Add checkReplicasChange function to detect changes in replicas field

[Warashi]

What this PR does:

• Add checkReplicasChange function to detect changes in replicas field
  • there is a bug in original checkReplicasChange, so I backported the fix
• Add support for rendering interface and pointer types in RenderPrimit…
  • We need this because reflect.Interface are returned as their kind when the replicas field is absent either of before/after manifests

Why we need it:

We chose a quick sync strategy when the diffs are only replicas.
We must build a summary message with the workload changed, so we must check it.

Which issue(s) this PR fixes:

Part of #4980

Does this PR introduce a user-facing change?: Yes

• How are users affected by this change:
  When users delete or add the spec.replicas field on the Deployment manifest, they can view the plan summary as expected. Without this PR, they will see an invalid value.

• Is this breaking change: No

• How to migrate (if breaking change): N/A

[Warashi]

🤔 oops, we should put this before as "nil"?
I could not determine whether the empty string or "nil" is better.

[Warashi]

@khanhtc1202 @t-kikuc @ffjlabo
WDYT about this?

[ffjlabo]

@Warashi
When does node.TypeX == nil occur?
I think we should clarify the situation to determine it.

[Warashi]

@ffjlabo Sorry for forgetting to write it.
When the replicas field is not found in the old manifests, node.TypeX becomes nil and node.ValueX becomes invalid value.

[ffjlabo]

@Warashi

@ffjlabo Sorry for forgetting to write it.
When the replicas field is not found in the old manifests, node.TypeX becomes nil and node.ValueX becomes invalid value.

Thanks.

When the replicas field is not found in the old manifests,

It seems that the node is the one that has spec.replicas extracting by the logic before.
So we might not need to check it.

	const replicasQuery = `^spec\.replicas$`
	node, err := ns.FindOne(replicasQuery)

I'm sorry if I misunderstood. 🙏

[Warashi]

Thanks 👍🏻

BTW, I realized it's better to return "<nil>" instead of an empty string because the before and after are used in this context.

pipecd/pkg/app/piped/planner/kubernetes/kubernetes.go

Lines 311 to 313 in 23eddac

	if before, after, changed := checkReplicasChange(d); changed {
	scales = append(scales, fmt.Sprintf("%s/%s from %s to %s", k.Kind, k.Name, before, after))
	}

[Warashi]

fixed on this commit
13625ca

[ffjlabo]

@Warashi
Nice catch! I agree with it! The case is when there is nothing spec.replicas.

I think the <nil> value should be defined as const value. WDYT?
We might use it to express the same situation. e.g. checkImageTags.

[Warashi]

@ffjlabo
I think it's too early to make "<nil>" as constant because we use this only two places in one function, and we should use "<nil>" carefully because whether the "<nil>" or an empty string should be used is case-by-case.

For example, I think the image nginx should be just nginx, not nginx:<nil>.

[ffjlabo]

@Warashi
I agree with it. Thanks. So let's rethink it when the same situation will occur. 👌

[codecov]

Codecov Report

Attention: Patch coverage is 67.56757% with 12 lines in your changes missing coverage. Please review.

Project coverage is 25.32%. Comparing base (00463a6) to head (13625ca).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
pkg/app/piped/planner/kubernetes/kubernetes.go	20.00%	10 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5341   +/-   ##
=======================================
  Coverage   25.31%   25.32%           
=======================================
  Files         444      444           
  Lines       47641    47688   +47     
=======================================
+ Hits        12059    12075   +16     
- Misses      34640    34668   +28     
- Partials      942      945    +3     

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[ffjlabo]

LGTM 🆗