I'm having trouble writing an "in-repo" plugin for a custom codegen. I have put it under

pants-plugins/tutugen

which contains a

register.py

file and a

BUILD

file. First, I'm not sure what I should put on the BUILD file. I read about python_source, python_requirement and pants_requirements. I'm not sure which ones should go in the file. Then, the plugin requires a 3rd party lib named

tutu

. If I try to exec any pants commands, I get a

No module named: 'tutu'

error. I'm not sure what is missing :-/

python_sources

should wrap your plugin's source files. Having that depend on a

pants_requirements()

target is handy shorthand for "depend on the version of Pants I am running in", so you don't have to repeat that version (and ensure it matches the

version=

value in your pants.toml), as you would if you used a regular

python_requirements

.

right now,

register.py

imports

tutu

. The error happens when pants tries to load the backend

And you may need to set

pythonpath = ["%(buildroot)s/path/to/plugin/source/root"]

in pants.toml

backend_packages and pythonpath are set. I think it is just a question of detecting my tutu dependency

Oh, wait, this tickles my memory

explicitly in a

python_requirement

on a BUILD file in the module (alongside register.py)

IIRC that is a known gotcha for in-repo plugins. The requirements have to be added to the

plugins

list.

yeah, it's a little confusing. You don't actually have to have the

pants_requirements

and

python_sources

targets for a plugin to work; all that matters is the

[GLOBAL].plugins

,

backend_packages

, and

pythonpath

options. But, it's a good idea to have

pants_requirements

and

python_sources

so that you can run Pants on your plugin code, e.g. format it and lint it

ok, the plugins was missing. It works now

the goal export-codegen doesn't exist

A relevant backend needs to be implemented. We hide irrelevant goals by default. Did you register a

UnionRule(GenerateSourcesRequest, ...)

?

I did but let me check for typo

a common error we sometimes do is not properly registering all the rules inside

register.py

. For example, we often have a dedicated file

rules.py

. You need to import that and then register its rules inside `register.py`'s

def rules()

function

right now, everything is in the

register.py

. I have the

UnionRule(...)

Okay. Simple test then to make sure the backend is being picked up in general...add a target type

from pants.engine.target import Target

class MyTarget(Target):
   alias = "my_target"
   core_fields = ()
   help = "blah"

def target_types():
   return [MyTarget]

Then

./pants help targets

yep the target is there.

Strange that

./pants export-codegen

isn't showing up then...

GenerateSourcesRequest

does have a class property

exportable: bool

, but it defaults to True

unfortunately I won't be able in this case. I followed https://www.pantsbuild.org/docs/plugins-codegen

The only difference (besides possible typos) is that the Request class parameters input and output have the same type

I think that's legal

Unknown goal: export-codegen

If you activate

pants.backend.codegen.protobuf.python

, does it show up at least?

oh, yes it does and if I do

./pants export-codegen ::

, it actually call my backend