x/exp/apidiff: ignore "internal" packages during comparison

[pohly]

What version of Go are you using (go version)?

$ go version
1.13 (only for building)

Does this issue reproduce with the latest release?

Yes (of apidiff).

What did you do?

We use apidiff in a Go project to prevent merging of PRs which break the API:
https://github.com/kubernetes/klog/blob/main/hack/verify-apidiff.sh

One PR removes an exported function from "internal/serialize": kubernetes/klog#326

What did you expect to see?

apidiff should not complain.

What did you see instead?

https://github.com/kubernetes/klog/runs/6372237998?check_suite_focus=true

Inspecting API of ../old...
go: downloading github.com/go-logr/logr v1.2.0
go: extracting github.com/go-logr/logr v1.2.0
go: finding github.com/go-logr/logr v1.2.0
Comparing with ../old...
FAIL: k8s.io/klog/v2/internal/serialize contains incompatible changes:
- TrimDuplicates: removed

[heschi]

cc @jba

[gopherbot]

Change https://go.dev/cl/406534 mentions this issue: apidiff: ignore internal pack

[jba]

@pohly, could you look at the above CL and see if it meets your needs?

I feel that it shouldn't be impossible to compare internal packages. I think a flag would help.

[pohly]

That change made it work for us without any changes on our side, thanks!

I agree that a flag may be useful for other scenarios, but disabled by default seems like the right choice.