I've working on a PR and am befuddled by some rule graph errors that behave differently between

PANTS_SOURCE=

and pants itself. I thought my code was working because when I run through various scenarios in another repo with

PANTS_SOURCE=/pants/with/my/change

my code seems to work (new CLI flags accepted, different behavior, new output, etc) But when I try to run

pants list ::

in pants itself I get

[ERROR] Encountered 8 rule graph errors

. I don't understand how the rules can be valid in one case, but not the other. • WIP change https://github.com/cburroughs/pants/commit/4a1f6d10ea82e09615c5d03669b0ba7c34c00b31 (Sorry it's very rough as uhh, I can't run

pants fmt

on it) • rule graph errors: https://gist.github.com/cburroughs/beb4054b73c377373f1195f20a6a477d

Possibly due to differences in config (particularly loaded plugins) between the other repo and the pants repo?

hmm, well to be concrete the "other repo" is

example-python

. I think

pants

itself is a superset of backends. I noticed most rules files just call

*collect_rules()

, but a few do something like:

def rules():
    return [
        *collect_rules(),
        *external_tool.rules(),
        *pex_environment.rules(),
        *adhoc_binaries.rules(),
    ]

Is there some rules dependency/bootstrapping one has to do when working with the python backend?

You have to make sure some backend brings in all the rules you're using, but unfortunately the error messages on rule graph construction errors are terrible right now

I have re-read that recently with renewed interest!

src/python/pants/backend/python/goals/lockfile.py | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/python/pants/core/goals/generate_lockfiles.py | 49 +++++++++++++++++++++++++++++++++++++++++++++++++

I think in this case though the everything in

lockfile.py

is safely within the python backend. The only thing different in this Get snippet is is the alternative return type

check_results = await MultiGet(
            Get(
                CheckLockfileResult,
                {
                    req: GenerateLockfile,
                    _preferred_environment(req, local_environment.val): EnvironmentName,
                },
            )
            for req in all_requests
        )

Yet when I "install" my rule:

@rule(desc="Checking Python lockfile", level=LogLevel.DEBUG)
async def check_lockfile(
        req: GeneratePythonLockfile,
        generate_lockfiles_subsystem: GenerateLockfilesSubsystem,
        python_setup: PythonSetup,
) -> CheckLockfileResult:

Pants (and only the pants repo) fails with

No installed rules return the type GeneratePythonLockfile

, yet this pre-existing rule can find

GeneratePythonLockfile

just fine.

@rule(desc="Generate Python lockfile", level=LogLevel.DEBUG)
async def generate_lockfile(
    req: GeneratePythonLockfile,
    generate_lockfiles_subsystem: GenerateLockfilesSubsystem,
    python_setup: PythonSetup,
) -> GenerateLockfileResult: