# target_types.py

from pants.engine.target import (
    COMMON_TARGET_FIELDS,
    MultipleSourcesField,
    SingleSourceField,
    Target,
    TargetFilesGenerator,
)


class MessageSourceField(SingleSourceField):
    expected_file_extensions = (".po",)


class MessageSourcesField(MultipleSourcesField):
    expected_file_extensions = (".po",)
    default = ("*.po",)


class MessageSourceTarget(Target):
    alias = "message_source"
    core_fields = (*COMMON_TARGET_FIELDS, MessageSourceField)


class MessageSourcesGeneratorTarget(TargetFilesGenerator):
    alias = "message_sources"
    core_fields = (*COMMON_TARGET_FIELDS, MessageSourcesField)
    copied_fields = COMMON_TARGET_FIELDS
    moved_fields = ()
    generated_target_cls = MessageSourceTarget
    copied_fields = COMMON_TARGET_FIELDS

# rules.py

from pants.core.target_types import ResourceSourceField
from pants.engine.internals.native_engine import EMPTY_SNAPSHOT
from pants.engine.rules import rule
from pants.engine.target import GeneratedSources, GenerateSourcesRequest
from pants.engine.unions import UnionRule
from pants.util.logging import LogLevel
from plugins.django.messages.target_types import MessageSourceField


class CompileMessageRequest(GenerateSourcesRequest):
    input = MessageSourceField
    output = ResourceSourceField


@rule(level=LogLevel.DEBUG, desc="Compile messages")
async def compile_messages(_: CompileMessageRequest) -> GeneratedSources:
    return GeneratedSources(EMPTY_SNAPSHOT)


def rules():
    return [compile_messages, UnionRule(GenerateSourcesRequest, CompileMessageRequest)]

# register.py

from plugins.django.messages.rules import rules as messages_rules
from plugins.django.messages.target_types import (
    MessageSourcesGeneratorTarget,
    MessageSourceTarget,
)


def target_types():
    return [MessageSourceTarget, MessageSourcesGeneratorTarget]


def ruiles():
    return [
        *messages_rules(),
    ]

message_sources

./pants --filter-target-type=message_source list ::

./pants export-codegen ::

No codegen files/targets matched. All codegen target types: docker_image, experimental_shell_command, protobuf_source

UnionRule(GenerateSourcesRequest, CompileMessageRequest)

export-codegen

def ruiles():

def rules():