codegen: I have a script that extracts info from python sources to generate a config file and an api spec. It seems like this is the doc I need: https://www.pantsbuild.org/docs/plugins-codegen But it seems to be very protobuf centric, talking about protocols and whatnot. I'm doing py -> ini and py -> json, not whatever protobuf does. Does anyone have a simple example like this?

its quite simple actually. I made one just the other day.

In the docker backend is a completely different use of codegen. It conditionally generates Dockerfile from an instructions field.

sorry, was pulled away to cook dinner.

and I to breakfast 😛

Following https://www.pantsbuild.org/docs/plugins-codegen I did: 1. Created a

SingleSourceField

subclass for my input on my

GenerateSourcesRequest

(I guess you'd use

PythonSourceField

) (Note: This file doesn't need to exist) 2. Used

PythonSourceField

as my output. (At a guess you'll need to create a

FrobulatorIniSourceField

) 3. Did Step #3 for the Union rule 4. For step #4 you can stick whatever you want in your

@rule

you just need to generate a

Snapshot

containing the files as you'd expect to see them on disk. (i.e.

src/python/foo.py

which I calculated with:

f"{target.address.spec_path}/{target.address.target_name}.py"

Because my 'codegen' code was pure-python, I just did it directly in the

@rule

. Less than 100 lines to: • get the target and it's files deps • strip the files source-roots • retrieve the contents of the files • parse the python • spit out a

Digest

&

Snapshot

I think it’s a learning curve, once you get over a certain threshold it’s a joy to work with, but it takes a while to get there. (applies to more than just codegen)

yeah.

😆 "Frobulator"

@proud-dentist-22844 I’ll take a stab at that explanation. Codegen only works in source_X => source_Y (X and Y may be the same, as used in the docker backend for example). In other words, you define a subclass of

GenerateSourcesRequest

for a setup of target/destination source field types. So whenever the sources for a target is hydrated, the engine looks for any such subclasses that can translate what you have into the target source type (provided that codegen is enabled on the source hydrate request).

ooh. The Dockerfile example was helpful. I'm slowly piecing it together.