feat(server): make deep copies of objects returned by informers (#22173)

[rumstead]

closes #22173

Checklist:

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[rumstead]

Another way we could go about this is to wrap the informers. Maybe something like this:

package application

import (
	"github.com/argoproj/argo-cd/v3/pkg/apis/application/v1alpha1"
	applisters "github.com/argoproj/argo-cd/v3/pkg/client/listers/application/v1alpha1"

	"k8s.io/apimachinery/pkg/labels"
)

// deepCopyApplicationLister wraps an ApplicationLister and returns deep copies of the applications.
type deepCopyApplicationLister struct {
	applisters.ApplicationLister
}

// List lists all Applications in the indexer and returns deep copies.
func (d *deepCopyApplicationLister) List(selector labels.Selector) ([]*v1alpha1.Application, error) {
	apps, err := d.ApplicationLister.List(selector)
	if err != nil {
		return nil, err
	}
	deepCopiedApps := make([]*v1alpha1.Application, len(apps))
	for i, app := range apps {
		deepCopiedApps[i] = app.DeepCopy()
	}
	return deepCopiedApps, nil
}

// Applications returns an object that can list and get Applications and returns deep copies.
func (d *deepCopyApplicationLister) Applications(namespace string) applisters.ApplicationNamespaceLister {
	return &deepCopyApplicationNamespaceLister{
		ApplicationNamespaceLister: d.ApplicationLister.Applications(namespace),
	}
}

// deepCopyApplicationNamespaceLister wraps an ApplicationNamespaceLister and returns deep copies of the applications.
type deepCopyApplicationNamespaceLister struct {
	applisters.ApplicationNamespaceLister
}

// List lists all Applications in the indexer for a given namespace and returns deep copies.
func (d *deepCopyApplicationNamespaceLister) List(selector labels.Selector) ([]*v1alpha1.Application, error) {
	apps, err := d.ApplicationNamespaceLister.List(selector)
	if err != nil {
		return nil, err
	}
	deepCopiedApps := make([]*v1alpha1.Application, len(apps))
	for i, app := range apps {
		deepCopiedApps[i] = app.DeepCopy()
	}
	return deepCopiedApps, nil
}

// Get retrieves the Application from the indexer for a given namespace and name and returns a deep copy.
func (d *deepCopyApplicationNamespaceLister) Get(name string) (*v1alpha1.Application, error) {
	app, err := d.ApplicationNamespaceLister.Get(name)
	if err != nil {
		return nil, err
	}
	return app.DeepCopy(), nil
}

[crenshaw-dev]

I think I like the wrapping idea... seems better than sprinkling deep copies across the code base.

[rumstead]

Trying to wrap the kubernetes.Interface i think is too large of a task :-p. there are so too many methods.

[codecov]

Codecov Report

Attention: Patch coverage is 81.39535% with 16 lines in your changes missing coverage. Please review.

Please upload report for BASE (master@fbd7f29). Learn more about missing BASE report.
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
server/application/deepinformer.go	81.25%	10 Missing and 5 partials ⚠️
server/application/application.go	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #22179   +/-   ##
=========================================
  Coverage          ?   55.84%           
=========================================
  Files             ?      343           
  Lines             ?    57290           
  Branches          ?        0           
=========================================
  Hits              ?    31996           
  Misses            ?    22650           
  Partials          ?     2644           

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[rumstead]

This is the "real" test. Ensuring the deep copy informers return an actual deep copy.

[gdsoumya]

LGTM