Lambda update_function_code not incrementing Version when Publish=True

[ekolve]

When running the following beneath moto

import boto3
client = boto3.client('lambda', region_name='us-east-2')
res = client.update_function_code(FunctionName='test-function', ZipFile=<somearchive>, Publish=True)
print(res["Version"])

After the first invocation this prints out 1, but this also prints out 1 for both results if the following is run:

import boto3
client = boto3.client('lambda', region_name='us-east-2')
res = client.update_function_code(FunctionName='test-function', ZipFile=<somearchive>, Publish=True)
print(res["Version"])
res = client.update_function_code(FunctionName='test-function', ZipFile=<somearchive>, Publish=True)
print(res["Version"])

I would expect the second invocation to print out 2 since a new version is getting published.

[ekolve]

I tracked down the issue to this:

moto/moto/awslambda/models.py

Line 1691 in edc7947

if latest_published.code_sha_256 == function.code_sha_256:

            if latest_published.code_sha_256 == function.code_sha_256:
                # Nothing has changed, don't publish
                return latest_published

AWS doesn't apply the same logic on their side when code is published. They seem to publish a new version even if the code hasn't changed.

[bblommers]

According to the documentation, AWS does not publish a new version when calling publish_version with the same code.
From https://docs.aws.amazon.com/lambda/latest/dg/configuration-versions.html:

Lambda publishes a new function version only if the code has never been published, or if the code has changed from the last published version. If there is no change, the function version remains at the last published version.

Does the update_function_code behave differently? If so, that would be.. confusing.

[ekolve]

Here is what I am observing with AWS:

import boto3
client = boto3.client('lambda', region_name='us-west-2')
res = client.update_function_code(FunctionName='test-handler', ZipFile=<archive>, Publish=True)
print(res["Version"]) # prints 1
res = client.update_function_code(FunctionName='test-handler', ZipFile=<archive>, Publish=True) # archive is identical to the first call
print(res["Version"]) # prints 2
res = client.publish_version(FunctionName='test-handler')
print(res["Version"]) # prints 2

So the docs for publish_version are correct, the docs for update_function_code https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/lambda/client/update_function_code.html
state the following:

Publish (boolean) – Set to true to publish a new version of the function after updating the code. 
This has the same effect as calling PublishVersion separately.

Given all this, I'm not sure what the right course of action is with respect to mocking. Their docs are ambiguous and I can modify my test to slightly modify my archive to trigger the version to get updated with moto, but it would be nice if AWS would state explicitly what should happen for this case.