Skip helm get hooks when --three-way-merge=true

[stanislav-zaprudskiy]

Hooks manifests would have been already added when --three-way-merge=true (by genManifest function). Unless --no-hooks=true have been supplied as well - making them being skipped earlier as well.

This results into only one case when hooks manifests should be added separately: --three-way-merge=false --no-hooks=false (the current defaults).

With the current code however, when charts contain hooks and --three-way-merge=true, some confusing output is returned (esp. on empty diff). That's because hooks manifests are added twice: first inside genManifest function, and then again by appending results of getHooks function.

$ helm diff upgrade my-release my-chart --values values.yaml --three-way-merge=true
2022/12/01 16:52:34 Error: Found duplicate key "my-ns, my-cm, ConfigMap (v1)" in manifest

The exit code is 0, though. A user thinking could be:

• Did helm diff fail, but did not reflect that in exit code?
• It did not fail, but because of the Error it could have missed diffing at all?
• Why the diff is empty - because of the Error or is it empty indeed?

Perhaps, replacing Error with Warning in the message would make sense as well.

[mumoshu]

@stanislav-zaprudskiy Thank you very much for the fix, along with your detailed report! This looks awesome! Merging.