Add diff command option for application path

[devholic77]

Summary

I'm using argocd app diff command to verify argocd manifest in jenkins pipeline.
I checked the argocd app diff documentation, but there is no option for diff the live state and a helm app using new values.

For example, this application is in live state.

apiVersion: argoproj.io/v1alpha1
kind: Application
metadata:
  name: myapp
  namespace: argocd
spec:
  destination:
    namespace: myapp
    server: https://kubernetes.default.svc
  project: default
  source:
    repoURL: 'https://my-repo.com'
    targetRevision: v0.0.1
    helm:
      parameters:
      - name: externalUrl
        value: http://example.com
  project: default

when changed as follows, argocd app diff command didn't catch the changes

    helm:
      parameters:
      - name: externalUrl
-      value: http://example.com
+      value: http://other-exmaple.com

Motivation

I added the code referring to this code for test, It worked what I want. : )

argo-cd/cmd/argocd/commands/app.go

Lines 834 to 841 in b37eee1

	if local != "" {
	conn, clusterIf := clientset.NewClusterClientOrDie()
	defer argoio.Close(conn)
	cluster, err := clusterIf.Get(context.Background(), &clusterpkg.ClusterQuery{Name: app.Spec.Destination.Name, Server: app.Spec.Destination.Server})
	errors.CheckError(err)
	localObjs := groupObjsByKey(getLocalObjects(app, local, localRepoRoot, argoSettings.AppLabelKey, cluster.ServerVersion, argoSettings.KustomizeOptions, argoSettings.ConfigManagementPlugins), liveObjs, app.Spec.Destination.Namespace)
	items = groupObjsForDiff(resources, localObjs, items, argoSettings, appName)
	} else if revision != "" {

			if local != "" {
+ 	                        newApp, err := cmdutil.ConstructApps( {{ application_manifest_path }} , appName, labels, annotations, args, appOpts, nil)
				conn, clusterIf := clientset.NewClusterClientOrDie()
				defer argoio.Close(conn)
				cluster, err := clusterIf.Get(context.Background(), &clusterpkg.ClusterQuery{Name: app.Spec.Destination.Name, Server: app.Spec.Destination.Server})
				errors.CheckError(err)
-				localObjs := groupObjsByKey(getLocalObjects(app, local, localRepoRoot, argoSettings.AppLabelKey, cluster.ServerVersion, argoSettings.KustomizeOptions, argoSettings.ConfigManagementPlugins, argoSettings.TrackingMethod), liveObjs, app.Spec.Destination.Namespace)
+                               localObjs := groupObjsByKey(getLocalObjects(newApp, local, localRepoRoot, argoSettings.AppLabelKey, cluster.ServerVersion, argoSettings.KustomizeOptions, argoSettings.ConfigManagementPlugins, argoSettings.TrackingMethod), liveObjs, app.Spec.Destination.Namespace)
				items = groupObjsForDiff(resources, localObjs, items, argoSettings, appName)
			} else if revision != "" {

Proposal

through the previous test, I think we need an option for this.
What if options like --local-appare added?

[gw0]

If I understand correctly, many argocd app diff issues are seem to be related (#4706, #4703, #7770, #6942, #6167, #5532).

Basically, we need an option to provide the whole App manifest (not just an option to update the revision). You are proposing that this is done client-side that looks like a trivial change, the PR #6247 does some magic on server-side, some others are also proposing server-side due to binary version incompatibilities.

I managed to pull together a manual workaround that basically renders on server-side, but does the diff client-side, see #4706 (comment).