Default values within sets cause crashes and/or incorrect behaviour

[maxb]

Module version

v1.3.1

Relevant provider source code

This is the entire source code of a single .go file provider that demonstrates the issues:

package main

import (
	"context"

	"github.com/hashicorp/terraform-plugin-framework/datasource"
	"github.com/hashicorp/terraform-plugin-framework/provider"
	"github.com/hashicorp/terraform-plugin-framework/providerserver"
	"github.com/hashicorp/terraform-plugin-framework/resource"
	"github.com/hashicorp/terraform-plugin-framework/resource/schema"
	"github.com/hashicorp/terraform-plugin-framework/resource/schema/stringdefault"
)

func main() {
	err := providerserver.Serve(
		context.Background(),
		func() provider.Provider {
			return new(bugProvider)
		},
		providerserver.ServeOpts{
			Address: "bug/bug/bug",
		},
	)
	if err != nil {
		panic(err)
	}
}

type bugProvider struct{}

func (p *bugProvider) Metadata(ctx context.Context, req provider.MetadataRequest, resp *provider.MetadataResponse) {
	resp.TypeName = "bug"
}

func (p *bugProvider) Schema(ctx context.Context, req provider.SchemaRequest, resp *provider.SchemaResponse) {
}

func (p *bugProvider) Configure(ctx context.Context, req provider.ConfigureRequest, resp *provider.ConfigureResponse) {
}

func (p *bugProvider) DataSources(ctx context.Context) []func() datasource.DataSource {
	return nil
}

func (p *bugProvider) Resources(ctx context.Context) []func() resource.Resource {
	return []func() resource.Resource{
		func() resource.Resource {
			return new(bugResource)
		},
	}
}

type bugResource struct{}

func (r bugResource) Metadata(ctx context.Context, req resource.MetadataRequest, resp *resource.MetadataResponse) {
	resp.TypeName = req.ProviderTypeName + "_bug"
}

func (r bugResource) Schema(ctx context.Context, req resource.SchemaRequest, resp *resource.SchemaResponse) {
	resp.Schema = schema.Schema{
		Attributes: map[string]schema.Attribute{
			"set": schema.SetNestedAttribute{
				Required: true,
				NestedObject: schema.NestedAttributeObject{
					Attributes: map[string]schema.Attribute{
						"fruit": schema.StringAttribute{
							Optional: true,
							Computed: true,
							Default:  stringdefault.StaticString("orange"),
						},
						"other": schema.StringAttribute{
							Optional: true,
							Computed: true,
							Default:  stringdefault.StaticString("other"),
						},
					},
				},
			},
		},
	}
}

func (r bugResource) Read(ctx context.Context, req resource.ReadRequest, resp *resource.ReadResponse) {
}

func (r bugResource) Create(ctx context.Context, req resource.CreateRequest, resp *resource.CreateResponse) {
	resp.State.Raw = req.Plan.Raw
}

func (r bugResource) Update(ctx context.Context, req resource.UpdateRequest, resp *resource.UpdateResponse) {
	resp.State.Raw = req.Plan.Raw
}

func (r bugResource) Delete(ctx context.Context, req resource.DeleteRequest, resp *resource.DeleteResponse) {
}

Terraform Configuration Files

terraform {
  required_providers {
    bug = {
      source = "bug/bug/bug"
    }
  }
}

resource "bug_bug" "this" {
  set = [
    { fruit = "apple" },
    { fruit = "banana" },
    { fruit = "kumquat" },
  ]
}

Debug Output

https://gist.github.com/maxb/f0b606530531a1f7e89c1ac122f141da

Steps to Reproduce

1. Copy the included provider source code to a file, add a go.mod including the latest version of terraform-plugin-framework (no other dependencies needed), build the provider.
2. Set up dev_overrides so you can test the provider.
3. Copy the included Terraform configuration to a file
4. Run terraform apply -auto-approve (no initial state is needed)
5. Run terraform apply -auto-approve again ... the provider panics/crashes

Secondary related bug:

1. Remove any terraform.tfstate from the above reproduction
2. Reduce the number of items in the set in the Terraform configuration from 3 to 1
3. Repeatedly run terraform apply -auto-approve ... observe that provider repeatedly changes the value back and forth on each run, oscillating between the value actually written in the configuration, and the value set as a default in the code.

Partial diagnosis

The terraform-plugin-framework appears to use a bafflingly complex algorithm to apply defaults, involving correlating the state and the configuration.

This is a victim of its own complexity when dealing with sets of objects, as the identity of an object within a set incorporates its own value ... a value that may itself have defaults. This means the identity of a set member in the config may omit unspecified attributes, whilst the identity of the same set member in the state will include unspecified attributes, now set to their default values.