Add diffArgs to helmDefaults

[yktakaha4]

This OSS always helps me. Thank you to all the maintainers.

In my use case, I want to keep diffArgs in helmfile.yaml. (Added in #959)
I think this is useful if you want to specify additional arguments to helm-diff only when using a specific helmfile.yaml.
(It is now possible to version control argument specifications for specific charts)

Please let me know if there is anything else I need to do to fix it.

---

For example,

$ ls -l helmfile.yaml 
-rw-r--r-- 1 tkhs tkhs 1567 Sep 13 00:03 helmfile.yaml

$ /home/runner/work/helmfile/helmfile/helmfile diff
Adding repo eks https://aws.github.io/eks-charts
"eks" has been added to your repositories

Comparing release=aws-load-balancer-controller, chart=eks/aws-load-balancer-controller
kube-system, aws-load-balancer-tls, Secret (v1) has changed:
  # Source: aws-load-balancer-controller/templates/webhook.yaml
  apiVersion: v1
  kind: Secret
  metadata:
    labels:
      app.kubernetes.io/instance: aws-load-balancer-controller
      app.kubernetes.io/managed-by: Helm
      app.kubernetes.io/name: aws-load-balancer-controller
      app.kubernetes.io/version: v2.4.5
      helm.sh/chart: aws-load-balancer-controller-1.4.6
    name: aws-load-balancer-tls
    namespace: kube-system
  data:
-   ca.crt: '-------- # (1188 bytes)'
-   tls.crt: '-------- # (1428 bytes)'
-   tls.key: '-------- # (1679 bytes)'
+   ca.crt: '++++++++ # (1188 bytes)'
+   tls.crt: '++++++++ # (1428 bytes)'
+   tls.key: '++++++++ # (1675 bytes)'
  type: kubernetes.io/tls
...

kube-system, aws-load-balancer-webhook, MutatingWebhookConfiguration (admissionregistration.k8s.io) has changed:
  # Source: aws-load-balancer-controller/templates/webhook.yaml
  apiVersion: admissionregistration.k8s.io/v1
  kind: MutatingWebhookConfiguration
  metadata:
    name: aws-load-balancer-webhook
    labels:
      helm.sh/chart: aws-load-balancer-controller-1.4.6
      app.kubernetes.io/name: aws-load-balancer-controller
      app.kubernetes.io/instance: aws-load-balancer-controller
      app.kubernetes.io/version: "v2.4.5"
      app.kubernetes.io/managed-by: Helm
  webhooks:
  - clientConfig:
-     caBundle: LS0tLxxxxx
+     caBundle: LS0tLyyyyy

Add helmDefaults.diffArgs to helmfile.yaml

helmDefaults:
  diffArgs:
    - --suppress-secrets
    - --suppress
    - MutatingWebhookConfiguration
    - --suppress
    - ValidatingWebhookConfiguration

Options are set for helm-diff only helmfile diff and helmfile apply .

$ /home/runner/work/helmfile/helmfile/helmfile diff
Adding repo eks https://aws.github.io/eks-charts
"eks" has been added to your repositories

Comparing release=aws-load-balancer-controller, chart=eks/aws-load-balancer-controller
kube-system, aws-load-balancer-tls, Secret (v1) has changed:
+ Changes suppressed on sensitive content of type Secret
kube-system, aws-load-balancer-webhook, MutatingWebhookConfiguration (admissionregistration.k8s.io) has changed:
+ Changes suppressed on sensitive content of type MutatingWebhookConfiguration
kube-system, aws-load-balancer-webhook, ValidatingWebhookConfiguration (admissionregistration.k8s.io) has changed:
+ Changes suppressed on sensitive content of type ValidatingWebhookConfiguration

Other subcommands, such as helmfile template, are not affected.

$ /home/runner/work/helmfile/helmfile/helmfile template | head
Adding repo eks https://aws.github.io/eks-charts
"eks" has been added to your repositories

Templating release=aws-load-balancer-controller, chart=eks/aws-load-balancer-controller
---
# Source: aws-load-balancer-controller/templates/serviceaccount.yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  name: aws-load-balancer-controller
  namespace: kube-system
  labels:
    helm.sh/chart: aws-load-balancer-controller-1.4.6
    app.kubernetes.io/name: aws-load-balancer-controller

[yxxhero]

@ yktakaha4 We can make this func more flexible. there will be more args like applyArgs, sync Args. WDYT?

[yktakaha4]

@yxxhero Thank you for your review.
Should I modify it so that I can get the type of subcommand currently being executed from HelmState , or define a struct like GetArgsOptions ?
I would be happy to hear your opinions on how to make it more maintainable.

[yxxhero]

@yktakaha4 we can try to define a struct like GetArgsOptions.

[yktakaha4]

Fixed to use GetArgsOptions.

In the current usage of GetArgs, It seems possible to change the interface to GetArgs(c ApplyConfigProvider, state *state.HelmState, opts *GetArgsOptions) and decide whether to include diffArgs inside GetArgs.
Should I make this change?

helmfile/pkg/app/app.go

Lines 1372 to 1375 in a08b986

	// join --args and --diff-args together to one string.
	args := strings.Join([]string{c.Args(), c.DiffArgs()}, " ")
	argsOpts := &argparser.GetArgsOptions{WithDiffArgs: true}
	helm.SetExtraArgs(argparser.GetArgs(args, r.state, argsOpts)...)

---

Edit: I looked at the code again and realized that making the above changes requires more abstraction to the ConfigProvider, so I'm retracting it.