fix: Update PrintNamespacesList to use a YAML parser for multiple manifest files

[katiexzhang]

Multiple manifests may be defined in a single YAML file. --- is used to separate the different manifests.

Before:

• strings.Split("---") is used to break the file into multiple manifests. If a string in the manifest contains "---" (i.e. "name: hello---123"), it will also break on that and won't be able to decode the manifest anymore.

After:

• YAML parser (https://pkg.go.dev/gopkg.in/yaml.v3) correctly parses file with multiple manifests.

Note: If a file just contains "---" it is considered empty and therefore valid and will just return an empty resourceToInfoMap.

[plumpy]

What about

yaml: "
  ---
"

[plumpy]

Also YAML explicitly allows \r\n as a valid line break (for Windows compatibility): https://yaml.org/spec/1.2.2/#54-line-break-characters

[katiexzhang]

What about

yaml: "
  ---
"

Right now this returns an error like:
2025/06/04 18:42:37 couldn't get version/kind; json parse error: json: cannot unmarshal string into Go value of type struct { APIVersion string "json:\"apiVersion,omitempty\""; Kind string "json:\"kind,omitempty\"" }

A file with just --- is technically empty so according to the comment "skip empty documents, Decode will fail on them" we should just skip it (and return nothing / no error). But, it is weird to have a manifest with just --- right?

[plumpy]

Sorry, that was a confusing example, but my point was that this is technically a valid YAML file:

foo: "
   ---
"

If you parse it, you get a map: {"foo": " --- "}. But your code is just going to split on ---\n and rip it into two different documents (neither of which is valid YAML).

My larger point is that trying to parse any structured format with a basic text-processing tools (like strings.Split) is not going to work very well. Just quickly perusing the spec, I can find all kinds of other ways to make valid YAML that won't work with your code. (You're allowed to have whitespace and comments and a variety of other things after the ---, for example; it doesn't need to be immediately followed by a newline.)

In short: if you want to parse YAML, use a YAML parser.

[katiexzhang]

Ok, updated to use https://pkg.go.dev/gopkg.in/yaml.v3 for parsing the multiple files, but kept the kubernetes file parser.

So for the file with just "---" --> should that be valid then?

[plumpy]

Yeah, I think this looks great, thanks.