Allow multiple APIs to register for the same API Group

[brendandburns]

Fixes #23831

@kubernetes/sig-api-machinery

---

This change is

[roberthbailey]

@brendandburns do you want to cherry pick this into the 1.3 branch?

[duglin]

are you able to build this? I'm seeing errors such as:

pkg/api/unversioned/zz_generated.deepcopy.go:28: DeepCopy_unversioned_APIGroup redeclared in this block

but to be honest it might be my env.

[caesarxuchao]

@duglin the error you see is caused by #25978, try make clean, then make all, which will generate the missing files.

[duglin]

@caesarxuchao thanks!

[brendandburns]

@lavalamp @caesarxuchao can I get a quick review on this?
@roberthbailey yes, I'll cherry-pick once it's in.

Thanks
--brendan

[caesarxuchao]

Thanks @brendandburns. LGTM.

[k8s-bot]

GCE e2e build/test passed for commit ca9a61b.

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[k8s-github-robot]

Automatic merge from submit-queue

[polvi]

This does not seem to fix the issue. Tested at ed3a29b

$ cat example-tprs.yml 
apiVersion: extensions/v1beta1
description: A foo
kind: ThirdPartyResource
metadata:
  name: foo.example.com
versions:
- name: v1
---
apiVersion: extensions/v1beta1
description: A bar
kind: ThirdPartyResource
metadata:
  name: bar.example.com
versions:
- name: v1
$ kubectl create -f example-tprs.yml 
thirdpartyresource "foo.example.com" created
thirdpartyresource "bar.example.com" created
$ curl localhost:8080/apis/example.com/v1/
{
  "kind": "APIResourceList",
  "apiVersion": "v1",
  "groupVersion": "example.com/v1",
  "resources": [
    {
      "name": "bars",
      "namespaced": true,
      "kind": "Bar"
    }
  ]
}

[hongchaodeng]

This unit test doesn't equal to real cases.
See here:

    hasResource, err := t.master.HasThirdPartyResource(rsrc)
    if !hasResource {
        return t.master.InstallThirdPartyResource(rsrc)
    }

The bug was caused in HasThirdPartyResource returning true because the API Group has been registered before despite of different resource kind.

I tried to fix it by comparing both API group and resource kind. But I got error:

[restful] WebService with duplicate root path detected:

Seems like rest path duplicate reg. Any suggestion on how to handle the install rest thing? @brendandburns

/cc @polvi @xiang90

[brendandburns]

@polvi let me try to repro this again. I did exactly the above with my branch...

[nebril]

The same thing is happening on c7ec11b

[brendandburns]

@polvi @nebril I believe this is fixed in #29724

Can you give it a test?

[goltermann]

@brendandburns @pwittrock This is in v1.4 milestone, but with cherrypick tags. Is the intent still to get into 1.3.x at some point?

[foxish]

This already went into 1.4. Removing cherrypick tags.

cc @brendandburns