Create validation function for cross namespace referencing

[yijie-04]

Fixes #7797

Proposed Changes

• :gift: New package created for cross namespace referencing and added validation.go

Pre-review Checklist

• [ ] At least 80% unit test coverage
• [ ] E2E tests for any new behavior
• [ ] Docs PR for any user-facing impact
• [ ] Spec PR for any new API feature
• [ ] Conformance test for any change to the spec

Release Note

Docs

[yijie-04]

\cc @Cali0707 @pierDipi

[pierDipi]

\cc @Cali0707 @pierDipi

the bot expects the forward slash /cc @Cali0707 @pierDipi

[Cali0707]

@yijie-04 if you look at the comments the github actions left on your code, you'll see that there are a few unused/undefined variables that are causing the build to fail. Would you be able to fix those?

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 17.80822% with 60 lines in your changes are missing coverage. Please review.

Project coverage is 69.29%. Comparing base (7e1c082) to head (3e323a0). Report is 21 commits behind head on main.

Files	Patch %	Lines
pkg/crossnamespace/validation.go	0.00%	46 Missing :warning:
pkg/apis/eventing/v1/trigger_types.go	0.00%	4 Missing :warning:
pkg/apis/eventing/v1/trigger_validation.go	66.66%	3 Missing and 1 partial :warning:
pkg/apis/messaging/v1/subscription_validation.go	0.00%	3 Missing and 1 partial :warning:
pkg/apis/messaging/v1/subscription_types.go	0.00%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7812      +/-   ##
==========================================
+ Coverage   69.22%   69.29%   +0.07%     
==========================================
  Files         339      341       +2     
  Lines       19494    15808    -3686     
==========================================
- Hits        13494    10954    -2540     
+ Misses       5337     4182    -1155     
- Partials      663      672       +9     

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[yijie-04]

I wrote down some notes as comments in the files, I'll clean them up in the end!

[Cali0707]

/retest-required

[yijie-04]

@yijie-04 this is great! I think this might be ready to review and merge, what do you think?

Also cc @pierDipi , anything you see in this PR that needs changing?

Sounds good! I'll clean up the comments. For checking the pointer, I'll just return an empty kreference?

[Cali0707]

@yijie-04 if you think this is ready, feel free to remove the [WIP] from the title, that should remove the hold label. You can also comment /unhold!

[yijie-04]

/unhold

[yijie-04]

@Cali0707 @pierDipi I think the unit tests are all passing now! I originally had a test checking if the namespace is empty or is missing, I just want to confirm that this would not be necessary since we would just assume it's the same as the object namespace?

[Cali0707]

/unhold

[Cali0707]

@yijie-04 this looks really good so far! Would you be able to also add some unit tests to the trigger validation, similar to what you did for the subscription?

[knative-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Cali0707, yijie-04

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