Parsing Helm template syntax

[reiv]

I'm using this library in an (arguably misguided) attempt to parse and generate Helm templates, which use Go's text/template double curly brace syntax for interpolations. This works fine as long as everything is quoted or would otherwise be parsed as a string, like this:

metadata:
  name: foo-{{ .Release.Name }}

but it quickly falls apart if you want to interpolate some non-string value like:

spec:
  replicas: {{ .Values.replicaCount }}

# warn: Keys with collection values will be stringified due to JS Object restrictions: ...

Is it feasible to extend the parser to be able to deal with {{ ... }} outside of strings as a discrete node (similarly to how the library already lets you define custom scalars)?

[eemeli]

Is it feasible to extend the parser to be able to deal with {{ ... }} outside of strings as a discrete node (similarly to how the library already lets you define custom scalars)?

No, because that's valid YAML that has a non-scalar meaning, and it's parsed as an object with an object key already by the lexer.

However, you could add a wrapper around the yaml parser to make it work:

1. Replace all of the {{ ... }} sequences with some string that's a valid YAML plain scalar, like __TEMPLATE_VAR_#__ where # is an identifier that you keep track of.
2. Parse the result with parseDocument().
3. Use a visitor to find and replace the __TEMPLATE_VAR_#__ strings with their original values.

[reiv]

Thank you for the suggestion. The preprocessor approach seems like a reasonable way of doing it (and also rather apt since Helm is a preprocessor itself).