Support for type declarations (for variable type)

[radeksimko]

Use-cases

Completion

Given a config

variable "test" {
  type = # HERE
}

when user triggers completion in the highlighted position, they are presented with all available types, e.g. string, number, bool, object() etc.

Hover

There doesn't seem to be any reasonable use case for hover - we would duplicate (and reformat) the type declaration, or just display "type declaration".

Semantic Tokens

Given a config

variable "test" {
  type = string
}
variable "foo" {
  type = list(number)
}
variable "bar" {
  type = object({
    foo = string
  })
}

all of string, list(number), object(...) will be highlighted accordingly by clients which support semantic tokens.

Proposal

• Introduce TypeDeclarationExpr (implementation of ExprConstraint) into hcl-lang.schema to help express what variable's type attribute is
• Reflect that new expression type in all relevant Decoder functions:
  • CandidatesAtPos - so that relevant types are returned
    • typeexpr.TypeString implementation might be helpful for implementing the completion as it will have all the different combinations of types listed there
  • HoverAtPos - not sure what useful hover data to return on hover over the type declarations - perhaps just say that it's "type declaration"?
  • SemanticTokensInFile - so that relevant types are reflected as tokens
    • "capsule" types such as map, list, or set can be reported as lang.TokenTypeCapsule (new)
    • primitive types such as string, number, bool can be reported as lang.TokenTypePrimitive (new)
    • attribute names within object() can be reported as lang.TokenAttrName
• Use TypeDeclaration in the schema of the variable block within terraform-schema, e.g.
  • https://github.com/hashicorp/terraform-schema/blob/6d07fd682f6596ef668e918fa29b605e72fbffb8/internal/schema/0.12/variable_block.go#L38
  • https://github.com/hashicorp/terraform-schema/blob/6d07fd682f6596ef668e918fa29b605e72fbffb8/internal/schema/0.14/variable_block.go#L37
• Bump hcl-lang in terraform-schema
• Bump terraform-schema & hcl-lang in terraform-schema

Notes

Terraform is currently running an experiment with "optional attributes" for object types. The relevant logic is currently only present in Terraform itself, and not typeexpr package, and so for simplicity it's better to just ignore that experiment, i.e. avoid completing optional().

https://www.terraform.io/docs/language/expressions/type-constraints.html#experimental-optional-object-type-attributes

[radeksimko]

Completion, hover and semantic highlighting for variable type will be provided in the upcoming release.

Here is a screenshot:

Please keep in mind that we do not yet support completion for "nested expressions" which means that you can complete an empty type = but not types within map, set, list etc.

This functionality is tracked under #496 - feel free to upvote and/or subscribe if that is important to you.

[github-actions]

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