Cannot define provider functions that are dependent on the provider configuration

[valentindeaconu]

Module version

github.com/hashicorp/terraform-plugin-framework v1.13.0

Relevant provider source code

https://github.com/valentindeaconu/terraform-provider-func/blob/a282896fd2da6427afb2340d21f575c30cc61121/internal/provider/provider.go#L111-L202

https://github.com/valentindeaconu/terraform-provider-func/blob/a282896fd2da6427afb2340d21f575c30cc61121/internal/provider/provider.go#L226-L250

Terraform Configuration Files

terraform {
  required_providers {
    func = {
      source  = "valentindeaconu/func"
      version = "0.1.0"
    }
  }
}

provider "func" {
  library {
    source = "file://${path.module}/library.js"
  }
}

output "results" {
  value = {
    sum = provider::func::sum(10, 5) # Expected result => 15
  }
}

Debug Output

https://gist.github.com/valentindeaconu/157501a91c011f3c719baed846076802

Expected Behavior

I am expecting Terraform to initially call the provider's Configure method, so the ProviderData is initialised, then call the Functions method, to get the provider's functions. Or, at least, call the Functions twice (at least once after the Configure method), as it does for Resources and DataSources methods and leave the graceful failure handling to the provider developer.

Actual Behavior

The Functions method gets called only once, and since the Functions slice is only known after parsing the provider configuration, it is empty at the time of the call, making Terraform crash.

Steps to Reproduce

1. terraform init
2. terraform plan

References

[austinvalle]

Hey there @valentindeaconu 👋🏻 , thanks for writing up the issue and sorry you're running into trouble here!

Unfortunately, what you're observing is by design, as Terraform core has certain "offline" operations (i.e. no configuration of provider needed) it is able to execute providers with, provider functions being one of those operations. Keeping provider functions offline allows Terraform to execute said provider functions anywhere that normal built-in Terraform functions can operate, like inside an import block, as it's evaluating the configuration.

As provider functions are expected to be offline/pure functions without side effects, terraform-plugin-framework itself doesn't have a mechanism to pass data from provider to function (like resources and data sources do), since it's not designed to operate that way.

---

Hypothetically, if the client calling your provider supported "online" provider functions which configure prior to executing, you could implement your own provider server (using terraform-plugin-go) that implements CallFunction, GetFunctions, ConfigureProvider and GetProviderSchema. You could then mux that bespoke provider server with a standard plugin framework server via: https://developer.hashicorp.com/terraform/plugin/mux

The kubernetes provider has done this (not for this exact reason), so that could be used as a reference.

---

Since there is nothing actionable for us to do ATM, I'm going to close this issue. If Terraform core wants to revisit the provider function design to enable them to be run "online", then we can create a new issue and proceed from there.