CODEWITHSUNDEEP
terraform
Darren
Darren

Reputation: 197

How can a nested block have a label in a custom terraform provider?

I am writing a provider for terraform and I'm trying to work out how to get labels on nested blocks.

https://www.terraform.io/docs/language/syntax/configuration.html#blocks states "A particular block type may have any number of required labels, or it may require none as with the nested network_interface block type."

If I have something like this in my config

resource "myprovider_thing" "test" {
  x = 1

  settings "set1" {
    y = 2
  }
}

where the settings in the schema has a Type of schema.TypeSet with an Elem of type &schema.Resource. When I try a plan I get told there is an extraneous label and no labels are expected for the block.

I can't find anything explaining how to set that an element requires a label or how to access it.

Is it possible to have a nested block with a label or am I misunderstanding what is written on the configuration page?

Upvotes: 1

Views: 462

Answers (1)

Martin Atkins
Martin Atkins

Reputation: 74199

The syntax documentation you referred to is making a general statement about the Terraform language grammar, but the mechanism of labeled blocks is generally reserved for constructs built in to the Terraform language, like resource blocks as we can see in your example.

The usual approach within resource-type-specific arguments is to create map-typed arguments and have the user assign map values to them, rather than using the block syntax. That approach also makes it easier for users to dynamically construct the map, for situations where statically-defined labels are not sufficient, because they can use arbitrary Terraform language expressions to generate the value.

The current Terraform SDK is built around the capabilities of all historical versions of Terraform and so it only supports maps of primitive types as a result of design constraints in Terraform v0.11 and earlier. That means there isn't a way to specify a map of objects, which would be the closest analog to a nested block type with a label.

At the time I'm writing this answer there is a new library under active development called Terraform Plugin Framework, which ends support for Terraform versions prior to v0.12 but then in return gets to make use of Terraform features introduced in that release, including the possibility of declaring maps of objects in your provider schema. It remains experimental at the time I'm writing this because the team is still iterating on the best way to represent all of the different capabilities, but for a green-field provider it could be a reasonable foundation if you're willing to respond to any potential breaking changes that might occur on the way to it reaching its first stable release.

Upvotes: 2

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