Recognize inputs and outputs of uninitialized remote (Terraform Registry) modules

[radeksimko]

Use-cases

Users may expect completion, hover, go to definition etc. to work automatically for a module block calling any publicly available module they write in their configuration, straight away, e.g.

module "eks" {
  source  = "terraform-aws-modules/eks/aws"
  version = "17.1.0"
}

Attempted Solutions / Workarounds

terraform get

Proposal

Pre-requisites

• Extract module address parsing logic #877
• module metadata: Decode module calls (for uninitialized modules) #882

hashicorp/terraform-ls

• Introduce new job GetModuleMetadataFromRegistry (alongside existing one such as LoadModuleMetadata) which will talk to the Registry API and cache responses keyed off the source address & version of a Registry module in memdb
• Ensure GetModuleMetadataFromRegistry is scheduled from didOpen and didChange and depends on LoadModuleMetadata (as that job provides module call metadata)
• state: Change ModuleStore.ModuleMeta(modPath string) to ModuleStore.InstalledModuleMeta(modPath string)
• state: Implement ModuleStore.DeclaredModuleMeta(modCall tfmod.DeclaredModuleCall) which pulls out any previously cached Registry module metadata from memdb

func GetModuleMetadataFromRegistry(ctx context.Context, modStore *state.ModuleStore) error {
  // TODO: loop over module calls
  // TODO: check if any source address is Registry address
  // TODO: check if that address was already cached
  // TODO: if not, cache it
}

hashicorp/terraform-schema

• schema: Introduce DeclaredModuleMeta(modCall tfmod.DeclaredModuleCall) (*tfmod.RemoteModuleMeta, error)
• schema: Use DeclaredModuleMeta() within SchemaMerger
• schema: For clarity, turn ModuleMeta(path string) into InstalledModuleMeta(path string) in ModuleReader interface

Implementation Notes

• https://pkg.go.dev/github.com/hashicorp/terraform-registry-address is available for parsing and representing registry-based module addresses
• Lookup of required module inputs can be done via Registry API v1
  • https://registry.terraform.io/v1/modules/{FULL_NAME}
  • e.g. curl 'https://registry.terraform.io/v1/modules/terraform-aws-modules/vpc/aws' | jq '.root.inputs[] | select(.required == true)'

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