Marking file as type "starlark" fails to allow it to be treated as a Starlark file.

[jtigger]

Reported by @Zebradil in #carvel. Thank you. 🙏

Steps to Reproduce

1. create the file star.test1:

   print(42)

2. by default, ytt regards this file a "unknown type" or "data" and so it is not evaluated (expected):

   $ ytt -f test.star1
   

3. rename the file to .star, and ytt regards this file a "starlark" file and evaluates it (expected):

   $ ytt -f test.star
   42
   

4. mark the file directly as type starlark, and ytt should regard this file a "starlark" file and evaluate it:

   $ ytt -f test.star1 --file-mark='test.star1:type=starlark'
   

   (but it does not 🛑)

Anything else you would like to add:

Key symptom is the way in which a file is determined to be a "library file":

https://github.com/vmware-tanzu/carvel-ytt/blob/92f7de5ca3a11dfa5f341134f15cbc0a6b0fb31f/pkg/files/file.go#L242-L251

which only regards the extension of a file.

• what can be done to respect the file mark for starlark type files?
• should there be a file mark for YAML files that are also "library file"s (e.g. type=yaml-library)?

Environment:

• ytt version (use ytt --version): 0.44.0 (likely introduced some versions back)
• OS (e.g. from /etc/os-release): (all)

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[Zebradil]

Thank you for creating the issue.

I have noticed that the code on the step 3 is incorrect. It should be something with the following:

ytt -f test.star

[jtigger]

Whops! Thanks, @Zebradil. I updated the description.