Allow configured providers to provide additional functions.

[cam72cam]

Prior to this change a single unconfigured lazy provider instance was used per provider type to supply functions. This used the functions provided by GetSchema only.

With this change, provider function calls are detected and supplied via GraphNodeReferencer and are used in the ProviderFunctionTransformer to add dependencies between referencers and the providers that supply their functions.

With that information EvalContextBuiltin can now assume that all providers that require configuration have been configured by the time a particular scope is requested. It can then use it's initialized providers to supply all requested functions.

At a high level, it allows providers to dynamically register functions based on their configurations.

main.lua

function main_a( input )
    local animal_sounds = {
        cat = 'meow',
        dog = 'woof',
        cow = 'moo'
    }
    return animal_sounds
end

main.tf

terraform {
  required_providers {
    tester = {
      source  = "terraform.local/local/testfunctions"
      version = "0.0.1"
    }
  }
}

provider "tester" {
        lua = file("./main.lua")
}

output "test" {
        value = provider::tester::main_a(tomap({"foo": {"bar": 190}}))
}

Output:

Changes to Outputs:
  + test = {
      + cat = "meow"
      + cow = "moo"
      + dog = "woof"
    }

This requires some enhancements to the HCL library and is currently pointing at my personal fork, with a PR into the main HCL repository: hashicorp/hcl#676. As this may take some time for the HCL Team to review, I will likely move the forked code under the OpenTofu umbrella before this is merged [done].

This PR will be accompanied by a simple provider framework for implementing function providers similar to the example above.

Related to #1326

Target Release

1.7.0

[github-actions]

Reminder for the PR assignee: If this is a user-visible change, please update the changelog as part of the PR.

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[Yantrio]

Overall I like it. I'm tempted to say that we should have some sort of ProviderFunctionFromString(input string) ProviderFunction method that parses the addr, and then from there we can have a IsCore() method.

That could help the readability of the code.

LGTM so far, once the TODOs are done I'll be happy to review again. (Also we could do with some more tests)

[cube2222]

WIP review: looking good!

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[janosdebugs]

Looks ok, but I can't really judge the completeness of the code as I'm not familiar with most parts of it.

[cube2222]

Left a couple nit comments.

LGTM overall!

[Yantrio]

Overall it looks good to me. I have some concerns around the performance of the graph transformation stuff, but I would need to benchmark and run it to see how performant it is.

My comments are mostly small nitpicks, which I would prefer are addressed, but I'll leave that up to others to decide based on timings.

Nice work! 👍

[cube2222]

LGTM!