Type mismatch warning in Python

The ability to add event sources to a Lambda is a cool feature, but inference of the common interface seems to fail for SQS event sources. The deployment seems to be successful anyway, which makes me believe the warning is incorrect.

The following snippet is a minimum working example:

class DeploymentsStack(core.Stack):

    def __init__(self, scope: core.Construct, id: str, **kwargs) -> None:
        super().__init__(scope, id, **kwargs)

        lambda = Function(
            self,
            id='id',
            handler='handler',
            runtime=Runtime.GO_1_X,
            code=Code.from_asset('...'),
        )

        queue = Queue(
            self,
            id='id',
            encryption=QueueEncryption.KMS_MANAGED
        )

        sqs_eventsource = SqsEventSource(
            batch_size=1,
            queue=queue
        )

        lambda.add_event_source(sqs_eventsource)

Even though the sqs_eventsource implements aws_cdk.aws_lambda.IEventSource according to the JSII annotation, and the method add_event_source() accepts the exact same interface, a warning is still issued.

I’m not sure whether this is a IDE problem (I’m developing with Intellij IDEA), a JSII issue or a CDK issue. My apologies if this is the wrong place for creating this issue.

Environment

• CDK Version : 1.11.0 (build 4ed4d96)
• OS : Mac OSX Catalina

---

This is 🐛 Bug Report

[nmussy]

Possibly. I’m not that familiar with JSII either.

To rule out any issue with the editor, you could try to invalidate IntelliJ’s cache, or see if another IDE has the same issue? I think Atom has an alright Python support.

[garnaat]

This seems to be IDE-specific. I created the following sample:

#!/usr/bin/env python3

from aws_cdk import (
    aws_lambda as _lambda,
    aws_lambda_event_sources as events,
    aws_sqs as sqs,
    core,
)


class FooStack(core.Stack):

    def __init__(self, scope: core.Construct, id: str, **kwargs) -> None:
        super().__init__(scope, id, **kwargs)

        function = _lambda.Function(
            self, "lambda_function",
            handler='lambda_handler.main',
            runtime=_lambda.Runtime.PYTHON_3_7,
            code=_lambda.Code.asset("./lambda"),
        )

        queue = sqs.Queue(
            self, "myqueue",
            encryption=sqs.QueueEncryption.KMS_MANAGED
        )

        sqs_eventsource = events.SqsEventSource(
            batch_size=1,
            queue=queue
        )

        function.add_event_source(sqs_eventsource)


app = core.App()
FooStack(app, "foo")

app.synth()

With a small no-op Lambda function and then tried editing it in VS Code. It doesn’t complain about the event source as shown above and everything synthesizes correctly.