fix: mimic --tla-code behavior from jsonnet for functions in main.jsonnet in env discovery

[sabeechen]

Problem

Some parts of tanka behave inconsistently with standard jsonnet when using inline environments with top level arguments. The differences can be illustrated by this inline environment:

main.jsonnet

function(foo="bar", fizz='buzz') {
  apiVersion: 'tanka.dev/v1alpha1',
  kind: 'Environment',
  // Other env stuff
}

And then running:

$ tk env list main.jsonnet
NAME    NAMESPACE    SERVER    

which finds no environments. Similarly running:

$ tk export export-dir main.jsonnet --recursive
{"level":"info","parallelism":8,"envs":0,"time":"2024-11-29T13:28:23-07:00","message":"Reducing parallelism to match number of environments"}

will export no manifests. For both commands, appending --tla-code foo=1 will resolve the issue, listing the environment and exporting manifests.

If instead main.jsonnet is a function taking no arguments, eg:

main.jsonnet

function() {
  apiVersion: 'tanka.dev/v1alpha1',
  kind: 'Environment',
  // Other env stuff
}

Then there is no combination of arguments that will cause tk env list or tk export --recursive to succeed. It will either do nothing or fail when a --tla-code argument is provided.

Expectation

These tk env list and tk export should permit the same flexibility as underlying jsonnet, namely that:

• A main.jsonnet whose TLA's are all optional should be usable without specifying any --tla-code arguments.
• A main.jsonnet with a function that takes no arguments should be useable.
• Calling tk env list main.jsonnet --tla-code badargument=0 on a mainfaile that isn't a function ignores the tla-code argument.
  This is the behavior I'd expect to see from tk, because its also how calling jsonnet works.

My current workaround for this is to always add a dummy unused TLA to my main.jsonnet and ensure that all my tk commands are run with --tla-code unused=0, which is cumbersome.

Cause

The root cause of this appears to be in how the EvalScript for finding environments is constructed. The presence of any --tla-code argument is used to determine if main.jsonnet should be used called as a function or not. This decision logic behaves incorrectly if a --tla-code is provided with a non-function main.jsonnet or if no --tla-code argument is provided to a main.jsonnet that has no required arguments.

Solution in this PR

Before running an EvalScript, jsonnet.Evaulate is called with std.isFunction on the imported mainfile to determine if it needs to be called as a function. This adds an extra evaluation every time an EvalScript is used, but since thats typically only done once per tk call and the std.isFunction doesn't manifest anything except a boolean, I'd expect it to have a minimal impact on performance.

[sabeechen]

Looking through issues in this repo, I believe this will resolve:

• Defaults for top-level arguments don't appear to work using inline environments #522
• tk env list doesn't work with tla function #653

And although it perpetuates the "hack" for finding environments without manifesting their data, I think it also solves it without having to do any complex AST parsing by just leaning into jsonnet VM to do the real work.

[zerok]

This looks awesome! Thank you very much and sorry for the late review!