

Getting the options right will be interesting though for sure

aloof-angle-91616 · Answer

gt but it can t automatically guess what repl someone wants from the source files if we have only a single jvm repl e g ammonite then this does become possible i believe

hundreds-breakfast-49010 · Answer

I don t think we want to only support one jvm repl

witty-crayon-22786 · Answer

It is similar to the only case select named $thing from a dynamic list based on backend I think

witty-crayon-22786 · Answer

Agreed with Greg there will be multiple repls per language

aloof-angle-91616 · Answer

and also i would tend to assume setting up a jupyter ipython notebook would be a different goal than asking for a repl because jupyter notebooks require e g connecting to or setting up some server which feels like it requires different configuration than a repl

hundreds-breakfast-49010 · Answer

I m not fond of only in this context becuase to me it implies that you could in principle run multiple repls simultaneously and you just happen to be restricting yourself to one

aloof-angle-91616 · Answer

sure if we re willing to do the extra work to support repls that nobody might use

witty-crayon-22786 · Answer

Java is getting its own repl in one of its upcoming releases

hundreds-father-404 · Answer

gt Java is getting its own repl in one of its upcoming releases already has it as of Java 9 iirc

hundreds-breakfast-49010 · Answer

I think we should expect that different shops or individual users will have different preferences for one repl over another

witty-crayon-22786 · Answer

9 is sortof a fantasy version still for us heh But yea

hundreds-breakfast-49010 · Answer

like I might personally want to use ammonite for scala even if the default is the sbt repl

hundreds-breakfast-49010 · Answer

I don t think pants should get in the way of that choice

hundreds-father-404 · Answer

gt I think we should expect that different shops or individual users will have different preferences for one repl over another Further Pants should be pluggable enough that plugin authors can hook up their favorite REPL easily

aloof-angle-91616 · Answer

if we re willing to do the work to maintain several different repls before we know whether anyone specifically wants to use them sure

aloof-angle-91616 · Answer

we currently allow pluggability by allowing people to override the classpath and the main class for the jvm repl

hundreds-father-404 · Answer

gt if we re willing to do the work to maintain several different repls before we know whether anyone specifically wants to use them sure Not necessarily that we will be the ones to support multiple REPLs Rather that Pants has an infrastructure to allow multiple

hundreds-breakfast-49010 · Answer

pants alreayd needs to support more than one repl program insofar as python and scala java are different languages and one s gonna require python or ipython and the other is going to require one of ammonite the java repl sbt repl

aloof-angle-91616 · Answer

is it likely that a single repo will want to have multiple repls available at once in a way that can t be configured via separate pants ini files

hundreds-breakfast-49010 · Answer

I do actually think the case where one individual user might want to use their own repl would be common enough

hundreds-breakfast-49010 · Answer

but in general a multi language repo needs to support multiple repls for different languages simultaneously

hundreds-breakfast-49010 · Answer

like if we just assume one language per repl we still would like it if ` pants repl py ` and ` pants repl scala ` worked right without the user having to figure out exactly which targets are scala only and which ones are python only

hundreds-breakfast-49010 · Answer

but we have no reason to make that one language per repl assumption anyway

aloof-angle-91616 · Answer

hm yea ok

hundreds-breakfast-49010 · Answer

I think I do actually like ` pants repl only=python ` better although I m still not sure if ` only` is the best name for that option

hundreds-father-404 · Answer

If we go with an option I think it would need to be something like ` pants repl name` instead of ` only` ` only` works well with `fmt` and `lint` because those goals usually run all linters so you are saying only run this one Here you should never run more than one REPL at a time Rather than not one vs many REPLs the question is which REPL

aloof-angle-91616 · Answer

yeah the above seems right to me now

hundreds-breakfast-49010 · Answer

yeah ` name` is fine by me

hundreds-father-404 · Answer

The reason I don t love ` pants repl name` is that you would always need to specify the name unless we try to infer it which complicates everything When an option must always be defined then that s a smell to be that it should be a distinct goal ` pants ipython` is more discoverable than ` pants repl name= ipython ` Naively I would try running ` pants repl` without thinking to check ` pants help repl` and seeing that I need to define ` name`

aloof-angle-91616 · Answer

ok but ` name` could be an enum option which could be discoverable in ` pants help repl`

aloof-angle-91616 · Answer

i also am pretty ok with individual goals but ` name` feels maybe more discoverable

hundreds-father-404 · Answer

gt ok but name could be an enum option which could be discoverable in pants help repl Agreed but there is still the friction of needing to know to run ` pants help relp` in the first place I can t think of any other goal that requires always passing an option outside of ` pants login`

hundreds-father-404 · Answer

Users are familiar with ` pants $goal path to target` Most users would try doing this the first time they run `repl` I suspect There s some tension to fail and say You need to also pass ` name= python `

aloof-angle-91616 · Answer

well we can always have ` name` default to something reasonable

hundreds-father-404 · Answer

gt well we can always have name default to something reasonable What would that be In a monolingual repo and in a multilingual repo I m thinking before any Pants config is set up This is a brand new Pants user who is just trying out the tool

aloof-angle-91616 · Answer

how does a user discover which repls are available

hundreds-father-404 · Answer

` pants goals`

hundreds-breakfast-49010 · Answer

it might not be a bad idea to just have `python` `ipython` etc all be top level goals

hundreds-breakfast-49010 · Answer

that implies that there s one top level goal for every repl a given installation of pants supports

aloof-angle-91616 · Answer

yeah

hundreds-father-404 · Answer

And we will only show the REPLs for the registered backends If you don t have `pants backend java` we won t show `ammonite` as a goal This is very similar to how we handle `setup py`

aloof-angle-91616 · Answer

this also then allows appropriate configuration for each repl to sprout instead of trying to jam all that configuration into the same options in the `repl` goal

hundreds-breakfast-49010 · Answer

the only thing we lose doing that is that we re no longer calling these goals repls

hundreds-breakfast-49010 · Answer

I can see a user looking through a list of goals and wondering what ammonite is if htey don t normally use scala

aloof-angle-91616 · Answer

we can make sure the goal descriptions have repl in them

hundreds-father-404 · Answer

gt the only thing we lose doing that is that we re no longer calling these goals repls In the case of `ipython` and `ammonite` I think that is totally fine But I do agree `python` and `java` are not great Maybe those are `python repl`

hundreds-breakfast-49010 · Answer

I had vaguely suggested earlier that we might want some additional level of namespacing that doesn t currently exist in pants

aloof-angle-91616 · Answer

hmmmmmmmmmmmm

aloof-angle-91616 · Answer

that s a great idea

hundreds-father-404 · Answer

gt I can see a user looking through a list of goals and wondering what ammonite is Keep in mind they will only see `ammonite` iff their repo has `pants backend scala` registered

hundreds-breakfast-49010 · Answer

` python repl ammonite lt target gt ` might be a goal that should live under a `repl ` meta goal in some way

hundreds-breakfast-49010 · Answer

that s definitely adding additional complexity to support a relatively minor use case though

hundreds-father-404 · Answer

Eh that takes us close to what we had with Task scopes afaict

hundreds-breakfast-49010 · Answer

I m not sure how task scopes work or if they re something we want to keep in v2

hundreds-father-404 · Answer

gt or if they re something we want to keep in v2 Generally we decided no Tasks don t fit into a V2 world and all options should live in a `GoalSubsystem` or ` Subsystem`

aloof-angle-91616 · Answer

i m definitely just thinking

hundreds-breakfast-49010 · Answer

anyway I think for now I m going to try to get my PR that assumes one goal called `repl2 python` merged and we can change exactly what that s called in subsequent work

aloof-angle-91616 · Answer

allow goals to have some tag hierarchical which means they display in a specific group in the output of ` pants goals`

aloof-angle-91616 · Answer

yeah none of this was supposed to block the current PR

hundreds-father-404 · Answer

gt allow goals to have some tag hierarchical which means they display in a specific group in the output of pants goals Benjy and I briefly discussed grouping the output of ` pants goals` I do think that would be very helpful

hundreds-breakfast-49010 · Answer

are there any other cases we can think of where we want to be able to add some kind of heirarchy to goals

hundreds-breakfast-49010 · Answer

sounds like there might be < hundreds father 404>

aloof-angle-91616 · Answer

in general this kind of hierarchy could be useful for goals which can t be run at the same time as each other unlike e g the various `fmt` and `lint` tasks

hundreds-father-404 · Answer

Well to clarify Benjy and I were not discussing adding a new type of options scope like `repl ipython` i e a task scope We only discussed grouping the output of ` pants goals`

aloof-angle-91616 · Answer

that is also what i thought i was discussing

aloof-angle-91616 · Answer

i don t know what a task scope is or why we are worried about adding it back it s not clear to me how that could be possible in the v2 model

hundreds-breakfast-49010 · Answer

actually now that I think about it I kinda like `repl python` as a naming schema

hundreds-father-404 · Answer

gt it s not clear to me how that could be possible in the v2 model Same not possible with the current design and I don t think there s a burning need to add it back Generally options living on `GoalSubsystem`s and `Subsystem`s seems to work well For example ` isort config` makes more sense to me than ` fmt isort config` and at the same time ` lint isort config`

aloof-angle-91616 · Answer

especially if we remove all the other usages of that naming scheme

hundreds-father-404 · Answer

gt actually now that I think about it I kinda like repl python as a naming schema So this would get really tricky with backwards compat with V1 V1 liberally uses that naming scheme such as `repl py` and `repl node` We would have clashes and competing concepts that in V1 this refers to a task whereas in V2 this refers to a subgoal

aloof-angle-91616 · Answer

`repl py`

aloof-angle-91616 · Answer

and then ` pants goals` could parse the goal name and generate the hierarchical output

hundreds-father-404 · Answer

gt repl py Hm interesting I believe it would destroy our `arg spliter py`being able to disambiguate between goals vs specs unfortunately

aloof-angle-91616 · Answer

i believe the same issue exists with single word goals though

aloof-angle-91616 · Answer

how can `ArgSplitter` differentiate between `repl` and `repl repl`

aloof-angle-91616 · Answer

there are other delimiters we could use too like `repl py`

aloof-angle-91616 · Answer

`repl gt py`

aloof-angle-91616 · Answer

`repl py` not really this one though because of escaping

hundreds-breakfast-49010 · Answer

< hundreds father 404> I don t understand the objection to the ` ` syntax

hundreds-breakfast-49010 · Answer

it s already the case that v1 uses tasks and v2 uses goals

hundreds-breakfast-49010 · Answer

if say ` pants v2 no v1 goals` output repl py` and `repl ammonite` among others

hundreds-breakfast-49010 · Answer

I m not sure how that would confuse people

hundreds-father-404 · Answer

In a world where V1 did not exist and we solely had V2 `repl python` is neat In today s world we currently have `repl py` and `rep node` as real tasks that you can use ` pants repl py path to target` How do you know that ` pants repl py` is the V1 task but ` pants repl python` is the V2 goal

hundreds-breakfast-49010 · Answer

right now running ` pants v1 no v2 goals` doesn t output any goals with a ` ` in the name

hundreds-breakfast-49010 · Answer

ooh I see what you mean

hundreds-breakfast-49010 · Answer

huh ok

hundreds-father-404 · Answer

gt right now running pants v1 no v2 goals doesn t output any goals with a in the name Which is exactly the issue Currently `goal subname` always means one thing We would be changing this so that `goal subname` sometimes means a goal and sometimes means a task

aloof-angle-91616 · Answer

isn t that why we do deprecations though and also v1 vs v2 is like the big breaking change in general it seems reasonable to me to use that distinction to play around with the space left by losing v1

hundreds-breakfast-49010 · Answer

< aloof angle 91616> for now I think we could just have a convention of using a ` ` instead of a ` ` `repl py` is not harder to type or recognize than `repl py` even though I think I like the look of the latter a little better also we can start out by just making sure to name different repl goals using the `repl ` convention without actually changing any code yet

witty-crayon-22786 · Answer

gt is not harder to type or recognize than `repl py` no one has to type repl py right now

witty-crayon-22786 · Answer

because an unambiguous repl is used

witty-crayon-22786 · Answer

a lot went on in this thread i can catch up on it but if someone wants to summarize the arguments on the ticket that would be appreciated

hundreds-breakfast-49010 · Answer

< witty crayon 22786>

witty-crayon-22786 · Answer

thanks will look after morning meetings